Blowoff valve

A blowoff valve is a pressure release system present in turbocharged engines, its purpose is to prevent compressor surge and reduce wear on the engine.


Definitions

A compressor bypass valve (CBV) also known as a compressor relief valve is a vacuum-actuated valve designed to release pressure in the intake system of a turbocharged or centrifugally supercharged car when the throttle is lifted or closed. This air pressure is re-circulated back into the non-pressurized end of the intake (before the turbo) but after the mass airflow sensor.

A blowoff valve, (BOV, sometimes hooter valve, dump valve) does basically the same thing, but releases the air to the atmosphere. This creates a very distinctive sound desired by many who own turbocharged sports cars. Some blowoff valves are sold with trumpet shaped exits that amplify the "Psshhhh" sound, these designs are normally marketed towards the keen boy racer. For some owners this is the only reason to fit a BOV. Motor sports governed by the FIA have made it illegal to vent unmuffled blowoff valves to the atmosphere. In the United States, Australia and Europe cars featuring unmuffled blowoff valves are illegal for street use.



Downsides of releasing air to atmosphere

This unique sound sometimes comes at a price. On a car with a mass airflow sensor, doing this confuses the engine control unit (ECU) of the car. The ECU is told it has a specific amount of air in the intake system, and injects fuel accordingly. The amount of air released by the blowoff valve is not taken into consideration and the engine runs rich for a period of time.*

Typically this isn't a major issue, but sometimes it can lead to hesitation or stalling of the engine when the throttle is closed. This situation worsens with higher boost pressures. Eventually this can foul spark plugs and destroy the catalytic converter (when running rich, not all the fuel is burned which can heat up on and melt the converter).

* Note that engines using a MAP (manifold absolute pressure) system are not affected.


Purpose of Relief and Blow Off Valves

Blowoff valves are used to prevent compressor surge. Compressor surge is a phenomenon that occurs when lifting off the throttle of a turbocharged car (with a non-existent or faulty bypass valve). When the throttle plate on a turbocharged engine running boost closes, high pressure in the intake system has nowhere to go. It is forced to travel back to the turbocharger in the form of a pressure wave. This results in the wheel rapidly decreasing speed and stalling. The driver will notice a fluttering air sound. In extreme cases the compressor wheel will stop completely or even go backwards. Compressor surge is very hard on the bearings in the turbocharger and can significantly decrease its lifespan. In addition, the now slower moving compressor wheel takes longer to spool (speed up) when throttle is applied. This is known as turbo lag.

With the implementation of either a bypass valve or a blowoff valve the pressurized air escapes, allowing the turbo to continue spinning. This allows the turbocharger to have less turbo lag when power is demanded next.



How it works




A blow-off-valve is connected by a vacuum hose to the intake manifold after the throttle plate. When the throttle is closed, underpressure develops in the intake manifold after the throttle plate and "sucks" the blowoff valve open. The excess pressure from the turbocharger is vented into the atmosphere or recirculated into the intake upstream of the compressor inlet.



Tuning adjustable valves

Most aftermarket valves are adjustable leaving customers curious on how to set them properly for their vehicle. Typically the adjustment lies in the spring preload. Here is how to set it.

You want the spring as soft as possible without leaking boost at peak pressure. If the spring is set too soft then the valve will not close fully resulting in a boost leak and idle problems. If you set it too hard then the valve will not fully open, close too early, and have compressor surge.

Trial and error with an accurate boost gauge is the perfect way to find the right setting for your vehicle....

Intercooler

An intercooler, or charge air cooler, is a device used on turbocharged and supercharged internal combustion engines to improve their volumetric efficiency by increasing the amount of charge in the engine and lowering charge air temperature thereby increasing power and reliability. It is also known as a charge air cooler, especially on larger engines that may easily self-destruct with high intake-air temperatures. The inter in the name refers to its location compared to the compressors; the coolers were typically installed between multiple stages of supercharging in aircraft engines. Modern automobile designs are technically aftercoolers because they appear most often at the very end of the chain, but this term is no longer used.


Turbocharging

Turbochargers and superchargers compress incoming air, causing it to become heated (see the ideal gas law). Since hot air is less dense than cooler air at the same pressure, the total charge delivered to the cylinders is higher than non-compressed air but still less than it could be. By cooling the charge after compression, the stream experiences further compression which is naturally tied with cooling of matter—upon cooling matter shrinks occupying less volume (usually, see Coefficient of Thermal Expansion). With this further compression even more charge can be delivered, increasing power. Additionally, intercoolers help to increase the total amount of boost possible without causing engine knocking. One of the most efficient intercoolers is water injection—it cools the intake charge and cools down the combustion temperature.

An intercooler or charge air cooler is essentially a radiator tuned for high volume flow rates and the increasing density of the charge as it cools. Most designs use ambient air for cooling, flowing through the radiator core, and often co-located with other radiators for oil or cooling fluid. This approach is also known as Air To Air (ATA).



Charge Cooling

An alternate design, often referred to as a chargecooler charge cooler, (heat exchanger) uses water or a water/antifreeze mix to cool the charge, then cools the water in a separate radiator. While heavier and more complex, charge coolers can often make arranging the rest of the engine much simpler. This approach is also known as Water To Air (WTA or A/W). A variation on this type of charge cooler substitutes a reservoir of coolant for the radiator, allowing the use of an icewater mixture or liquid nitrogen that can bring outlet temperatures well below ambient air temperature even under very high boost pressure. Because of the limitations on the volume of coolant that can be stored and circulated, this approach to charge cooling is only practical for short durations, making it most common in drag racing and land speed record attempts.

In at least one land speed record attempt, Gale Banks used nitrous oxide, not internally as a power-adder, but as the medium into which the heat was transferred from the charge air. The nitrous oxide was held in bottles and released through the intercoolers' cooling fins and exhausted directly to the atmosphere. Extra cooling by nitrous oxide spraying on the front of the intercooler is now a related commercially available upgrade.

Extra cooling of the charge air can be achieved also by externally spraying water on the front of the intercooler. This can be activated automatically or manually, and is far cheaper to refill than nitrous oxide.

Air to air intercoolers need to be mounted so as to maximize air flow and promote efficient cooling. Most cars such as the Toyota Supra, Nissan Skyline, Saab (except the Subaru WRX-based 9-2X Aero), Dodge SRT-4, Mitsubishi Lancer Evolution, Volkswagen and Audi use front mounted intercooler(s) (FMIC) mounted vertically near the front bumper, in line with the car's radiator. Many older turbo-charged cars, such as the Saab 900, and Turbo Mitsubishi Eclipse use side-mounted intercoolers (SMIC), which are mounted in the front corner of a bumper, in front of one of the wheels. Side-mounted intercoolers are generally smaller and less efficient than front-mounted intercoolers. Cars such as the Subaru Impreza WRX, MINI Cooper S and the MAZDASPEED 6 use top mounted intercoolers (TMIC) which are mounted horizontally on top of the engine (due to a low hood line) and use a hood scoop to force air over the intercooler. Some World Rally Championship cars use a reverse-induction setup, where air from ducts in the front bumper is forced up over a horizontally-mounted intercooler and then vented through ducts in the top of the hood to further maximize aerodynamic benefits.

Homogeneous Charge Compression Ignition (HCCI)

Introduction

Homogeneous Charge Compression Ignition, or HCCI, is a form of internal combustion in which well mixed fuel and oxidizer (typically air) are compressed to the point of auto-ignition. As in other forms of combustion, this exothermic reaction releases chemical energy into a sensible form that can be translated by an engine into work and heat.

HCCI has characteristics from each of the two most popular forms of combustion used in IC engines: homogeneous charge spark ignition (gasoline engines) and stratified charge compression ignition (diesel engines). As in homogeneous charge spark ignition, the fuel and oxidizer are mixed together. However, rather than using an electric discharge to ignite a portion of the mixture, the concentration and temperature of the mixture are raised by compression until the entire mixture reacts simultaneously. Stratified charge compression ignition also relies on the heat and concentration resulting from compression, but combustion occurs at the boundary of unmixed fuel which is injected to initiate combustion.

The defining characteristic of HCCI is that the ignition occurs at several places at a time which makes the fuel/air mixture burn nearly simultaneously. There is no direct initiator of combustion. This makes the process inherently challenging to control. However, with advances in microprocessors and a physical understanding of the ignition process, HCCI can be controlled to achieve gasoline engine like emissions along with diesel engine like efficiency. In fact, HCCI engines have been shown to achieve extremely low levels of Nitrogen oxide emissions (NOx) without aftertreatment catalytic converter. The unburned hydrocarbon and carbon monoxide emissions are still high (due to lower peak temperatures), as in gasoline engines, and must still be treated to meet automotive emission regulations.



History

HCCI engines have a long history, even though HCCI has not been as widely implemented as spark ignition or diesel injection. It is essentially an Otto combustion cycle. In fact, HCCI was popular before electronic spark ignition was used. One example is the hot-bulb engine which used a torch-heated head to add heat to the inducted gases. The extra heat combined with compression induced the conditions for combustion to occur.


Operation


Methods

A mixture of fuel and air will ignite when the concentration and temperature of reactants is sufficiently high. The concentration and/or temperature can be increased several different ways:

* High compression ratio
* Pre-heat induction gases
* Forced induction
* Retain or reinduct exhaust

Once ignited, combustion occurs very quickly. When auto-ignition occurs too early or with too much chemical energy combustion is too fast. In such cases, high in-cylinder pressures can destroy an engine. For this reason, HCCI is typically operated at lean overall fuel mixtures.



Advantages

* HCCI is closer to the ideal Otto cycle than spark ignited combustion.

* Lean operation leads to higher efficiency than in spark ignited gasoline engines

* Homogeneous mixing of fuel and air leads to cleaner combustion and lower emissions. In fact, due to the fact that peak temperatures are significantly lower than in typical spark ignited engines, NOx levels are almost negligible.

* Since HCCI runs throttleless, it eliminates throttling losses



Disadvantages

* High peak pressures
* High heat release rates
* Difficulty of control
* Limited power range
* High carbon monoxide and hydrocarbon pre-catalyst emissions




Control

Controlling HCCI is a major hurdle to more widespread commercialization. HCCI is more difficult to control than other popular modern combustion methods.

In a typical gasoline engine, a spark is used to ignite the pre-mixed fuel and air. In diesel engines, combustion begins when the fuel is injected into compressed air. In both cases, the timing of combustion is explicitly controlled. In an HCCI engine, however, the homogeneous mixture of fuel and air is compressed, and combustion begins whenever the appropriate conditions are reached. This means that there is no well-defined combustion initiator that can be directly controlled. An engine can be designed so that the ignition conditions occur at a desirable timing. However, this would only happen at one operating point. The engine could not change the amount of work it produces. This could work in a hybrid vehicle, but most engines change their energy production to meet user demand.

To achieve dynamic operation in an HCCI engine, the control system must change the conditions that induce combustion. Thus, the engine must control either the compression ratio, inducted gas temperature, inducted gas pressure, or quantity of retained or reinducted exhaust.

Several approaches have been suggested for control



Variable compression ratio

There are several methods of modulating both the geometric and effective compression ratio. The geometric compression ratio can be changed with a movable plunger at the top of the cylinder head. The effective compression ratio can be reduced from the geometric ratio by closing the intake valve either very late or very early with some form of variable valve actuation. Both of the approaches mentioned above require large amounts of energy to achieve fast responses and are expensive.



Variable induction temperature

This technique is also known as fast thermal management. It is accomplished by rapidly varying the cycle to cycle intake charge temperature. It is also expensive to implement and has limited bandwidth associated with actuator energy.



Variable exhaust gas percentage

Exhaust gas can be very hot if retained or reinducted from the previous combustion cycle or cool if recirculated through the intake as in conventional EGR systems. The exhaust has dual effects on HCCI combustion. It dilutes the fresh charge, delaying ignition and reducing the chemical energy and engine work. Hot combustion products conversely will increase the temperature of the gases in the cylinder and advance ignition.



Variable valve actuation

Variable valve actuation allows control over the compression ratio and the exhaust gas percentage. However, fully variable valve actuation is complicated and the componentry is expensive.



High peak pressures and heat release rates

In a typical gasoline or diesel engine, combustion occurs via a flame. Hence at any point in time, only a fraction of the total fuel is burning. This results in low peak pressures and low energy release rates as fuel is burnt over a longer period of time. In HCCI, however, the entire fuel/air mixture ignites and burns nearly simultaneously resulting in high peak pressures and energy release rates. To withstand the higher pressures, the engine has to be structurally stronger, and that means heavier.

Several strategies have been proposed to lower the rate of combustion. Two different blends of fuel can be used. That way, the two fuels will ignite at different points of time resulting in lesser combustion speed. The problem with this idea is the requirement to set up an infrastructure to supply the blended fuel. Dillution, for example with exhaust, reduces the pressure and combustion rate at the cost of work production.



Power

In a gasoline engine, power can be increased by increasing the fuel/air charge. In a diesel engine, power can be increased by increasing the amount of fuel injected. The engines can withstand a boost in power because the heat release rate in these engines is slow. In HCCI however, the entire mixture burns nearly simultaneously. Increasing the fuel/air ratio will result in even higher peak pressures and heat release rates. Also, increasing the fuel/air ratio (also called the equivalence ratio) increases the danger of knock. In addition, many of the viable control strategies for HCCI require thermal preheating of the charge which reduces the density and hence the mass of the air/fuel charge in the combustion chamber, reducing power. These factors makes increasing the power in HCCI inherently challenging.

One way to increase power is to use different blends of fuel. This will lower the heat release rate and peak pressures and will make it possible to increase the equivalence ratio. Another way is to thermally stratify the charge so that different points in the compressed charge will have different temperatures and will burn at different times lowering the heat release rate making it possible to increase power. A third way is to run the engine in HCCI mode only at part load conditions and run it as a diesel or spark ignition engine at full or near full load conditions. Since much more research is required to successfully implement thermal stratification in the compressed charge, the last approach is being studied more intensively.


Carbon Monoxide and Hydrocarbon emissions

Since HCCI operates on lean mixtures, the peak temperatures are lower in comparison to spark ignition and diesel engines. The low peak temperatures prevent the formation of NOx. However they also lead to incomplete burning of fuel especially near the walls of the combustion chamber. This leads to high carbon monoxide and hydrocarbon emissions. An oxidizing catalyst would be effective at removing the regulated species since the exhaust is still oxygen rich.


Difference from Knock

Engine knock or pinging occurs when some of the unburnt gases ahead of the flame in a spark ignited engine spontaneously ignite. The unburnt gas ahead of the flame is compressed as the flame propagates and the pressure in the combustion chamber rises. The high pressure and corresponding high temperature of unburnt reactants can cause them to spontaneously ignite. This causes a shock wave to traverse from the end gas region and an expansion wave to traverse into the end gas region. The two waves reflect off the boundaries of the combustion chamber and interact to produce high amplitude standing waves.

A similar ignition process occurs in HCCI. However, rather than part of the reactant mixture being ignited by compression heating ahead of a flame front, ignition in HCCI engines occurs due to piston compression. In HCCI, the entire reactant mixture ignites (nearly) simultaneaously. Since there are very little or no pressure differences between the different regions of the gas, there is no shock wave propagation and hence no knocking. However at high loads (i.e. high fuel/air ratios), knocking is a possibility even in HCCI.

Stirling engine Applications

Combined heat and power applications

The principal use of Stirling engines today is as an economical source of electrical power often utilising a heat source from an industrial process. WhisperGen, a New Zealand firm with offices in Christchurch, has developed an "AC Micro Combined Heat and Power" stirling cycle engine. These microCHP units are gas-fired central heating boilers which sell power back into the electricity grid. WhisperGen announced in 2004 that they were producing 80,000 units for the residential market in the United Kingdom. A 20 unit trial in Germany started in 2006.


Solar power generation

Placed at the focus of a parabolic mirror a Stirling engine can convert solar energy to electricity with an efficiency better than photovoltaic cells. On August 11, 2005, Southern California Edison announced an agreement to purchase solar powered Stirling engines from Stirling Energy Systems[7] over a twenty year period and in quantity (20,000 units) sufficient to generate 500 megawatts of electricity. These systems, on a 4,500 acre (19 km²) solar farm, will use mirrors to direct and concentrate sunlight onto the engines which will in turn drive generators.


Stirling cryocoolers

Any Stirling engine will also work in reverse as a heat pump: i.e. when a motion is applied to the shaft, a temperature difference appears between the reservoirs. One of their modern uses is in refrigeration and cryogenics.

The essential mechanical components of a Stirling cryocooler are identical to a Stirling engine. The turning of the shaft will compress the working gas causing its temperature to rise. This heat will then be dissipated by pushing the gas against a heat exchanger. Heat would then flow from the gas into this heat exchanger which would probably be cooled by passing a flow of air or other fluid over its exterior. The further turning of the shaft will then expand the working gas. Since it had just been cooled the expansion will reduce its temperature even further. The now very cold gas will be pushed against the other heat exchanger and heat would flow from it into the gas. The external side of this heat exchanger would be inside a thermally insulated compartment such as a refrigerator. This cycle would be repeated once for each turn of the shaft. Heat is in effect pumped out of this compartment, through the working gas of the cryocooler and dumped into the environment. The temperature inside the compartment will drop because its insulation prevents ambient heat from coming in to replace that pumped out.

As with the Stirling engine, efficiency is improved by passing the gas through a “Regenerator” which buffers the flow of heat between the hot and cold ends of the gas chamber.

The first Stirling-cycle cryocooler was developed at Philips in the 1950s and commercialized in such places as liquid nitrogen production plants. The Philips Cryogenics business evolved until it was split off in 1990 to form the Stirling Cryogenics & Refrigeration BV, Stirling The Netherlands. This company is still active in the development and manufacturing Stirling cryocoolers and cryogenic cooling systems.

A wide variety of smaller size Stirling cryocoolers are commercially available for tasks such as the cooling of sensors.

Thermoacoustic refrigeration uses a Stirling cycle in a working gas which is created by high amplitude sound waves.


Heat pump

A Stirling heat pump is very similar to a Stirling cryocooler, the main difference being that it usually operates at room-temperature and its principal application to date is to pump heat from the outside of a building to the inside, thus cheaply heating it.

As with any other Stirling device, heat flows from the expansion space to the compression space; however, in contrast to the Stirling engine, the expansion space is at a lower temperature than the compression space, so instead of producing work, an input of mechanical work is required by the system (in order to satisfy the second law of thermodynamics). When the mechanical work for the heat-pump is provided by a second Stirling engine, then the overall system is called a "heat-driven, heat-pump".

The expansion-side of the heat-pump is thermally coupled to the heat-source, which is often the external environment. The compression side of the Stirling device is placed in the environment to be heated, for example a building, and heat is "pumped" into it. Typically there will be thermal insulation between the two sides so there will be a temperature rise inside the insulated space.

Heat-pumps are by far the most energy-efficient types of heating systems. Stirling heat-pumps also often have a higher coefficient of performance than conventional heat-pumps. To date, these systems have seen limited commercial use; however, use is expected to increase along with market demand for energy conservation, and adoption will likely be accelerated by technological refinements.


Marine engines

Kockums, the Swedish shipbuilder, had built at least 10 commercially successful Stirling powered submarines during the 1980s. As of 2005 they have started to carry compressed oxygen with them. (No endurance stated.)


Nuclear power

There is a potential for nuclear-powered Stirling engines in electric power generation plants. Replacing the steam turbines of nuclear power plants with Stirling engines might simplify the plant, yield greater efficiency, and reduce the radioactive by-products. A number of breeder reactor designs use liquid sodium as coolant. If the heat is to be employed in a steam plant, a water/sodium heat exchanger is required, which raises some concern as sodium reacts violently with water. A Stirling engine obviates the need for water anywhere in the cycle.

United States government labs have developed a modern Stirling engine design known as the Stirling Radioisotope Generator for use in space exploration. It is designed to generate electricity for deep space probes on missions lasting decades. The engine uses a single displacer to reduce moving parts and uses high energy acoustics to transfer energy. The heat source is a dry solid nuclear fuel slug and the cold source is space itself.


Aircraft engines

They hold theoretical promise as aircraft engines. They are quieter, less polluting, gain efficiency with altitude (internal combustion piston engines lose efficiency), are more reliable due to fewer parts and the absence of an ignition system, produce much less vibration (airframes last longer) and safer, less explosive fuels may be used. (see below "Argument on why the Stirling engine can be applied in aviation" or "Why Aviation Needs the Stirling Engine" by Darryl Phillips, a 4-part series in the March 1993 to March 1994 issues of Stirling Machine World)


Geothermal energy

Some believe that the ability of the Stirling engine to convert geothermal energy to electricity and then to hydrogen may well hold the key to replacement of fossil fuels in a future hydrogen economy.


Low temperature difference engines

A low temperature difference (Low Delta T) Stirling engine will run on any low temperature differential, for example the difference between the palm of a hand and room-temperature. Usually they are designed in a gamma configuration, for simplicity, and without a regenerator. They are typically unpressurized, running at near-atmospheric pressure. The power produced is less than one watt, and they are intended for demonstration purposes only. As of 2006, this is the only type of Stirling that is widely sold at affordable prices.

Advantages and Disadvantage of Stirling engines

Advantages of Stirling engines

* The heat is external and the burning of a fuel-air mixture can be more accurately controlled.

* They can run directly on any available heat source, not just one produced by combustion, so they can be employed to run on heat from solar, geothermal, biological or nuclear sources.

* A continuous combustion process can be used to supply heat, so emission of unburned fuel can be greatly reduced.

* Most types of Stirling engines have the bearing and seals on the cool side; consequently, they require less lubricant and last significantly longer between overhauls than other reciprocating engine types.

* The engine as a whole is much less complex than other reciprocating engine types. No valves are needed. Fuel and intake systems are very simple.

* They operate at relatively low pressure and thus are much safer than typical steam engines.

* Low operating pressure allows the usage of less robust cylinders and of less weight.

* They can be built to run very quietly and without air, for use in submarines or in space.

* They start easily and run more efficiently in cold weather, features lacking in their internal combustion cousins.

* A Stirling engine which is pumping water can be configured so that the pumped water cools the cool side. This is, of course, most effective when pumping cold water.

* They are extremely flexible. They can be used as CHP (Combined Heat and Power) in winters and as coolers in summers (cryocooling).



Disadvantages of Stirling engines

* Some Stirling engine designs require both input and output heat exchangers, which must contain the pressure of the working fluid, and which must resist any corrosive effects due to the heat source. These increase the cost of the engine, especially when they are designed to the high level of "effectiveness" (heat exchanger efficiency) needed for optimizing fuel economy. Fuel economy may not be an issue with the advantages of using unlimited but unusual fuel sources that a Stirling engine can make use of.

* Stirling engines that run on small temperature differentials are quite large for the amount of power that they produce, due to the heat exchangers. Increasing the temperature differential (and pressure) allows smaller Stirling engines to produce more power.

* Dissipation of waste heat is especially complicated because the coolant temperature is kept as low as possible to maximize thermal efficiency. This drives up the size of the radiators markedly, which can make packaging difficult. This has been one of the factors limiting the adoption of Stirling engines as automotive prime movers. (Conversely, it is convenient for domestic or business heating systems where combined heat and power (CHP) systems show promise. ref)

* A "pure" Stirling engine cannot start instantly; it literally needs to "warm up". This is true of all external combustion engines, but the warm up time may be shorter for Stirlings than for others of this type such as steam engines. Stirling engines are best used as constant run, constant speed engines.

* Power output of a Stirling is constant and hard to change rapidly from one level to another. Typically, changes in output are achieved by varying the displacement of the engine (often through use of a swashplate crankshaft arrangement) or by changing the mass of entrained working fluid (generally helium or hydrogen). This property is less of a drawback in hybrid electric propulsion or base load utility generation where a constant power output is actually desirable.

* Hydrogen's low viscosity, high thermal conductivity and specific heat makes it the most efficient working gas, in terms of thermodynamics and fluid dynamics, to use in a Stirling engine. However, given the high diffusion rate associated with this low molecular weight gas, hydrogen will leak through solid metal, thus it is very difficult to maintain pressure inside the engine for any length of time without replacement. Typically, auxiliary systems need to be added to maintain the proper quantity of working fluid. These systems can be a gas storage bottle or a gas generator. Hydrogen can be generated either by electrolysis of water, or by the reaction of acid on metal. Hydrogen can also cause the embrittlement of metals. Helium must be supplied by bottled gas. Some engines use air as the working fluid which is less thermodynamically efficient but minimizes the problems of gas containment and supply. Most technically advanced Stirling engines like those developed for United States government labs use helium as the working gas, because it functions close to the efficiency and power density of hydrogen with fewer of the material containment issues. Hydrogen is also a very flammable gas, while helium is inert. Compressed air can also be explosive because it contains a high partial pressure of oxygen. Oxygen can be removed from air through an oxidation reaction, or equivalently, bottled nitrogen can be used.

Stirling engine

The Stirling engine is a heat engine of the external combustion piston engine type. It was invented and developed by Reverend Dr Robert Stirling in 1816.

A well-designed Stirling engine can achieve 50% to 80% of the ideal efficiency in the conversion of heat into mechanical work, limited only by friction and material properties. The engines can theoretically run on any heat source of sufficient temperature, including solar energy, chemical and nuclear fuels.

While the Stirling engine is more expensive and larger than an internal combustion engine of the same power rating, its many unique advantages make it preferred for a variety of niche applications. Compared to internal combustion engines, Stirling engines can be made very energy efficient, quiet, reliable, long-lasting and low-maintenance. In recent years, these advantages have become increasingly significant given the general rise in energy costs and the environmental concerns of climate change. This growing interest in Stirling technology has led to the ongoing development of Stirling devices for many applications, including renewable power generation and Astronautics.

Functional Description


The engine cycle

Since the Stirling engine is a closed cycle, it contains a fixed quantity of gas called a "working fluid", most commonly air, hydrogen or helium. In normal operation, the engine is sealed and no gas enters or leaves the engine. No valves are required, unlike other types of piston engines. The Stirling engine, like most heat-engines, cycles through four main processes: cooling, compression, heating and expansion. This is accomplished by moving the gas back and forth between hot and cold heat exchangers. The hot heat exchanger is in thermal contact with an external heat source, e.g. a fuel burner, and the cold heat exchanger being in thermal contact with an external heat sink, e.g. air fins. A change in gas temperature will cause a corresponding change in gas pressure, while the motion of the piston causes the gas to be alternately expanded and compressed.

The gas follows the behavior described by the gas laws which describe how a gas's pressure, temperature and volume are related. When the gas is heated, because it is in a sealed chamber, the pressure rises and this then acts on the power piston to produce a power stroke. When the gas is cooled the pressure drops and this means that less work needs to be done by the piston to compress the gas on the return stroke, thus yielding a net power output.

When one side of the piston is open to the atmosphere, the operation of the cold cycle is slightly different. As the sealed volume of working gas comes in contact with the hot side, it expands, doing work on both the piston and on the atmosphere. When the working gas contacts the cold side, the atmosphere does work on the gas and "compresses" it. Atmospheric pressure, which is greater than the cooled working gas, pushes on the piston.

To summarize, the Stirling engine uses the potential energy difference between its hot end and cold end to establish a cycle of a fixed amount of gas expanding and contracting within the engine, thus converting a temperature difference across the machine into mechanical power.

The greater the temperature difference between the hot and cold sources, the greater the power produced, and thus, the lower the efficiency required for the engine to run.

Small demonstration engines have been built which will run on a temperature difference of around 15 °C, e.g. between the palm of a hand and the surrounding air, or between room temperature and melting water ice.



The Regenerator

In true Stirling engines a regenerator, typically a mass of metal wire, is located in the path of the gas between the hot and cold heat exchangers. As the gas cycles between the hot and cold sides, its heat is temporarily transferred to and from the regenerator. In some designs, there is a displacer piston but no regenerator. The displacer piston does not have a seal, and with loose fit tolerances a small air gap between the piston and the cylinder allows the gas to flow around the displacer as it is displaced to the other end of the cylinder. In some designs, the surfaces of the displacer and cylinder alone can provide some regeneration. The regenerator contributes greatly to the overall efficiency and power produced by the Stirling engine. The regenerator was the key feature invented by Robert Stirling in 1816 which greatly improved his machine and distinguished it from other "hot air engines".

The regenerator is a reverse flow heat exchanger, which tends to improve thermal efficiency wherever it is found in technology or in nature.



Engine configurations

The Beta and Gamma type Stirling engines use a displacer piston to move the working gas back and forth between hot and cold heat exchangers. The alpha type engine relies on interconnecting the power pistons of multiple cylinders to move the working gas, with the cylinders held at different temperatures.

The ideal Stirling engine cycle has the same theoretical efficiency as a Carnot heat engine (for the same input and output temperatures). The thermodynamic efficiency varies, but can be higher than steam engines and many modern internal combustion engines (Diesel or Gasoline ).


Engineers classify Stirling engines into three distinct types:


Alpha Stirling

* An alpha Stirling contains two separate power pistons in separate cylinders, one "hot" piston and one "cold" piston. The hot piston cylinder is situated inside the higher temperature heat exchanger and the cold piston cylinder is situated inside the low temperature heat exchanger. This type of engine has a very high power-to-volume ratio but has technical problems due to the usually high temperature of the "hot" piston and the durability of its seals.


Beta Stirling

* A beta Stirling has a single power piston arranged within the same cylinder on the same shaft as a displacer piston. The displacer piston is a loose fit and does not extract any power from the expanding gas but only serves to shuttle the working gas from the hot heat exchanger to the cold heat exchanger. When the working gas is pushed to the hot end of the cylinder it expands and pushes the power piston. When it is pushed to the cold end of the cylinder it contracts and the momentum of the machine, usually enhanced by a flywheel, pushes the power piston the other way to compress the gas. Unlike the alpha type, the beta type avoids the technical problems of hot moving seals.



Gamma Stirling

* A gamma Stirling is simply a beta Stirling in which the power piston is mounted in a separate cylinder alongside the displacer piston cylinder, but is still connected to the same flywheel. The gas in the two cylinders can flow freely between them but remains a single body. This configuration produces a lower compression ratio but is mechanically simpler and often used in multi-cylinder Stirling engines.



Other types

Changes to the configuration of mechanical Stirling engines continue to interest engineers and inventors. Notably, some are in pursuit of the rotary Stirling engine; the goal here is to convert power from the Stirling cycle directly into torque, a similar goal to that which led to the design of the rotary combustion engine. No practical engine has yet been built but a number of concepts, models and patents have been produced.

There is also a field of "free piston" Stirling cycles engines, including those with liquid pistons and those with diaphragms as pistons.

An alternative to the mechanical Stirling engine is the fluidyne pump, which uses the Stirling cycle via a hydraulic piston. In its most basic form it contains a working gas, a liquid and two non-return valves. The work produced by the fluidyne goes into pumping the liquid.



Heat sources

Any temperature difference will power a Stirling engine and the term "external combustion engine" often applied to it is misleading. A heat source may be the result of combustion but can also be solar, geothermal, or nuclear or even biological. Likewise a "cold source" below the ambient temperature can be used as the temperature difference. A cold source may be the result of a cryogenic fluid or iced water. Since small differential temperatures require large mass flows, parasitic losses in pumping the heating or cooling fluids rise and tend to reduce the efficiency of the cycle.

Because a heat exchanger separates the working gas from the heat source, a wide range of combustion fuels can be used, or the engine can be adapted to run on waste heat from some other process. Since the combustion products do not contact the internal moving parts of the engine, a Stirling engine can run on landfill gas containing siloxanes without the accumulation of silica that damages internal combustion engines running on this fuel. The life of lubricating oil is longer than for internal-combustion engines.

The U.S. Department of Energy in Washington, NASA Glenn Research Center in Cleveland, and Stirling Technology Co. of Kennewick, Wash., are developing a free-piston Stirling converter for a Stirling Radioisotope Generator. This device would use a plutonium source to supply heat.



History and development

Invention of the Stirling engine is credited to the Scottish clergyman Rev. Robert Stirling who, in 1816, made significant improvements to earlier designs and took out the first patent. He was later assisted in its development by his engineer brother James Stirling.

The inventors sought to create a safer alternative to the steam engines of the time, whose boilers often exploded due to the high pressure of the steam and the inadequate materials. Stirling engines will convert any temperature difference directly into movement.

Devices called air engines have been recorded from as early as 1699 around the time when the laws of gases were first set out. The English inventor Sir George Cayley is known to have devised air engines c. 1807. Robert Stirling's innovative contribution of 1816 was what he called the 'Economiser'. Now known as the regenerator, it stored heat from the hot portion of the engine as the air passed to the cold side, and released heat to the cooled air as it returned to the hot side. This innovation improved the efficiency of Stirling's engine enough to make it commercially successful in particular applications, and has since been a component of every air engine that is called a Stirling engine.

During the nineteenth century the Stirling engine found applications anywhere a source of low to medium power was required, a role that was eventually usurped by the electric motor at the century's end.

It was also employed in reverse as a heat pump to produce early refrigeration.

In the late 1940s, the Philips Electronics company in The Netherlands was searching for a versatile electricity generator to enable worldwide expansion of sales of its electronic devices in areas with no reliable electricity infrastructure. The company put a huge R&D research effort into Stirling engines building on research it had started in the 1930s and which lasted until the 1970s. The only lasting commercial product for Philips was its reversed Stirling engine: the Stirling cryocooler.

Los Alamos National Laboratory has developed an "Acoustic Stirling Heat Engine" with no moving parts. It converts heat into intense acoustic power which (quoted from given source) "can be used directly in acoustic refrigerators or pulse-tube refrigerators to provide heat-driven refrigeration with no moving parts, or ... to generate electricity via a linear alternator or other electroacoustic power transducer".



The Stirling Cycle

The ideal stirling cycle consists of four thermodynamic processes acting on the working fluid:

* 1. Isothermal Compression
* 2. Constant-Volume (or isometric) heat-addition
* 3. Isothermal Expansion
* 4. Constant-Volume (or isometric) heat-removal

Overhead valve

In automotive engineering, an overhead valve internal combustion engine is one in which the intake and exhaust valves and ports are contained in the cylinder head.

The original overhead valve or OHV piston engine was developed by the Scottish-American David Dunbar Buick. It employed pushrod-actuated valves parallel to the pistons and this is still in use today. This contrasts with previous designs which made use of side valves and sleeve valves.

Today the technology is widespread, and the term, "OHV", is generally used to differentiate a pushrod engine from one which uses overhead cams, although both types employ overhead valves and so are both OHV engines.

Overhead camshaft

Overhead camshaft (OHC) valvetrain configurations place the camshaft within the cylinder heads, above the combustion chambers, and drive the valves or lifters directly instead of using pushrods. When compared directly with pushrod (or I-Head) systems with the same number of valves, the reciprocating components of the OHC system are fewer and in total will have less mass. Though the system that drives the cams may become more complex, most engine manufacturers easily accept the added complexity in trade for better engine performance and greater design flexibility. The OHC system can be driven using the same methods as an I-Head system, these methods may include using a timing belt, chain, or in less common cases, gears.

Many OHC engines today employ Variable Valve Timing and multiple valves to improve efficiency and power. OHC also inherently allows for greater engine speeds over comparable cam-in-block designs.

There are two overhead camshaft layouts:

* Single overhead camshaft (SOHC)
* Double overhead camshafts (DOHC)



Single overhead camshaft

Single overhead camshaft is a design in which one camshaft is placed within the cylinder head. In an inline engine this means there is one camshaft in the head, while in a V engine there are two camshafts: one per cylinder bank.

The SOHC design is inherently mechanically more efficient than a comparable pushrod design. This allows for higher engine speeds, which in turn will by definition increase power output for a given torque. The cam operates the valves directly or through a rocker arm as opposed to overhead valve pushrod engines, which have tappets, long pushrods and rocker arms to transfer the movement of the lobes on the camshaft in the engine block to the valves in the cylinder head.

SOHC designs offer reduced complexity compared to pushrod designs when used for multivalve heads, in which each cylinder has more than two valves.



Double overhead camshafts

A double overhead camshaft (also called double overhead cam, dual overhead cam or twincam) valvetrain layout is characterized by two camshafts being located within the cylinder head, where there are separate camshafts for inlet and exhaust valves. In engines with more than one cylinder bank (V engines) this designation means two camshafts per bank, for a total of four.

Double overhead camshafts are not required in order to have multiple inlet or exhaust valves, but are necessary for more than 2 valves that are directly actuated (though still usually via tappets). Not all DOHC engines are multivalve engines — DOHC was common in two valve per cylinder heads for decades before multivalve heads appeared, however today DOHC is synonymous with multivalve heads, since almost all DOHC engines have between three and five valves per cylinder.



History

The first DOHC engines were two valve per cylinder designs from companies like Fiat (1912), Peugeot (1913), Alfa Romeo (6C- 1925, 512 - 1940), Maserati (Tipo 26, 1926), and Bugatti (Type 51, 1931). Most Ferraris used two valve per cylinder DOHC engines as well.

When DOHC technology was introduced in mainstream vehicles, it was common for the technology to be heavily advertised. While the technology was used at first in limited production and sports cars, the Fiat group is historically credited as the first car company to use a belt driven DOHC engine across their complete product line, comprised of coupes, sedans, convertibles and station wagons, in the mid-1960s.

Honda D engine

The Honda D engine is a family of inline 4-cylinder engines used in a variety of compact Honda models, most commonly the Honda Civic, but also used in the Integra, Logo, CRX, Stream and others. Displacement ranges between 1.2 L and 1.7 L, and the engine is available in SOHC and DOHC versions. Some SOHC models are equipped with VTEC. Power range started from 62 hp (currently the smallest engine uses a 1.4 L 90 hp engine, code D14A4) to 135 hp. The D-series was introduced in 1984 and ended production in 2005 with the introduction of the 8th generation Honda Civic.



Hot-rodding the D series

Although the availability of used D-series engines at low prices makes it somewhat popular among those who modify it for high performance (as well as a popular item for swapping into earlier or less powerful Civics for an instant and trouble free power upgrade), the unmodified engine won't survive quite as much power enhancement by use of such external modifications as turbochargers, superchargers, or nitrous oxide as the more powerful, somewhat more robust, and much more expensive B-series;

The Achilles heel of the D-series seems to be the connecting rods, which will withstand a substantial and noticeable increase in power up to a certain point, but will break if that limit is exceeded. Generally, a D-series motor can handle up to about 220 bhp, as long as care is taken to avoid detonation through careful spark and fuel management. Of course, the connecting rods, pistons, and other internal parts can be replaced with more durable aftermarket parts which will survive almost any amount of power desired, but some people choose to swap to a B-series motor instead in order to avoid the potential risks of engine building. In all practicality though, the B series is much more expensive to swap in than most D-series engine builds with forced induction or nitrous combined. The D-series also has the ability to swap some parts between different motors and among some B-series parts as well.

When employing forced induction on a D16, at a minimum the stock hypereutectic pistons should be replaced as well as the connecting rods if the commonly used "stock parts" limit of 220 HP is to be exceeded, although it should be noted that the D series crankshaft in particular has been found to reliably handle up to 600HP.

High compression OEM pistons are a quick way to gain horsepower in a naturally aspirated motor. All D-series motors run the same bore (75 mm) however, most factory motor variations (i.e. d16a1, d15b7, d16y7) have used a different piston compression height as well as a different dome or dish. In general, the older D motors have a higher compression height and a larger combustion chamber which create around a 9.1:1 - 9.4:1 compression ratio from the factory. The newer variants have slightly lower compression height combined with a much smaller combustion chamber to create a compression ratio of 9.4:1 - 9.9:1. Now if you combine an older d16 motor's piston with that of a newer d16 head you can end up with a compression ratio of about 10.7:1 with no other work (i.e. D16A1 piston, D16A6 head). There are a few websites that have compression ratio calculators for Honda motors.

·D15 has smaller main bearing diameters. D16 and D17 cranks share the same size main bearing diameters.

·D16 and D17 rods all have the same major dimensions. The D15 rod is shorter (in general) and has a smaller bearing size, although the wrist pin bore is the same.

·D15Z1 and D15B motors have a rod that is the same length as a D16. Other than the rod length, the rest of the bottom end is D15 spec (i.e. rod and crank bearings). D15B has D16 sized rod journals. D15B uses the same p28 rods that the D16z6 does. All other D15s have smaller rod journals.

·The B18A/B Rod has the same bearing bore as a D16. It is 0.044" wider, so the sides of the "big end" of the rod have to be shaved down for use in a D16/17. The wrist pin bore is larger so a conventional D15/16/17 piston can only be used if the stock "small end" bushing in the rod is replaced with one of the proper size. These affordable rods are generally considered to be able to handle up to 300 HP.

·There is a D16 motor that runs on compressed natural gas (96-98 Civic GX). The pistons from that motor have a 12.5:1 CR. The wrist pin bore in the 98-00 D16B5 is 21 mm, like the B18B rod. D17A7 01-05 Civic GX uses 19 mm wrist pins.

·Interestingly enough, the Suzuki Vitara has a 75mm bore as well, so engine builders have occasionally used these pistons in the D16 motor. These pistons are commonly referred to as Vitaras, and they provide an 8.5:1 compression ratio, and thicker ring lands. Lowering the stock compression ratio lowers compression heat, which raises the detonation thresh-hold and is useful when employing forced induction.



Mini-Me

One of the most popular and effective methods of achieving greater power from a D-series motor is replacing the cylinder head with one from a more powerful D-series motor. This is usually done between D16A6 and D16Z6 or D16Y7 and D16Y8 engines. The Z6 and Y8 heads are VTEC (Variable Valve Timing and Lift Electronic Control) equipped, and increase horsepower significantly over stock levels. This operation is known as a "Mini Me" or partial swap. Mini Me's are popular because they offer a substantial performance upgrade by adding VTEC to the motor at a relatively low cost.


Engine Specs


D13 Series Engines (1.3 Litre)

D13B1

* Found in:
o 1987-1991 Honda Civic DX (European Market)
+ Displacement : 1343 cm3
+ Bore and Stroke : 75 mm X 76 mm
+ Compression : 9.5:1
+ Power, Torque : n/s (Not stated in Owners Manual)
+ Valvetrain : SOHC, 4 valves per cylinder
+ Fuel Control : Single Carburettor


D13B2

* Found in:
o 1992-1995 Honda Civic DX (European Market)
+ Displacement : 1343 cm3
+ Bore and Stroke : 75 mm X 76 mm
+ Compression : 9:1
+ Power, Torque : 75 hp @ 5300 rpm
+ Valvetrain : SOHC, 4 valves per cylinder
+ Fuel Control : Carburettor


D14 Series Engines (1.4 Litre)

D14A1

* Found in:
o 1987-1991 Honda Civic GL and 1990 CRX (European Market)
+ Displacement : 1396 cm3
+ Bore and Stroke : 75 mm X 79 mm
+ Compression : 9.3:1
+ Power, Torque : 90 ps (90 bhp) @ 6300 rpm, 112Nm @ 4500 rpm
+ Valvetrain : SOHC, 4 valves per cylinder
+ Fuel Control : Dual Carburettor


D14A2

* Found in:
o 1995-1996 Honda Civic MA8 (European Market)
+ Displacement : 1396 cm3
+ Bore and Stroke : 75.0 mm X 79.0 mm
+ Compression : 9.2:1
+ Power, Torque : 66kW @ 6100 rpm, 117Nm @ 5000 rpm
+ Valvetrain : SOHC, 4 valves per cylinder
+ Fuel Control : PGM-FI


D15 Series Engines (1.5 Liters)

D15A2

* Found in:
o 1984-1987 Honda CRX HF
+ Displacement : 1488 cm3
+ Bore and Stroke : 74 mm X 86.5 mm
+ Compression : 9.6:1
+ Power : 58 hp @ 4500 rpm & 80 ft·lbf @ 2500 rpm
+ Valvetrain : SOHC
+ Fuel Control : carburete


D15A3

* Found in:
o 1985-1987 Honda CRX Si and 1987 Civic Si (AU/NZ)
+ Displacement : 1488 cm3
+ Bore and Stroke : 74 mm X 86.5 mm
+ Compression : 8.7:1
+ Power : 91 hp @ 5500 rpm & 93 ft·lbf @ 4500 rpm
+ Valvetrain : SOHC, 3 valves/cylinder
+ Fuel Control : Fuel Injected, Multi-point PGM-FI


D15B

* VTEC
* Found in:
o 1991-1999 Honda Civic VTi EG4 (Japanese Market)
+ Displacement : 1493 cm3
+ Bore and Stroke : 75 mm X 84.5 mm
+ Rod Length : 137 mm
+ Compression : 9.6:1
+ Power : 130 hp @ 6800 rpm & 102 ft·lbf @ 5200 rpm
+ Valvetrain : SOHC VTEC
+ Fuel Control : OBD-1 MPFI

* 3-stage VTEC
* Found in:
o 1996-1999 Honda Civic VTi EK3 and Ferio Vi
+ Displacement : 1493 cm3
+ Bore and Stroke : 75 mm X 84.5 mm
+ Rod Length : 137 mm
+ Compression : 9.6:1
+ Power : 130 hp @ 6800 rpm & 102 ft·lbf @ 5200 rpm
+ Valvetrain : SOHC VTEC
+ Fuel Control : OBD-2 MPFI


D15B1

(Essentially a D15B2 engine with a mild camshaft, a restrictor plate under the DPFI, and an air flow restricton in the DPFI unit)

* Found in:
o 1988-1991 Honda Civic STD Hatchback
+ Displacement : 1493 cm3
+ Bore and stroke : 75 mm X 84.5 mm
+ Compression : 9.2:1
+ Power : 70 hp @ 5500 rpm & 83 ft·lbf @ 3000 rpm
+ Valvetrain : SOHC (4 valves per cylinder)
+ Fuel Control : OBD-O DPFI


D15B2

* Found in:
o 1988-1991 Honda Civic DX/LX, CRX DX, Civic Wagon DX/Wagovan,
o 1992-1995 Honda Civic Hatchback LSi (European Market)
+ Displacement : 1493 cm3
+ Bore and Stroke : 75 mm X 84.5 mm
+ Compression : 9.2:1
+ Power : 92 hp @ 6000 rpm & 89 ft·lbf @ 4500 rpm
+ Valvetrain : SOHC (4 valves per cylinder)
+ Fuel Control : OBD-0 DPFI


D15B6

* Found in:
o 1988-1991 Honda CRX HF
+ Displacement : 1493 cm3
+ Bore and Stroke : 75 mm X 84.5 mm
+ Compression : 9.1:1
+ Power : 62 hp(88-89) 70 hp(90-91)@ 4500 & 83 ft·lbf @ 3000 rpm
+ Valvetrain : SOHC (2 valves per cylinder)
+ Fuel Control : OBD-0 MPFI


D15B7

* Found in:
o 1992-1995 Honda Civic DX/LX
o 1992-1995 Honda Civic LSi Coupe (European Market)
+ Displacement : 1493 cm3
+ Bore and Stroke : 75 mm X 84.5 mm
+ Compression : 9.2:1
+ Power : 102 hp @ 5900 rpm & 98 ft·lbf @ 5000 rpm
+ Valvetrain : SOHC (4 valves per cylinder)
+ Fuel Control : OBD-1 MPFI


D15B8

* Found in:
o 1992-1995 Honda Civic CX
+ Displacement : 1493 cm3
+ Bore and Stroke : 75 mm X 84.5 mm
+ Compression : 9.1:1
+ Power : 100 hp @ 4500 rpm & 83 ft·lbf @ 3000 rpm
+ Valvetrain : SOHC (2 valves per cylinder)
+ Fuel Control : OBD-1 MPFI

ITS 70 HP!!


D15Z1

* VTEC-E
* Found in:
o 1992-1995 Honda Civic VX
o 1992-1995 Honda Civic VEi (European Market)
+ Displacement : 1493 cm3
+ Bore and Stroke : 75 mm X 84.5 mm
+ Rod Length : 137 mm
+ Compression : 9.3:1
+ Power : 92 hp @ 5500 rpm & 97 ft·lbf @ 4500 rpm
+ VTEC Switchover : 2500 rpm
+ Valvetrain : SOHC VTEC-E (4 valves per cylinder)
+ Fuel Control : OBD-1 MPFI


D16 Series Engines (1.6 Liters)

D16A1

* Found in:
o 1986-89 Acura Integra (North America)
+ Displacement : 1590 cm3
+ Bore and Stroke : 75 mm X 90 mm
+ Compression : 9.3:1
+ Power : 113 hp @ 6250 rpm & 99 ft·lbf @ 5500 rpm
+ Valvetrain : DOHC
+ Fuel Control : OBD-0 MPFI


D16A3

* Found in:
o 1986-89 Acura Integra (Australia)
+ Displacement : 1590 cm3
+ Bore and Stroke : 75 mm X 90 mm
+ Compression : 9.5:1
+ Power : 118 hp @ 6500 rpm & 103 ft·lbf @ 5500 rpm
+ Valvetrain : DOHC
+ Fuel Control : OBD-0 MPFI


D16A6

* Found in:
o 1988-1991 Honda Civic Si, CRX Si, Civic Wagon RT4WD
o 1988-1995 Honda Civic Shuttle RT4WD (UK/Europe/Asia/AU/NZ)
o 1989-1996 Rover 216/416 GTI (UK/Europe)
+ Displacement : 1590 cm3
+ Bore and Stroke : 75 mm X 90 mm
+ Compression : 9.6:1
+ Power : 110 hp @ 6000 rpm & 100 ft·lbf @ 5000 rpm
+ Valvetrain : SOHC
+ Fuel Control : OBD-0 Multi-point PGM-FI
+ Head Code : PM3


D16A8

* Found in:
o 1988-1991 Civic/CRX/Concerto (UK/Europe/Australia)
o 1990-1995 Rover 216/416 (UK/Europe)
+ Displacement : 1590 cm3
+ Bore and Stroke : 75 mm X 90 mm
+ Compression : 9.5:1
+ Power : 122 hp @ 6800 rpm & 108 ft·lbf @ 5700 rpm
+ Valvetrain : DOHC
+ Fuel Control : OBD-0 MPFI


D16A9

* Found in:
o 1988-1991 Civic/CRX/Concerto (UK/Europe)
o 1989-1996 Rover 216/416 GTI (UK/Europe)
o 1992-1995 Civic Si (Peruvian version)
o 1992-1995 Civic GTi
+ Displacement : 1590 cm3
+ Bore and Stroke : 75 mm X 90 mm
+ Compression : 9.5:1
+ Power : 130 hp @ 6800 rpm & 108 ft·lbf @ 5700 rpm
+ Valvetrain : DOHC
+ Fuel Control : OBD-0 MPFI


D16Y5

* VTEC-E
* Found in:
o 1996-2000 Honda Civic HX
+ Displacement : 1590 cm3
+ Bore and Stroke : 75 mm X 90 mm
+ Compression : 9.4:1
+ Power : 115 hp@ 6200 rpm & 104 ft·lbf @ 5400 rpm
+ Valvetrain : SOHC VTEC-E
+ Fuel Control : OBD-2 MPFI
+ Head Code : PJ2


D16Y7

* Found in:
o 1996-2000 Honda Civic DX/LX/CX, 1996-97 Del Sol S
+ Displacement : 1593 cm3
+ Bore and Stroke : 75.5 mm X 90 mm
+ Compression : 9.4:1
+ Power : 106 hp @ 6200 rpm
+ Torque (ft·lb@rpm): 103 (141 N·m) @ 4,600 rpm
+ Valvetrain : SOHC
+ Fuel Control : OBD-2 MPFI
+ Head Code : P2F


D16Y8

* VTEC
* Found in:
o 1996-2000 Honda Civic EX
o 1996-1998 Honda Civic Coupe SiR (UK model
o 1997-2000 Acura 1.6EL
o 1996-1998 Honda Civic Si
+ Displacement : 1590 cm3
+ Bore and Stroke : 75 mm X 90 mm
+ Compression : 9.6:1
+ Power : 127 hp @ 6600 rpm & 107 ft·lbf @ 5500 rpm
+ VTEC Switchover: 5200 rpm
+ Valvetrain : SOHC VTEC
+ Fuel Control : OBD-2 MPFI
+ Head Code : P2J


D16Z6

* VTEC
* Found in:
o 1992-1995 Honda Civic EX/Si, Del Sol Si,
o 1992-1995 Honda Civic ESi (European Market)
+ Displacement : 1590 cm3
+ Bore and Stroke : 75 mm X 90 mm
+ Compression : 9.4:1
+ Power : 125 hp @ 6500 rpm & 106 ft·lbf @ 5200 rpm
+ VTEC Switchover 4800 rpm
+ Valvetrain : SOHC VTEC
+ Fuel Control : OBD-1 MPFI
+ Head Code : P08


D17 Series Engines (1.7 Liters)

D17A1

* Found in:
o 2001-2005 Honda Civic DX/LX/VP
+ Displacement : 1668 cm3
+ Bore and Stroke : 75 mm X 94.4 mm
+ Compression : 9.5:1
+ Power : 5646 hp @ 6100 rpm & 110 ft·lbf @ 4500 rpm
+ Valvetrain : SOHC
+ Fuel Control : OBD-2 MPFI


D17A2

* VTEC
* Found in:
o 2001-2005 Honda Civic EX
+ Displacement : 1668 cm3
+ Bore and Stroke : 74.98 mm X 94.4 mm
+ Compression : 9.9:1
+ Power : 127 hp @ 6300 rpm & 114 ft·lbf @ 4400 rpm
+ Valvetrain : SOHC VTEC-E
+ Fuel Control : OBD-2 MPFI


D17A6

* VTEC-E
* Found in:
o 2001-2005 Honda Civic HX
+ Displacement : 1668 cm3
+ Bore and Stroke : 75 mm X 94.4 mm
+ Compression : 9.5:1
+ Power : 170 hp @ 6100 rpm & 111 ft·lbf @ 4500 rpm
+ Valvetrain : SOHC VTEC-E
+ Fuel Control : OBD-2 MPFI


D17A7

* Found in:
o 2004-2005 Honda Civic DX
o Uses CNG (Compressed Natural Gas)
+ Displacement : 1668 cm3
+ Bore and Stroke : 75 mm X 94.4 mm
+ Compression : 12.5:1
+ Power : 100 @ 6100 rpm & 98 ft·lbf @ 4000 rpm
+ Valvetrain : SOHC
+ Fuel Control : OBD-2 MPFI

Initial List created from Honda Engine List (6-19-2006). on HondaSwap.com



ZC (similar to D16A1, D16A3, D16A6, D16A8 and D16A9 engines)

A few D-series variants are labelled "ZC" (usually JDM), but they are not truly a different series. There are both SOHC and DOHC ZC engines. The SOHC ZC is similar to the D16A6 engine, and the DOHC ZC is similar to the D16A1, D16A3, D16A8 and D16A9 engines.

Euro Mk1 (85-87) 1.6 CRX's are fitted with an engine designated "ZC1" which is a higher spec 125bhp version of the D16a1.

Types of bearings

There are many types of rolling-element bearings, each tuned for a specific kind of load and with specific advantages and disadvantages. For example:


Ball bearings

Ball bearings use spheres instead of cylinders. Clever use of surface tension allows balls of high accuracy to be made much more cheaply than comparable cylinders. Ball bearings can support both radial (perpendicular to the shaft) and axial loads (parallel to the shaft). For lightly-loaded bearings, balls offer lower friction than rollers. Ball bearings can operate when the bearing races are misaligned.



Roller bearings

Common roller bearings use cylinders of slightly greater length than diameter. Roller bearings typically have higher radial load capacity than ball bearings, but a low axial capacity and higher friction under axial loads. If the inner and outer races are misaligned, the bearing capacity often drops quickly compared to either a ball bearing or a spherical roller bearing.

Roller bearings are the earliest known type of rolling-element-bearing, dating back to at least 40 BC.



Needle bearing

Needle roller bearings use very long and thin cylinders. Since the rollers are thin, the outside diameter of the bearing is only slightly larger than the hole in the middle. However, the small-diameter rollers must bend sharply where they contact the races, and thus the bearing fatigues relatively quickly.



Tapered roller bearing

Tapered roller bearings use conical rollers that run on conical races. Most roller bearings only take radial loads, but taper roller bearings support both radial and axial loads, and generally can carry higher loads than ball bearings due to greater contact area. Taper roller bearings are used, for example, as the wheel bearings of most cars, trucks, buses, and so on. The downsides to this bearing is that due to manufacturing complexities, tapered roller bearings are usually more expensive than ball bearings; and additionally under heavy loads the tapered roller is like a wedge and bearing loads tend to try to eject the roller; the force from the collar which keeps the roller in the bearing adds to bearing friction compared to ball bearings.




Spherical roller bearings

* Spherical roller bearings use rollers that are thicker in the middle and thinner at the ends; the race is shaped to match. Spherical roller bearings can thus adjust to support misaligned loads. However, spherical rollers are difficult to produce and thus expensive. And, the bearings have higher friction than a comparable ball bearing since different parts of the spherical rollers run at different speeds on the rounded race and thus there are opposing forces along the bearing/race contact.




Thrust bearing

An axial load is supported by this type, typically to support a vertical shaft against gravitational loads. (Contrary to the illustration, either spherical or conical rollers are typically used.)



Other types

Most rolling-element bearing designs are for rotating or oscillating loads, but there are also linear bearing designs. A common example is drawer-support hardware. Another example is a bearing for a shaft which moves axially in a hole. Axial-motion bearings often work like the stone-and-log example, with a pathway so rolling elements that fall off the end are pushed around to the other end, and the load rolls on to it. These are called recirculating bearings and were used in automotive steering units before the extensive introduction of the rack and pinion unit.



Bearing failure

Rolling-element bearings often work well in non-ideal conditions. But sometimes minor problems cause bearings to fail quickly and mysteriously. For example, with a stationary (non-rotating) load, small vibrations can gradually press out the lubricant between the races and rollers or balls (False brinelling). Without lubricant the bearing fails, even though it is not rotating and thus is apparently not being used. For these sorts of reasons, much of bearing design is about failure analysis.

There are three usual limits to the lifetime or load capacity of a bearing: abrasion, fatigue and pressure-induced welding. Abrasion is when the surface is eroded by hard contaminants scraping at the bearing materials. Fatigue is when a material breaks after it is repeatedly bent and released. Where the ball or roller touches the race there is always some bending, and hence a risk of fatigue. Smaller balls or rollers bend more sharply, and so tend to fatigue faster. Pressure-induced welding is when two metal pieces are pressed together at very high pressure and they become one. Although balls, rollers and races may look smooth, they are microscopically rough. Thus, there are high-pressure spots which push away the bearing lubricant. Sometimes, the resulting metal-to-metal contact welds a tiny part of the ball or roller to the race. As the bearing continues to rotate, the weld is then torn apart, but it may leave race welded to bearing or bearing welded to race.

Although there are many other apparent causes of bearing failure, most can be reduced to these three. For example, a bearing which is run dry of lubricant fails not because it is "without lubricant", but because lack of lubrication leads to fatigue and welding, and the resulting wear debris can cause abrasion. Similar events occur in false brinelling damage.



Constraints and trade-offs

All parts of a bearing are subject to many design constraints. For example, the inner and outer races are often complex shapes, making them difficult to manufacture. Balls and rollers, though simpler in shape, are small; since they bend sharply where they run on the races, the bearings are prone to fatigue. The loads within a bearing assembly are also affected by the speed of operation: rolling-element bearings may spin over 100,000 rpm, and the principal load in such a bearing may be centrifugal force rather than the applied load. Smaller rolling elements are lighter and thus have less centrifugal force, but smaller elements also bend more sharply where they contact the race, causing them to fail more rapidly from fatigue.

There are also many material issues: a harder material may be more durable against abrasion but more likely to suffer fatigue fracture, so the material varies with the application, and while steel is most common for rolling-element bearings, plastics, glass, and ceramics are all in common use. A small defect (irregularity) in the material is often responsible for bearing failure; one of the biggest improvements in the life of common bearings during the second half of the 1900s was the use of more homogeneous materials, rather than better materials or lubricants (though both were also significant). Lubricant properties vary with temperature and load, so the best lubricant varies with application.

Although bearings tend to wear out with use, designers can make tradeoffs of bearing size and cost versus lifetime. A bearing can last indefinitely -- longer than the rest of the machine -- if it is kept cool, clean, lubricated, is run within the rated load, and if the bearing materials are sufficiently free of microscopic defects. Note that cooling, lubrication, and sealing are thus important parts of the bearing design.

The needed bearing lifetime also varies with the application. For example, Harris reports on an oxygen pump bearing in the U.S. Space Shuttle which could not be adequately isolated from the liquid oxygen being pumped, but all lubricants reacted with the oxygen leading to fires and other failures. The solution was to lubricate the bearing with the oxygen. Although liquid oxygen is a poor lubricant, it was adequate, since the service life of the pump was just a few hours.

The operating environment and service needs are also important design considerations. Some bearing assemblies require routine addition of lubricants, while others are factory sealed, requiring no further maintenance for the life of the mechanical assembly. Although seals are appealing, they increase friction, and a permanently-sealed bearing may have the lubricant contaminated by hard particles, such as steel chips from the race or bearing, sand, or grit that got past the seal. Contamination in the lubricant is abrasive and greatly reduces the operating life of the bearing assembly.

Rolling-element bearing

A rolling-element bearing is a bearing which carries a load by placing round elements between the two pieces. The relative motion of the pieces causes the round elements to roll (tumble) with little sliding.

One of the earliest and best-known rolling-element bearings are sets of logs laid on the ground with a large stone block on top. As the stone is pulled, the logs roll along the ground with little sliding friction. As each log comes out the back, it is moved to the front where the block then rolls on to it. You can imitate such a bearing by placing several pens or pencils on a table and placing your hand on top of them. See "bearings" for more on the historical development of bearings.

A rolling-element rotary bearing uses a shaft in a much larger hole, and cylinders called "rollers" tightly fill the space between the shaft and hole. As the shaft turns, each roller acts as the logs in the above example. However, since the bearing is round, the rollers never fall out from under the load.

Rolling-element bearings have the advantage of a good tradeoff between cost, size, weight, carrying capacity, durability, accuracy, friction, and so on. Other bearing designs are often better on one specific attribute, but worse in most other attributes, although fluid bearings can sometimes simultaneously outperform on carrying capacity, durability, accuracy, friction, rotation rate and sometimes cost. Only plain bearings have as wide use as rolling-element bearings.



Design

Typical rolling-element bearings range in size from 10 mm diameter to a few metres diameter, and have load-carrying capacity from a few tens of grams to many thousands of tonnes.

A particularly common kind of rolling-element bearing is the ball bearing. The bearing has inner and outer races and a set of balls. Each race is a ring with a groove where the balls rest. The groove is usually shaped so the ball is a slightly loose fit in the groove. Thus, in principle, the ball contacts each race at a single point. However, a load on an infinitely small point would cause infinitely high contact pressure. In practice, the ball deforms (flattens) slightly where it contacts each race, much as a tire flattens where it touches the road. The race also dents slightly where each ball presses on it. Thus, the contact between ball and race is of finite size and has finite pressure. Note also that the deformed ball and race do not roll entirely smoothly because different parts of the ball are moving at different speeds as it rolls. Thus, there are opposing forces and sliding motions at each ball/race contact. Overall, these cause bearing drag.

Most rolling element bearings use cages to keep the balls separate. This reduces wear and friction, since it avoids the balls rubbing against each other as they roll, and precludes them from jamming. Caged roller bearings were invented by John Harrison in the mid 1700s as part of his work on chronographs.

Crank pin

In a reciprocating engine, the crank pins are the bearing journals of the big end bearings, at the opposite ends of the connecting rods to the pistons. If the engine has a crankshaft, then the crank pins are the journals of the off-centre bearings of the crankshaft. In a beam engine the single crank pin is mounted on the flywheel; In a steam locomotive the crank pins are often mounted directly on the driving wheels.

Big end bearings are commonly plain bearings, but less commonly may be roller bearings, see crankshaft.

In a multi-cylinder engine, a crank pin can serve one or many cylinders, for example:

* In a straight engine each crank pin normally serves only one cylinder.

* In a V engine each crank pin usually serves two cylinders, one in each cylinder bank.

* In a radial engine each crank pin serves an entire row of cylinders.



Big end design

There are three common configurations of big end bearing:

* If a crank pin serves only one cylinder, then the big end is a relatively simple design, accommodating only one connecting rod. This design is the cheapest to produce, and is used in:
o All single cylinder engines.
o Most straight engines.
o All boxer engines.
o Some V-twin engines.

* If a crank pin serves more than one cylinder, then the corresponding cylinders may have an offset, to simplify the design of the big end bearing. This design is used in:
o Most V engines.
o Multiple row radial engines.

* If more than one cylinder is served by a single crank pin but there is no offset, then some or all of the connecting rods must be forked at the big end. This design in theory provides better engine balance than designs with an offset, but at the cost of considerable extra complexity and cost in both design and manufacture, and either more weight or closer manufacturing tolerances or both to achieve the same strength and reliability. Any extra weight added to the big end itself also carries a penalty of adding vibration and reducing balance. As the number of cylinders grows, the effect of the offset on balance becomes less important, and forked connecting rods become less common. They are mainly used in:
o Single-row radial engines.
o Some V-twin engines, notably including motorcycle engines.

Connecting rod

In a reciprocating piston engine, the connecting rod or conrod connects the piston to the crank or crankshaft.


Internal combustion engines

In modern automotive internal combustion engines, the connecting rods are most usually made of steel for production engines, but can be made of aluminium (for lightness and the ability to absorb high impact at the expense of durability) or titanium (for a combination of strength and lightness at the expense of affordability) for high performance engines, or of cast iron for applications such as motor scooters. They are not rigidly fixed at either end, so that the angle between the con rod and the piston can change as the rod moves up and down and rotates around the crankshaft.

The small end attaches to the piston pin, gudgeon pin (the usual British term) or wrist pin, which is currently most often press fit into the con rod but can swivel in the piston, a "floating wrist pin" design. The big end connects to the bearing journal on the crank throw, running on replaceable bearing shells accessible via the con rod bolts which hold the bearing "cap" onto the big end; typically there is a pinhole bored through the bearing and the big end of the con rod so that pressurized lubricating motor oil squirts out onto the thrust side of the cylinder wall to lubricate the travel of the pistons and piston rings.

The con rod is under tremendous stress from the reciprocating load represented by the piston, actually stretching and relaxing with every rotation, and the load increases rapidly with increasing engine speed. Failure of a connecting rod is one of the most common causes of catastrophic engine failure in cars, frequently putting the broken rod through the side of the crankcase and thereby rendering the engine irreparable; it can result from overheating, fatigue near a physical defect in the rod, lubrication failure in a bearing due to faulty maintenance, or from failure of the rod bolts from a defect, improper tightening, or re-use of already used (stressed) bolts where not recommended. Despite their frequent occurrence on televised competitive automobile events, such failures are quite rare on production cars during normal daily driving. This is because production auto parts have a much larger factor of safety, and often more systematic quality control.

When building a high performance engine, great attention is paid to the con rods, eliminating stress risers by such techniques as grinding the edges of the rod to a smooth radius, shot peening to relieve internal stress, balancing all con rod/piston assemblies to the same weight and Magnafluxing to reveal otherwise invisible small cracks which would cause the rod to fail under stress. In addition, great care is taken to torque the con rod bolts to the exact value specified; often these bolts must be replaced rather than reused. The big end of the rod is fabricated as a unit and cut or cracked in two to establish precision fit around the big end bearing shell. Therefore, the big end "caps" are not interchangeable between con rods, and when rebuilding an engine, care must be taken to ensure that the caps of the different con rods are not mixed up. Both the con rod and its bearing cap are usually embossed with the corresponding position number in the engine block.

Recent engines such as the Ford 4.6 liter engine and the Chrysler 2.0 liter engine, have connecting rods made using powder metallurgy, which allows more precise control of size and weight with less machining and less excess mass to be machined off for balancing. The cap is then separated from the rod by a fracturing process, which results in an uneven mating surface due to the grain of the powdered metal. This ensures that upon reassembly, the cap will be perfectly positioned with respect to the rod, compared to the minor misalignments which can occur if the mating surfaces are both flat.

A major source of engine wear is the sideways force exerted on the piston through the con rod by the crankshaft, which typically wears the cylinder into an oval cross-section rather than circular, making it impossible for piston rings to correctly seal against the cylinder walls. Geometrically, it can be seen that longer con rods will reduce the amount of this sideways force, and therefore lead to longer engine life. However, for a given engine block, the sum of the length of the con rod plus the piston stroke is a fixed number, determined by the fixed distance between the crankshaft axis and the top of the cylinder block where the cylinder head fastens; thus, for a given cylinder block longer stroke, giving greater engine displacement and power, requires a shorter connecting rod (or a piston with smaller compression height), resulting in accelerated cylinder wear.

In certain types of engine, master/slave rods are used rather than the simple type shown in the picture above. The master rod carries one or more ring pins to which are bolted the much smaller big ends of slave rods on other cylinders. Radial engines typically have a master rod for one cylinder and slave rods for all the other cylinders in the same bank. Certain designs of V engines use a master/slave rod for each pair of opposite cylinders. On the other hand, some V engines use simple rods side by side on a single crankpin, or separate crankpins for each cylinder.


Steam engines

In a steam locomotive, the crank pins are often mounted directly on one or more pairs of driving wheels, and the axle of these wheels serves as the crankshaft. The connecting rods, also called the main rods, run between the crank pins and crosshead bearings, where they connect to the piston rods. Crosshead rod systems are also used on large diesel engines manufactured for marine service.

See also steam locomotive nomenclature.

Cam

A cam is a projecting part of a rotating wheel or shaft that strikes a lever at one or more points on its circular path. The cam can be a simple tooth, as is used to deliver pulses of power to a steam hammer, for example, or an eccentric disc or other shape that produces a smooth oscillating motion in the follower which is a lever making contact with the cam.


The cam can be seen as a device that translates movement from circular to linear. Another common example is the camshaft of a car or automobile, which takes the rotary motion of the engine and translates it into the linear motion necessary to operate the intake and exhaust valves of the cylinders.

The opposite operation, translation of linear motion to circular motion, is done by a crank. An example is the crankshaft of a car, which takes the linear motion of the pistons and translates it into the rotary motion necessary to operate the wheels.

Certain cams can be characterized by their displacement diagrams which reflect the changing position a roller follower would make as the cam rotates about an axis. These diagrams relate angular position to the radial displacement experienced at that position. Several key terms are relevant in such a construction of plate cams: base circle, prime circle (with radius equal to the sum of the follower radius and the base circle radius), and the pitch curve which is the radial curve traced out by appling the radial displacements away from the prime circle across all angles. Displacement diagrams are traditionally presented as graphs with non-negative values.

Ignition coil

An ignition coil (also called a spark coil) is an induction coil in an automobile's ignition system which transforms a storage battery's 12 volts to the thousands of volts needed to spark the spark plugs.

This specific form of the autotransformer, together with the contact breaker, converts low voltage from a battery into the high voltage required by spark plugs in an internal combustion engine.

In older vehicles a single (large) coil would serve all the spark plugs via the ignition distributor.

In modern systems, the distributor is omitted and ignition is instead electronically controlled. Much smaller coils are used with one coil for each spark plug or one coil serving two spark plugs (so two coils in a four-cylinder car). These coils may be remote-mounted or they may be placed on top of the spark plug (coil-on-plug or Direct Ignition). Where one coil serves two spark plugs (in two cylinders), it is through the "wasted spark" system. In this arrangement the coil generates two sparks per cycle to both the cylinders. The fuel in the cylinder that is nearing the end of its compression stroke is ignited, whereas the spark in its companion that is nearing the end of its exhaust stroke has no effect. The wasted spark system is more reliable than a single coil system with a distributor and cheaper than coil-on-plug.

Where the coils are remote mounted they may all be contained in a single moulded block with multiple high-tension terminals. This is commonly called a coil-pack.

Modern ignition systems

Mechanically timed ignition

Most four-stroke engines have used a mechanically timed electrical ignition system. The heart of the system is the distributor which contains a rotating cam running off the engine's drive, a set of breaker points, a condenser, a rotor and a distributor cap. External to the distributor is the ignition coil, the spark plugs, and wires linking the spark plugs and ignition coil to the distributor.

The power source is a lead-acid battery, kept charged by the car's electrical system, which generates electricity using a dynamo or alternator. The engine operates contact breaker points, which interrupt the current flow to an induction coil (known as the ignition coil).

The ignition coil consists of two transformer windings sharing a common magnetic core -- the primary and secondary windings. An alternating current in the primary induces alternating magnetic field in the coil's core. Because the ignition coil's secondary has far more windings than the primary, the coil is a step-up transformer which induces a much higher voltage across the secondary windings. For an ignition coil, one end of windings of both the primary and secondary are connected together. This common point is connected to the battery (usually through a current-limiting resistor). The other end of the primary is connected to the points within the distributor. The other end of the secondary is connected, via the distributor cap and rotor, to the spark plugs.

The ignition firing sequence begins with the points (or contact breaker) closed. A steady current flows from the battery, through the current-limiting resistor, through the coil primary, across the closed breaker points and finally back to the battery. This steady current produces a magnetic field within the coil's core. This magnetic field forms the energy reservoir that will be used to drive the ignition spark.

As the engine turns, so does the cam inside the distributor. The points ride on the cam so that as the engine turns and reaches the top of the engine's compression cycle, a high point in the cam causes the breaker points to open. This breaks the primary winding's circuit and abruptly stops the current flow through the breaker points.

Without the steady current flow through the points, the magnetic field generated in the coil immediately begins to quickly collapse. This rapid decay of the magnetic field induces a high voltage in the coil's secondary windings.

At the same time, current exits the coil's primary winding and begin to charge up the capacitor ("condenser") that lies across the now-open breaker points. This capacitor and the coil’s primary windings form an oscillating LC circuit. This LC circuit produces a damped, oscillating current which bounces energy between the capacitor’s electric field and the ignition coil’s magnetic field. The oscillating current in the coil’s primary, which produces an oscillating magnetic field in the coil, extends the high voltage pulse at the output of the secondary windings. This high voltage thus continues beyond the time of the initial field collapse pulse. The oscillation continues until the circuit’s energy is consumed.

The ignition coil's secondary windings are connected to the distributor cap. A turning rotor, located on top of the breaker cam within the distributor cap, sequentially connects the coil's secondary windings to one of the several wires leading to each engine's spark plugs. The extremely high voltage from the coil's secondary – often higher than 1000 volts -- causes a spark to form across the gap of the spark plug. This, in turn, ignites the compressed air-fuel mixture within the engine. It is the creation of this spark which consumes the energy that was originally stored in the ignition coil’s magnetic field.

High performance engines with 8 or more cylinders that operate at high r.p.m. as in motor racing that demand higher rate and energy of sparks than the simple ignition circuit can provide may use either of these adaptations:

* Two complete sets of coil, breaker and condenser can be provided for each half of the engine which is arranged in V-8 or V-12 configuration. Although the two ignition system halves are electrically independent, they typically share a single distributor which in this case contains two breakers driven by the rotating cam, and a rotor with two isolated conducting planes for the two high voltage inputs.

* A single breaker driven by a cam and a return spring is limited in spark rate by the onset of contact bounce or float at high rpm. This limit can be overcome by substituting for the breaker a pair of breakers that are connected electrically in parallel but spaced on opposite sides of the cam so they are driven out of phase. Each breaker then switches at half the rate of a single breaker and the "dwell" time for current buildup in the coil is maximised since it is shared between the breakers.

The Lamborghini V-12 engine has both these adaptations and therefore uses two ignition coils and a single distributor that contains 4 contact breakers.

Except that more separate elements are involved, a distributor-based system is not greatly different from a magneto system. There are also advantages to this arrangement. For example, the position of the contact breaker points relative to the engine angle can be changed a small amount dynamically, allowing the ignition timing to be automatically advanced with increasing revolutions per minute (RPM) and/or increased manifold vacuum, giving better efficiency. However it is necessary to check periodically the maximum opening gap of the breaker(s), using a feeler gauge, since this mechanical adjustment affects the "dwell" time during which the coil charges, and breakers should be replaced when they have become pitted by electric arcing.

This system was used almost universally until the late 1970s, when electronic ignition systems started to appear.



Electronic ignition

The disadvantage of the mechanical system is the use of breaker points to interrupt the low voltage high current through the primary winding of the coil; the points are subject to mechanical wear where they ride the cam to open and shut, as well as oxidation and burning at the contact surfaces from the constant sparking. They require regular adjustment to compensate for wear, and the opening of the contact breakers, which is responsible for spark timing, is subject to mechanical variations. In addition, the spark voltage is also dependent on contact effectiveness, and poor sparking can lead to lower engine efficiency. A mechanical contact breaker system cannot control an average ignition current of more than about 3 A while still giving a reasonable service life, and this may limit the power of the spark and ultimate engine speed.

Electronic ignition (EI) solves these problems. In the initial systems, points were still used but they only handled a low current which was used to control the high primary current through a solid state switching system. Soon, however, even these contact breaker points were replaced by an angular sensor of some kind - either optical, where a vaned rotor breaks a light beam, or more commonly using a Hall effect sensor, which responds to a rotating magnet mounted on a suitable shaft. The sensor output is shaped and processed by suitable circuitry, then used to trigger a switching device such as a thyristor, which switches a large flow of current through the coil. The rest of the system (distributor and spark plugs) remains as for the mechanical system. The lack of moving parts compared with the mechanical system leads to greater reliability and longer service intervals. For older cars, it is usually possible to retrofit an EI system in place of the mechanical one. In some cases, a modern distributor will fit into the older engine with no other modifications.

Other innovations are currently available on various cars. In some models, rather than one central coil, there are individual coils on each spark plug. This allows the coil a longer time to accumulate a charge between sparks, and therefore a higher energy spark. A variation on this has each coil handle two plugs, on cylinders which are 360 degrees out of phase (and therefore reach TDC at the same time); in the four cycle engine this means that one plug will be sparking during the end of the exhaust stroke while the other fires at the usual time, a so-called "wasted spark" arrangement which has no drawbacks apart from faster spark plug erosion; the paired cylinders are 1/4 and 2/3. Other systems do away with the distributor as a timing apparatus and use a magnetic crank angle sensor mounted on the crankshaft to trigger the ignition at the proper time.

During the 1980s, EI systems were developed alongside other improvements such as fuel injection systems. After a while it became logical to combine the functions of fuel control and ignition into one electronic system known as an engine management system.



Engine management

In an Engine Management System (EMS), electronics control fuel delivery, ignition timing and firing order. Primary sensors on the system are engine angle (crank or Top Dead Center (TDC) position), airflow into the engine and throttle demand position. The circuitry determines which cylinder needs fuel and how much, opens the requisite injector to deliver it, then causes a spark at the right moment to burn it. Early EMS systems used analogue computer circuit designs to accomplish this, but as embedded systems became fast enough to keep up with the changing inputs at high revolutions, digital systems started to appear.

Some designs using EMS retain the original coil, distributor and spark plugs found on cars throughout history. Other systems dispense with the distributor and coil and use special spark plugs which each contain their own coil (Direct Ignition). This means high voltages are not routed all over the engine, they are created at the point at which they are needed. Such designs offer potentially much greater reliability than conventional arrangements.

Modern EMS systems usually monitor other engine parameters such as temperature and the amount of uncombined oxygen in the exhaust. This allows them to control the engine to minimise unburnt or partially burnt fuel and other noxious gases, leading to much cleaner and more efficient engines.