The Main Differences Between the Gasoline Engine and the Diesel Engine Are

How Diesel Engines Work by Marshall Brain

Photo courtesy DaimlerChrysler 2.7-Liter CRD Direct-Injection diesel engine, 2003 Jeep® Grand Cherokee

The Diesel Cycle Rudolf Diesel was the man behind the idea for the diesel engine and he got the German patent for it in 1892. His wanted to create an engine with high efficiency. Gasoline engines had been invented in 1876 and, especially at that time, were not very efficient.

The main differences between the gasoline engine and the diesel engine are:

 A gasoline engine takes in a mixture of gas and air, compresses it and ignites the mixture with a spark. A diesel engine takes in just air, compresses it and then injects fuel into the compressed air. The heat of the compressed air lights the fuel spontaneously.  A gasoline engine compresses at a ratio of 8:1 to 12:1, while a diesel engine compresses at a ratio of 14:1 to as high as 25:1. The higher compression ratio of the diesel engine leads to better efficiency.  Gasoline engines generally use either carburetion, in which the air and fuel is mixed long before the air enters the cylinder, or port fuel injection, in which the fuel is injected just before the intake stroke (outside the cylinder). Diesel engines use direct fuel injection -- the diesel fuel is injected directly into the cylinder. The following illustrations show the diesel cycle in action.

Note that the diesel engine has no spark plug, that it takes in air and compresses it, and that it then injects the fuel directly into the combustion chamber (direct injection). It is the heat of the compressed air that lights the fuel in a diesel engine.

Photo courtesy DaimlerChrysler Atego six-cylinder diesel engine

1. stroke 2.stroke 3.stroke

4.stroke The Injector A fuel injector is nothing but an electronically controlled valve. It is supplied with pressurized fuel by the fuel pump in your car, and it is capable of opening and closing many times per second.

Inside a fuel injector

When the injector is energized, an electromagnet moves a plunger that opens the valve, allowing the pressurized fuel to squirt out through a tiny nozzle. The nozzle is designed to atomize the fuel -- to make as fine a mist as possible so that it can burn easily. A fuel injector firing

The amount of fuel supplied to the engine is determined by the amount of time the fuel injector stays open. This is called the pulse width, and it is controlled by the ECU.

Fuel injectors mounted in the intake manifold of the engine

The injectors are mounted in the intake manifold so that they spray fuel directly at the intake valves. A pipe called the fuel rail supplies pressurized fuel to all of the injectors. In this picture, you can see three of the injectors. The fuel rail is the pipe on the left.

In order to provide the right amount of fuel, the engine control unit is equipped with a whole lot of sensors. Let's take a look at some of them. Mechanical Fuel Injection

As this subject is large and fairly comprehensive it has been broken into the following sections:

Introduction and operational 1 2 The fuel tank overview 3 The fuel pump 4 The fuel pump relay 5 The accumulator 6 The fuel filter 7 Systems pressure 8 The airflow sensor 9 The fuel distribution unit 10 The warm up regulator 11 The cold start injector 12 The auxiliary air valve 13 The fuel injectors 14 System overview diagram

NOTE:- whilst working on any fuel system, care and attention should be taken to avoid the petrol coming in contact with any source of ignition, this can include: hot engine components, High Tension (HT) sparks and smoking.

Introduction

This form of mechanical fuel injection has been used on the internal combustion engine for many years. Mechanical fuel injection systems first saw light of day at the turn of the century, however the following 100 years has seen the system evolve from a very basic and almost crude fuel delivery system, to the recent mass produced versions of the Bosch K and KE Jetronic. The mechanical fuel injection system has recently been overshadowed by modern electronic injection, which enables the use of lambda closed loop control. The electronically modified Bosch KE also has this capability although it never achieved the popularity of the pure mechanical system.

This following overview is a brief description of the system.

Bosch K Jetronic operational overview

The system may seem very complicated at first, but it can be broken down into specific areas and fault finding is therefore made easier. Fuel is delivered from the fuel pump to a metering (or fuel distribution) head and depending on the engine's temperature, the correct amount of fuel is delivered via the injectors to the engine. The injectors on this system spray fuel continuously in a fine atomised spray into the inlet manifold.

Cold start and the warm-up period are also catered for by a cold start injector and a reduction in the control pressure. The idle speed is increased by the auxiliary air valve. The fuel pump will have the ability to provide a huge amount of fuel from the tank of which 99% will be returned. Due to the nature of this system, specialised equipment may be needed.

The Fuel Tank

The fuel tank is the obvious place to start in any fuel system explanation - unlike the tanks on early carburetor fuelled engines it is a sealed unit. This allows the natural gassing of the fuel to aid delivery to the pump by slightly pressurising the tank It may be noted that when the filler cap is removed, pressure is heard to escape. Filler caps are no longer vented as previously found. The Fuel Pump

This type of high pressure fuel pump is denoted as a roller cell pump, with the fuel entering the pump and being compressed by rotating cells that force it through the pump at high pressure. The pump is capable of producing a pressure of 8 bar (120 psi) with a delivery rate of approximately 4 to 5 litres per minute. Within the pump is a pressure relief valve that lifts off its seat at 8 bar to arrest the pressure should the filter, fuel lines or other eventualities cause it to become obstructed. The other end of the pump (output) is home to a non-return valve that, when the voltage to the pump is removed, closes the return and maintains pressure within the system, as illustrated in figure 6.1.

The normal operating pressure within this system is approximately 5 bar (75 psi) and at this pressure the current draw on the pump is 5 to 8 amps. Fuel passing across the fuel pump's armature will be subjected to sparks and arcing, this on the surface appears quite dangerous, but the absence of oxygen means that there will not be an explosion!

Some systems operate a small lift pump situated inside the tank. The supply voltage to the pump in the majority of cases is 12 volts. Some systems do however operate at 6 volts, and see a higher voltage under cranking to pressurise the system faster. This voltage reduction is made possible by using a ballast resistor, which is then by-passed when cranking.

The voltage supply to the pump is via the fuel pump relay.

Fig. 6.1

Figure 6.1 shows a cross section of an electric fuel pump.

The Fuel Pump Relay

This type of relay is known as a tachometric relay, which means that it only responds and sends a voltage to the pump when the engine is cranking or running. The relay receives a signal from the negative terminal of the coil - this confirms that the engine is turning. This type of relay is used as a safety device: if the vehicle is involved in an accident when there is a possibility of a fuel line being fractured, the engine will stop due to a lack of fuel, the signal from the coil stops and the supply voltage to the pump is removed. Typical fuel pump relay connections are as follows: Terminal Connection Number 30 Permanent battery live 31 Earth 1 or 31b Coil negative 15 Switched 'Ignition on ' voltage 87 Output to fuel pump

NOTE :- while the connections are correct for certain vehicles, the appropriate pins must be identified before testing. Certain relays also perform a pressurisation purge by allowing the pump to run for a second before shutting off, to prime the system.

The location of the relay will vary between motor manufacturers and is in no set position.

When fault finding or fuel pressure testing it will be necessary to have the pump running when the engine is stationary, this can be achieved by bridging terminals 30 and 87 with a small length of wire. For safety reasons it is good practice to insert a ten amp fuse into the bridging wire.

If the engine runs for a while but then stops, failing to restart for a few minutes, feel the relay to see if it is getting warm as this could be the faulty area. Bridging with the fused link wire will confirm the problem.

CAUTION :- do not be tempted to by-pass the relay by bridging between terminal 15 (switched live) and 87 (fuel pump) as this will start the car, but is potentially dangerous.

The Accumulator

The accumulator is the first of the components in the fuel system after the pump. This unit has an important role to fill in the operation of the Bosch K Jetronic system. Its first job is to help smooth out any pulses in the flow of the fuel, this is achieved by passing the fuel through a series of baffles and into a chamber giving it slight capacitance and a much smother flow. Its other and possibly more important role is to maintain pressure within the system when the fuel pump has been switched off; this is achieved by the accumulator spring and diaphragm pushing against the fuel. For the duration that the engine is running, the diaphragm will be against its stop within the spring's chamber. When the engine is stopped and all of the non-return valves close, the spring pressure against the diaphragm will maintain the residual or holding pressure and overcome any slight seepage.

Within the data books for this system, it is shown that the critical time for maintaining these pressures, is between 5 and 20 minutes. After a journey, when the engine is switched off, the under bonnet temperature increases causing the fuel in the lines to heat and it attempts to evaporate. Maintaining the pressure eliminates this problem and ensures a clean start when the vehicle has been standing with a hot engine. Fig. 6.2

Figure 6.2 shows an accumulator full of fuel.

The Fuel Filter

Due to the extremely fine tolerances within the Bosch K Jetronic system, it is vital that the filter has excellent filtration properties without impeding the flow on the fuel. The filter is a large metal canister with different fittings at either end to avoid the unit being installed incorrectly and compromising its efficiency. A visual inspection of the filter is not possible but the current draw of the fuel pump, measured in amps, can indicate a blocked or obscured filter. The current can be recorded by inserting a multimeter in series with the circuit, the usual place to do this is to bridge the relay's terminal block. If however the relay is not easily accessible the fuse to the pump can be removed as this also provide a convenient place to measure the current.

A typical current draw will generally be between 5 to 8 amps. The current recorded will be lower if the systems pressure is less than the quoted specifications and higher if the flow of fuel is restricted in any way, for example: a blocked filter or a damaged fuel line.

Fig. 6.3

Figure 6.3 shows an example fuel filter.

Systems Pressure

This is the pressure that is seen within the system between the fuel pump and the metering head. This pressure is determined by the primary pressure regulator, situated within the metering head. When the required pressure is obtained, the plunger within the regulator lifts off its seat and excess fuel is returned to the tank. This system due to the nature of its operation will automatically compensate for different fuel demands under different conditions. For example if the fuel requirement is low at engine idle, the plunger will lift and return a greater volume of fuel back to the tank than when the demand is higher, when a smaller amount of fuel is returned.

When the engine is switched off, the fuel pump relay looses the coil negative signals that energise it and the voltage to the pump is removed: this subsequent loss of pressure will cause the primary pressure regulator to close. This action subsequently blocks the return flow to the tank and helps the accumulator to maintain pressure in the system.

The systems pressure is determined by the tension of the spring reacting against the plunger, if a higher pressure is required, small shims can be placed behind the spring, changing it's effective length and increasing the pressure. A shim of approximately 2 mm will increase the pressure by about 10 psi

Located within the pressure regulator is the transfer valve. This component is operated by the movement of the plunger and opens as the plunger moves off it's seat. The transfer valve's function is to block the return flow of fuel from the warm-up-regulator back to the tank, also helping to maintain residual or holding pressure.

Fig. 6.4

Figure 6.4 shows the fuel distributor, primary pressure regulator and air flow sensor from the Bosch K Jetronic system.

The following table is a guide to the fuel paths marked by each blue arrow in figure 6.4.

A To fuel injectors B To warm up regulator C From warm up regulator D To cold start injector E From fuel filter F Return to fuel tank The Airflow Sensor

The airflow sensor, in most cases, is located on the air filter housing and is responsible for measuring the amount of air entering the engine. The sensor housing is conical in shape, into which the airflow sensor plate is fitted. The airflow sensor plate lifts as the throttle is opened by the incoming air. The amount of lift is proportional to the volume of air entering the engine. The shape and angle of the cone will determine this ratio.

A neutral plate position is normally level with the bottom of the cone, this is adjustable by bending a small clip / spring that acts as a stop at the bottom of the unit. The purpose of this spring is to allow the flap to move beyond its neutral position to allow excessive pressure to escape if the engine was to backfire, passing a large volume of air back into the air filter housing. If the system did not have this facility the pressure could split or blow off the rubber air trunking. Any splits or ill fitting air hoses that allow unmonitored air into the engine require rectification. As the airflow lifts the sensor plate this subsequencially lifts the control plunger - the higher the lift the greater the amount of fuel delivered to the injectors.

To adjust the fuel mixture a small 3 mm Allen screw is located within the airflow sensor; this alters the relationship between the sensor arm and the control plunger. Turning the screw clockwise enriches the mixture and vice-versa. It should be noted that the screw should be turned in very small increments and the Allen key should be removed before the engine speed is raised.

NOTE :- Failure to remove the Allen key, before starting the engine, can result in damage to the airflow sensing unit.

The Fuel Distribution Unit

This unit delivers the correct amount of fuel to the engine via the injectors referencing to the airflow sensor plate height. As the sensor plate is lifted with inducted air volume, the control plunger is lifted proportionately, exposing small slits within the fuel distributor's barrel assembly. The barrel assembly has a series (one for each cylinder) of small slits that are machined into the barrel, and it is through these openings that the fuel passes en-route to the injector.

The width of these metered slits is only 0.2 mm across and it is this dimension, together with the plunger height, that determines the fuel delivery rate to the injectors.

At low engine speed the air volume into the engine will be minimal, this will only raise the plunger a small amount giving the requisite quantity of fuel for these engine conditions. As the throttle is opened and fuel demand is higher, the plate raises, which in turn lifts the plunger and a higher volume of fuel is delivered to the engine to match the air. The lift on the plunger will be proportionate to the air volume, this will however be exaggerated during the warm-up period when additional fuel is required by reducing the pressure acting onto the top of the control plunger.

This pressure is called the control pressure (as it controls the lift of the plunger under different operating temperatures) and is determined by the warm-up-regulator.

The Warm-up-Regulator

This simple device is responsible for controlling the amount of fuel delivered to the engine during it's warm-up period. The pressure acting upon the top of the control plunger varies depending on the engine temperature and provides an effective method of enrichment.

The control pressure is tapped off from the primary pressure circuit in the metering head's lower chamber through a tiny restrictive hole which gives it the ability to differentiate between the two pressures. A flexible pipe then connects the control plunger gallery to the warm-up-regulator and returns back to the metering head to a connection next to the primary pressure regulator's transfer valve. This valve is in the circuit to close the fuel from the control circuit when the engine is off, avoiding the total loss of system pressure while the engine is stationary.

The internals of the warm-up-regulator are quite simple comprising an inlet and outlet port, a stainless steel shim, a bi-metalic heated strip and a spring.

The input to the warm-up-regulator flows into a small chamber in the top of the unit, its return is through a small drilling and back to the metering head. By controlling this return flow it will cause a change in pressure acting on the top of the control plunger. With a cold engine the flow must be fairly free giving it a lower pressure. This will allow a higher lift of the plunger which in turn will enrich the mixture under these conditions. The free flow is obtained by the internal bi-metalic strip exerting a downward pressure on the spring which decreases the pressure acting upon the shim, this lower force allows the fuel to flow almost uninterrupted.

As the bi-metalic strip is heated, by either it's heater element or natural heat soak from the engine, the downward pressure acting on the spring is gradually decreased, increasing the force of the spring, which in turn increases the control pressure.

Typical cold engine control pressure will be as low as 1.0 bar increasing over approx. 10 minutes to around 3.5 bar. Some warm-up-regulators have a vacuum connection that will sense a drop in vacuum and lower the control pressure during these acceleration periods.

The voltage supply to the regulator is from the fuel pump relay, because if the ignition was on without the engine running, all enrichment would be removed as the bi-metalic strip would be heated prematurely and the driver would not benefit from the cold engine enrichment.

The two pipes that connect to the warm-up-regulator have different sized 'banjo unions' to avoid them being connected incorrectly. The control pressures quoted are as an example only and reference should be made to the technical data as these pressures can be specific to the part number located on the unit's housing. This unit will have a resistance value of approximately 20 to 26 Ohms.

NOTE :- it is important to disconnect the electrical connection to the unit before any pressure testing on the control circuit is performed as this will prematurely heat the bi- metalic strip and cold control pressures will not be available. Fig. 6.6

Fig. 6.5

Figure 6.5 shows a diagram of a warm up regulator. Figure 6.6 shows a photograph of a warm up regulator.

The connections shown in figure 6.5, marked with blue arrows are listed below:

Vacuum connection A B Return to fuel tank (inlet manifold) Control pressure C (from fuel distributor)

The Cold Start Injector

To aid the starting of the engine an additional injector is located into the inlet manifold, this sprays fuel into the engine at systems pressure when the engine temperature is cold and the starter motor is activated. The length of time that this additional injector sprays is determined by the engine's temperature, seen by the thermo time switch. The thermo time switch provides the earth path for the cold start injector via a heated bi-metalic strip, this heater is activated by a voltage from the starter motor. As the strip heats, over a period of approximately 8 to 10 seconds (when cranking only), the legs on the bi-metalic strip separate and the earth path is lost. A warm engine will perhaps only require 2 seconds before the circuit is broken and a hot engine will already show open circuit. This simple circuit is to avoid the engine being flooded when cranking and the additional enrichment only given when essential, see illustration below.

Fig. 6.7

Figure 6.7 shows the relationship between the thermo timer switch and the cold start injector.

The Auxiliary Air Valve

This item is a device to aid the engine when cold by opening a small port to increase the engine's idle speed. The fast idle control is achieved by the port being held open by a bi-metalic strip that when heated by it's own heater element, or via natural heat soak from the engine, the port closes. The voltage supply to the air valve is the same as the feed to the fuel pump and the warm-up- regulator. If it is found that the idle speed will not reduce and that the speed is maintained artificially high when warm, clamp the rubber pipe between the air valve and the inlet manifold. If this action causes the engine rev's to return to normal, the fault is within a sticking auxiliary air valve. It is worth cleaning the valve, lubricating it and re-test it's operation. The internal heater element can also be checked for continuity using a multimeter.

Fig. 6.8 Fig. 6.9

Figure 6.8 shows an auxiliary air valve diagram and figure 6.9 an auxiliary air valve photograph. The Fuel Injectors

The injectors fitted to this system will open at a predetermined pressure and will spray a fine atomised 'mist' of fuel behind the inlet valve, waiting to be drawn in on the induction stroke. The fuel is delivered into the engine in a continuous spray and is not timed or pulsed as on other systems. The opening pressure of the injector is at approximately 3.3 bar at which point fuel is injected into the manifold; when the injector pintle opens this will cause the pressure to drop, subsequently closing the injector, which causes the pressure to rise once again and this will of course open the injector. This pintle vibration is called 'chatter' and helps to atomise the fuel before it's induction.

When the engine is switched off the fuel pressure drops below 3.3 bar and the injector closes forming a fuel tight seal, helping to avoid fuel dripping into the inlet manifold.

The spray pattern should be a conical shape and when clean and working efficiently, should emit a high frequency noise: this is the sound of the pintle 'chatter'.

Fig. 6.10

Figure 6.10 shows a cross section of a mechanical injector. System overview diagram

Fig. 6.11

Figure 6.11 shows an overview of the Bosch K-Jetronic system. Fuel Injectors

A typical fuel injector is shown below. It can be seen to be two basic parts, the nozzle and the nozzle holder or body. The high-pressure fuel enters and travels down a passage in the body and then into a passage in the nozzle, ending finally in a chamber surrounding the needle valve. The needle valve is held closed on a mitred seat by an intermediate spindle and a spring in the injector body. The spring pressure, and hence the injector opening pressure, can be set by a compression nut which acts on the spring. The nozzle and injector body are manufacture as a matching pair and are accurately ground to give a good oil seal. The two are joined by a nozzle nut.

The needle valve will open when the fuel pressure acting on the needle valve tapered face exerts a sufficient force to overcome the spring compression. The fuel then flows into a lower chamber and is forced out through a series of tiny holes. The small holes are sized and arranged to atomise, or break into tiny drops, all of the fuel oil, which will then readily burn.

Once the injector pump or timing valve cuts off the high pressure fuel supply the needle valve will shut quickly under the spring compression force. All slow-speed two-strike engines and many medium-speed four-stroke engines are now operated almost continuously on heavy fuel. A fuel circulating system is therefore necessary and this is usually arranged within the fuel injector. During injection the high-pressure fuel will shut the circulation valve for injection to take place. When the engine is stopped the fuel booster pump supplies fuel which the circulation valve directs around the injector body.

Older engine designs may have fuel injectors which are circulated with cooling water.

The figure shows a section through a hydraulically operated fuel injector as fitted to a large two- stroke diesel engine. The general design is similar for most engines and consists of a spring loaded non-return needle valve operated hydraulically by a fuel pressure wave from the fuel pump to discharge fuel at high pressure through an atomiser nozzle. A typical fuel injector will consist of a valve body or nozzle holder to which the nozzle or atomiser is secured by a retaining nut. The valve body contains the spring and its compression nut, with an intermediate spindle if required. Surfaces between the body and atomiser are ground and lapped to form an oil pressure-tight seal. A dowel ensures alignment of the oil passages. The needle valve is lapped into the bore of the atomiser and these must be kept as a matched unit. As shown in the figure there are two chambers in the nozzle, the upper one being charged with fuel oil from the fuel pump and sealed by the needle valve when closed. The lower chamber, or sac, is sealed by the mitre seat of the needle valve and has a number of small atomiser holes of correct size and pattern to atomise and distribute the fuel spray into the combustion chamber.

Injector spring compression is adjusted under test and a compression ring fitted. It is set to allow the needle valve to lift or open at a predetermined fuel pressure. The intermediate spindle conveys the spring compression to the needle valve and may be arranged to limit its lift. The valve will open when the pressure from the fuel pump action on the shoulder of the needle valve overcomes the spring compression. As the needle valve lifts, oil flows to the lower chamber in the atomiser. The additional area of the needle mitre now subjected to pressure causes the needle to lift rapidly, allowing fuel at high pressure through the atomiser holes into the combustion chamber.

When the fuel pump cuts off pressure, the valve will close under spring compression. Since the full area of the needle is now exposed to pressure, closing will occur at a pressure lower than that at which it opened. The action of the needle valve must be rapid and positive with no oil leakage.

A find edge strainer may be fitted at the fuel inlet and a priming or venting plug is fitted to the fuel passage. Valves should be primed if the engine has been out of service or during preparation for commencement of a voyage. Fuel injectors must be overhauled at regular intervals to ensure correct operation and combustion. The Fuel Injectors must be overhauled and tested in a separate Injection Workshop, the workshop must be maintained in a clean, sterile and tidy condition. The Testing Fluid containment vessel connected to the test pump, must be cleaned out on a regular basis with the system flushed through and the testing fluid replaced complete with new. Carbon and sulphur particles can get entrained in the testing fluid thus giving a false test result. A very fine lapping in compound must be used during the lapping in process. Carborundum type grinding paste’s particles can get impregnated in the lapping surfaces and cause problems. If the fine lapping in of injector parts is unsuccessful, the parts should be forwarded to a reputable fuel injection company for refurbishment. The injector compression spring must be screwed back before slackening the retaining nut. Parts are cleaned, inspected and renewed if necessary. Lapped surfaces must be free of damage and correctly aligned, springs inspected for distortion, atomiser holes must be clear and unworn. Defects in injectors, while in use, may be choking due to dirt in the fuel or carbon building up at the atomiser. A leaking needle valve will cause secondary burning and reduce combustion efficiency.

After assembly the injector is tested with a test pump. Operating pressure and fuel spray pattern are checked and there must be no leakages. Care should be taken as the high pressure fuel will puncture the skin and if this happens immediate first aid must be carried out.

Fuel injectors are inserted into pockets in the cylinder cover and must form a gas-tight joint at their lower landing. They are secured by studs and nuts.

Fuel pipes between pumps and injectors are subjected to extremely high internal oil pressure with cyclic pressure fluctuations which also cause vibrations. The pipes and their connections are therefore subjected to considerable stress and fatigue. Failure may cause a very dangerous spray of high temperature, atomised oil which is both a health hazard and a fire risk. Where such pipes are exposed, they should be enclosed in a double skin tube. The outer skin will collect any oil leakage and return it to a safe place.

Medium and high speed engines may be designed with the whole fuel pump system enclosed within protective casings. Some engines have the fuel pipe to the injector placed in a passage cast within the cylinder to the valve pocket.

When burning heavy fuel the injectors will require to be cooled. In many engines this is accomplished by circulating water or oil through additional passages in the injector assembly. Due to the risk of contamination of this coolant with fuel, an independent system is required. If atomise tip temperatures are too high, carbon may form and impede the spray; at high or low temperatures, corrosion may occur.

The design of modern two-stroke engines ensure the injectors are adequately cooled by the transfer of heat to the surrounding bore-cooled cylinder cover. Each injector is also fitted with a spring-loaded circulating valve which permits hot fuel at the circulating pump pressure to pass through passages in the valve body before returning to a buffer tank in the oil system. This maintains the valve at the correct temperature at all times, allowing the engine to be manoeuvred on heavy fuels. The high pressure wave of the engine fuel pump immediately depressed the spring, ensuring that the circulating passages are sealed off before the high pressure lifts the needle valve and injects fuel into the cylinder. A fuel valve of this type is shown below.

The ideal position or a fuel injector is in the centre of the cylinder cover, allowing a symmetrical, conical spray pattern in the combustion chamber. This is achieved in most four-stroke engines. In large engines with a centrally placed exhaust valve, injectors (usually three) are placed symmetrically around the cover and charged from a common distributor connections to inject equal quantities of fuel simultaneously.

Engine fuel systems are designed for normal working conditions. If an engine is run for long periods at low power, combustion may be inefficient, leading to fouling and possible wear. When long periods at low power are anticipated a set of low-power injectors may be fitted which have reduced orifice area giving high atomisation and peak pressure. It may also be necessary to adjust fuel pump timing. Engines with variable ignition timing fitted can adjust to low powers automatically. They may also be fitted with fuel injectors which maintain high efficiency over a wide range of operating conditions, including slow speeds.

 This illustration shows the overhead cam, rocker arms, valves, injector pump, injector, pre-combustion chamber, glow plug, and piston.

The injection equipment consists of unit injectors fitted on each cylinder of the engine. The pumping element of the unit injector is provided with a one-way feeding system.

The figure shows the unit injector layout of the FOCS engine series. This new type of unit injector is shaped at an 85° angle, so that the injector nozzle matches the top face of the precombustion chamber slightly inclined and the pumping element lies flat over the camshaft. This layout keeps the height of the engine to a minimum.

The elimination of high pressure fuel pipes, together with delivery valve optimization, keeps the injection timing constant throughout the entire range of operating speed.  Shown here is the, Model LDW 603 FOCS, engine with the valve cover removed, note the efficient component layout. This unique arrangement reduces smog emissions. (