The C.I. Engines Fuel System  The C.I. engine demands that the fuel supplied is –  Timed to inject when the piston is near the end of the compression stroke.  The fuel is atomised (broken up) into fine particles if efficient combustion and reduced pollution are to be obtained.  The fuel is forced with sufficient pressure into to the hot air in the combustion engine.  All C.I.engines require some form of cold start device, this is because when the engine is cold, heat loss can result in the heat generated by the compression stroke insufficient to ignite the fuel. To overcome this, most C.I.engine inject addition fuel when cold (excess fuel) and use some form of electrical heating device, to raise the temperature of the air (glow plugs).  If theses demands are not met, the engine will produce excessive noise (combustion knock) and pollution.  The fuel system consists basically of a fuel tank, one or more filters, a low pressure fuel (lift) pump, a high pressure injection pump and a injector for each cylinder. Air must not be allowed to get into the fuel injection system, the engine will not run, some systems require bleeding if air is present e.g. when the fuel filter is replaced, or the vehicle runs out of fuel.

Typical C.I. Fuel System Layout (Simplified) Fuel Tank Water Trap Lift Pump Fuel Filters Fuel Injection Pump Fuel Injectors Leak Off Engine combustion Chamber

Fuel Lift Pump (Low Pressure) Typically a diaphragm pump driven off of the engine camshaft, or built into the injection pump or electrically driven in later systems May Have manual priming Function is to supply steady flow of fuel to injection pump. May incorporate a strainer filter which requires cleaning at service intervals.

Main Fuel Filters Maybe of replaceable element or cartridge type. Filter material must be of large enough surface area to allow for fuel flow, which will stop very small partials of dirt reaching the injection system Maybe large single units or consist of a ‘primary’ & ‘secondary’ filter. Must be changed at the correct service interval Incorporate the water trap

High Pressure Fuel Injection Pumps Can be of ‘Rotary’ or ‘In line’ design. Driven by the engine at half crankshaft speed Pressurises the fuel and delivers it to the injections at the correct time for combustion Accurately meters the fuel quantity to match engine load demands Incorporates a governor to control engine speed and prevent the engine over speeding and damaging itself

Fuel Injectors Each injector is fitted in the cylinder head above each combustion chamber Fuel is delivered to the injectors via thick walled high pressure steel pipes Injector pipes are of equal volume/length to ensure accuracy of timing between cylinders Each injector sprays atomized fuel in to the combustion chamber to insure complete combustion

Combustion Chambers (where the fuel is burnt) In the C.I. engine the fuel is injected into the combustion chamber, it the has to mix thoroughly with the air, ignite and burn all at the same time. To insure this happens, two types of combustion chamber have been developed. DirectInjection Indirect Injection

Some words of Caution Special care is required when working on high pressure side of system, do not allow fuel spray from an injector to contact the skin. Do not disconnect any high pressure pipes unless the system is depressurised Use barrier creams to protect skin from reaction to diesel fuel and always wash thoroughly Look after the environment by collecting & disposing of all drained oil/ fuel responsibly.