Fuel Systems: Diesel Fuel Systems

Diesel fuel systems	Diesel fuel injection	Diesel engines draw air only, past the intake valve into the cylinder. Fuel is injected into the cylinder at high pressure. The amount of fuel injected varies to suit load, and control engine speed.
	High pressure components	For all diesel engines, at a fixed fuel setting, the amount of fuel delivered to the engine will increase as engine and pump speed increases. It must be controlled, or over-speeding of the engine will occur.
	Diesel fuel	The cetane rating of a diesel fuel defines how easily the fuel will ignite when it is injected into the cylinder. The lower a fuel's cetane rating, the longer it takes to reach ignition point.
	Diesel fuel characteristics	The primary factors that affect the performance of diesel fuel are: the cetane rating, viscosity, its cloud point, the the extent to which the fuel is contaminated.
	Quiet diesel technology	The annoying rattle of a diesel engine has largely been subdued by a combination of engineering and fuel improvements, leading to quieter engines more suitable for use in passenger vehicles.
	Clean diesel technology	Clean diesel technology is a combination of better fuel delivery and control systems, better combustion chamber design, turbocharging, and other improvements including lower sulfur fuels and dual-fuel systems.

Diesel fuel system components	Diesel tanks & lines	The fuel tank stores fuel away from the engine. Baffles ensure the pickup tube is always submerged in fuel. This stops air entering the system.
	Diesel fuel filters	Fuel filters remove abrasive particles and water.
	Lift pump	A diaphragm-type lift pump can be mounted on the engine, or the injection pump. An eccentric on a camshaft pushes on a rocker arm. It acts on a diaphragm to create a pressure difference, which lifts fuel from the tank to the injection system.
	Plunger pump	A plunger-type lift pump is mounted on the in-line injection pump, and driven by a cam inside the in-line injection pump housing.
	Priming pump	Light vehicle diesel engines use a priming pump to remove air from the fuel system. Otherwise, the engine would have to be cranked over with the starter motor, to bleed and prime the system.
	Inline injection pump	An in-line injection pump meters the fuel and raises its pressure. The basic principle is for a plunger to act on a column of fuel, to lift an injector needle off its seat.
	Mechanical or pneumatic governors	A mechanical governor uses rotating fly weights to control movement of a rack against a spring. A pneumatic governor has a venturi unit, linked to a diaphragm assembly, on the in-line injection pump housing.
	Distributor-type injection pump	The distributor-type pump uses a vane-type transfer pump to fill the single pumping element. This then raises fuel pressure to injection pressure. A distribution system then distributes fuel to each cylinder, in the firing order of the engine.
	Diesel injectors	The injection pump delivers fuel to the injector. As fuel pressure rises, it acts on the needle valve, eventually lifting it from its seat. Highly-pressurised fuel enters the engine in an atomised spray at a high velocity.
	Glow plugs	Glow plugs pre-heat the incoming air so that ignition can more easily occur. This assists a cold engine to start more reliably, and once the engine is running, the glow plugs are no longer required.
	Cummins & Detroit Diesel injection	Unit injectors have been available for many years in heavy commercial diesel engines. These include the 'Cummins Pressure Time System' and the 'Detroit Diesel System'. For both systems actuation is a result of an extra lobe on the engine camshaft for each cylinder.

Diesel electronic control	Diesel electronic control systems	Electronic controlled diesel systems give very precise control of the fuel injection and combustion process.
	Common rail diesel injection system	The Common Rail Diesel Injection System delivers a more controlled quantity of atomised fuel, which leads to better fuel economy; a reduction in exhaust emissions; and a significant decrease in engine noise during operation.
	HEUI diesel injection system	The Hydraulically actuated, Electronically controlled Unit Injector or HEUI system of diesel fuel injection operates by drawing fuel from the tank using a tandem high and low pressure fuel pump.

Topic group	Topic	Summary