How Diesel Works – Diesel Injectors

How diesel works – diesel injectors

Diesel is broadly divided into

Rotary diesel and Common Rail diesel.

This is diesel equipment which we now call early diesel. It generally has little or no electronic control and has been replaced in passenger cars by the common rail system.

Bosch and Lucas injectors
Picture (below) shows typical
Bosch and Lucas type rotary injectors…

This page is a very brief, everyday description of the different types of diesel equipment.

The main components of a diesel engine are injectors, pressure pump and glow plugs

Diesel is injected into highly compressed, hot air

Diesel engines of any type work because diesel fuel is injected into a cylinder of highly compressed air.

Because the air is compressed it is very hot ; the fuel ignites forcing the piston down into the cylinder and turning the crankshaft.

Diesel fuel has to be atomised (turned to mist or microscopic droplets) the injectors are designed to make this happen.

diesel injectors
note the absence of any electronic fittings.


A rotary diesel engine typically has a distribution pump and injectors. The pump is timed to the engine so it sends fuel under pressure to each injector at the correct time in the engine’s combustion sequence.

Typically a rotary diesel pump has a solenoid which allows the driver to cut off the supply of fuel and stop the engine; without this the engine will continue to run as long as it has a supply of fuel!

Rotary diesel can be divided into ”direct’ and ‘indirect’ injection.
Direct injection engines are designed for the fuel to be injected directly into the cylinder, typically into a bowl recess in the crown of the piston.
With indirect injection the fuel ignites in a separate combustion chamber recessed into the cylinder head.

The rate of combustion is slowed down and the engine is generally quieter and less stressed than direct injection. When starting, indirect engines generally require glowplugs to warm the fuel until the engine is running and getting warm.

Later Ford Transit 8 valve diesel engines (up to c.1999) are of the direct injection type and have a characteristically noisy diesel sound.