Cylinders
The cylinder is the part of the engine that produces power. It is the combustion chamber that is sealed from the environment by a piston at bottom dead center. Diesel engines use either a two-stroke or four-stroke cycle to produce power. They operate on a compression-ignition principle.
In gasoline engines, a mixture of fuel vapour and air is compressed in the cylinder and ignited by a spark shortly before BDC. In the diesel engines, a small amount of highly atomized fuel is injected into the air already at a high temperature. The fuel is then spontaneously burned in a diffusion flame. The resulting combustion creates pressure that moves the piston to top dead center (TDC) in the compression stroke. It also pushes exhaust gases through the exhaust valve. The camshaft, which is driven by the crankshaft’s revolutions, controls the timing of fuel injection and the opening of the intake and exhaust valves. The camshaft’s lobes do this by spraying the fuel into the combustion chamber in a precisely controlled pattern.
Camshaft
Located at the top of each cylinder, the camshaft takes the crank’s rotary motion and converts it into reciprocating motion. This, in turn, operates the intake and exhaust valves in each cylinder. The camshaft is long and marked with egg-shaped lobes, which are designed to open and close the engine’s valves at exactly the right times.
The cam lobes’ shape and design dictate critical factors like power output, fuel efficiency and emissions. The timing of their movement is also crucial, since it determines how well the fuel mixes with the air to initiate the combustion process. The peaks of the camshaft’s lobes push against each exhaust and intake valve, opening them to allow the air-fuel mixture to enter the cylinder for combustion and then pushing back up to close them as the piston moves downwards. A high-quality camshaft is made from chilled cast iron, a hard material that’s easy to work with, and is machined to strict tolerances.
Fuel Injection
The fuel injection system forces the right amount of diesel fuel into air that has been compressed to high pressure inside the cylinder. It is the key to efficient combustion that enables the used generators to run smoothly, reliably and with low emissions.
It consists of a fuel pump that accurately meters the diesel charge and pumps it to an accumulator (fuel rail) at high pressure. Then electrically operated camshaft-controlled mechanical valves open the injection nozzle at just the right moment to dispense the fuel into the engine.
The fuel injector nozzle has tiny holes that break up the spray into fine droplets, called atomisation. Then the atomised fuel mixes thoroughly with the air in the engine cylinder during the power stroke, helping ensure complete combustion. Typical diesel engines use common rail injection, which is more sophisticated than the single-point injection used on some older models. A Perkins fuel injector is carefully engineered to provide the best possible atomisation and mix, to deliver optimal performance and meet stringent emission standards.