Diesel engines power the world’s biggest trucks, trains and ships. They’re also found in cars, SUVs and minivans.
Compression Ratio
The compression ratio of a diesel engine is what makes it so efficient. High compression ratios allow the fuel to be burned under a higher pressure so that it can expand and create the force to push the piston back supplying power to the crankshaft.
The lower the compression ratio is, the less mechanical work is done by the engine. This is due to the higher temperatures that are created during combustion. The combustion process of a diesel engine differs from that of gasoline engines in two ways: During the intake stroke, the diesel's intake valve(s) opens and "unthrottled" air is drawn into the cylinder. Then the compression stroke starts, the gas is compressed and a great deal of heat is generated. This causes the cylinder pressure to rise, but is then reduced by friction and leakage past the rings and gaskets. Regardless, the cylinder pressure is still high compared to a gasoline engine and this can cause detonation to occur if the fuel is of a lower octane rating.
Fuel Injection
The fuel injection system controls the amount of diesel engines that reaches the combustion chamber. It also controls how the fuel is injected. Diesel injectors spray the fuel into the combustion chamber through a spray nozzle. The nozzles are designed to have a variety of shapes and sizes for the best air utilization.
The earliest systems used a single nozzle, which sprays the fuel in an intake manifold shared by all cylinders. This is called Single-Point Injection (SPI). It works, but has lower performance than newer systems and can be prone to failure as the nozzle can break. More advanced electronic systems use multiple nozzles to inject the fuel directly into each cylinder. This is called Direct Injection (DI). This has higher efficiency than the previous transitional technology and can maintain optimum engine performance, while meeting current emissions standards. The electronic systems monitor the nozzles for pressure changes and closely control fuel distribution to optimize SFOC (Specific Fuel Oil Consumption). The fuel consumption of a used generators is non-linear and varies by load.
Valve Timing
The timing of the intake valve is a key factor in engine performance. It is done by adjusting the camshaft profiles to change the duration of the intake and exhaust strokes, resulting in different valve overlap periods.
During the induction stroke, air moves past the open intake valve during its descent to bottom dead center (BDC). This air can't be forced back through the valve at BDC because it has momentum. So, to prevent unscavenged exhaust gas from entering the fresh charge at the start of the compression stroke, it is advisable for the valve to close a little bit after reaching. This is achieved by modifying the intake cam profile to delay the IVC time relative. This affects engine performance and emissions. In particular, at low engine speeds it reduces the maximum in-cylinder pressure and the volumetric efficiency.
Comments