Supercharging is used only for aircraft and racing car engines. This is because the increase in supercharging pressure increases the tendency to detonate and pre-ignition. Supercharging is used in the engine to increase the volumetric efficiency of the engine. In this article, I will discuss the effect of Supercharging on the Performance of the Engine.
Effects of supercharging on the performance of the engine–
The power output of a supercharged engine is higher than its naturally aspirated counterpart due to the following reasons :
- The amount of air inducted per cycle for a given swept volume is increased.
- The mechanical efficiency is slightly improved.
- During the gas exchange process, some of the work done on the supercharger is recovered.
- Supercharging results in better scavenging and reduced exhaust gas temperatures in the engine. The reduced residual gas fraction helps in better combustion and reduced temperature improves volumetric efficiency.
An increase in the supercharging pressure increases the gas load and hence large bearing areas and heavier components are needed. This increases the frictional forces. However, the increase in bmep is much more than an increase in frictional forces. The mechanical efficiencies of supercharged engines are slightly better than those of naturally aspirated engines.
Supercharging of engines–
Supercharging does not result in any combustion problem, rather it improves combustion. in a diesel engine. An increase in pressure and temperature of the intake air reduces ignition delay and hence the rate of pressure rise resulting in better, quieter, and smoother combustion. This improvement in combustion allows a poor quality fuel to be used in a diesel engine and it is also not sensitive to the type of fuel used. The increase in intake air temperature reduces volumetric and thermal efficiency but the increase in the density due to pressure compensates for this and inter-cooling is not necessary except for highly supercharged engines. However. mechanical and thermal loading increases with an increase in supercharging. But this increases with an increase in supercharging. But this increase in mechanical and thermal loading is only moderate because of the use of lower compression ratios and the effect of cooling due to increased valve overlap of the supercharged engine. It is possible to use lower fuel-air ratios in a supercharged engine as the increase in fuel flow is less than the increase in airflow. This results in lower temperatures over the full engine cycle and reduced smoke from the engine. Low fuel-air ratio and high expansion ratio result in lower exhaust temperature. This results in an increased life of the exhaust valves.