Why is the compression ignition engine more efficient than the spark ignition?

The efficiency of a compression ignition engine, commonly referred to as a diesel engine, is primarily attributed to its ability to operate at a higher compression ratio compared to spark ignition engines, which typically use gasoline. The higher compression ratio allows for a more complete combustion of the fuel-air mixture.

In a compression ignition engine, the air is compressed to such a degree that it reaches a temperature high enough to ignite the fuel spontaneously when it is injected. This process results in a more efficient conversion of energy from the fuel into useful work. The increased pressure also leads to higher thermal efficiency because it allows the engine to extract more energy from the fuel before it is expelled as exhaust.

In contrast, spark ignition engines rely on a spark to ignite the fuel-air mixture, which tends to limit their compression ratios to avoid knocking and misfiring. Consequently, while they can produce adequate power for many applications, they generally do not achieve the same levels of thermal efficiency as compression ignition engines.

Overall, the high compression ratio in compression ignition engines plays a crucial role in enabling higher efficiency by enhancing fuel combustion and reducing fuel consumption for the same level of power output.