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How does the diesel cycle differ from the Otto cycle?
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diesel engine
Diesel engine equipped with a precombustion chamber.
The primary difference between the diesel cycle and the Otto cycle lies in the method of ignition and the combustion process.
- Ignition Method: The diesel engine is a compression-ignition engine; it induces only air into the cylinder and relies on the high temperature of compressed air to ignite the fuel spontaneously. In contrast, the Otto cycle typically involves the intake of an air-fuel mixture that is ignited by an electric spark.12
- Combustion Process: In an ideal diesel cycle, combustion occurs as a constant-pressure process as fuel is injected into the hot, compressed air. The Otto cycle is characterized by a constant-volume combustion process where the air-fuel mixture is ignited and explodes.132
- Compression Ratios: Because diesel engines do not compress a premixed air-fuel charge, they are not limited by the preignition (knocking) issues that restrict gasoline engines. Consequently, diesel engines operate at significantly higher compression ratios, which generally allows for superior thermal efficiency.14
Would you like to know more about how these differences affect engine performance or emissions?