1, different injection methods
Ordinary gasoline engines (except direct injection engines) mix gasoline with fuel and enter the cylinder. The diesel engine directly injects diesel into the cylinder that has been filled with compressed air.
2. Different ignition methods
Diesel engines ignite spontaneously through compressors, while gasoline engines need spark plugs to ignite the mixture.
3. Different compression ratios
The compression ratio of diesel engine is generally larger than that of gasoline engine, so its expansion ratio and thermal efficiency are higher than that of gasoline engine, and its fuel consumption is lower than that of gasoline engine. If we compare gasoline engines and diesel engines with the same displacement, we will find that gasoline engines have high power and diesel engines have high torque. This is mainly because the diesel engine has large compression ratio, large piston stroke and large torque. But because of the low speed, the power is not very large.
Working principle of diesel engine
The working process of diesel engine is actually the same as that of gasoline engine, and each working cycle has to go through four strokes: intake, compression, work and exhaust. Diesel engines inhale pure air in the intake stroke. At the end of the compression stroke, the oil pressure of diesel oil is increased from the fuel injection pump to above 10MPa, and is injected into the cylinder by the fuel injector, which is mixed with compressed high-temperature air in a short time to form a combustible mixture.
Due to the high compression ratio of diesel engine (generally 16-22), the in-cylinder air pressure can reach 3.5-4.5MPa and the temperature can reach 750- 1000K at the end of compression (while the mixed gas pressure of gasoline engine will be 0.6- 1.2MPa and the temperature will reach 600-700K).
Therefore, after diesel oil is injected into the cylinder, it will spontaneously combust immediately after being mixed with air in a short time. The air pressure in the cylinder rises rapidly to 6-9MPa, and the temperature also rises to 2,000-2,500 K. Driven by high-pressure gas, the piston moves downward, which drives the crankshaft to rotate and do work, and the exhaust gas is also discharged into the atmosphere through the exhaust pipe.
Baidu encyclopedia-diesel engine