Characteristics of traditional diesel engines: they offer good thermal efficiency and fuel economy. Diesel engines use compressed air to increase air temperature until it exceeds the self-ignition point of diesel fuel. Diesel is then injected, and the diesel spray ignites and burns automatically as it mixes with the air. Therefore, diesel engines do not require an ignition system.

At the same time, the fuel supply system of diesel engines is relatively simple, so diesel engines are more reliable than gasoline engines.

Because diesel engines are not restricted by knock and also require diesel self-ignition, their compression ratio is very high. Their thermal efficiency and fuel economy are both better than those of gasoline engines. In addition, under the same power output, diesel engines provide greater torque and lower speed at maximum power, making them suitable for truck applications.

However, because diesel engines operate under high pressure, the related components are required to have higher structural strength and rigidity, so diesel engines are relatively heavy and bulky. The manufacturing precision required for diesel injection pumps and nozzles is also high, so costs are relatively high. In addition, diesel engines run more roughly, with greater vibration and noise. Diesel fuel does not evaporate easily, making cold starting difficult in winter.

Because of the above characteristics, diesel engines were previously generally used in large and medium-duty trucks. Traditionally, diesel engines were rarely favored in passenger cars because they are relatively heavy, have lower specific power indicators than gasoline engines due to lower speed, produce higher noise and vibration, and generate more serious soot and particulate matter (PM) emissions. In particular, with the new development of small high-speed diesel engines, a series of advanced technologies, such as electronically controlled direct injection, common rail, turbocharging, and intercooling, have been applied to small diesel engines. This has effectively addressed the original drawbacks of diesel engines, while the advantages of diesel engines in energy saving and CO2 emissions remain unmatched by all heat engines, including gasoline engines, making them a green engine.

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