What is a characteristic of diesel engines compared to SI engines regarding combustion pressure?

Diesel engines are designed to operate at significantly higher peak combustion pressures compared to spark ignition (SI) engines. This characteristic arises from the fundamental differences in how diesel and SI engines operate.

Diesel engines rely on compression ignition, where the air is compressed to a much higher pressure and temperature before fuel is injected. This high pressure is necessary to achieve the conditions required for the diesel fuel to ignite when injected into the pre-compressed hot air. The resulting combustion process generates greater force on the piston due to the higher peak combustion pressures typically seen at top dead center (TDC).

In contrast, SI engines use a spark plug to ignite a pre-mixed air-fuel mixture, which operates at lower compression ratios and therefore generates lower combustion pressures. As a result, the inherent design and operating principles of diesel engines lead to this significant difference in combustion pressure, which is a critical factor influencing engine performance, efficiency, and power output.