Fuel Efficiency of Diesel Engines Under Different Load Conditions

The fuel efficiency of diesel engines varies significantly under different load conditions, which are mainly influenced by factors such as load magnitude, engine speed, and the combustion process.

Under low-load conditions, diesel engines typically operate under light load, with low rotational speed and incomplete combustion—leading to fuel waste. At this point, the engine’s thermal efficiency is low; especially during idling, the combustion chamber temperature is insufficient, fuel consumption is higher, and fuel economy is not as good as under medium and high loads.

When entering medium-load conditions, the engine speed and temperature gradually increase, the combustion process is gradually optimized, thermal efficiency begins to improve, and fuel economy also reaches a relatively ideal level. At this stage, the engine can fully burn fuel and provide stable output power.

Under high-load conditions, the diesel engine operates at high speed and under heavy load. The combustion temperature rises, the combustion process is close to an optimal state, and mechanical losses are low—allowing fuel to be efficiently converted into energy, and fuel economy to reach an ideal level. This characteristic enables diesel engines to perform particularly well in the medium-to-high load range. However, overloading can lead to incomplete combustion, which may reduce fuel economy.

In general, the fuel efficiency of diesel engines is best under medium and high load conditions. This is because combustion is relatively sufficient at these stages, fuel utilization efficiency is high, and thus low fuel consumption can be achieved.