The fuel efficiency of diesel engine shows significant differences under different load conditions, which are mainly affected by load size, engine speed and combustion process. Under the condition of low load, diesel engines are usually in a light load state, with low speed and incomplete combustion, which leads to fuel waste. At this time, the thermal efficiency of the engine is low, especially at idle speed, the combustion chamber temperature is insufficient, the fuel consumption is high, and the fuel efficiency is not as good as that at medium and high load. When entering the medium load, the engine speed and temperature gradually increase, the combustion process is gradually optimized, the thermal efficiency begins to improve, and the fuel efficiency also reaches an ideal level. At this time, the engine can fully burn fuel and provide stable power output.

        Under high load, the diesel engine runs at high speed and heavy load, the combustion temperature rises, the combustion process is close to a good state, the mechanical loss is low, the fuel can be converted into power, and the fuel efficiency also reaches an ideal state. This characteristic makes the diesel engine perform particularly well in the middle to high load range. However, when it is overloaded, it may lead to incomplete combustion and reduce fuel efficiency. Generally speaking, the fuel efficiency of diesel engine is the best under the condition of medium to high load, because at this time, the combustion is more sufficient, the fuel utilization efficiency is high, and it can provide lower fuel consumption.