An electronically controlled diesel engine for commercial vehicle was taken as a research object

and bench test and combustion analysis were carried out to investigate the combustion heat release characteristics at constant speed with increased torque. The combustion characteristics at different transition time and different constant speeds with increased torque were analyzed. The results showed that when the torque of the engine was increased too rapidly

it was easy to cause a sudden increase in fuel supply and a decrease in fuel energy conversion efficiency. However

when the engine was loaded gently for a long time

the fuel energy conversion efficiency might still decrease due to high mixture concentration. In addition

in the process of increasing torque at constant speed

when the engine speed went up

the crank shaft angle corresponding to rapid increase in pressure was advanced

the rapid combustion period was prolonged

the post combustion was shortened

and the heat and power conversion efficiency was improved. In short

the mixture concentration and the law of combustion heat release were closely related to the combustion efficiency of each cycle in the transient process of increasing torque.