To effectively improve the emissions of a diesel engine without reducing its performance in power and fuel economy

the effects of cold and hot EGR on engine performance

combustion and emissions characteristics were experimentally studied. The experiment was conducted on a four-cylinder diesel engine at three different loads of 6

12 and 24 mg of fuel injected a cycle. The three loads hereinafter are temporarily referred to as low

medium and high loads. The experimental results show that the introduction of EGR can reduce the fresh air inflow

extend the ignition delay and slow down the heat release rate

thus reducing the cylinder pressure rise rate. The hot EGR

on the one hand

decreases HC emission effectively and increases the thermal efficiency at the low load due to its heating intake air; on the other hand

it obviously reduces the thermal efficiency at the high load with high EGR rate because of lower excess air coefficient. The effect of the hot EGR on reducing the maximum pressure rise rate is smaller than that of the cold EGR. With the increase of EGR rate

NOx emission decreases significantly at the three different loads

and soot emission keeps small at the low and medium loads

but increases quickly at the high load with high EGR rate

requiring a trade-off between NOx and soot. The cold EGR

however

can effectively ease this requirement due to its slow increase in soot emission. The thermal efficiency and emissions at the three loads being considered

the hot EGR is appropriate at the low load to improve thermal efficiency

and the cold EGR is more suitable at the high load to maintain high thermal efficiency and reduce the excessive pressure rise rate.