柴油机瞬态工况烟度排放特性及分析

为了研究车用柴油机瞬态工况中，燃烧边界条件对燃烧过程的影响，在试验台上针对增压中冷柴油机在恒转速增转矩瞬态工况下的烟度排放特性进行了试验，并用商业计算软件STAR-CD对此瞬态工况下柴油机的燃烧过程进行了数值模拟分析。针对增压柴油机低转速大负荷排烟较差的特点，试验中发动机转速定为1000r／min，以3种不同的转矩变化率来考察柴油机瞬态工况下的排烟特性。结果表明，柴油机瞬态工况下和稳态工况下的燃烧边界条件有很大的差别，这种差别导致了柴油机瞬态工况下的烟度排放值要明显高于其相应的稳态工况。计算结果表明，随着转矩变化率的升高，最大初始放热率升高及燃烧持续期延长，这些差异同样导致排气烟度值增加。

Investigation of Smoke Emission Behaviors from a Diesel Engine under Transient Operating Conditions

Smoke emission behaviors were investigated from a turbocharged inter-cooled diesel engine under constant speed and increasing torque (CSIT) operating conditions for clarifying the effect of combustion boundary conditions on combustion process. The engine combustion processes were simulated with a commercial computational fluid dynamics software STAR-CD. With respect to the worse smoke emission behaviors of turbocharged diesel engine under low speed and heavy load operation, the engine speed was chosen as 1 000 r/min. The smoke emission behaviors were investigated at three torque increasing rates. The combustion boundary conditions under transient operating conditions are different from those of steady operating conditions, and they have large influence on engine combustion process and the exhaust emissions. Under CSIT operating conditions, smoke emission increases with the increasing of engine torque increasing rate. Meanwhile, the simulated results showed that with the increasing of engine torque increasing rate, the maximum heat release rate and combustion duration increased, leading to the increase of smoke emission.