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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1 000 r/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。
In order to study the influence of combustion boundary conditions on the combustion process in transient condition of vehicle diesel engine, the smoke emission characteristics of turbocharged and intercooled diesel engine under the condition of transient torque with constant speed and transient torque were tested on the test stand. The combustion process of diesel engine under transient condition was simulated by STAR-CD, a commercial computing software. Aiming at the poor smoke exhaust performance of turbocharged diesel engine at low speed and large load, the engine speed was set at 1 000 r / min in the experiment, and the exhaust smoke characteristics under transient conditions were examined with three different torque change rates. The results show that there are significant differences between the combustion conditions under transient conditions and those under steady-state conditions. This difference causes the values of smoke emissions under transient conditions to be significantly higher than the corresponding steady states Condition. The results show that with the increase of torque rate, the increase of maximum initial heat release rate and the prolongation of combustion duration, these differences also lead to the increase of exhaust smoke value.