实际环境下柴油轿车冷起动的排放特性

Exhaust Emissions of a Diesel Car During Cold Start in Real World

研究了实际环境下柴油轿车低温冷起动时的气态排放和经济性,并与其热起动的性能进行了对比。结果表明,实际环境下柴油轿车冷起动时有害气体排放量大部分高于热起动,且发动机的供油量较高。这是由于在整个冷起动过程中存在较多的不完全燃烧循环,导致排气中的CO和HC明显较高,而氧化催化转换器(DOC)在较低温度下工作性能欠佳,使有害气体排放的转化率降低。在冷起动初期,瞬时燃烧放热较高导致NOx排放量高于热起动,而后期发动机工作逐渐稳定后,废气再循环系统(EGR)降低NOx排放效果明显,并低于热起动的排放量。

Fuel economy and pollution emissions of a diesel car were studied during cold start in real world, compared to those from warm start. The results show that the exhaust emissions during the cold start process are higher than those during the warm start process, and the fuel consumption is also higher. This is because the incomplete combustion cycles during the cold start process are more than those during the warm start process, so CO and HC emissions during the cold start are significantly higher. At the same time, the performance of diesel oxidation catalyst （DOC） is not good at lower temperature, so the conversion ratios of CO and HC emissions during the cold start process are lower. In the initial stage of the cold start, because of the high releasing heat ratio from instantaneous combustion, the NOx emissions are higher than those during the warm start. However, when the engine works steadily, the NOx emissions are reduced by exhaust gas recirculation （EGR） to be even lower than those during the warm start.