燃烧室沉积物对火花点火发动机碳氢排放的影响

Effect of Combustion Chamber Deposits on Hydrocarbon Emisions in a Spark Ignition Engine

为了弄清燃烧室沉积物对发动机排气碳氢的影响，使用一台实验用单缸火花点火发动机来形成燃烧室沉积物。在燃烧室沉积物存在的条件下，开展了不同工况下碳氢排放的实验研究，分析了燃烧室沉积物对发动机动力性和燃油经济性的影响。实验结果表明：当发动机运行一段时间后，其燃烧室表面沉积物将达到一稳定平衡厚度，此时排气碳氢浓度随转速的升高、冷却水温的增加以及点火推迟而降低。在本实验各类工况下，沉积物的存在将使发动机排气碳氢浓度增加２０％～３０％。同时沉积物的存在将使发动机的功率和燃油经济性有所提高（功率增加１．１％～１．６％，燃油经济性提高２．７％～３．０％），此现象被认为主要是因沉积物的隔热作用，而不是压缩比的增加所致。

To understand the effect of deposits in combustion chamber on engine out hydrocarbon emissions, a single cylinder spark ignition test engine is used to accumulate the combustion deposits. The experiments are conducted on hydrocarbon emissions under various operating conditions in the presence of combustion chamber deposits. The effects of combustion chamber deposits on engine power and fuel efficiency are also analyzed. The experimental results show that there exists an equilibrium thickness of deposits in combustion chamber if the engine operates for a certain period of time, the engine out hydrocarbon emissions contributed by combustion chamber deposits decreases with the increasing of engine speed, the coolant temperature, and the retarding of spark advance angle. The hydrocarbon emissions in the presence of deposits in combustion chamber increases by about 20～30 percent than that without deposits on various operating conditions in the experiments. The study also shows that deposits in combustion chamber will give a little benefit to engine power output and fuel efficiency (1.1～1.6 percent increasing in power and 2.7～3.0 percent increasing in fuel efficiency), and this contribution is considered mainly by the effect of thermal insulation rather than the effect of compression ratio due to the presence of deposits in combustion chamber.