Emission Control Strategy and Technologies on Chinese-made Four-stroke Non-road Small Spark-ignition Engines

One popular Chinese-made non-road small spark-ignition engine was selected in this paper and the average emissions of this kind of engine couldn't meet U.S. EPA-II 2005 model year limits when considering the emission durability by multiplying the fresh emission by appointed deterioration factor (DF). To help this kind of engine satisfy the corresponding U.S. EPA limits, the emission characteristic of this engine was firstly analyzed and then appropriate control strategy was selected and applied. The emission reduction strategy was air/fuel ratio optimization. Further more, actual emission durability test was conducted on this engine in order to gain the real DF instead of using the appointed DF. During reducing the emission of 133F engine, which is a one-cylinder, OHV and four-stroke engine, the concept of mode emission contribution ratio (MECR) was put forward and then used to direct the air/fuel ratio optimization work. Finally, the engine met the U.S. EPA-II 2005 model year limits only by carburetor tuning and MECR was proved to be a useful tool when reducing emission of non-road small spark-ignition engines.