EFFECTS OF ETHANOL ON PM EMISSIONS FROM CAI COMBUSTION IN A 2-STROKE POPPET VALVE GASOLINE DIRECT INJECTION ENGINE

摘要

Gasoline direct injection engines are staging a come-back because of its potential for improved fuel economy through principally the engine down-sizing by boosting or 2-stroke operation, and possibly stratified charge combustion or Controlled Auto Ignition (CAI) at part-load operations. Due to the limited time available for complete fuel evaporation and the mixing of fuel and air mixture, locally fuel rich mixture or even liquid fuel can be present during the combustion process. This causes a significant increase in Particulate Matter (PM) emissions from direct injection gasoline engines compared to the conventional port fuel injection gasoline engines, which are of major concerns because of its health implications. Controlled Auto Ignition (CAI) is one of the most promising advanced combustion technologies that reduce fuel consumption, NO_x emissions and possibly particulate numbers and improve the performance of the engine. In order to take advantage of the synergy of 2-stroke cycle for engine downsizing and CAI operations, research has been carried out in a single cylinder direct injection gasoline engines. The 2-stroke CAI combustion was achieved by opening both intake and exhaust valves around BDC at each engine revolution. In this paper, the gaseous and particulate emission results are presented at different load conditions during the 2-stroke CAI combustion operations. Both the particulate number and mass distributions were measured and compared with gasoline, E15 and E85 fuels. The results showed that the addition of ethanol can lead to significant reduction in particulate mass but greater number of nano particles at the operating conditions investigated.