Evaluation of injection and ignition schemes for the ultra-lean combustion direct-injection LPG engine to control particulate emissions

The high level of particulate emission in ultra-lean combustion direct injection engine was obstacles for real application and satisfying the further upcoming regulation. The use of LPG (liquefied petroleum gas) in lean direct injection engines has the potential to reduce carbon-related emissions owing to its simple structure, and it can become an easily stratified mixture because of its higher vapor pressure. In this respect, the effects of the injection and ignition schemes on combustion and emission characteristics, including particle emission of ultra-lean combustion through LPG, were investigated. Four. different injections schemes in order for forming stratified mixture and two ignition schemes (single charge ignition and multi-charge ignition) were employed to achieve simultaneous harmful emissions and fuel consumption reduction. The experimental results reveal that the fully stratified injection strategies indicate an improvement of approximately 18% in thermal efficiency, but combustion fluctuation was observed owing to stratification. Moreover, simultaneous reductions in the NOx (Nitric Oxides) and CO (Carbon monoxide) emissions were observed (when compared to homogeneous stoichiometric combustion) while increasing the particulate matter emission. In order to stabilize the combustion and reduce the level of soot, a multi charge ignition was introduced to the selected injection strategies (LBM1 and LBM2). Multi-charge ignition successfully reduces particulate mass by about 10% and secures the combustion stability slightly; however, it increases the particle number concentration. (C) 2017 Elsevier Ltd. All rights reserved.