Lower particulate matter emissions with a stoichiometric LPG direct injection engine

The direct injection (DI) engine is considered as a promising technology that can improve fuel economy compared to the conventional port fuel injection engine. However, studies have shown that relatively high levels of particulate matter (PM) are emitted by gasoline fuel engines. This is a concern in view of more stringent emission regulations expected in the future. In this respect, the use of Liquefied Petroleum Gas (LPG) in direct injection engines has the following advantages: (1) lower carbon dioxide (CO2) emissions due to its low carbon content; and (2) reduced PM emission because it is a premixed mixture. This study used an LPG direct injection engine that was converted from a 2000-cm3, 4-cylinder gasoline port fuel injection (PFI) engine. The engine head was redesigned for the spray-guided direct injection combustion system. The conventional LPG for transportation in South Korea was used as the fuel, and the engine was operated under stoichiometric condition. In this study, the engine operation map that covers the entire operating envelope was provided to investigate its particle number concentrations and exhaust emissions, including total hydrocarbon (THC), carbon monoxide (CO), carbon dioxide (CO2) and nitrogen oxides (NOx) as a function of engine operating points. Also, the particle number size distribution was shown as a function of engine operating conditions. The results of this study indicated that a lower occurrence of THC and NOx emissions compared to previous gasoline studies. The main finding in this study was that particulate matter emissions of a LPG direct injection engine were substantially lower than those from a gasoline direct injection engine.