Emission Characteristics of Gasoline and LPG in a Spray-Guided-Type Direct Injection Engine

Nowadays, automobile manufacturers are focusing on reducing exhaust-gas emissions because of their harmful effects on humans and the environment, such as global warming due to greenhouse gases. Direct injection combustion is a promising technology that can significantly improve fuel economy compared to conventional port fuel injection spark ignition engines. However, previous studies indicate that relatively high levels of nitrogen oxide (NO_x) emission were produced with gasoline fuel in a spray-guided-type combustion system as a result of the stratified combustion characteristics. Because a lean-burn engine cannot employ a three-way catalyst, NO_x emissions can be an obstacle to commercializing a lean-burn direct injection engine.

Liquefied petroleum gas (LPG) fuel was proposed as an alternative for reducing NO_x emission because it has a higher vapor pressure than gasoline and decreases the local rich mixture region as a result of an improved mixing process. The combustion and emission characteristics of LPG and gasoline fuels were compared in a multi-cylinder engine with a spray-guided-type combustion system. A lower NO_x emission value could be achieved with a single injection of LPG, while the hydrocarbon emissions increased.