Investigation of injection characteristics for optimization of liquefied petroleum gas applied to a direct-injection engine

Abstract

With the strengthening of emission regulations for internal combustion engines, studies on alternative fuels that can be immediately adopted are being conducted worldwide. As liquefied petroleum gas (LPG), which is an alternative fuel, emits fewer pollutants, it is considered a practical solution in situations where it is difficult to switch from a conventional engine system to an electric powertrain immediately. Several attempts have been made to convert the fuel in a conventional engine system to LPG for fuel efficiency, but research on optimizing the performance of LPG conversion engine remains insufficient. Since most recent gasoline engines operate with direct-injection fuel supply system, the LPG conversion engine should also consider direct-injection. Injection characteristics such as injection quantity and spray image are used as basic data to optimize engine control parameters. Therefore, in this study, the injection characteristics were analyzed according to fuel type for optimizing the LPG applied to in a gasoline direct-injection engine. According to the analysis results of the spray image acquired with a high-speed camera, the atomization properties of LPG are superior to those of gasoline. And similar to the actual engine condition, the difference is expected to increase as the ambient temperature increases. Since gasoline has a relatively higher density than LPG, the injection quantity of LPG is smaller than that of gasoline fuel. However, it can be calibrated by increasing the injection duration by 2%–5% or increasing the injection pressure by 4%–10% for the LPG conversion engine.