Direct Fuel Injection of LPG in Small Two-Stroke Engines

The commonly used carburetted two-stroke engines in developing countries have high exhaust emission and poor fuel efficiency. To meet more rigid emissions requirements, two-stroke vehicles are typically phase out in favour of four-stroke engines. The problems of ubiquitous legacy two-stroke vehicles remain unsolved by these measures and they are likely to be a major source of transport for many years to come. A number of technologies are available for solving the problems associated with two-stroke engines such as catalytic after-treatment and direct fuel injection (DI). However, these solutions are relatively high cost and have shown only slow market acceptance for applications in developing countries. Research in recent years has demonstrated that direct fuel injection is a well developed and readily deployable solution to existing two-stroke engines. Gaseous fuels such as Liquefied Petroleum Gas (LPG) are considered a promising energy source and in many countries provide fuel cost savings. LPG coupled with DI two-stroke technologies, is expected to be clean and cost effective retrofit solution for two-stroke engines. In this research project, direct injection (DI) of Liquefied Petroleum Gas (LPG) is introduced and tested on a typical two-stroke engine. Results of in cylinder combustion pressure translated to fuel mass fraction burned, engine performance and exhaust emissions are taken and compared for various injection timings from premixed (early injection) to fully direct injection mode (late injection). Results show that DI of LPG effectively reduces exhaust hydrocarbon and can substantially improve the fuel economy of two-stroke engines.