Turkish J. Eng. Env. Sci. 32(2008),7–12. c  T ¨ UB ˙ ITAK Performance and Emission Characteristics of LPG-Fuelled Variable Compression Ratio SI Engine Syed YOUSUFUDDIN Department of Mechanical Engineering, Vasavi College of Engineering, Hyderabad-31, Andhra Pradesh-INDIA e-mail: yousufuddin2k3@yahoo.co.in Syed Nawazish MEHDI Department of Mechanical Engineering, M.J. College of Engineering and Technology, Hyderabad-34, Andhra Pradesh-INDIA Received 15.02.2007 Abstract The growing concern about the fast depletion of petroleum-based fuels and the environmental pollution caused by their combustion has been a compelling incentive to many researchers to find ways to use en- vironmentally friendly and renewable sources of energy. Research and experiments on liquefied petroleum gas (LPG) have demonstrated that this fuel is suitable as an alternative to conventional fuel. Its perfor- mance and efficiency parameters are better than the conventional fuel and it can run cleaner at attractive prices and in larger operating range. Among the alternatives found to be superior to the present gasoline is natural gas, hydrogen (H2), and LPG (i.e. liquefied petroleum gas in the form of either propane, C3H8; butane, C4H10; or a mixture of both). In the present paper, LPG in the form of propane as a fuel has been considered. The present paper evaluates the performance and emission characteristics of a single cylinder, 4-stroke, air-cooled, variable compression ratio spark ignition engine when fuelled with LPG at different compression ratios. The results obtained show that the engine running on an LPG fuel system delivered a substantial improvement in power and torque in a high-load condition. Conversion of the engine using LPG as fuel showed an average reduction of CO and HC exhaust gas emissions in comparison to the original fuel. Key words: Variable compression ratio engine, LPG, Performance, Emissions, Spark Ignition. Introduction Oil reserve all over the world is depleting at an alarm- ing rate. In addition, the deteriorating quality of air we breathe is becoming another great public concern. Emissions of sulfur dioxide, hydrocarbons, carbon monoxide, nitrogen oxides, lead, etc. have stimu- lated scientists to find ways to reduce these emissions because of their impact on human health and ecologi- cal imbalance. These factors along with the oil crisis in the 1970s have led scientists and researchers to search for clean and environmentally friendly alter- natives to the conventional fuels used to power in- ternal combustion engines. Various alternative fuels suited for spark ignition (SI) engines can be clas- sified as synthetic gasoline, alcohols, and gaseous fuels according to the studies conducted by Thring (1983) and Prausnitz et al., (1987). Gaseous fuels in general are promising alternative fuels due to their low cost, high octane number, high calorific values, and lower polluting exhaust emissions (Badr et al., 1989; Richard Stone, 1989; Beer, 2002). During the last decade, gaseous fuels such as liquefied natural gas (LNG) and liquefied petroleum gas (LPG) have been widely used in commercial vehicles, and promis- ing results have been obtained in terms of the fuel economy and exhaust emissions. These results have also been confirmed by different published works of Yamin (2002) and Johnson (2003). Existing liter- atures of Bayraktar (2003), Dagaut et al., (2003), and Selim (2004) on the use of gaseous fuels as en- gine fuel have obtained for a limited number of spe- 7