Experimental Investigations on the Effect of Alcohol Addition on Performance, Emission and Combustion Characteristics of LPG Fuelled Lean Burn Spark Ignition Engine

Rising energy demands, ecological deterioration and diminution of fossil fuels has necessitated the researchers to search for alternatives. With alternate fuels like Liquefied Petroleum Gas (LPG), hydrogen and alcohol based fuels, it is easier to substitute with the present engine without many alterations. Excellent chemical properties of these fuels make them favorable for lean burn operation which makes it a cost effective option to achieve goals of better fuel economy and controlled emissions. In this regard, experimental studies were carried out to examine the effects of LPG with different proportions of alcohols like ethanol and methanol (5, 10 and 20%) on the performance, emission and combustion characteristics of a single cylinder SI engine operated at a constant speed of 1500 rpm with a optimized compression ratio of 10.5:1 under full throttle opening conditions at varying equivalence ratio. Devoted electronic manifold injection system was developed for alcohols while LPG was inducted and the blend ratio was calculated on energy basis. Experimental results show that 10% addition of alcohol (ethanol or methanol) to LPG exhibited significant improvement in brake power and brake thermal efficiency and extended the lean limit of operation, however, beyond 10% alcohol addition, no significant improvements were seen. It was observed that depending on the rate of alcohols increase in mixture, HC and NOx emission concentrations in the engine exhaust decreased. Since the experiments were carried out under lean operating ranges, CO emissions were negligible. Significant rise in peak in-cylinder pressure and heat release rate was observed with 10% alcohol addition. On the whole, experimental results suggest that LPG with 10% ethanol addition was best suited for manifold injection lean burn SI engine in terms of performance, emission and combustion characteristics when compared to other test blends.