This paper is based on the available evidence for the performance evaluation of single cylinder 4-stroke petrol engine using petrol-ethanol blend fuels and also focuses on regulated and unregulated air pollutant emissions from vehicles running on petrol-ethanol blended fuels. Automobile have become a very important part of our modern life style. But the future of automobile based on internal combustion engines has been badly affected by two major problems. That is less availability of fuel and environmental degradation. So it is very important to found some new renewable non polluting alternative fuels to ensure the proper and safe survival of internal combustion engines. In present study we evaluate the performance of four stroke single cylinder spark ignition engine with different percentage ratio of ethanol and petrol by volume. This study is an attempt towards finding the effect of alternative fuel (particularly ethanol) as substitute over petrol, in petrol engine to reduce petrol consumption and also most outstanding result of using ethanol additive is significant reduction in pollutions emitting from engine.