Comparison of performance and combustion analysis of a VCR SI engine using audio transducers

Abstract

The world today mostly relies on four-stroke gas engines as its primary mover for automotive applications and specifically prefers gasoline engine as it provides more comfort, ease of starting. Some of the most common combustion parameters responsible for the loss of efficiency in an SI engine is Knock, fluctuations load, misfiring, cycle by cycle fluctuations etc. In this experiment, an effort has been made to sense engine combustion with help of audio technology, microphone sensor, and a few android software combined together to capture the fine the behaviour of engine combustion with petrol fuel. Earlier researchers have made the same efforts using engine pressure sensors located inside the engine cylinder head which is also an effective method to sense pressure variations however complicated in practical engines and a poor lifetime of sensors.In this work an SI engine is retrofit in order to increase its compression ratio by modifying the engine head & gasket. The retrofitting is done in such a way that the highest compression ratio induces a forced knock in the cylinder. The performance parameters of this VCR engine have been studied for five different loadings both with petrol as the fuel and combustion analysis has been done by using audio technology. For identifying and measurement of knock, a novel arrangement using Audio transducers were made and fixed on the engine cylinder, many different audio transducers were experimented such as round piezo, straight piezo and the electret of which the electret condenser-based condenser showed better performance. The signals are modified & interpreted by the intermediate software’s which have been analysed for various compression ratios, it was found that the Audio technology can efficiently pick up engine sounds which can be processed by interfaces for identification of Knock.