Engine Block Vibration Level as a Tool for Fuel Recognition

The availability of gaseous fuels like natural gas and propane butane mixtures has lead to worldwide popularity of internal combustion engines running dual fuel or alternatively gas powered. These gaseous fuels are known as fuels more resistant to knocking than conventional liquid fuels and as ones less pollutant, their better mixing with air is also well recognized. There have been many published works on the use of gaseous fuels but actually the problem of the combustion noise, as a very important source of acoustic discomfort is not receiving attention. Combustion noise occurs in two forms, direct and indirect. It is transmitted throughout the engine block as a vibration at a different spectrum of frequencies. In this study an attempt is made to relate the combustion noise to the operating parameters for LPG powered engine as compared to petrol fueled engine. Combustion pressure and vibration of cylinder block data are measured and presented for engine running on LPG and compared to the results obtained for engine fed by petrol. Signals of multiple resonances in combustion chamber and corresponding vibration signals of cylinder block of engine were considered for one combustion cycle. A four cylinder, 1.6 dm³ spark-ignition engine converted to run on LPG was tested in the project. The engine test stand was fully computerized and the cylinder pressure data, acceleration of vibration of engine block, crank angle data were stored on a PC. The influence of engine speed, load on combustion and engine block vibration was examined for two fuels. A few of well know diagnostic parameters were used for comparison of the engine noise for operation on petrol and LPG.