Using Vibroacoustic Signals in Evaluation of Knocking Combustion in a Dual Fuel Engine

Current development of automotive domain heading towards the ever decreasing pollution emission as well as using the alternative fuels resulted in analysis of the possibilities to power the combustion engines with combinations of several fuels. The multi-fuel engines designed in such a way can use the advantages of specific fuel. The most popular trend uses self-ignition engines to operate on the fluid fuels such as the diesel oil or its mixtures, and on the gaseous fuel such as CNG or LPG. In Poland, because of the extensive network of LPG stations, the interest in adapting vehicles to this type of fuelling increases. This is particularly vital for heavy and large goods vehicles, in the case of which the fuel saving possibility of a few to a dozen or so percent is very interesting. Using gaseous fuels in engines with the self-ignition results in the occurrence of the previously unknown phenomena. Such a phenomenon is, among others, the knocking combustion, the cause for which is the premature ignition of the air-fuel mixture most frequently occurring in the area of the top dead centre. The knocking combustion is characterized by a faster increase in pressure as compared to normal combustion, and it is a detrimental phenomenon to the engine operation, especially before the top dead centre. The growth speed of the combustion pressure can be correlated with the manner of combustion, which is also evident in the vibroacoustic signal, whose characteristics will undergo changes alongside the combustion speed. The analysis of the remaining work parameters influencing the vibroacoustic signal will enable determining the moments of the knocking combustion occurrence and will thus allow for optimization of the gaseous fuel dose, which directly influences the pollution emission as well as the economical aspect.