Knock Rating of Gaseous Fuels in the Presence of Diluents

The current rapidly growing interests on utilization of various alternative fuels, including low heating value fuels such as land filled gases and biogases, are prompted due to the energy security concerns and the environmental advantages. It is nevertheless augmented due to the recent high price of the conventional petroleum based fuels. Generally, the low heating value (Btu) fuels contain substantial amounts of the diluents such as carbon dioxide, nitrogen, water vapor and other trace gases in the fuel composition. This paper describes the results of the investigation of knock in a single cylinder variable compression ratio spark ignition engine fueled with gaseous fuels such as natural gas, methane and hydrogen in the presence of different amounts of diluents specifically carbon dioxide in the fuel mixture in order to represent closely the general composition of land filled and biogases in practice. The knock characteristics of the fuels were quantitatively evaluated and presented in terms of the Methane Number using various methods namely KLST and KLCR. The general guidelines and optimization of the operation of the SI engines fueled by fuel-diluent mixtures are outlined.