IMPACT OF LEANING HYDROGEN-AIR MIXTURES ON ENGINE COMBUSTION KNOCK

Combustion of lean hydrogen-air mixtures in an internal combustion (IC) spark ignited (SI) engine in respect of combustion knock effect is presented in this paper. It is known that making the combustible mixture leaner leads to both decreasing in-cylinder peak temperature of combustion and lengthening ignition lag. It also increases combustion duration. Having these issues on mind it could be concluded that combustion knock intensity decreases as well. It is reported that such a hypothesis is also correct when hydrogen based fuels are combusted in the IC engine, although hydrogen as an engine fuel, on the contrary to gasoline, is very susceptible to knock generation throughout the entire combustion duration. At the beginning the paper examines the combustion knock intensity on the basis of in-cylinder pressure traces. Next, a test-bed and obtained experimental results of hydrogen combustion in the IC single cylinder CFR engine are showed. Finally, analysis of knock intensity referring to lean hydrogen-air mixture ratio, expressed by the excess air number so-called lambda, is carried out. Significant conclusion from the analysis is that there is strong negative correlation between the hydrogen knock intensity and the excess air number lambda. In the end, comparison with exhaust gas recirculation as alternative way to reduce combustion knock, and constraints for leaning the hydrogen-air combustible mixture for the IC engine are discussed in the paper