Hydrogen resistance to knock combustion in spark ignition internal combustion engines

Abstract

The results of investigations focusing on knock combustion analysis of a hydrogen-fueled engine have been presented in the paper. Knock intensity was determined as the intensity of the in-cylinder combustion pressure pulsations (recorded with a sampling frequency of 100 kHz) and filtered through high-pass filtering with cut-off frequency of 3.5 kHz. The research was conducted on the CFR engine with a variable compression ratio ranging from 6 to 14. The research has shown a rapid increase in pressure pulsations amplitude was observed while the compression ratio was changed from 11 to 12. This was interpreted as a result of in-cylinder hydrogen-air mixture self-ignition at the end of the spark ignition controlled combustion. Supporting this observation the theorem of dual nature of hydrogen knock combustion was postulated. Intensity of the pressure pulsations that accompany normal combustion without hydrogen self-ignition was in an exponential correlation with the compression ratio, which directly translates into a similar correlation of the pulsations and temperature of hydrogen-air mixture at the moment of ignition.

Possible applications of prechambers in hydrogen internal combustion engines

“…4. Combustion process temperature influence on self-ignition delay for stoichiometric air-hydrogen mixture [29] The results of the research indicate the optimal value of excess air coefficient (λ) at the level of 2.2 [24,25], whose exceeded value does not have significant effects in terms of emissivity and efficiency. Research by Lee et al [10] shows that the next step to increase the overall efficiency of a hydrogen-powered internal combustion engine is to burn a stratified charge.…”

“…It describes the resistance of the fuel to knocking combustion, and in the case of hydrogen, its research value (RON) is 130 [23]. On the other hand, practice shows that hydrogen combustion promotes the formation of pressure waves much higher than in the case of gasoline combustion with a research octane number close to 100 [26]. The index used in that case called the motorized octane number (MON) is at level of 60 [32].…”

“…Knocking combustion that generates pressure pulsations in the main combustion chamber leads to excessive wear of the crankshaft bearings and is an additional source of thermal loads. In addition to affecting durability, the phenomenon of hydrogen knock also contributes to a significant reduction in engine performance [29].…”

Hydrogen as a fuel for spark ignition combustion engines – state of knowledge and concept

“…6. Compression ratio influence on pressure pulsation intensity [38] There are many ways to hamper knock occurrence in H2ICE among which the most effective ones are lean engine operation with SCC [22], modification of engine operation cycle (ex. Miller cycle with split injection) [45], water anti-detonant direct injection [9] into combustion chamber or dilution of hydrogen rich gases with exhaust gas recirculation [39].…”