Knock Phenomenon Investigation In SI Engine fuelled with Ammonia-Hydrogen mixture

Ammonia is one of the most promising carbon-free fuels for decarbonizing sectors relying on thermal conversion processes, such as energy production and transportation. However, ammonia exhibits combustion properties that differ significantly from conventional fuels, including a low laminar burning velocity, narrow flammability limits, and a high autoignition temperature. To enhance the efficiency and stability of ammonia combustion in internal combustion engines (ICEs), high compression ratio engines are often combined with ignition promoters such as hydrogen, which can be obtained through on-board ammonia cracking. Nevertheless, the addition of hydrogen to ammonia fuel can promote the occurrence of knock. The objective of this study is to investigate knock propensity as a function of engine parameters as combustion chamber geometries and compression ratios. Experiments were conducted at different engine speeds (1000, 1500, and 2000 RPM), across several intake pressure conditions (from 1 bar to 1.8 bar, in 0.2 bar increments) and equivalence ratios (from 0.9 to 1.1, in 0.1 steps) to vary the load. 10 vol.% H₂ and 90 vol.% NH₃ was considered as fuel. This study aims to identify the key parameters influencing knock intensity, onset, and distribution, as well as overall combustion properties.