A Comprehensive Experimental Investigation of NO x Emission Characteristics in Hydrogen Engine Using an Ultra-Fast Crank Domain Measurement

Adopting zero-carbon fuels, like hydrogen, can significantly reduce environmental harm and pave the way for a decarbonised trajectory with zero carbon emissions. The hydrogen internal combustion engine (ICE) technology has demonstrated its reliability and capacity to seamlessly integrate into the current ICE platform, originally designed for diesel and gasoline operation. The direct utilisation of pure hydrogen eradicates steady-state carbon dioxide and hydrocarbon emissions. It is important to highlight that efforts to comprehend and comprehensively tackle NO x emissions are underway. A comprehensive study was carried out to assess the NO x emissions for a hydrogen ICE with different injection modes from gasoline. The study involved varying the relative air-to-fuel ratio (AFR) from stoichiometric to the lean-burn limit in a boosted spark ignition (SI) engine fuelled with gasoline or hydrogen. A fast NO x emissions analyser was employed to measure the instantaneous NO and NO 2 emissions in the engine exhaust. The study provides a detailed analysis of NO x emissions, including steady-state averaged emissions, average crank angle domain NO x distribution and emissions, in-cylinder pressure analysis, as well as time and cycle analyses of NO x emissions’ temporal and cyclic variations. The primary discovery was that NO x emissions are almost zero between lambda 2.75 and 3.7, and hydrogen produces 13.8% less NO x emissions than gasoline at stoichiometric operation. Finally, the full NO x time analysis revealed that the consistency of NO x emissions is higher with hydrogen than with gasoline by using a novel approach by identifying the coefficient of variation of the NO x emission of each cycle.