A Comprehensive Experimental Investigation of NOx 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 NOx emissions are underway. A comprehensive study was carried out to assess the NOx 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 NOx emissions analyser was employed to measure the instantaneous NO and NO2 emissions in the engine exhaust. The study provides a detailed analysis of NOx emissions, including steady-state averaged emissions, average crank angle domain NOx distribution and emissions, in-cylinder pressure analysis, as well as time and cycle analyses of NOx emissions' temporal and cyclic variations. The primary discovery was that NOx emissions are almost zero between lambda 2.75 and 3.7, and hydrogen produces 13.8% less NOx emissions than gasoline at stoichiometric operation. Finally, the full NOx time analysis revealed that the consistency of NOx emissions is higher with hydrogen than with gasoline by using a novel approach by identifying the coefficient of variation of the NOx emission of each cycle.