Experimental Investigation of NOx Emission Characteristics in Hydrogen Internal Combustion Engine

The adoption of zero-carbon fuels, like hydrogen, has the potential to 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. 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 still in progress.

A comprehensive study was carried out to assess the NOx emissions for a hydrogen ICE with different injection modes compared to 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 offers a comprehensive analysis of NOx emissions at multiple levels. It begins with an analysis of steady-state averaged emissions, followed by an analysis of average crank-angle domain NOx distribution and emissions, along with in-cylinder pressure analysis. Furthermore, time and cycle analyses are performed to assess the temporal and cyclic variations of NOx emissions. The study’s primary discovery is that NOx emissions are almost zero between lambda 2.75 and 3.7, and hydrogen produces 13.8% less NOx emissions than gasoline at sociometric operation. Finally, the full NOx time analysis reveals that the consistency of NOx emissions is higher with hydrogen than with gasoline.