Progress on the studies about NOx emission in PFI-H2ICE

Abstract

Owing to its brilliant combustion performance and cleanest combustion products, hydrogen has been widely considered as one best alternative fuel for internal combustion engines. However, in the cylinder of hydrogen internal combustion engines, high combustion temperature and oxygen enrichment make NOx is still one but the only combustion pollutant. Therefore, it is particularly important to control NOx emission for hydrogen fuelled engines. Since PFI-H2ICE (port-fuel-injection hydrogen internal combustion engine) is the normal type of hydrogen fuelled engines, the present article will focus on the studies about NOx emission in PFI-H2ICE researches. First, the present article reviews the mechanism of NOx generation in PFI-H2ICE; upon chemical kinetics, the generation of NOx will be summarized and discussed into three major paths which including thermal NO path, NNH–NO path and N2O–NO path. Then, the researches on the control methods of NOx for PFI-H2ICE in recent years will be systematically reviewed, the influencing factors to reduce NOx emission will be summarized in some aspects which including combustion component control strategy, injection control strategy, ignition control strategy and engine compression ratio control strategy. To the PFI-H2ICE operated at lean fuel conditions (like equivalence ratio is less than 0.5) or rich fuel conditions (like equivalence ratio is higher than 1), the technologies and the strategies of EGR (exhaust gas re-circulation) will be reviewed and discussed. It is hoped this literature review would enable researchers to systematically understand the progress of NOx emissions research in PFI-H2ICE and explore further research directions.