A comparative study of NOx mitigating techniques EGR and spark delay on combustion and NOx emission of ammonia/hydrogen and hydrogen fuelled SI engine

Abstract

IC engines, the backbone of the transportation sector is facing energy insecurity and stringent environmental norms motivating researchers to look for alternate ways of revival. In pursuit hydrogen and its careers are seen as promising option. Aiming the same comparative-study is performed on NH<inf>3</inf>/H<inf>2</inf> (7:3) and hydrogen under varying ignition (from −24°CA to −12°CA) and EGR rates (till 25%). Results indicate improved combustion for NH<inf>3</inf>/H<inf>2</inf> for a small range of ignition than hydrogen, ∂P/∂θ and ∂Q/∂θ is improved before TDC and deteriorates after it. Cycle-by-cycle variations increase for a longer ignition range for NH<inf>3</inf>/H<inf>2</inf>, but NO<inf>x</inf> drops more rapidly. At −24°CA, NH<inf>3</inf>/H<inf>2</inf> has observed a minimal gap in peak pressure, CoV and performance from hydrogen. Though a small EGR helps reduce NO<inf>x</inf>, cycle-by-cycle variations and CA90 reduce due to improved combustion for NH<inf>3</inf>/H<inf>2</inf>. ∂P/∂θ and ∂Q/∂θ improve for the same range too. However, hydrogen suffers adverse effects due to EGR that intensify with increasing EGR-rate. At higher EGR, unstable combustion and heterogeneity prevail, resulting in increased cycle-by-cycle variations and a rapid drop in peak pressure. The prolonged combustion witnesses a massive decline in NO<inf>x</inf> for both fuels; however, the gap between NH<inf>3</inf>/H<inf>2</inf> and hydrogen entities reduces. NH<inf>3</inf>/H<inf>2</inf> shows better efficiency than hydrogen for an efficient NO<inf>x</inf> control. However, higher fuel NO<inf>x</inf> maintains a significant difference for NH<inf>3</inf>/H<inf>2</inf> than hydrogen. The study limits quantitative analysis of it and also NH<inf>3</inf> emissions, which is another primary concern. © 2023 Elsevier Ltd