Effects of Intake Humidification Strategies on NO <i><sub>X</sub></i> /CO/CO<sub>2</sub>/Soot Emissions of A Low-Speed Diesel Engine.

Abstract

In response to the escalating global energy crisis and increasingly stringent environmental regulations, optimization of low-speed two-stroke marine diesel engines has become a pressing necessity. This study develops a simulation model based on real ship, operational data and engine logs to investigate the combined effects of a humidified air intake (HAM) strategy and elevated fuel injection pressure on engine combustion and emission performance. Through quantitative analysis, the study elucidates the chemical mechanisms underlying nitrogen oxide (NOx) reduction, highlighting the role of water decomposition in inhibiting key reactive radicals. This dual strategy addresses critical gaps in real-ship engine simulation and the mechanistic understanding of HAM-based NOx suppression. Results indicate that the optimal configuration (3% intake water content and a 10° crank angle injection duration) enhances thermal efficiency, substantially reduces carbon monoxide (CO) and soot emissions, and the engine's emission factor decreases significantly from 16.12 g/kWh under the Tier I standard to 11.85 g/kWh under the Tier II standard. This achievement goes beyond meeting IMO Tier II emission standards to forge a vital link between microscopic mechanisms, macro-level engineering practice, and regulatory policies.