Effect of intake-air heating on combustion, performance and emissions in a light-duty engine under CNG-diesel RCCI Operation

Reactivity Controlled Compression Ignition (RCCI) is a promising low-temperature combustion (LTC) strategy that offers high thermal efficiency with reduced NOx and soot emissions. However, at low loads, RCCI operation often suffers from incomplete combustion, leading to elevated unburned hydrocarbons (THC) and carbon monoxide (CO) emissions, which can hinder oxidation catalyst (DOC) light-off and reduce overall efficiency. Intake-air heating is a potential strategy to address this issue by enhancing fuel reactivity and promoting more complete combustion. In this study, the effects of intake-air heating (from ambient to 100°C) on performance and emissions are experimentally investigated in a light-duty diesel engine operated under CNG-diesel RCCI mode. The experiments were conducted at low and intermediate load and speed conditions. The influence of intake-air heating on cycle-to-cycle variations of the gross indicated mean effective pressure (GIMEP) is also discussed. The CO and THC emissions were significantly reduced at low loads with intake-air heating improving oxidation, potentially aiding DOC performance. However, as expected, NOx emissions increased with increase in intake-air temperature, attributed to higher local combustion temperatures. With intake-air heating, cycle-to-cycle variations in GIMEP decreased. The findings from the study provides insight into the role of intake conditions in enhancing RCCI performance, particularly at low loads, where combustion inefficiencies are most prevalent.