Impact of higher alcohol injection rates and exhaust gas recirculation on efficiency, combustion, and NOx emissions in reactivity controlled compression ignition engines

• Diesel and Higher Alcohol in RCCI Engine with varied injection durations and EGR Levels. • Peak BTE of 31.20% was achieved at 6 ms isobutanol injection. • Moderate EGR (5%) achieved a BTE of 30.40% under full-load with improved combustion stability. • NO x emissions were reduced to 900 ppm at 15% EGR during Iso-butanol RCCI operation. Despite their high efficiency, Compression Ignition (CI) engines generate significant nitrogen oxides (NOx) and particulate emissions. This led to advanced combustion strategies like Reactivity Controlled Compression Ignition (RCCI). This paper examines performance and emission characteristics of an RCCI engine, using low-reactivity fuel (LRF, Iso-butanol) and high-reactivity fuel (HRF, diesel) with varying exhaust gas recirculation (EGR) rate. At full load condition, maximum brake thermal efficiency (BTE) of 31.20% with 6 ms Iso-butanol injection without EGR and 30% with 5% EGR was found, superior to conventional diesel operation. Diesel operation gave maximum cylinder pressure of 84 bar due to higher cetane number. With RCCI without EGR, 2 ms Iso-butanol injection produced 82 bar cylinder pressure while 5% EGR produced 77 bar pressure with 6 ms. Cylinder pressure reduced to 68 bar at 15% EGR. Maximum net heat release rate (NHRR) of 71 J/deg CA occurred during diesel operation and 68 J/deg CA with Iso-butanol at 2 ms injection. NHRR reduced to 63–60 J/deg CA as EGR increased from 5 to 15%. RCCI operation with Iso-butanol showed lower NOx compared to diesel operation, with levels reducing to 900 ppm at 15% EGR from 990 ppm without EGR. Combining Iso-butanol injection with EGR was able to provide an optimal trade-off between engine efficiency and emissions