What question did this study set out to answer?

The central aim is to evaluate the efficiency and emissions characteristics of RCCI engines using isobutanol and diesel with different EGR rates.

April 29, 2026Open Access

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

Key Points

The central aim is to evaluate the efficiency and emissions characteristics of RCCI engines using isobutanol and diesel with different EGR rates.
Utilized varying isobutanol injection durations (2 ms, 6 ms) and EGR levels (0%, 5%, 15%) in RCCI engines.
Measured brake thermal efficiency (BTE) and nitrogen oxides (NOx) emissions at full load conditions.
Compared performance metrics against conventional diesel operation.
Peak BTE of 31.20% achieved at 6 ms isobutanol injection without EGR.
NOx emissions reduced to 900 ppm at 15% EGR compared to 990 ppm without EGR.
Cylinder pressure decreased from 82 bar to 68 bar as EGR increased from 5% to 15%.

Abstract

• 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

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