Low temperature reactivity controlled compression ignition strategy using compressed natural gas-isobutanol blends and exhaust gas recirculation for enhanced emission control

Compression Ignition (CI) engines are highly regarded for their superior efficiency; however, they are also associated with significant emissions of nitrogen oxides (NOx) and particulate matter (PM). Reactivity controlled compression ignition (RCCI) presents a viable solution through dual-fuel operation, facilitating improved control over combustion phasing. In this investigation, an RCCI engine was fueled using compressed natural gas (CNG) as a low-reactivity fuel and a 20 % isobutanol–diesel blend as the high-reactivity fuel. The CNG injection durations were varied at 2 ms, 4 ms, 6 ms, and 8 ms, while exhaust gas recirculation (EGR) rates were set at 5 %, 10 %, and 15 %. The novelty of this study resides in the unique combination of CNG and isobutanol within an RCCI framework, alongside the systematic optimization of injection duration and EGR. Experimental findings indicated that the optimal configuration of a 6 ms CNG injection with 5 % EGR yielded a brake thermal efficiency (BTE) of 34.1 % at full load, representing an 8.6 % improvement over diesel, and reduced brake specific fuel consumption (BSFC) by 36.8 % to 0.24 kg/kWhr. The peak cylinder pressure reached 78.66 bar, and the net heat release rate (NHRR) increased to 75.48 J/°CA. The maximum in-cylinder temperature decreased from 1597.2 °C to 1483.2 °C, while EGR further reduced NOx emissions by 33 %. These results demonstrate that an RCCI strategy with optimized CNG injection and EGR can simultaneously enhance efficiency and reduce NOx emissions while maintaining combustion stability, positioning RCCI as a promising alternative as conventional fuels decline.