Synergistic effects of n-butanol and hydrogen on combustion stability, efficiency, and emissions in a gasoline engine at low load

To explore low-carbon and zero-carbon alternative fuels for spark-ignition engines, this study investigates the effects of blending renewable n-butanol and hydrogen with gasoline on performance of the gasoline engine under low-load conditions. Five fuel strategies were evaluated, including pure gasoline (B0G100), two n-butanol/gasoline blends (B30G70 and B50G50), and their hydrogen-enriched counterparts (B30G70&H2 and B50G50&H2). Experimental results showed that simultaneous use of n-butanol and hydrogen greatly enhanced combustion stability. The coefficient of variation (COV) of indicated mean effective pressure (IMEP) and peak combustion pressure (PCP) decreased from 2.4 % to 9.66 %–1.55 % and 4.86 %, respectively. Additionally, the distribution of PCP became more concentrated near top dead center, indicating suppression of late-burn phenomena and improved combustion consistency. Increasing butanol ratio and introducing hydrogen also advanced CA50 and steepened heat release rate (HRR), leading to enhanced flame propagation and faster heat-to-work conversion. Adding hydrogen in B30G70 and B50G50 further improved thermal efficiency of the engine, increasing indicated thermal efficiency (ITE) by 9.5 % and 9.6 %, respectively. Compared to pure gasoline, using B30G70&H2 in the test engine achieved the highest efficiency gain, with an 18.8 % increase in ITE. From an emissions perspective, the dual-fuel strategy effectively reduced CO, HC, and CO2 emissions, indicating more complete combustion and lower carbon emissions output. However, the associated rise in combustion temperature resulted in higher NOx emissions. These findings highlight the synergistic benefits of n-butanol and hydrogen as complementary fuels, and suggest that further optimization—such as implementing cooled EGR—could mitigate NOx emissions while preserving thermal efficiency.