A review of hydrogen–ethanol–gasoline blends as alternative fuels for spark ignition engines

Abstract The increasing demand and stringent emission norms for sustainable energy have accelerated research into alternative fuels for both SI and CI engines. As promising options, hydrogen‐enriched ethanol‐gasoline and hydrogen‐CNG fuel blends were evaluated for combustion characteristics, engine performance, emission behavior, and design modifications. A bibliometric analysis from 2010 to 2025 was conducted to identify research trends, contributing countries, and related topics. The findings show that hydrogen's inherent properties improve BTE. Various studies consistently report BTE improvements ranging from 5% to 28% across experiments. For instance, hydrogen additions of 3–11% by volume increased thermal efficiency by 7–28%, while in hydrogen‐ethanol‐gasoline blends, BTE values exceeded 32–38% under lean conditions. Similar trends were also observed in BSFC, which decreased by 8–20%. Stable combustion is a benefit of hydrogen enrichment, as reflected in a peak in‐cylinder pressure and reduced ignition delay, resulting in improved power output and thermal efficiency. Hydrogen is carbon‐free, so emissions are significantly reduced. Studies show the drop in CO and HC by 15% to 80%, while a 20% drop in CO 2 . A higher combustion temperature increases NO x emissions by 10–45%. The review also highlights design modifications to the fuel injection system and spark plugs, as well as the optimization of the compression ratio and hydrogen storage and delivery systems. Overall, hydrogen enrichment in gasoline, CNG and ethanol offers a viable pathway. To address NO x emission, storage challenges, and optimized blending strategies. This review provides a strong foundation and identifies future research directions for hydrogen‐assisted SI engine systems.