Effects of Methane Addition on Combustion Flow Field and Combustion Characteristics of Ethanol

This study employs numerical simulations to systematically investigate the combustion characteristics of methane/ethanol blended fuel–air mixtures under non-premixed turbulent conditions. The effects of the methane blending ratio on the flow-field structure, flame morphology, NO emissions, and combustion efficiency are analyzed. The results show that, with increasing methane blending ratio, the recirculation mechanism gradually shifts from near-field local entrainment to far-field transport, accompanied by a reduction in local shear intensity. Methane addition enhances flame intensity, accelerates combustion, shortens flame length, mitigates heat transfer limitations, and reduces combustion delay. At the initial 10% and the final 20% of the methane blending range, the combustion process exhibits pronounced instability. Methane addition significantly suppresses NO formation, with temperature being the dominant controlling factor, while fuel composition also plays an important role. The overall combustion efficiency is improved. However, a slight decrease is observed at low blending ratios (0–0.1), and the enhancement becomes marginal when the methane blending ratio exceeds 0.6.