Investigation of Combustion Characteristics, Energy Flow Distribution and Thermal Conversion Process of Methanol-Gasoline Blended Fuel Engines Under High Compression Ratio Conditions

Abstract

In light of the global energy and environmental challenges, this study thoroughly assesses the performance of methanol-gasoline blends (M100, M85) compared to pure gasoline in a spark-ignition engine. Through experimental data and numerical simulations, the combustion characteristics, energy flow distribution and thermomechanical conversion processes of the three fuels were comparatively analyzed across compression ratios (CR) ranging from 11 to 15. Under full-load conditions at 3500 r/min, gasoline respectively exhibited 7.58% and 8.69% higher power output than M100 and M85.However, when operating under high load (exceeding 125 NM), methanol has better fuel economy than gasoline due to its 50% oxygen content and relatively high flame propagation speed.  The optimized methanol-gasoline blend increases the thermal efficiency by 8% to 12%. This improvement stems from increased high-pressure cycle work, reduced heat transfer and incomplete combustion losses. Both the effective expansion ratio (EER) and energy economy efficiency (EEE) peaked at a CR around 13, after which efficiency gains plateaued while knock propensity intensified. Between 2500 and 3500 r/min with CR exceeding 13, methanol blends exhibited 18%–23% higher efficiency than gasoline owing to their superior knock resistance from high octane sensitivity. The combustion characteristics of M85 are between those of gasoline and M100, making it a very promising alternative fuel. This study offers essential insights for enhancing methanol-gasoline engines through CR optimization, combustion phasing (CA50) calibration, and implementation of effective thermal conversion process. Furthermore, it also validates the feasibility of methanol blends in low-carbon powertrain development.

Keywords: Methanol-gasoline blends, Combustion characteristics, Compression ratio, Effective expansion ratio