Methanol-gasoline blends in spark-ignition engines: A review of research progress and application prospects

Spark-ignition engines remain widely used in passenger cars, motorcycles, hybrid vehicles, and light-duty transport, making fuel flexibility and emission reduction important during the transition to low-carbon mobility. Methanol-gasoline blends have attracted attention as alternative fuels because methanol has high oxygen content, high octane quality, strong charge-cooling capacity, and flexible production routes.This review summarizes recent progress in methanol-gasoline blends for spark-ignition engines, covering fuel properties, blending ratios, combustion behavior, engine performance, regulated and unregulated emissions, life-cycle impacts, and application prospects. The literature shows that methanol addition can enhance knock resistance, promote oxygenated combustion, reduce soot-forming tendency, and support higher compression ratios, optimized ignition timing, and lean-burn operation. However, its lower energy density increases fuel consumption, while water affinity, phase separation, cold-start difficulty, corrosion, and material compatibility remain key barriers. Emission responses are strongly condition-dependent. CO and particulate emissions are often reduced, whereas HC and NOx vary with operating condition, mixture preparation, injection strategy, and after-treatment performance. Formaldehyde, unburned methanol, and cold-start oxygenated emissions require further attention. Life-cycle benefits depend mainly on methanol production pathways. Low-level blends are more suitable for near-term use in existing engines, while higher blends require optimized engines, compatible fuel systems, green methanol supply, infrastructure readiness, and cost reduction.