Effects of Two-Stage Injection on Combustion and Particulate Emissions of a Direct Injection Spark-Ignition Engine Fueled with Methanol–Gasoline Blends

Methanol is widely recognized as a promising alternative fuel for achieving carbon neutrality in internal combustion engines. Its use in direct injection spark-ignition (DISI) engines, either as pure methanol or blended fuels, has demonstrated improvements in thermal efficiency and reductions in certain gaseous pollutants. However, due to the complex influencing factors and the great harm to human health, its particulate emissions need to be further explored and controlled, which is also an inevitable requirement for the development of energy conservation and carbon reduction in internal combustion engines. This study explores the effects of two-stage injection strategies combined with fuel blending on the combustion characteristics, stability, and particulate emissions of DISI engines. By testing four methanol blending ratios and four injection ratios, the presented study identifies that M20 fuel with an 8:2 injection ratio achieves optimal combustion performance, stability, and increased indicated mean effective pressure. Furthermore, under low methanol blending ratios, the 8:2 injection ratio can reduce particulate number concentrations by approximately 20%. These findings suggest that a well-designed two-stage injection strategy combined with methanol–gasoline blends can effectively control particulate emissions while maintaining the power, efficiency, and combustion stability of DISI engines.