Effects of Lean Burn on Combustion and Emissions of a DISI Engine Fueled with Methanol–Gasoline Blends

Abstract

Methanol has significant potential as an alternative fuel for internal combustion engines. Using methanol–gasoline blends with lean-burn technology in traditional spark-ignition engines can enhance fuel economy and reduce emissions. This paper investigates the effects of lean burn on the combustion and emissions in a commercial direct-injection gasoline engine fueled with methanol–gasoline blends. The lean-burn mode is adjusted by controlling the injection strategy. The results show that homogeneous lean burn (HLB) has earlier combustion phase and better power performance when the excess air ratio (λ) is less than 1.3, while its combustion phase extends more than stratified lean burn (SLB) when λ exceeds 1.4. Both lean-burn modes achieve optimal fuel economy at λ = 1.2–1.3. Under stable conditions, BSFC decreases with higher methanol blending ratios, with SLB being more economical at low blending ratios and HLB at higher ratios. The lowest HC and particulate matter emissions for both modes are achieved around λ = 1.3. SLB has lower NOX emissions when λ < 1.3, while HLB shows lower NOX emissions when λ > 1.3. The particulate size distribution is bimodal for blending lean-burn conditions, with SLB having the highest nucleation mode peak and HLB the highest accumulation mode peak. M20 (20% volume of methanol) corresponds to the highest particle emissions under lean-burn conditions. This study can provide a deeper understanding of methanol–gasoline blending lean burn, and provide a reference for emission control of spark-ignition engines.