The current rate of depletion of fossil fuels has created an imbalance in the energy exchange. Stricter emission standards are enforced in order to control the environmental pollution and global warming. Both these factors have led to a shift from usage of conventional fossil fuels to other alternative resources. LPG serves as a viable alternative option owing to its suitability to fuel SI engines and its obtainability from large scale shale gas reserves. Being a gas at atmospheric condition, it offers proper homogenization and is best suited for lean-burn conditions. Adding methanol in small amount to LPG lowers the combustion temperature due to the latent heat of vaporization and improves lean operation due to oxygen content contributing in reduction of NOx. This work is focused on NOx reduction as it is hazardous and main constituent in the formation of PM, smog and acid rains. An experimental study is conducted in a single cylinder diesel engine modified to operate as SI engine at an optimized compression ratio of 10.5:1 and 1500 rpm fueled by LPG. The effects of methanol substitution were investigated in reduction of NOx emissions at 100% throttle condition by injecting 10, 20 and 30% of methanol on energy basis into the intake port of engine. The results have been analyzed with Brake Effective Mean Pressure (BMEP) as it serves as an important yardstick to compare different criteria. The experiments were performed at BMEPs of 4, 4.5,5 and 5.5 bar. There is a significant improvement in brake thermal efficiency along with decrease in the NOx emission as the percentage of methanol in the fuel goes higher. The decrease in NOx is significant ranging from 83% at 4 bar BMEP to 12% at 5.5 bar. The lean operation was also improved on addition of methanol. © 2021, Springer Nature Singapore Pte Ltd.