Unveiling the Dynamics of Methanol-Diesel Dual Direct Injection Compression Ignition Combustion: A Synergistic Experimental and Numerical Study

The pressing global need for de-fossilization of the transport sector, especially within the heavy-duty segment, has intensified the exploration of alternative clean fuels. While light-duty applications are rapidly transitioning towards electrification, the heavy-duty sector remains a challenging frontier due to its high-power demand and extended runtimes. In this context, methanol gained traction due to their renewable production pathways, carbon-neutrality, and are being highly promoted by the Indian government to reduce CO2 emissions by 1 billion tons by 2030. This study presents a comprehensive investigation into the dual direct injection compression ignition (DDICI) strategy using methanol as primary fuel and diesel as a pilot for ignition assistance. In contrast to spark-ignited premixed methanol engines, this strategy involves a diffusion combustion of the methanol flame, thereby eliminating the knocking issue and running with high compression ratios. The work benchmarks the methanol DDICI operation against baseline diesel operation, catering the combustion chamber modifications required, fuel injection strategy, system layout and capturing key metrics like thermal efficiency and emissions. The experimental results demonstrate that methanol DDICI achieves a thermal efficiency improvement of up to 2.5-3.0%-pts at high load and a NOx reduction of ~50% at similar exhaust gas recirculation (EGR) ratio compared to the baseline diesel. Additionally, it demonstrated soot-free combustion and lower in-cylinder temperatures reducing thermal stresses. The 3D-CFD model is validated against experimental data to capture in-cylinder combustion dynamics and emission trends. The simulation framework helps analyze the methanol-diesel spray interaction and its impact, which is relatively underexplored in existing literature. The numerical study details the effect of pilot injector spray hole orientation, positioning of the pilot injector, flow rate and piston bowl geometry adjustments on the charge distribution and the ignition. The proposed DDICI strategy presents a compelling pathway for reducing carbon intensity in sectors where full electrification remains impractical.