Role of the Compression Ratio in Dual-Fuel Compression Ignition Combustion with Hydrogen and Methanol.

Renewable hydrogen and e-fuels, synthesized from captured CO2 and renewable H2, are feasible ways to achieve transport decarbonization, particularly in medium/heavy-duty applications and the maritime sector, where compression ignition engines predominate. Hydrogen and methanol are low carbon-intensive fuels, which can be used in these engines by carrying out dual-fuel combustion with a diesel-like fuel. Under low load engine conditions, reaching very high substitutions of the fossil diesel fuel can be a major challenge as the presence of these fuels affects negatively the autoignition process. Therefore, this work explores the substitution limits in dual-fuel mode with hydrogen and methanol under low load conditions (5.2 bar IMEP) for two different compression ratios (15.84:1 and 18.04:1) using a 1.13 L single-cylinder engine. Increasing the compression ratio allowed improvement of the maximum diesel substitution from 55 to 82% (also achieving a significant improvement of the thermal efficiency) with methanol and from 91 to 93% with H2 (but decreasing the thermal efficiency due to higher heat transfer losses).