Hydrogen or hydrogen-derived methanol for dual-fuel compression-ignition combustion: An engine perspective

Abstract

Synthetic fuels or e-fuels, produced from captured CO2 and renewable hydrogen, are envisaged as a feasible path towards a climate-neutral transportation in medium/heavy-duty and maritime sectors. EU is presently debating energy targets by 2030 for these fuels. As their production involves chemical processing of hydrogen, it must be evaluated if the extra cost is worthy, at least in applications where hydrogen use is possible. This manuscript focuses on the performance and environmental impact when hydrogen and methanol are fed to a heavy-duty compression-ignition engine working under dual-fuel combustion. The trade-off thermal efficiency-NOx emissions is primary considered in the assessment by combining both variables in an own defined function. During the work, engine operating settings were adjusted to exploit the potential of methanol and hydrogen. Compared to conventional combustion, methanol required centering the combustion towards TDC and doubling the EGR rate, resulting in a low temperature, highly premixed combustion, almost soot-free and with extremely low NOx emissions. The best settings for hydrogen were in the middle of those for methanol and conventional combustion. Results showed great dependance with the engine load, but methanol proved superior to hydrogen for all conditions. At high load, 20–60 % methanol even improved the efficiency and reduced the NOx emissions obtained by conventional combustion. However, at low load hydrogen could substitute 90 % of the diesel fuel, while methanol failed at substitutions higher than 55 %.