Evaluation and extension of ignition delay correlations for dual-fuel operation with hydrogen or methanol in a medium speed single cylinder engine

Abstract

Hydrogen (H2) and methanol (MeOH) are promising fuels for sustainable transport, owing to their ideal properties for use in internal combustion engines: CO2 neutral (when produced renewably), ultralow emissions, and high efficiencies. The dual-fuel (DF) technology where diesel is used as a pilot to ignite port fuel injected H2 or MeOH is of particular interest for retrofitting existing diesel engines (DE). Although some experimental work has been conducted on high-speed DE, there has been limited numerical investigation in this area. Therefore this work focuses on medium speed large bore engines and on the ignition delay (ID) timing of the diesel pilot, a crucial parameter to well predict numerically as it denotes the start of heat release. Experiments were carried out using H2 and MeOH in DF on the same single cylinder engine. The measured IDs are reported and visualize the difference of the effect of both fuels. Next, diesel ID correlations are evaluated on their predictive capabilities in DF. They fail however to predict the increasing ID from the inhibition effect of MeOH. Therefore, new ID correlations were developed for DF with H2 and MeOH, emphasizing the importance of additional terms such as the methanol equivalence ratio to describe this inhibition effect. Finally, the new correlations were compared with correlations for DF with natural gas to explore similarities and differences.