A Novel Chemical Kinetics-Based Approach for Studying Feasibility and Optimise Retrofitting Strategies of Hydrogen CI Engines: Application to a Laboratory-Scale Single-Cylinder Engine

The climate emergency has prompted countries to adopt strategies to limit the rise in global temperatures by promoting low-carbon technologies. In this context, hydrogen (H₂) can be considered a viable solution, especially in road and marine transportation, where Compression Ignition (CI) internal combustion engines (ICEs) are widely used. Despite its potential to significantly reduce pollutant emissions compared to fossil fuels, hydrogen presents a major challenge for CI engines due to its high autoignition temperature (greater than diesel). To overcome this problem, a novel methodology is proposed to evaluate the feasibility of hydrogen retrofitting. Each engine operating point is simulated as an ideal zero-dimensional (0D) reactor into which a diesel-hydrogen-air mixture is introduced. A fully detailed kinetic mechanism is used to simulate the complex chemical interactions between the two fuels, as well as its significant effect on engine behaviour, obtaining accurate predictions of autoignition timing. Three distinct time-based criteria are introduced to assess whether autoignition occurs during the compression stroke, and if so, to identify the corresponding crank angle. This information guides the selection of an appropriate hydrogen retrofitting strategy. The proposed methodology is validated against experimental data from a 500 cm³ CI single-cylinder research engine (SCRE) operated at CNR-STEMS. Two dual-fuel test cases at 1500 and 2000 revolutions per minute (rpm) are simulated. The comparison of the numerical results with respect to the experimental data demonstrates a good prediction within a discrepancy of 7°. Finally, for the mentioned test cases, the numerical model is applied to a local subdomain for estimating the local mixture composition at which autoignition experimentally occurs.