CFD Analysis of Different Methane/Hydrogen Blends in a CI Engine Operating in Dual Fuel Mode

Nowadays, the stricter regulations in terms of emissions have limited the use of diesel engines on urban roads. On the contrary, for marine and off-road applications the diesel engine still represents the most feasible solution for work production. In the last decades, dual fuel operation with methane supply has been widely investigated. Starting from previous studies on a research engine, where diesel-methane dual fuel combustion has been deepened both experimentally and numerically with the aid of a CFD code, the authors implemented and tested a kinetic mechanism. It is obtained from the combination of the well-established GRIMECH 3.0 and a detailed scheme for a diesel surrogate oxidation. Moreover, the Autoignition-Induced Flame Propagation model, included in the ANSYS Forte® software, is applied because it can be considered the most appropriate model to describe dual fuel combustion. However, the higher emissions of unburned hydrocarbons have pushed researchers to move towards a more eco-friendly gaseous fuel such as hydrogen. Since the former scheme is capable to deal with H2 oxidation as well, in this work an increasing substitution of methane with H2 is analyzed for a critical engine operating condition at 1500 rpm with a low load level and poor equivalence ratio; in particular, three percentages of hydrogen substitution are simulated, 20, 50 and 80%. The results of this activity have shown that the contribution of H2 an increased peak pressure and a better combustion efficiency, confirming the reduction of CO2 and unburned hydrocarbon emissions.