CFD Analysis of Combustion of Gasoline, Hydrogen, CNG and HCNG Blends in Internal Combustion Engine

Abstract

Despite the rise of renewables and EVs, IC engines are expected to be useful in applications requiring a reliable, compact, remote and scalable power source. As a result, improving engine performance and addressing environmental concerns associated with NO_x and soot emissions becomes important. The current study explores viability of alternative fuels like H₂ and CNG to achieve lower emissions and better efficiency. CFD simulations using CONVERGE software with detailed chemical kinetics are used to model engine combustion and predict heat release rate and pressure rise for a canonical geometry in spark ignited mode. In the first part of the study, gasoline fuel combustion is simulated to validate the CFD tool with previous experiments and predictions and good agreement has been observed. In the second part of the project, simulations for the same engine geometry were performed with the fuels as: pure CH₄, 50/50 CH₄/H₂ by volume and pure H₂. Due to high-flame speed and extremely low ‘minimum ignition energy requirement’ of H₂, combustion duration is low and pressure rise is extremely steep. Consequently, for H₂ case the piston ends up working against the hot gases, while for a similar operating condition, peak pressure is considerably low for pure methane. The engine with the HCNG blend as the fuel can achieve higher cycle work than either of the two cases by the fuels compensating for shortcomings of the individual fuels: H₂ and CH₄. The amount of NO_x produced was predicted to undergo a non-linear increment with hydrogen enrichment. Therefore, higher engine power can be achieved in the 50/50 mixture with less than half of the NO_x produced for pure hydrogen.