Numerical analysis of the influence of SOI and injection duration on the homogenization of hydrogen-air mixtures in a PFI SI engine under lean operation

Abstract

<div class="section abstract"><div class="htmlview paragraph">The use of green hydrogen as a fuel for internal combustion engines is a cleaner alternative to conventional fuels for the automotive industry. Hydrogen combustion produces only water vapor and nitrogen oxides, which can be avoided with ultra-lean operation, thus, eliminating carbon emissions, from a tank-to-wheel perspective. In this context, the aim of this study is to investigate the influence of hydrogen injection timing and duration on the homogeneity of the hydrogen-air mixtures. Computational fluid dynamic (CFD) simulations were performed to analyze the distribution of air-fuel ratios along the engine's combustion chamber. The simulation software was CONVERGE 3.0, which offers the advantage of automatic mesh generation, reducing the modeling efforts to adjusting the operating conditions of the studied case. Before comparing the injection parameters, a mesh independence test was conducted along with model validation using experimental data. To properly evaluate the start of injection (SOI) angle, three points were considered, ranging from 90° before to 90° after the intake valve opening (IVO). Additionally, three values of injection duration were examined: 90°, 70° and 50° CAD, while keeping the mass flow rate of hydrogen and SOI constant. The standard deviation of the fuel-air equivalence ratio (φ) was used as a metric to compare the homogeneity of the in-cylinder hydrogen-air mixture. The results highlighted the significant impact of correctly selecting these two parameters on mixture preparation. More advanced SOI and longer injection durations resulted in a more homogeneous mixture, which can improve conditions for flame propagation and combustion efficiency. However, in cases where SOI occurred after IVO, hydrogen mass fraction gradients were higher. Moreover, depending on the injection timing and duration, the amount of hydrogen that returns to the intake manifold may increase, reducing the amount of hydrogen entering the combustion chamber, thus lowering power and increasing consumption. Therefore, the study of a hydrogen internal combustion engine in CFD proves crucial for identifying potential critical points for enhancing efficiency and improving safety during operation.</div></div>