Parametric Analysis of Liquid Ammonia Direct Injection for Optimal Ammonia-Hydrogen Combustion in Spark-Ignition Engines

As the global effort to reduce carbon emissions intensifies, ammonia has emerged as a promising fuel alternative due to its carbon-free molecular composition. This study explores the potential of direct liquid ammonia injection combined with port fuel hydrogen injection technology in a spark ignition engine, leveraging Computational Fluid Dynamics (CFD) simulations informed by experimental data and literature. The methodology involves reproducing and validating an evaporation model sourced from the literature. Once validated, the fraction of injected liquid ammonia actively participating in combustion was quantified, an essential step in refining the engine combustion simulation. The engine model was divided into two key simulations: (i) a Volume of Fluid (VoF) simulation of the injector to characterize ammonia behavior at the nozzle outlet, and (ii) an engine simulation utilizing a Lagrangian spray configuration, based on the VoF results and the validated evaporation model. The primary objective of this study is to analyze the impact of injection timing, injection pressure, combustion chamber geometry, and compression ratio on mixture formation and combustion propagation. A secondary focus is to mitigate direct contact between liquid ammonia droplets and the cylinder liner, thereby reducing lubricant degradation. The findings provide critical insights into optimizing injection strategies to enhance combustion efficiency while minimizing unburned NH₃ emissions, offering a pathway toward more sustainable internal combustion engine technologies.