Numerical Study on Laminar Flame Structure of Propane with Different Ammonia Blending Ratios

Abstract

To address the challenges of energy shortage and environmental pollution in the internal combustion engine industry, ammonia has emerged as a promising carbon-free alternative fuel to achieve the goals of carbon peaking and carbon neutrality. However, the low laminar burning velocity of ammonia leads to issues such as incomplete combustion and misfire, making the blended combustion of propane and ammonia a research hotspot. In this study, a three-dimensional numerical model was established based on the CONVERGE 3.0 platform to investigate the laminar combustion characteristics of propane flames with different ammonia blending ratios (γ=0, 0.2, 0.3, 0.4, 0.5). The research focused on flame temperature distribution, flame structure at the fuel tube outlet, hydroxyl (OH) radical concentration distribution, heat release rate (HRR) and flame attachment characteristics. The results show that with the increase of ammonia blending ratio, the high-temperature region of the flame shrinks significantly, and the peak flame temperature decreases monotonously due to the low lower heating value of ammonia, the increased incomplete combustion of propane and the endothermic decomposition of ammonia. At the fuel tube outlet, the mole fractions of propane and ammonia are lower than the injection values due to the bidirectional diffusion effect and pyrolysis reaction, and the temperature inside the burner tube is less affected by the ammonia volume fraction due to the balance between endothermic pyrolysis and heat transfer from the upstream flame. The peak HRR decreases with the increase of ammonia blending ratio, while the flame attachment depth increases, indicating the enhanced flame attachment effect. In addition, the OH distribution region shortens with the increase of ammonia blending ratio, and the peak OH concentration shows a decreasing trend, which reflects the regulatory effect of ammonia blending on the flame reaction zone. This study reveals the intrinsic mechanism of ammonia blending on the laminar flame structure of propane, providing a theoretical basis for the optimization of propane-ammonia blended fuel combustion performance and flame structure regulation.