Numerical Investigation of Combustion Characteristics in a Binary Fuel Blend of C ₈ H ₁₈ and H ₂

Abstract

<div>The escalating energy demand in today’s world has amplified exhaust emissions, contributing significantly to climate change. One viable solution to mitigate carbon dioxide emissions is the utilization of hydrogen alongside gasoline in internal combustion engines. In pursuit of this objective, combustion characteristics of iso-octane/hydrogen/air mixtures are numerically investigated to determine the impact of hydrogen enrichment. Simulations are conducted at 400 K over a wide range of equivalence ratio 0.7 ≤ Ф ≤ 1.4 and pressure 1–10 atm. Adiabatic flame temperature, thermal diffusivity, laminar burning velocity, and chemical participation are assessed by varying hydrogen concentration from 0 to 90% of fuel molar fraction. As a result of changes in thermal properties and chemical participation, it is noticed that the laminar burning velocity (LBV) increases with higher hydrogen concentration and decreases as pressure increases. Chemical participation and mass diffusion were found to be the main contributors to the LBV increase in binary fuel blends. To circumvent NO_X formation, a binary fuel blend at Ф = 0.7 and 80% H₂ is selected to increase combustion intensity while maintaining a relatively low flame temperature and retaining 85% of energy density by volume. It is noted that the concentration of H, O, and OH radicals increase with hydrogen enrichment. Furthermore, the analysis revealed that the LBV increases linearly with the peak mole fraction of radicals. Key reactions are identified through sensitivity analysis and net reaction rates. A significant increase in net reaction rate is observed for H₂ + O &lt;=&gt; H + OH and H₂ + OH &lt;=&gt; H + H₂O, which in turn increases the pool of radicals. This is evident by the increase in the net production rate of H, O, and OH radicals.</div>