Numerical study and cellular instability analysis of E30-air mixtures at elevated temperatures and pressures

Ethanol is used as a gasoline blending component in numerous countries throughout the world. In the present work, the Chemkin Pro package was used to study the chemical kinetic behavior of E30 (a blended fuel containing 30% ethanol and 70% gasoline on volume basis). The effects of chemical kinetics and adiabatic flame temperature on the laminar flame propagation speed at different initial temperatures were studied and the relative importance of the thermal and chemical effects of ethanol at different initial temperatures was investigated. With increasing initial temperature, the rate of main branching reactions (R1:O2 + H ⇔ O + OH and R29: CO + OH ⇔ CO2 + H) increases much more than that of the main termination reactions (R13:H20 + M ⇔ H + OH + M, R15:O2 + H(+M) ⇔ HO2(+M)). The laminar flame propagation speed shows a linear relationship with the sum of the peak concentrations of H and OH. The chemical effect of ethanol was far greater than its thermal effect which was characterized by adiabatic flame temperature. In addition, the cellular instabilities of the E30-Air flame were studied. As the initial pressure and equivalence ratio change, the dominant instability shifts between hydrodynamic and diffusional-thermal. The theoretical critical Peclet number (Pe_cr) decreases with increased equivalence ratio and is insensitive to the initial temperature and pressure; these trends are consistent with the experimental findings. Furthermore, [Formula presented] Q₂ is the dominant parameter affecting Pe_cr with varying equivalence ratio.