Experimental and chemical kinetic study on the laminar flame characteristics of the blends of n-propanol and isooctane at elevated temperature and pressure

Laminar flame characteristics of n-propanol-isooctane blends were investigated at the initial temperature of 433 K, two pressures of 0.1 and 0.5 MPa, different equivalence ratios of 0.7-1.6 and various fuel blending ratios in a constant volume bomb. Laminar flame speeds and flame instability parameters were determined, and the effect of initial conditions were evaluated. It was found that laminar flame speeds of n-propanol decrease with the pressure increases, and the addition of n-propanol into isooctane results in the rise of laminar flame speed. To interpret the flame speed variation, the thermal and diffusion properties were discussed by determining the adiabatic flame temperature and Markstein length. However, the chemical kinetics is concluded as the dominant factor since the variation of adiabatic flame temperature and Markstein length exert different behaviors with laminar flame speed does. A high temperature chemical kinetic model was developed, and the model accuracy was validated with present data as well as several sets of data published previously. With this model, detailed sensitivity and reaction pathway analyses were carried out to aid the understanding of the inherent mechanism. It was found that the laminar flame speed is mainly sensitive to the small molecule reactions. The addition of npropanol into isooctane induces limited effect on the reaction pathways of each fuel. Finally, the flame thickness and density ratio were presented with the hydrodynamic instability evaluated. Combining the schlieren pictures and the flame instability parameters, it was concluded that the thermal-diffusional mechanism dominates the flame instability variation with the addition of n-propanol.