Laminar flame speeds of C5 to C8 n-Alkanes at elevated pressures and temperatures

Experimental data of high fidelity on the laminar flame speeds and Markstein lengths of C₅ to C₈ n-alkane mixtures with air at elevated pressures were determined from the propagation velocities of spark-ignited, expanding flames in a newly-designed heated, high- and constant-pressure chamber, using nonlinear extrapolation. Results show that the laminar flame speeds of these fuels are basically similar, hence extending previous observations of the fuel similarity to the high-pressure range of 10 to 20 atm. A companion analysis of the computed flame structure reveals comparable similarity for the thermal properties as well as the key intermediates and reactions, thereby supporting the observed global flame speed similarity. The study further shows that the influence of stretch diminishes with increasing pressure because of the concomitant reduction of the flame thickness, implying not only reduced error in the determination of laminar flame speeds from stretched flames at elevated pressures, but also substantial simplification in the modeling of turbulent flames because of the diminished importance of stretch.