A computational study and correlation of premixed isooctane–air laminar reaction front properties under spark ignited and spark assisted compression ignition engine conditions

To address the need for reliable premixed laminar burning velocity and thickness information within the spark assisted compression ignition (SACI) combustion regime, a large dataset of simulated reaction fronts has been generated in this work. A transient one dimensional premixed laminar flame simulation was applied to isooctane–air mixtures using a 215 species chemical kinetic mechanism. The simulation was exercised over fuel–air equivalence ratios, unburned gas temperatures and pressures ranging from 0.1 to 1.0, 298 to 1000 K and 1 to 250 bar, respectively, a range that extends beyond that of previous researchers. Steady reaction fronts with burning velocities in excess of 5 cm/s could not be established under all of these conditions, especially when burned gas temperatures were below 1500 K and/or when characteristic reaction front times were on the order of the unburned gas ignition delay. Steady premixed laminar burning velocities were correlated using a modified two-equation form based upon the asymptotic structure of a laminar flame, which produced an average error of 2.5% between the simulated and correlated laminar burning velocities, with a standard deviation of 3.0%. Additional correlations were constructed for reaction front thickness and adiabatic flame temperature. The resulting premixed laminar burning velocity correlation showed good agreement with experiments and existing correlations within the spark-ignited (SI) regime. Analysis of the simulated characteristic reaction front times and ignition delays suggests that homogeneous SACI combustion is most useful under medium and high load operating conditions.