Laminar Flame Speeds of Premixed Iso-Octane/Air Flames at High Temperatures with CO ₂ Dilution

Spherically expanding flames are employed to measure the laminar flame speed of premixed iso-octane/air mixtures at elevated temperatures through both experiments and numerical simulations. Iso-octane (2,2,4-trimethlypentane) is an important gasoline primary reference fuel (PRF). While most studies on laminar burning velocity of iso-octane focus on low temperatures (less than 400 K), the experiments here were conducted in an optically accessible constant volume combustion chamber between 373 K-473 K, at a pressure of 1 bar, and from ϕ=0.8 to ϕ=1.6. The effect of diluent is investigated through the addition of 15% CO₂ dilution in order to simulate the effect of exhaust gas recirculation. The decreased reactivity with diluent addition reduces mixture reactivity, which can reduce the propensity for knock in spark ignition engines. All laminar flame speeds were calculated using the constant pressure method enabled via schlieren visualization of the spherically propagating flame front. Results show that laminar flame speeds of iso-octane/air mixtures at 1 bar increase by 46-51% with initial temperature increases from 373 K to 473 K. However, the addition of 15% CO₂ dilution to the iso-octane/air mixtures at 1 bar and 473 K results in a 47-51% decrease in the laminar burning velocity. Numerical results obtained with CHEMKIN [1] using the kinetic mechanism of Chaos et al. [2] show excellent agreement with experimental data for ϕ=0.8-1.2; however, the kinetic mechanism slightly underestimates the experimentally observed laminar flame speeds between ϕ=1.3-1.6.