Study of Cool Flames of Octane Isomers in the Counterflow Burner

Abstract

ABSTRACT At present, due to the great influence of cool flame on the ignition and combustion characteristics of subsequent hot flame, the researches on cool flame have attracted extensive attention, especially with the counterflow platform. Octane has a strong cool flame effect as the common engine fuel, and it has been figured out that the molecular structure has a direct impact on the effect. The cool flames behaviors of octane isomers in the counterflow burner were studied by adding ozone in this work. The extinction limits and combustion products were measured and results showed that n-octane has higher low-temperature reactivity than iso-octane which reveals the reaction zone of n-octane is closer to the oxidizer side. Octane cool flames are unable to be observed without ozone assistance. Several mechanisms were tested to ensure the accuracy of the simulation. The selected model captured the trends for both fuels well but still needs to be improved. The simulations of flame temperature, reaction path, and heat release rate were carried out with the tested mechanism. Due to the difference in fuel molecular structure, n-octane and iso-octane have different tendencies in the reaction path. Specifically, because it is a straight chain, N-octane is easier to produce small hydrocarbon radicals through β-pyrolysis reaction, and more active radicals in the process. Iso-octane has a complex branched-chain structure and tends to maintain the form of large carbon.