Abstract
Experimental and computational investigations are carried out to elucidate the fundamental mechanisms of autoignition of surrogates of jet-fuels at elevated pressures up to 6 bar. The jet-fuels tested are JP-8, Jet-A, and JP-5, and the surrogates tested are the Aachen Surrogate made up of 80 % n-decane and 20 % 1,3,5-trimethylbenzene by mass, Surrogate C made up of 60 % n-dodecane, 20 % methylcyclohexane and 20 % o-xylene by volume, and the 2nd generation Princeton Surrogate made up of 40.4 % n-dodecane, 29.5 % 2,2,4-trimethylpentane, 7.3 % 1,3,5-trimethylbenzene and 22.8 % n-propylbenzene by mole. Using the counterflow configuration, an axisymmetric flow of a gaseous oxidizer stream, made up of a mixture of oxygen and nitrogen, is directed over the surface of an evaporating pool of a liquid fuel. The experiments are conducted at a fixed value of mass fraction of oxygen in the oxidizer stream and at a fixed value of the strain rate. The temperature of the oxidizer stream at autoignition, Tig, is measured as a function of pressure, p. Experimental results show that the critical conditions, of autoignition of the surrogates are close to that of the jet-fuels. Overall the critical conditions of autoignition of Surrogate C agree best with those of the jet-fuels. Computations were performed using skeletal mechanisms constructed from a detailed mechanism. Predictions of the critical conditions of autoignition of the surrogates are found to agree well with measurements. Computations show that low-temperature chemistry plays a significant role in promoting autoignition for all surrogates. The low-temperature chemistry, of the component of the surrogate with the greatest volatility, was found to have the most influence on the critical conditions of autoignition.
Highlights
Improved understanding of the combustion of jet-fuels at elevated pressures is essential for accurate predictions of chemical processes taking place in air-breathing propulsion systems
The present study addresses this deficiency, and is focused on elucidating the mechanisms of autoignition of surrogates of jet-fuels at elevated pressures up to 6 bar
Experimental and computational studies described here show that the Aachen Surrogate, Surrogate C, and the 2nd generation Princeton Surrogate reproduce the critical conditions of autoignition of the jet fuels JP-8, and Jet-A reasonably well
Summary
Improved understanding of the combustion of jet-fuels at elevated pressures is essential for accurate predictions of chemical processes taking place in air-breathing propulsion systems. Computational and analytical studies have addressed combustion of jet-fuels, surrogates of jet-fuels, and high-molecular weight hydrocarbon fuels at elevated pressures [2,3,4,5,6,7,8]. These studies include measurements and prediction of combustion processes in homogeneous systems at normal and elevated pressures [2,3,4,5], extinction of counterflow nonpremixed flames [7], autoignition in nonpremixed flows [6,9,10,11], and laminar premixed flames [12]. The present study extends this to jet-fuels and its surrogates
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