Studies of Ionization in Flames by Means of Langmuir Probes

Calcote, H.F.; King, I. R.

doi:10.21236/ad0062243

Cited by 6 publications

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“…20 The concentration of positive ions in the combustion zone of a hydrocarbon flame was estimated to be about 10 12 ions/cc in experiments (ion concentration in the range of 10 9 -10 12 ions/cc has also been reported 21 ). Calcote and King attempted to explain the data inferred from experiments by computing ion concentrations in propane-air flames assuming an adiabatic flame temperature of 2200 K and assuming thermal equilibrium using Saha's equations.…”

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confidence: 95%

“…Calcote and King found that at 2200 K, NO + has the highest ion concentration at 1.7 x 10 7 ions/cc (excluding Na + and C + ), as shown in Table 1 of their paper. 20 Based on the ion concentrations reported in that table, Calcote and King concluded that "ions are produced not by thermal processes but by chemi-ionization or events similar to those using abnormal electronic excitation in flames. The results have also been taken as evidence that thermal equilibrium does not exist between the species in the flame front."…”

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confidence: 99%

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Numerical Investigation of Ion and Radical Compositions in Fuel-Air Mixtures for High-Speed Flows

Aithal¹

2015

20th AIAA International Space Planes and Hypersonic Systems and Technologies Conference

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Advanced ignition techniques such as plasma-assisted combustion are being investigated for various aerospace applications. Charged species and radicals are needed for initiation and sustenance of the combustion kernel in these advanced ignition methods. Identifying the important ions and radicals needed to sustain the early combustion kernel is necessary for the design and development of these systems. Experimental measurement of species (ions and radicals) is difficult and expensive. Numerical simulations can be used to investigate the ion and radical concentrations in various fuel-air mixtures at various operating conditions (temperature and pressure) and equivalence ratios. In this work, combustion products of a given fuel-air mixture were computed by using both equilibrium and finite-rate chemistry. The initial fuel-air mixture was maintained at a temperature and pressure representative of conditions in high-speed aerospace applications. Three different fuel -air mixtures-CH 4 -air, C 2 H 2 -air, and H 2 -ai r-typically investigated in scramjet engines were studied. Concentrations of various radicals such as H, O, and OH along with the charged specieswere obtained as a function of equivalence ratio for these fuel-air mixtures. The ignition delay predicted by using finite-rate kinetic mechanisms for the conditions investigated ranged from 2 ms to 20 ms depending on the fuel-air mixture and initial conditions. The results show that H 3 O + , e -, NO + , and OH -are the dominant charged species in the final mixture for all equivalence ratios and fuels considered in this work. The ion concentrations predicted by the equilibrium model yield results consistent with experimental observations. The results also show that steady-state concentration of various radicals can be computed by using equilibrium assumptions for evaluating the efficacy of advanced ignition methods when the time to reach steady-state is less than the flow residence time.

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confidence: 99%