Sensitivity analysis based on an efficient brute-force method, applied to an experimental CH4O2 premixed laminar flame
✍ Scribed by Jim O. Olsson; Lars L. Andersson
- Publisher
- Elsevier Science
- Year
- 1987
- Tongue
- English
- Weight
- 702 KB
- Volume
- 67
- Category
- Article
- ISSN
- 0010-2180
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✦ Synopsis
An exact (brute-force) method for sensitivity analysis is presented. It is based on an efficient time-dependent flame code. Each reaction rate constant of a steady-state reference state is changed, one at a time. For each parameter, the computations continue until a new steady-state is reached. The time to reach a new steady-state is approximately proportional to the sensitivity of the system to the changed parameter. Thereby, only the important parameters contribute significantly to the total execution time, increasing the efficiency. The absolute differences between the new and the reference profiles, integrated along the distance from the burner, are used as sensitivity measures. For the dominating reactions, the steady-state profiles of species are studied in detail.
A detailed computational study including sensitivity analysis is carried out using the Westbrook-Dryer-Schugh mechanism. The experimental premixed laminar methane-oxygen flame (9.5%, 90.5%) at 0.052 atm (Peeters and Mahnen, 14th Symp. (Int'l) on Combustion) is used as an application example. The computational profiles were strikingly delayed and broader than the corresponding experimental profiles. The difference between computational and experimental maxima for certain minority species, a factor of 150-200 for C2H6, emphasizes the need for more studies of simple combustion systems. In the sensitivity analysis, the 10 most important reactions used 85% of the execution time. Results are presented for a factor of 2 increase of the rate constants using 30-49 grid points, most of them concentrated in the flame zone. The sensitivity analysis shows that the dominating reactions were CO + OH = CO2 + H and HCO + M = CO + H + M. For the latter reaction the rate constant 7.2 x l014 exp(-9561/T), a factor of 5 higher than the value in the base mechanism, was determined. Of the 9 reaction rate constants determined by Peeters and Mahnen, only that for the reaction CO + OH was found to have a sensitivity which allows accurate rate determinations.