Differences between direct relation graph and error-propagation-based reduction methods for large hydrocarbons

Large hydrocarbons, such as n-heptane and iso-octane, are always the main fuels of fire experiments. The detailed mechanisms of these large hydrocarbons provide a powerful tool for the numerical simulation to study complex turbulent reacting flows. But it is necessary to reduce the mechanisms because of the huge computational cost for detailed mechanisms. The directed relation graphs (DRG) and DRG with error propagation (DRGER) methods are almost the most efficient models to reduce detailed mechanisms. The differences between these two methods have been analyzed in this paper. The results show that the numbers of species in the skeletal mechanisms obtained by DRG have a significant drop when the threshold limits are between 10(-1) and 10(-2):, both for n-heptane and iso-octane. Main products are essential to be included in the target species when the DRGEP method is used, while the main reactants are enough as the target species for the DRG method. Validation of the skeletal mechanisms shows good accuracy for both DRG and DRGEP methods over wide parameter ranges when the species numbers of the skeletal mechanisms are more than 87. The results also indicate that the skeletal mechanisms obtained by DRG method have a smaller ratio of reactions numbers to species numbers, and the skeletal mechanisms obtained by the DRG method have a better performance than that of DRGEP when the species numbers of the mechanisms are of the same scale. (C) 2013 International Association for Fire Safety Science. Published by Elsevier Ltd. Open access under CC BY-NC-ND license. Selection and peer-review under responsibility of the Asian-Oceania Association of Fire Science and Technology