577 / 2019-01-18 14:54:34

Research on Reduced Method of Chemical Reaction Mechanism Based on Direct Relation Graph and Its Derivatives Methods

direct relation graph; mechanism reduction; threshold; multiple reduction

全体主题 > 燃料利用与化学循环技术

Quantitative numerical simulation of combustion process can be achieved by coupling chemical reaction kinetics with numerical simulation of flow. However, the coupling of detailed chemical reaction kinetics model will bring enormous amount of calculation. Therefore, constructing a chemical reaction kinetics model which is as simplified as possible and meets the requirements of accuracy is the key to solve the problem.
It is found that if only one threshold is selected within the recommended range and the mechanism is reduced once by using directed relation graph (DRG) or directed relation graph with error propagation (DRGEP), there will be insufficient mechanism reduction. That is to say, under the condition of maintaining the initial setting accuracy, the component and elementary reactions can be further reduced. It is also found that the ability of using only one mechanism reduction method to identify redundant components and elementary reactions is limited. After fully eliminating redundant components and elementary reactions, one problem will be observed that no matter how the threshold is chosen, the component and elementary reactions can not be reduced under the condition of maintaining accuracy continuously.
Aiming at the above problems, this paper proposes a mechanism reduction method. For a certain reduction method, the threshold is set from small to large gradually within the recommended range to form multiple reductions. When the reduction ability of the method is empity, other methods are cross-used, to greatly reduce the components and elementary reactions, while maintain the initial setting accuracy. By Closed Homogeneous Reactor, under the initial setting error 30%, the threshold is set from small to large, DRG and its derivative methods are used to the detailed mechanism model of n-heptane oxidation reaction proposed by Lawrence Livermore Laboratory in the United States named LLNL3.1 (654 components and 2827 elementary reactions). The reduced mechanism model contains 162 components and 692 elementary reactions. Furthermore, The Closed Internal Combustion Engine Simulation is used to calculate the in-cylinder pressure, temperature, carbon dioxide and the main intermediate products (CO, OH) under different operating conditions. The results show that the reduced mechanism is agreement with the detailed mechanism very well. So the effectiveness of the reduction method and the accuracy of the reduced mechanism are verified.