Correlations for the ignition delay times of hydrogen/air mixtures

Abstract

Correlations for the ignition delay times of hydrogen/air mixtures were developed using the method of High Dimensional Model Representation (HDMR). The hydrogen/air ignition delay times for initial conditions over a wide range of temperatures from 800 to 1600 K, pressures from 0.1 to 100 atm, and equivalence ratios from 0.2 to 10 were first calculated utilizing the full chemical mechanism. Correlations were then developed based on these ignition delay times. Two forms of correlations were constructed: the first one is an overall general model covering the whole range of the initial conditions; while the second one is a piecewise correlation model valid for initial conditions within different sub-domains. The performance of these correlations was studied through comparison with results from the full chemical mechanism as well as experimental data. It was shown that these correlations work well over the whole range of initial conditions and that the accuracy can be significantly improved by using different piecewise correlations for different sub-domains. Therefore, piecewise correlations can be used as an effective replacement for the full mechanism when the prediction of chemical time scale is needed in certain combustion modeling. Ignition delay time or reaction time [1-3] is one of the most important parameters characterizing the combustion process of different fuels and thus is very important for combustion modeling. Accurate calculation of the ignition delay time, especially for the combustion process with a variety of fuel blends in gas turbines and other combustion engines, is a complicated procedure because of the complex interaction between flows and chemical kinetics [4]. For hydrocarbon and synthetic bio-fuels with a large number of species and a broad range of time scales, enormous computation time is required to handle the detailed chemistry in reactive flow simulation [5]. Moreover, it is required to couple a full chemistry solver with a full-scale numerical flow solver which makes the whole procedure time-consuming and far beyond the limitation of current computers [3]. Therefore, there is an increasing need to find simplified alternatives which can accurately and efficiently predict the over-all behavior of all chemical reactions.*Corresponding author (email: cz@pku.edu.cn)In order to reduce the computational time due to complex chemistry, different correlations were developed to calculate the ignition delay times for different mixtures. For example, Molnar and Marek [6,7] developed reduced equations from fitted kinetics modeling for jet-A and methane fuels. More recently, Donato and Petersen [3] provided simplified correlation equations to calculate the ignition delay times of syngas/air mixtures at different initial temperatures, pressures, and equivalence ratios. These correlations [3,6,7] were obtained through curve fitting and thus the accuracy was highly constrained by the nonlinear regression process. Instead of conducting nonlinear regression, the method of High Dimensional Model Represen...

Theoretical and numerical study of the combustion properties of premixed hydrogen/natural gas/air at a sub-atmospheric pressure of 0.849 Bar

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Numerical methods for complicated chemical mechanism involved in combustion simulation

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