Kazui Fukumoto

Simulation of CO-H2-Air Turbulent Nonpremixed Flame Using the Eddy Dissipation Concept Model with Lookup Table Approach

We present a new combustion simulation technique based on a lookup table approach. In the proposed technique, a flow solver extracts the reaction rates from the look-up table using the mixture fraction, progress variable, and reaction time. Look-up table building and combustion simulation are carried out simultaneously. The reaction rates of the chemical species are recorded in the look-up table according to the mixture fraction, progress variable, and time scale of the reaction. Once the reaction rates are recorded, a direct integration to solve the chemical equations becomes unnecessary; thus, the time for computing the reaction rates is shortened. The proposed technique is applied to an eddy dissipation concept (EDC) model and it is validated through a simulation of a CO-H2-air nonpremixed flame. The results obtained by using the proposed technique are compared with experimental and computational data obtained by using the EDC model with direct integration. Good agreement between our method and the EDC model and the experimental data was found. Moreover, the computation time for the proposed technique is approximately 99.2% lower than that of the EDC model with direct integration.

Simulation of H2-Air Non-Premixed Flame Using Combustion Simulation Technique to Reduce Chemical Mechanisms

Combustion simulation that uses computational fluid dynamics (CFD) has been widely adopted as the design tool for combustion equipment. Because flow inside such equipment is generally turbulent, turbulence and combustion models are needed to simulate combustion; many combustion simulations have been performed to verify a system’s internal state, such as velocity, pressure, mole fractions of chemical species, and temperature. Combustion simulation of a confined impinging jet reactor has been performed by the large eddy simulation (LES) model serving as the turbulence model and the presumed probability density function (PDF) serving as the combustion model (Daniele, 2009). The analysis shows that a confined impinging jet reactor is indeed an interesting device because of its high mixing efficiency and absence of stagnant and recirculation zones. Under the condition of moderate or intense low-oxygen dilution (MILD), the effect of H2 on H2-CH4 turbulent non-premixed flames was investigated with the improved standard k   model as the turbulence model and with the eddy dissipation concept (EDC) model (Amir et al., 2010). Simulation results show that H2 addition to CH4 leads to improved mixing, increase in turbulent kinetic energy decay along the flame axis, increase in flame entrainment, higher reaction intensities, and increase in mixture ignitability and rate of heat release. Although combustion simulation was considered to be an efficient designing tool, considerable computational time was needed to calculate the chemical reaction. Combustion models that detail chemical mechanisms require reaction calculations involving ndimensional ordinary differential equations (ODEs) that are solved according to the number of chemical species involved. Therefore, reducing computation time for the combustion simulation is a significant problem. If computation time could be easily reduced according to the required prediction accuracy, we would be able to obtain the results more quickly. For example, O is a significant species whose mass fraction is necessary to compute the amount of NO present; therefore, the accuracy of the mass fraction of O cannot be neglected. To determine this mass fraction with sufficient accuracy, it is necessary to build a reduced mechanism including O. Generally, a quasi-steady state or partial equilibrium is assumed when the reduced mechanism is built (Warrants et al., 2006). The chemical equilibrium method (Nagai et al., 2002) does not use reaction equations; instead, the equilibrium composition of a chemical system is determined by minimizing the

Simulation of H2-Air Turbulent Diffusion Flame by the Combustion Model Using Chemical Equilibrium Combined With the Eddy Dissipation Concept

This research aims at developing a turbulent diffusion combustion model based on the chemical equilibrium method and chemical kinetics for simplifying complex chemical mechanisms. This paper presents a combustion model based on the chemical equilibrium method and the eddy dissipation concept (CE-EDC model); the CE-EDC model is validated by simulating a H2 -air turbulent diffusion flame. In this model, the reaction rate of fuels and intermediate species is estimated by using the equations of the EDC model. Further, the reacted fuels and intermediate species are assumed to be in chemical equilibrium; the amount of the other species is determined from the amount of the reacted fuels, intermediate species, and air as reactants by using the Gibbs free energy minimization method. An advantage of the CE-EDC model is that the amount of the combustion products can be determined without using detailed chemical mechanisms. The results obtained by using this model were in good agreement with the experimental and computational data obtained by using the EDC model. Using this model, the amount of combustion products can be calculated without using detailed chemical mechanisms. Further, the accuracy of this model is same as that of the EDC model.Copyright

Simulation of a CO-H2-Air Turbulent Diffusion Flame by the Chemical Equilibrium Method With a Few Chemical Reactions

The aim of our research is to build a model that can evaluate the amount of combustion products by using the chemical equilibrium method with a few chemical reactions. This paper presents an eddy dissipation concept/chemical equilibrium model (EDC/CE) and validates it by simulating a CO-H2 air turbulent diffusion flame. The obtained results were compared with Correa’s experimental data, Gran’s computational data, and the computational data obtained by using a chemical equilibrium model in FLUENT. An advantage of the EDC/CE model is that the amount of any combustion products are obtained without using detailed chemical mechanisms. The results obtained by the EDC/CE model are in good agreement with the reference data. With the combustion model that we have developed, the amount of combustion products can be calculated without detail chemical mechanisms, and the accuracy of this model is in the same order as that of the EDC model.Copyright

Simulation of H2-Air Turbulent Diffusion Flame by the Partial Chemical Equilibrium Method

This paper describes an application of the partial chemical equilibrium method considered chemical kinetics in computational fluid dynamics (CFD). In this method, fuels and oxidants are mixed at a turbulent rate so that a mixture gas of fuel and oxygen is generated. Next, the mixture gas of fuel and oxygen is burnt by molecular diffusion thereby resulting in combustion gases. The turbulent mixture rate is estimated by the eddy dissipation model and the burning velocity is evaluated by the Arrhenius equation. Finally, the combustion products are calculated by the chemical equilibrium method by using the combustion gases. One of the advantages of this method is its ability to calculate the combustion products without using chemical equations. The chemical equilibrium method requires only thermo-chemical functions (specific heat, standard enthalpy, etc). This method can be applied to incinerators or some complex combustion instruments and it can predict the intermediate chemical species of dioxins, etc.Copyright