Properties Of Combustion Gases Research Articles

Modeling and analysis of 3D radiative heat transfer in combustor

Abstract Compared with wall emission, gas thermal radiation is much more complicated because of its nongray and volumetric property. In this paper, a numerical method is established to calculate 3D radiative heat transfer in combustor by modelling radiative transfer as well as nongray radiative properties of combustion gases. Energy exchanges caused by thermal radiation and conduction are calculated and compared in a rectangular combustor, which shows the significant role of thermal radiation in heating fuel-air mixtures and prompting internal combustion reactions. Besides, radiative heat flux on the wall is also quite obvious although a non-contacting flow case, revealing the special challenges for thermal protections brought by radiant energy. Lastly, increasing the working pressure means much more participating species in radiative transfer process and the radiative effects will be also magnified. The numerical method in this paper provides a direct technique to analyze the role of thermal radiation in complex thermochemical reactions while the application case proves the necessity of coupling a high-accuracy radiation model when simulating combustion and flame propagation.

HTPB Heat of Formation: Literature Survey, Group Additive Estimations, and Theoretical Effects

Hydroxyl-terminated polybutadiene (HTPB) is a common ingredient in rocket propellants, but its thermochemical properties (composition, density, and heat of formation) are not well defined. A survey of the literature and thermochemical databases indicated wide ranges for these properties, especially heat of formation. Six group additive schemes were used to estimate the heat of formation of HTPB and analyze the effects of hydroxyl functionalization and curing reactions. Good agreement is observed between the methods for HTPB isomer units, but cumulative differences result in significant disparities for larger, practical polymers. Increased hydroxyl functionality and the curing reaction are predicted to yield nonnegligible decreases in the heat of formation. The heat of formation of propellant-grade, isophorone-diisocayante-cured HTPB R-45M () was computed as or . Chemical equilibrium analyses were completed for solid propellants composed of ammonium perchlorate and HTPB, and for hybrid rocket engines based on HTPB burning with liquid oxygen or nitrous oxide, where the heat of formation of HTPB was varied within a reasonable range. The chemical equilibrium analysis computations indicated that combustion gas properties and theoretical propellant performance can vary up to 5% within practical operating conditions for the range of HTPB heats of formation implemented.

Simulation and analysis of hot plume infrared signature based on SNB model

Abstract Numerical calculation of infrared emission from hot plume is of great significance for flight monitoring and detections. In this paper, the SNB (statistical narrow band) model established with parameters derived from the high-resolution spectral database HITEMP 2010 is used to perform the hot plume infrared signature simulations. Accuracy of the model is examined by the exact LBL (line by line) method, which proves the model’s reliability to predict radiative properties of combustion gases. In the application part, the SNB model is used to analyze infrared signatures of aircraft plumes cruising at different flight altitudes. The results show that cruising at a higher-altitude will obviously reduce the plume infrared emission. Besides, the plume infrared emissive energy mainly concentrates in a special wavenumber interval and can be strongly absorbed by atmosphere.

Simulation and analysis of hot plume infrared signature based on SNB model

Abstract Numerical calculation of infrared emission from hot plume is of great significance for flight monitoring and detections. In this paper, the SNB (statistical narrow band) model established with parameters derived from the high-resolution spectral database HITEMP 2010 is used to perform the hot plume infrared signature simulations. Accuracy of the model is examined by the exact LBL (line by line) method, which proves the model’s reliability to predict radiative properties of combustion gases. In the application part, the SNB model is used to analyze infrared signatures of aircraft plumes cruising at different flight altitudes. The results show that cruising at a higher-altitude will obviously reduce the plume infrared emission. Besides, the plume infrared emissive energy mainly concentrates in a special wavenumber interval and can be strongly absorbed by atmosphere.

Assessments on SGG and WSGG spectral models in high-ash coal combustion

In radiation process, a variety of models can be used to represent the spectral radiative properties of combustion gases. In coal combustion, the high level of soot concentration brings higher complexity to the formulation. Several pieces of research are found, comparing different radiation models usually applied to idealized laboratory situations. Only a few works explore the behavior of such models in real scale applications, such as coal-fired furnaces. Comparisons among different arrangements of the SGG and WSGG models were carried out by means of CFD simulations, applied to a boiler of a real 160 MW coal-fired power plant. Five different cases were simulated. The most simple case was set with a fixed absorption coefficient SGG model, while the most detailed case was achieved by employing a WSGG model with gas and soot absorption coefficients overlay. Temperature fields were well represented by all cases, with maximum deviations of 6%. Predictions on radiative heat flux for the SGG models were significantly lower than the WSGG simulations, with relative deviations up to 16.46%. Even though deviations on radiative heat flux are significant, results suggest the suitability of simple gray gas models in fast assessments of industrial applications such as coal-fired furnaces.

Analysis of Combustion Gas Properties According to Combustion of Wood Materials Based in Korea

Analysis of Combustion Gas Properties According to Combustion of Wood Materials Based in Korea

Effect of limestone addition on radiative heat transfer during co-firing of high-sulfur content lignite with biomass in fluidized bed combustors

ABSTRACTIn this study, influence of limestone addition on radiative heat transfer during co-firing of high-sulfur content lignite with olive residue in the freeboard of 300 kWt Atmospheric Bubbling Fluidized Bed Combustor (ABFBC) is investigated by using an in-house developed radiation code based on Method of Lines (MOL) solution of Discrete Ordinates Method (DOM). The freeboard is treated as a 3D rectangular enclosure containing gray, absorbing, emitting gas with absorbing, emitting, anisotropically scattering particles surrounded by black/gray diffuse walls. Radiative properties of combustion gases and particles are evaluated by using Leckner’s correlations and Mie theory, respectively. Input data required for the model are provided from four combustion tests which were previously carried out sequentially for lignite only, lignite with limestone addition followed by 30 and 50 wt % shares of olive residue in the fuel mixture for the same Ca/S ratio. The results show that addition of limestone affects the radiative properties of the particles in the freeboard through the change of particle size distribution and load rather than optical properties and decreases the radiative wall heat fluxes along the freeboard. On the other hand, co-firing with biomass compensates this decrease as less limestone is utilized in almost direct proportion to the coal replacement.

Thermodynamic Property Calculations for Equilibrium Mixtures

Modeling of chemical equilibrium is fundamental to the analysis of rocket motors. Related modeling supports performance calculations, combustion gas properties, and important interactions between reactive gases and ablative insulators. Available computer programs for providing these types of calculations were primarily developed decades ago and are known to have solution instabilities and limited capabilities. The authors have previously presented mathematical solution methods for determining compositions of systems in chemical equilibrium. Here, the methodology is extended to include calculations for thermodynamic properties. This requires certain modeling assumptions and complex calculations to determine composition derivatives. Detailed derivations are provided so that modeling assumptions and property definitions are clear, and all mathematics are presented in matrix–vector form to support program implementation using modern programming methods. This methodology has been implemented into a computer program named Chemics, and verification of this approach and implementation is presented here by demonstrating accuracy against property data for air over a wide range of temperatures and by comparing thermodynamic property calculations for the combustion products of an aluminized propellant against results using a legacy modeling program. The Chemics program provides a modern platform for equilibrium calculations, extends applicability, and improves stability over legacy programs. Continued development is underway to provide advanced implementation into rocket performance and ablation heat transfer modeling programs.

Analytical study of power generation efficiency of WtE systems operating in Tokyo special ward district

This paper attempts to present a fundamental system analysis for the performances of currently operating waste-to-energy incinerators in Tokyo special ward district. Firstly, it is stated that the gross thermal efficiency η G of any steam turbine generation system could be expressed as a product of four parameters: the boiler efficiency η b, turbine steam utilization fraction R t, heat cycle constant R h, and turbine generator chamber efficiency η tg. Secondly, reliable heat inputs to waste-to-energy systems were established by the ideal boiler efficiencies η b,ids which are based on the versatility of the standardized combustion gas properties, to avoid totally depending on the conventional low calorific value measurements of the fed-waste which occasionally include dubious results. Thirdly, the achievement of technological progress of power generation in waste-to-energy systems over the past 3 decades was reviewed. The advantage of 4 MPa class incinerators (installed after 2001) over 3 MPa class incinerators (installed before 1999) in η G by 33.1% on average was clarified. Fourthly, the difference in operational modes which affects the η G was studied to seek for the optimum operation in terms of energy recovery. In conclusion, this paper evaluated that the overall η G of the 20 incinerators in FY2015 proved to be 15.0%.

A full spectrum k-distribution based weighted-sum-of-gray-gases model for oxy-fuel combustion

Oxy-fuel combustion has become one of the most promising technologies for carbon capture and storage (CCS) in coal-fired plants. Radiative properties of combustion gases in oxy-fuel combustion are significantly different from those found in air-fired due to the change of the gas composition. A few modified weighted-sum-of-gray-gases (WSGG) models had been proposed to consider the wide H2O to CO2 ratio for oxy-fuel combustion in recent years. As most of the models are validated using simple homogenous benchmark, the applicability of such models to non-homogeneous media is questionable. In this paper, based on the up-to-date HITEMP 2010 database, we obtain new parameters of WSGG model for oxy-fuel combustion by combining the features of full-spectrum k-distribution (FSK) model with WSGG model, in which the weighting factors and absorption coefficients are directly obtained from the k-distribution, and the polynomial expression of absorption coefficient is improved. The new parameters of WSGG model are extensively validated by comparing the radiative source terms and radiative heat fluxes, predicted with the line-by-line (LBL) model integration of HITEMP 2010 database at a one-dimensional slab system. The predictions by different parameters of WSGG model from the literature are also included in comparison. The investigative cases include the non-isothermal and/or non-homogeneous gas mixture. The maximum relative error of heat fluxes is 11.2% for the new parameters, 33.5% for Yin model (Yin et al., 2010) and 23.0% for Johansson model (Johansson et al., 2011) in non-isothermal non-homogeneous gas mixture. The results show the new parameters can significantly improve the prediction accuracy in non-isothermal non-homogeneous CO2/H2O mixture.

Assessment of radiative heat transfer characteristics of a combustion mixture in a three-dimensional enclosure using RAD-NETT (with application to a fire resistance test furnace)

Using RAD-NETT, a neural network correlation of the non-gray radiative absorption properties of combustion gases (CO2 and H2O) and soot, the emissivity and hemispherical absorptivity of a combustion mixture to a boundary in a rectangular enclosure is determined. Results show that the both the emissivity and hemispherical absorptivity have a strong dependence on the mixture properties, as well as the medium temperature and wall temperature. The gray assumption with emissivity equal to absorptivity is generally inaccurate. The numerical model is used to analyze temperature and heat transfer data generated from a fire resistance test furnace. Results show that emission and reflection from the wall boundaries have a major effect of the radiative heat flux measurement in a test sample in a fire resistance test. Numerical results also demonstrate that the furnace was operating essentially in an isothermal condition. From the perspective of a compartment fire, numerical data show that soot emission and emission from the wall are essential in the initiation of flashover in a compartment fire.

New correlations for the weighted-sum-of-gray-gases model in oxy-fuel conditions based on HITEMP 2010 database

Oxy-fuel combustion is one of the promising options for carbon dioxide capture in future coal power plants. Radiative properties of combustion gases and heat transfer characteristics inside oxy-fuel furnaces are different from those found in air-fired furnace. Nowadays, few publications provide appropriate radiation property correlations for oxy-fuel conditions. The available correlations are based on previous versions of HITRAN database, which is not accurate for prediction of spectral intensities at high temperature in combustion applications or above 1000K. This paper considers the determination and evaluation of new correlations for the weighted-sum-of-gray-gases model to predict the radiative transfer in gases under oxy-fuel conditions. The new correlations are fitted from emittance charts calculated from the up-to-date HITEMP 2010 database for molar ratios of water vapor to carbon dioxide between 0.125 and 4, temperature range of 400–2500K, and pressure path-length varying from 0.001 to 60barm. The new correlations are validated by comparing the radiative source term with line-by-line calculations from HITEMP 2010 database for a one-dimensional slab system. The radiative transfer equation is solved with the discrete ordinate method.

Experimental correction of combustion gas properties of AN-based composite solid propellants used for turbo-pump starter

Solid propellant gas generators play a role as a turbo-pump starter in liquid propellant propulsion systems by supplying pressurized gas to power turbines for engine start. Among the required combustion gas properties provided by solid propellant gas generators, the combustion gas temperature should not exceed a certain temperature which may damage the turbine blades. For such purposes, phase stabilized ammonium nitrate (AN)-based propellants have been widely used with a low combustion temperature. However, gas generator propellants with ammonium nitrate have historically exhibited incomplete combustion resulting in increased flame temperatures differing significantly from equilibrium values. In consideration of design requirements, an engineering model of solid propellant gas generator was manufactured using the combustion gas properties calculated by a chemical equilibrium code and then hot-fire tests were performed. Procedures for the correction of T 0 , k and M w of the combustion gas from the experimental results are introduced and the following effects on the design of the solid propellant gas generator are presented. From the experimental correction of the combustion gas properties, it is found that the amount of the propellant could be reduced while providing the same amount of available power to the turbines and consequently, the size of the gas generator could also be decreased.

Account for variations in the H 2O to CO 2 molar ratio when modelling gaseous radiative heat transfer with the weighted-sum-of-grey-gases model

This work focuses on models suitable for taking into account the spectral properties of combustion gases in computationally demanding applications, such as computational fluid dynamics. One such model, which is often applied in combustion modelling, is the weighted-sum-of-grey-gases (WSGG) model. The standard formulation of this model uses parameters fitted to a wide range of temperatures, but only for specific ratios of H 2O to CO 2. Then, the model is limited to gases from fuels with a given composition of hydrogen and carbon, unless several sets of fitted parameters are used. Here, the WSGG model is modified to account for various ratios of H 2O to CO 2 concentrations. The range of molar ratios covers both oxy-fuel combustion of coal, with dry- or wet flue gas recycling, as well as combustion of natural gas. The non-grey formulation of the modified WSGG model is tested by comparing predictions of the radiative source term and wall fluxes in a gaseous domain between two infinite plates with predictions by a statistical narrow-band model. Two grey approximations are also included in the comparison, since such models are frequently used for calculation of gas radiation in comprehensive combustion computations. It is shown that the modified WSGG model significantly improves the estimation of the radiative source term compared to the grey models, while the accuracy of wall fluxes is similar to that of the grey models or better.

Numerical simulation of the infrared radiative signatures of liquid and solid rocket plumes

In this paper, a finite volume method was developed to compute the infrared radiative signatures of both liquid and solid rocket plumes, and to investigate the radiative signatures on two wavebands, 2–6 and 8–12 μm bands, respectively. This method is based on the radiative transport equation for local thermodynamic equilibrium, which accounts for radiative heat transfer in inhomogeneous emitting, absorbing, and non-isotropic scattering media. The radiative properties of combustion gases are computed by using the Elsasser narrow band model, and that of particles are computed by using the Mie scattering theory. A numerical method is applied to solve the following three problems. The first one is the computation of the radiative heat transfer in an absorbing, emitting and isotropic scattering homogeneous cylindrical medium in which the radiative flux is presented. The other two are the computations of the infrared radiation of plumes from the liquid and solid rockets in which both the source and apparent radiant intensities are presented as results. The atmospheric absorption effect on the radiation of plumes is also considered by calculating the atmospheric transmittance using MODTRAN. Some of these results, compared with those available in the literature, have shown satisfactory agreement in most cases.

Effective optical properties of pulverized coal particles determined from FT-IR spectrometer experiments

For accurate modeling of radiative transfer in combustion systems, radiative properties of combustion gases and particles are required. The particle properties are usually determined from the Lorenz-Mie theory assuming they are spherical in shape and their optical properties, i.e., the complex index of refraction data, are available. In the present study, an FT-IR spectrometer has been used to determine the «effective» optical properties of Blind Canyon and Kentucky no. 9 coals suspended in KBr pellets, within the wavelength interval of 2-20 μm. A detailed inversion analysis based on the Lorenz-Mie theory is employed to reduce the measured transmission data to a complex index of refraction spectra. In the analysis, the effects of both absorption and scattering by coal particles are accounted for

Prediction of thermophysical properties of gas turbine combustion gases using the Mansour-Najjar equation of state

A number of thermophysical properties of combustion gases occurring in turbine engines have been compared with experimental data by using the Mansour-Najjar equation of state. The values obtained are shown to be more accurate than those derived from the virial equation of state. The following properties were studied: density, specific heat, enthalpy, entropy, viscosity, and thermal conductivity in the temperature range 200–2600 K at pressures of 3–12 atm.

Combustion Gas Properties: Part III—Prediction of the Thermodynamic Properties of Combustion Gases of Aviation and Diesel Fuels

Empirical formulae are presented by means of which the specific heat, mean molecular weight, density, and specific heat ratio of aviation fuel-air and diesel fuel-air systems can be calculated as functions of pressure, temperature, equivalence ratio, and hydrogen-to-carbon atomic ratio of the fuel. The formulae have been developed by fitting the data from a detailed chemical equilibrium code to a functional expression. Comparisons of the results from the proposed formulae with the results obtained from a chemical equilibrium code have shown that the mean absolute error in predicted specific heat is 0.8 percent, and that for molecular weight is 0.25 percent. These formulae provide a very fast and easy means of predicting the thermodynamic properties of combustion gases as compared to detailed equilibrium calculations, and they are also valid for a wide range of complex hydrocarbon mixtures and pure hydrocarbons as well as aviation and diesel fuels.

Evaluation of srk equation of state in calculating the thermophysical properties of gas turbine combustion gases

The purpose of this work is to evaluate the thermophysical properties of combustion gases of the gas turbine engine using the Soave-Redlich-Kwong equation of state and to compare the results with those obtained from the virial equation of state and the experimental values obtained from experiment and the generalized charts. The properties which have been considered in this work were, density, specific heat at constant pressure, enthalpy, entropy, viscosity and thermal conductivity. The temperature range was (200–2600 K) theoretically, while the pressure range was (3–12 atmospheres). The Soave-Redlich-Kwong (SRK) equation of state generally predicted better values for thermophysical properties than those predicted by the virial equation of state. A computer program, to evaluate the departure of thermophysical properties using virial and SRK equations of state, was used.

On the Thermodynamic Properties of Combustion Gases

In this paper, a linear correction method of deviation function and an interpolation method have been proposed to consider the real gas effect of combustion gases and the variety of hydrocarbon fuel. And, the thermodynamic properties of combustion gases in dissociated states are calculated to 4000K on the basis of chemical equilibrium theory. The whole work has resulted in compiling a new combustion gas table.Copyright © 1985 by ASME