Numerical Simulation Of Combustion Research Articles

Long-Duration Dynamic Numerical Simulation of Combustion and Flow in Hybrid Rocket Motors Considering Nozzle Erosion

Long-Duration Dynamic Numerical Simulation of Combustion and Flow in Hybrid Rocket Motors Considering Nozzle Erosion

NOx emissions estimation methodology for air-breathing reusable access to space vehicle in conceptual design

With an expected global revenue exceeding 1 trillion USD by 2040, the space industry is one of the world's fastest-growing sectors. Given the booming investment in the space industry and the anticipated space tourism era, it is crucial to assess the impact of already operative launch assets as well as to adopt design-to-sustainability strategies for the under-development and future launchers. This paper discloses an integrated methodology to estimate nitrogen oxides emissions of a hydrogen-fuelled air-breathing concept. The proposed strategy combines multi-fidelity propulsive system modelling with 0D chemical-kinetic air/hydrogen combustion numerical simulations to define a high-fidelity emissive database representative of various on-ground and in-flight operative conditions. The propulsive and emissive databases are then used to suggest an analytical formulation able to predict nitrogen oxides emission indices in any in-flight conditions, perfectly fitting the conceptual design needs. Throughout the paper, the Skylon spaceplane and its Synergetic Air Breathing Rocket Engine are used as case study. The methodology disclosed allows proving the high competitiveness of this air-breathing space launchers with respect to famous past and current competitors, as the Space Shuttle and the Falcon 9.

Numerical Simulation of Combustion in 660 MW Tangentially Fired Pulverized Coal Boiler on Ultra-Low Load Operation

Numerical Simulation of Combustion in 660 MW Tangentially Fired Pulverized Coal Boiler on Ultra-Low Load Operation

Study on the dynamic numerical simulation of flow and combustion in hybrid rocket motors based on a discrete phase model

Numerical simulation based on the discrete phase model and dynamic mesh model can more accurately simulate the working process for hybrid rockets, including the motion and evaporation process of particles and regression process of the fuel grain. The dynamic numerical simulation of combustion and flow in hybrid rocket motors based on a discrete phase model is carried out. Aluminum and aluminum hydride are added to the internal flow field as discrete droplets. Then, a hybrid rocket is designed with 95 % hydrogen peroxide as oxidizer and 38 % aluminum hydride+20 % aluminum+42 % hydroxyl-terminated polybutadiene as the fuel and used to verify the model by firing test. A high degree of agreement between experiment and simulation findings is found. The average deviations for thrust and pressure are 3.6 % and 5.9 %, respectively. It offers the required backing for using the simulation method to investigate the flow and combustion process for the hybrid rockets. The results also demonstrate the transient characteristics of the inner flow field, including the separation and merging of vortexes in the pre-chamber. It is found that a peak of the regression rate appears at the front of the grain and moves backward. This is mainly because the vortex appears here and enhances its heat transfer. Through the discrete phase model, it is worth noting that the aluminum droplet content gradually decreases at the nozzle over time, which is consistent with the firing test. Further research on the impact of aluminum hydride content on the performance of the hybrid rockets has been carried out. The results show that the higher aluminum hydride content can lead to better performance for the hybrid rockets. The thrust, pressure, specific impulse, and characteristic velocity enhance with the increase of aluminum hydride content. An interesting discovery is that the average regression rate is maximum at 48 % aluminum hydride content. This research innovatively couples dynamic mesh and discrete phase models, which can help better understand the working process for hybrid rockets and provide important guidance for the selection of fuel formula.

Numerical Simulation of Combustion in Kerosene Fueled Ramp Cavity Based Scramjet Combustor

The flow field of a ramp cavity based scramjet combustor with kerosene fuel is explored numerically using commercial CFD software. Three-dimensional Navier-Stokes equations are solved alongwith K - e turbulence model and fast rate chemical kinetics. Liquid kerosene is considered as disperse phase fluid and is modeled through Lagrangian tracking method. Simulation captures all essential features of the flow field. Good agreement between computational and experimental values forms the basis of further analysis. The flow phenomena in the combustor are presented through the distribution of important thermochemical parameters at different cross sections. Normal shock is seen to occur in the combustor and significant upstream interaction was observed due to heat release. The computed combustion efficiency is near unity as the fuel equivalence ratio is small.

Generating simplified ammonia reaction model using genetic algorithm and its integration into numerical combustion simulation of 1 MW test facility

A small reaction model for ammonia is necessary for the design and development of large-scale ammonia combustion systems using computational fluid dynamics (CFD) simulation. The present study generated a simplified reaction model for ammonia using a genetic algorithm (14 species and 45 reactions). Optimization was applied to reproduce the combustion properties of ignition delay times, mole fractions of ammonia and nitric oxide at the exit of a single perfectly stirred reactor (PSR), those of a two-staged PSR, and laminar flame speed. The generated simplified reaction model for ammonia was applied to combustion CFD simulation for a 1 MW boiler test facility. Results of CFD simulation reproduced the characteristics of two-staged combustion well. Nitrous oxide emissions predicted by the simulation agreed well with experimental results.

Reactive molecular dynamics simulation and chemical kinetic modeling of ammonia/methane co-combustion

Under the vision of “low carbonization”, ammonia (NH3), as a carbon-free hydrogen-rich fuel, blended with reactive additives, is an effective means to achieve low carbon emissions and reduce the consumption of traditional fossil fuels. In this work, the combustion behaviors of NH3 and CH4, the distribution of main products and the formation and reduction characteristics of NO at different temperatures, CH4 mixing ratios, and O2 equivalence ratios are explored by means of reactive molecular dynamics simulation to reveal the microscopic mechanism of NH3/CH4 co-combustion. The calculated results show that CH4 takes the lead in producing H radicals which react with O2 to generate OH radicals to promote the oxidation of NH3, and it is found that the co-combustion process of NH3/CH4 in the radical chain transfer stage is similar to the respective pyrolysis and oxidation reactions of CH4 and NH3. Accordingly, an optimized kinetic mechanism of NH3/CH4 co-combustion is constructed based on the mechanisms proposed by Glarborg et al. and Okafor et al. by incorporating the NH3 pyrolysis sub-mechanisms related to NH2, HNO, and N2H2 and the skeletal mechanism of CH4 oxidation. The optimized mechanisms of NH3/CH4 co-combustion are found to improve the prediction of the ignition delay time (IDT) and laminar burning velocity (LBV) of NH3/CH4 mixture under wide ranges of conditions compared to the original mechanisms of Glarborg et al. and Okafor et al. To decrease the computational cost of three-dimensional combustion numerical simulations, the skeletal mechanism models are established by simplification of the optimized mechanisms of NH3/CH4 co-combustion using direct relation graph method with error propagation and sensitivity analysis, which can provide nearly the same estimates of IDTs and LBVs as the optimized mechanisms mentioned above.

Modeling of Sandia Flame D with the non-adiabatic chemistry tabulation approach: the effects of different laminar flames on NO X prediction.

The effects of different one-dimensional laminar flames on the prediction of nitrogen oxide (NO X ) emission in Sandia Flame D are numerically investigated using a flamelet method in the present work. In addition to the basic control variables of the mixture fraction and the reaction progress variable for chemistry tabulation in this combustion model, two additional variables of mixture fraction variance and enthalpy loss are added to the control variable space to improve prediction accuracy of the NO X pollutant. The former variable of mixture fraction variance is used for the presumed probability density function integration, and the latter takes into account the non-adiabatic effect. Two flamelet libraries are generated based on the one-dimensional unstretched premixed flame and the one-dimensional counterflow diffusion flame, respectively. An additional transport equation for the mass fraction of nitrogen oxide (NO) is solved for improving prediction accuracy. The unsteady Reynolds-averaged Navier-Stokes (URANS) simulation results are compared and analyzed with experimental data. The simulation results show dependence on the type of laminar flame. In the four-dimensional control variable space, the results with steady unstretched premixed flame indicate great agreement on the predictions of temperature and NO field. The computational method proposed in the present work sheds light on the high-precision combustion numerical simulation of NO X emission.

Study on Combustion Characteristics and NOx Formation in 600 MW Coal-Fired Boiler Based on Numerical Simulation

The variations in the boiler operation conditions have a great effect on the combustion characteristics and the pollutant formation in furnaces. This work aims to investigate the effects of operational parameters on NOx formation and its distribution in furnaces using the numerical simulation method to obtain the optimum control strategy for reducing NOx emissions. The numerical simulation models of pulverized coal combustion in furnaces involving flow, heat transfer, combustion and NOx formation are established. Taking a 600 MW supercritical opposed firing pulverized coal boiler as the study object, a full-scale three-dimensional physical model of the boiler is constructed with Gambit software. On this basis, the pulverized coal combustion and the NOx formation under various boiler loads are numerically simulated using the software of Ansys Fluent 2021R1, and the accuracy and the reliability of the models established are verified by comparing the simulation data with the field test data. According to the combustion numerical simulation of 128 groups of operating conditions, the effects of boiler load, the air rate and the air temperature on combustion and NOx formation have been emphatically investigated. The simulation results indicate that the formation of NOx and the NOx concentration distribution are mainly affected by the oxygen concentration and the temperature in the furnace. Especially, the effects of the variation in the excess air coefficient, the over-fire air (OFA) ratio, the primary air ratio and the internal secondary air ratio on NOx concentration distribution vary greatly. When the air temperature increases the overall NOx concentration in the furnace increases, and the influence of the secondary air temperature and the OFA temperature is greater than that of the primary air temperature. Large amounts of simulation data are a necessary data source for further study on the NOx prediction model at the economizer outlet, which can improve the prediction ability and the generalization ability of the NOx prediction model.

Особенности расчета нестационарного теплообмена в стенах вращающихся печей

A refined calculation of the non-stationary temperature of the walls of a rotary kiln is proposed, taking into account the non-stationary thermal conductivity in the enclosing walls and the accumulation of heat in them, intended for use in numerical simulation of combustion and heat transfer processes. The influence on heat transfer of the alternating contact of the inner surface of the walls of a rotary kiln with a gaseous medium and a layer of technological material is considered. The adequacy of the method was verified by numerical solution of the differential equation of non-stationary thermal conductivity of walls in the conditions of a computational experiment.

Introducing the “Mathematical Modelling and Numerical Simulation of Combustion and Fire” Section of the Journal Fire

It is my immense pleasure to assume the role of Editor-in-Chief for the “Mathematical Modelling and Numerical Simulation of Combustion and Fire” Section of Fire, which is intended to take a leading role in the dissemination of high-quality research in this area [...]

Numerical Simulation of Combustion and Emission Characteristics during Gas Turbine Startup Procedure

The annual operation data of an F-class gas turbine generator set revealed that the duration of the startup process accounts for about 8.5% of the whole operation process. The three combustion models of a DLN2.0+ combustor demonstrated higher NOx emissions than the premixed mode under normal load during the startup process. In order to evaluate the scale of NOx emissions at this stage, numerical simulation was carried out for the startup process to discern the NOx emission pattern. Typical simulation conditions for each season were established to calculate the total annual NOx emissions at the initial stage based on operating data. On this basis, the characteristics of NOx emissions influenced by changes in the atmospheric environment were studied in depth. The results of this study provide referential data for evaluating the pollution characteristics and combustion adjustment of a ground gas turbine during startup.

Numerical Simulation of Combustion of a Composite Solid Propellant Containing Boron Powder

Numerical Simulation of Combustion of a Composite Solid Propellant Containing Boron Powder

A multi-component surrogate mechanism of diesel from indirect coal liquefaction for diesel engine combustion and emission simulations

Diesel from indirect coal liquefaction (DICL) is a kind of extremely promising alternative fuel to alleviate the oil security problem caused by excessive dependence on imported oil and reduce the pollutant emission. However, the mechanism of diesel from indirect coal liquefaction is very few, and the numerical simulation of combustion and emission characteristics of diesel from indirect coal liquefaction is even less. Therefore, a reduced mechanism of DICL, entailing 178 components and 650 reactions, was put forward to research the combustion and emission characteristics of engines fueled with DICL under different loads in this work. n-Hexadecane (HXN) mechanism and 2,2,4,4,6,8,8-heptamethylnonane mechanism (HMN) were respectively considered as representative species of straight-chain paraffin and branched alkane in surrogate model. Firstly, direct relation graph and direct relation graph with error propagation were used in turn. Then, sensitivity analysis coupled with rate of production analysis has been used to further reduce the detail 2,2,4,4,6,8,8-heptamethylnonane mechanism. After that, the skeleton mechanism of n-hexadecane and the reduced polycyclic aromatic hydrocarbon (PAH) mechanism were combined with the simplified HMN mechanism to develop a novel multi-component mechanism of HXN-HMN-PAH. Brute-force sensitivity analyses were respectively conducted at different temperatures to find out these key reactions that have great effects on the ignition delay times (IDTs). Then, the optimizations of the reduced mechanism were made based on the ignition delay times of the experimental datum and the detail mechanism. A proportion of 71.5% HXN and 28.5% HMN by mole fraction was determined according to the properties of practical DICL. Furthermore, the optimized mechanism was employed to verify experimental values including the ignition delay times, the species concentrations on jet-stirred reactors (JSR) and the laminar flame speeds. Eventually, the mechanism was coupled into computational fluid dynamic (CFD) to perform multi-dimensional numerical simulation validation in a directed injection compression ignition (DICI) engine under different loads.

Numerical simulation of combustion of sulfide- biomass concentrate ingredients and contaminants in copper furnace smelting

Co-firing biomass and fossil fuels in industrial furnaces is a suitable way to reduce the environmental impact of human activities with acceptable investment. In this paper, the results of numerical simulation co-firing of sulfide concentrate and three auxiliary fuels, including gasoil, kerosene, and sawdust biomass, are compared in the flash furnace copper smelting. For modeling of turbulent flow and combustion, RNG, k-ε model, and probability density function model (pdf) have been used, respectively. This study has been carried out to investigate the furnace temperature and combustion pollutants distribution. The numerical simulation results show that the flame temperature resulting from the combustion of diesel fuel and sawdust as auxiliary fuel is the highest and lowest, respectively. In biomass combustion, despite that the flame temperature is low, but the NOx mass fraction increases because there is nitrogen in the sawdust chemical composition. Also in sawdust combustion, the oxygen content is high, the SO2 and SO3 sulfur pollutants increase in the high temperatures regions of the furnace and the lower temperature of the auxiliary fuel burner, respectively. Because SO2 is formed at high temperatures (> 1273K), oxygen-rich and SO3 species are produced at relatively low temperatures with excess oxygen. The amount of CO emissions in sawdust combustion is much lower than the amount of combustion of diesel and oil. In the peak of the flash furnace for sawdust and diesel auxiliary fuels, the temperature is 2.29E+03 K, and the distribution of NOx, CO2, O2, SO2, and SO3 are 1.51E-04, 9.72E-02, 2.33E-03, 1.71E-01 and 2.45E-02 respectively.

A hybrid non-gray gas radiation heat transfer solver based on OpenFOAM

Radiation heat transfer is important in many combustion conditions. Efficient and accurate predictions of the radiation energy is essential for numerical simulation of combustion. A hybrid non-gray gas radiation solver is developed based on the open-source OpenFOAM framework. The weighted-sum-of-gray-gases (WSGG) model is used for the non-gray gas radiative properties. The discrete ordinates method (DOM) and first order spherical harmonics (P1) method are adopted to solve the different gray gas RTEs in the WSGG model. The performance of the hybrid solver is analyzed in detail for three cases. Results show that the accuracy of the hybrid solver decreases with increasing the number of gray gases solved by the P1 method, while the computational time increases. The advantage of the hybrid solver is more obvious in isotherm and homogenous cases, in which the relative mean errors in terms of radiative heat flux and heat source can be less than 5% while reducing half of the computational time.

Feeding H2-admixtures to domestic condensing boilers: Numerical simulations of combustion and pollutant formation in multi-hole burners

Hydrogen can be produced through electrolysis from excess wind and solar power. Then, its injection into the natural gas network allows mitigating the challenges posed by the variability and intermittency of renewables, by exploiting the existing infrastructure for storage and distribution. However, the addition of hydrogen to natural gas affects gas properties; hence we need to ensure the safe and efficient operation of existing end-user equipment, such as domestic burners and boilers. This work intends to investigate the effect of H2 addition on the combustion process and pollutant emissions in domestic condensing boilers. To this purpose, 3-dimensional numerical simulations of multi-hole geometries mimicking perforated burners, typically encountered in such appliances, are performed by using detailed kinetics and taking into account different hole-to-hole distances. Indeed, since the burner holes are located very close to each other, the neighbour premixed flames can interact, thus differing from single flame behaviour. The impact of H2 on the operating conditions, i.e. equivalence ratio and thermal load, is preliminarily evaluated to ensure that the numerical model closely emulates the practical situation we expect from the fuel composition change. Anticipation of the reaction zone occurs with H2-admixtures, while the downstream temperature decreases because the boiler naturally shifts towards leaner conditions and smaller thermal loads when adding H2 to natural gas. This behaviour has a positive impact on pollutant emissions as the NO thermal formation route is suppressed in a larger measure than the increase of the NNH-intermediate contribution.

Numerical simulation of combustion, flow, and heat transfer process of an oilfield heating furnace under different production conditions

AbstractHeating furnace is an important energy‐consuming equipment in oilfield. In order to evaluate the operation status of heating furnace more accurately, in this paper, the production process of heating furnace in an oilfield is studied by numerical simulation technology, and the specific reasons affecting its thermal efficiency are deeply explored. First, the numerical simulation model of oilfield heating furnace production process is established, which is to digitize the geometric structure of the heating furnace, study the characteristics of the geometric shape, and generate the appropriate calculation grid. Second, numerical simulation and analysis are carried out for the working process of the heating furnace under rated and nonrated conditions, respectively. The medium flow characteristics, flame shape, temperature distribution, and pipe temperature distribution in the heating furnace under different conditions are systematically discussed. Finally, through the simulation analysis, it is found that the burner rotating device is beneficial to strengthen the heat transfer, and the change of load will affect the efficiency of the heating furnace. Under the rated working condition, design exhaust temperature is 260℃, numerical result is 225.8℃, and the error is −13.2%; design export temperature of water is 60℃, numerical result is 58.1℃, and the error is −3.2%; design temperature difference between inlet and outlet of water is 30℃, numerical result is 28.1℃, and the error is −6.3%. The working process of oilfield heating furnace is a complex coupling heat transfer process of combustion, flow, and heat transfer. The numerical results show that the working process of oilfield heating furnace could be successfully realized by means of numerical simulation. Under variable load conditions, in order to ensure that the export temperature of water is close to design temperature, it is necessary to change the fuel quantity in equal proportion to the water quantity. It is hoped that the reported results provide interesting information among the oilfield heating furnace operators.

Numerical Simulation of Combustion of a Mixed Solid Fuel Containing Boron Powder

Numerical Simulation of Combustion of a Mixed Solid Fuel Containing Boron Powder

Numerical Simulation of Combustion and Characteristics of Fly Ash and Slag in a “V-type” Waste Incinerator

This study is focused on a “V-type” waste incinerator for municipal solid waste (MSW) combustion. Computational fluid dynamics (CFD) methods are used to study the MSW combustion process. The characteristics of fly ash and slag are analyzed by using a laser particle analyzer, scanning electron microscope, X-ray fluorescence, and X-ray diffraction. The results show that the error between the CFD simulation data and measured data is less than 10%, and the changing trend of the combustion process is well-modeled. The fly ash mainly has an irregular spherical or ellipsoid structure, whereas the slag mainly has an irregular porous structure. The main constituents of the ash and slag are CaO and SiO2, along with heavy metal elements such as Cu, Pb, and Cr.