Simulation Of Combustion Process Research Articles

A rigorous model for the simulation of chemical reaction in gas-particle bubbling fluidized bed: II. Application to gas combustion case

Simulation of gas combustion process in bubbling fluidized beds (BFB) using the model proposed in Part I is carried out. The predictions are compared against the experimental measurements and good agreement is observed. It demonstrates that the turbulent Schmidt number is changing throughout the BFB. Therefore, the conventional way of using constant turbulent Schmidt number for the simulation of BFB is questionable.

Technology for Transient Simulation of Vibration during Combustion Process in Rocket Thruster

The article describes the technology for simulation of transient combustion processes in the rocket thruster for determination of vibration frequency occurs during combustion. The engine operates on gaseous propellant: oxygen and hydrogen. Combustion simulation was performed using the ANSYS CFX software. Three reaction mechanisms for the stationary mode were considered and described in detail. The way for obtaining quick CFD-results with intermediate combustion components using an EDM model was found. The way to generate the Flamelet library with CFX-RIF was described. A technique for modeling transient combustion processes in the rocket thruster was proposed based on the Flamelet library. A cyclic irregularity of the temperature field like vortex core precession was detected in the chamber. Frequency of flame precession was obtained with the proposed simulation technique.

Kinetics of methyl methacrylate combustion over a Pt/alumina catalyst

The combustion of methyl methacrylate (MMA) over a commercial Pt/?-alumina catalyst was investigated, in the lean air mixtures specific for the depollution applications. The experiments were performed at temperatures between 150 and 360?C, with MMA concentrations of 460 to 800 ppmv and the gas flow rates between 200 and 300 mL min-1. The results evidenced a negative influence of MMA concentration on the combustion kinetics. A kinetic model of the combustion process was developed, based on the Langmuir?Hinshelwood mechanism, assuming the surface reaction between adsorbed oxygen atoms and adsorbed MMA molecules as the controlling step. The rate expression included the inhibition effects of MMA and water adsorption on the process kinetics. The MMA combustion process simulations evidenced the significant influences of the bulk gas to catalyst particle mass transfer, on the overall kinetics.

Dynamic simulation of fluidized bed chemical looping combustion process with iron based oxygen carrier

Chemical looping combustion is a promising energy conversion technology for fossil fuel combustion with inherent carbon dioxide separation and minimum energy losses. A full understanding of the dynamic behavior is of paramount importance to successfully implement this technology at commercial scale. In this work, a dynamic mathematical model has been developed to simulate interconnected fluidized bed reactors of a 1 MWth syngas-based chemical looping combustion process with iron based oxygen carrier. The model consists of mass and energy balances equations as well as the equations that describe the hydrodynamics and heat transfer processes. The particles distribution inside the fluidized bed reactors is described by a 1.5-D hydrodynamic model. The model showed two zones in axial direction (an upper lean zone and a bottom dense zone) and a horizontal separation between core region and wall layer. Different heat transfer mechanisms have been taken into account: convection between gas phase and the oxygen carrier particles; convection of the moving particle phase with wall and radiation. The developed model was used to predict (in space and time): gas and solid velocity distribution, gas composition distribution, behavior of oxygen carrier, and temperature profiles inside the air and fuel reactor. The dynamic behavior of the chemical looping combustion process was studied by step and ramp input changes in the input gas flow rate.

Effects of gas-solid drag model on Eulerian-Eulerian CFD simulation of coal combustion in a circulating fluidized bed

The Eulerian-Eulerian two fluid model (TFM) has been widely used to simulate the fluidized bed combustion/gasification process, where the dense gas-solid flow, heat and mass transfer, and various chemical reactions are coupled. Significance of the drag coefficient in determining the gas-solid flow characteristics is well known. However, effects of the drag coefficient on the overall performance of the fluidized bed combustion/gasification are not emphasized. In the present work, two widely used drag models, namely the EMMS model and the Gidaspow model, are applied to simulate the coal combustion in a circulating fluidized bed combustor. Performance of the hydrodynamics, temperature, and species distribution by the two models is compared in details. It is found that the EMMS result has a better agreement with the experimental data compared to the Gidaspow result in this work. This work indicates that reliability of the gas-solid drag coefficient lays a solid foundation for the comprehensive simulation of the fluidized bed combustion process, not only for the gas-solid flow characteristics.

Численное моделирование процессов горения водородовоздушной смеси в канале переменного сечения

Численное моделирование процессов горения водородовоздушной смеси в канале переменного сечения

Real-time capable simulation of diesel combustion processes for HiL applications

The complexity of the development processes for advanced diesel engines has significantly increased during the last decades. A further increase is to be expected, due to more restrictive emission legislations and new certification cycles. This trend leads to a higher time exposure at engine test benches, thus resulting in higher costs. To counter this problem, virtual engine development strategies are being increasingly used. To calibrate the complete powertrain and various driving situations, model in the loop and hardware in the loop concepts have become more important. The main effort in this context is the development of very accurate but also real-time capable engine models. Besides the correct modeling of ambient condition and driver behavior, the simulation of the combustion process is a major objective. The main challenge of modeling a diesel combustion process is the description of mixture formation, self-ignition and combustion as precisely as possible. For this purpose, this article introduces a novel combustion simulation approach that is capable of predicting various combustion properties of a diesel process. This includes the calculation of crank angle resolved combustion traces, such as heat release and other thermodynamic in-cylinder states. Furthermore, various combustion characteristics, such as combustion phasing, maximum gradients and engine-out temperature, are available as simulation output. All calculations are based on a physical zero-dimensional heat release model. The resulting reduction of the calibration effort and the improved model robustness are the major benefits in comparison to conventional data-driven combustion models. The calibration parameters directly refer to geometric and thermodynamic properties of a given engine configuration. Main input variables to the model are the fuel injection profile and air path–related states such as exhaust gas recirculation rate and boost pressure. Thus, multiple injection event strategies or novel air path control structures for future engine control concepts can be analyzed.

Co-Combustion of Pulverized Coal and Biomass in Fluidized Bed of Furnace

Combustion processes of two fuels, pulverized coal and biomass, in furnaces take place at steady state. Combustion of condensed fuels involves one-way interfacial flux due to phenomena in the condensed phase (evaporation or pyrolysis) and reciprocal ones (heterogeneous combustion and gasification). Many of the species injected in the gas phase are later involved in gas phase combustion. This paper presents results of combustion process of two-phase charge contained coal and wetted biomass, where the carrier was the air with given flow rate. The furnace has three inlets with assumed inlet flow rate of coal, biomass, and air, and combustion process takes place in the furnace fluidized space. The simulation of such combustion process was carried out by numerical code of open source computational fluid dynamics (CFD) program code_saturne. For both fuels, the moist biomass with following mass contents: C = 53%, H = 5.8%, O = 37.62%, ash = 3.6, and mean diameter of molecules equal to 0.0008 m and pulverized coal with following mass contents: C = 76.65%, H = 5.16%, O = 9.9%, ash = 6.21%, and mean molecule diameter 0.000025 m were used. Devolatilization process with kinetic reactions was taken into account. Distribution of the main combustion product in furnace space is presented with disappearance of the molecules of fuels. This paper presents theoretical description of the two-phase charge, specification of the thermodynamic state of the charge in inlet boundaries and furnace space, and thermal parameters of solid fuel molecules obtained from the open source postprocessor paraview.

Numerical simulation of hydrogen combustion process in rotary engine with laser ignition system

In this paper the combustion and ignition process in the hydrogen-fueled peripheral-ported rotary engine with single and dual laser ignition systems was studied numerically. The computational method was established for the process simulation including interaction between turbulence and chemical reactions. The detailed chemical kinetic model of hydrogen combustion was used. It was shown that the ignition and combustion process in the H2-fueled rotary engine is highly transient with specific distortion and stretching of the combustion front in the combustion chamber due to complex motion of the rotor relative to the engine housing. The single and dual laser ignition systems were simulated to compare the ignition efficiency and the rate of hydrogen burning out. The evaluation of pressure in the combustion chamber was performed and compared with the experimental data obtained for the rotary engine fueled by natural gas. It was shown that the H2-fueled rotary engine with the dual laser ignition system has potential application in alternative automotive industry due to high efficiency and near-zero carbon-based emission.

Effect of diesel injection strategies on natural gas/diesel RCCI combustion characteristics in a light duty diesel engine

Reactivity controlled compression ignition (RCCI) combustion mode is an attractive combustion strategy due to its potential in satisfying the strict emission standards. In this study, the effects of direct injection (DI) strategies on the combustion and emission characteristics of a modified light duty RCCI engine, fueled with natural gas (NG) and diesel were numerically investigated. In this way, Converge CFD code employing a detail chemical kinetics mechanism was used for 3D simulation of combustion process and emissions prediction. NG with higher octane number (ON) is mixed with air through intake port, while diesel fuel with lower ON is directly injected into the combustion chamber during compression stroke by means of split injection strategy. The effects of several parameters, including the premixed ratio (PR) of NG, diesel fuel fraction in first and second injection pulses, first and second start of injection timing (SOI1 and 2), injection pressure and the spray angle on the engine performance and emission characteristics are investigated. The results indicate that these parameters have significant effects on the light duty RCCI engine performance and engine out emissions. Also, it was demonstrated that by decreasing the first injection pressure from 450 to 300bar, the gross indicated efficiency increases by 5% and CA50 is retarded by 4 CAD. Moreover, by reducing the spray angle from 144° to 100°, the gross indicated efficiency decreases by 4% and CA50 is advanced by 6 CAD. The results showed that reduction in NOx emission is achievable, while controlling HC and CO emissions, by means of increasing the NG fraction, advancing the SOI1, increasing the fuel fraction in first DI injection with lower injection pressure and employing a wider injector spray angle.

Numerical investigation on low calorific syngas combustion in the opposed-piston engine

The aim of this study was to investigate a possibility of using gaseous fuels of a low calorific value as a fuel for internal combustion engines. Such fuels can come from organic matter decomposition (biogas), oil production (flare gas) or gasification of materials containing carbon (syngas). The utilization of syngas in the barrel type Opposed-Piston (OP) engine arrangement is of particular interest for the authors. A robust design, high mechanical efficiency and relatively easy incorporation of Variable Compression Ratio (VCR) makes the OP engine an ideal candidate for running on a low calorific fuel of various compostion. Furthermore, the possibility of online compression ratio adjustment allows for engine the operation in Controlled Auto-Ignition (CAI) mode for high efficiency and low emission. In order to investigate engine operation on low calorific gaseous fuel authors performed 3D CFD numerical simulations of scavenging and combustion processes in the 2-stroke barrel type Opposed-Piston engine with use of the AVL Fire solver. Firstly, engine operation on natural gas with ignition from diesel pilot was analysed as a reference. Then, combustion of syngas in two different modes was investigated – with ignition from diesel pilot and with Controlled Auto-Ignition. Final engine operating points were specified and corresponding emissions were calculated and compared. Results suggest that engine operation on syngas might be limited due to misfire of diesel pilot or excessive heat releas which might lead to knock. A solution proposed by authors for syngas is CAI combustion which can be controlled with application of VCR and with adjustment of air excess ratio. Based on preformed simulations it was shown that low calorific syngas can be used as a fuel for power generation in the Opposed-Piston engine which is currently under development at Warsaw University of Technology.

Combustion Efficiency and Pollution Risk Analysis Based on Different Type of Coal

Air pollution such as PM2.5 and PM10 has become a serious problem for many cities in China. One of the key factors for the causation of air pollution is the exhausts of coal combustion. The combustion efficiency and emission will be affected by different type of coal. Thus, four raw coals include Gaoping anthracite coal, Tangshan bituminous coal, Liupanshui lean coal, and Indonesia lignite coal are selected for the combustion process simulation and analysis based on Aspen Plus. The results show that the combustion heat of anthracite coal reached the highest level based on same combustion condition. According to the emission results of the selected coal, the combustion temperature just has a little impact on the emission of SOX, while the emission of NOX will increase when the combustion temperature increase. The study may provide a constructive strategy for the selection and utilization of different type of coal for relevant industry.

Modelling and simulation of chemical looping combustion process in a double loop circulating fluidized bed reactor

A reactive CFD model has been developed and implemented numerically in an in-house code for a coupled double loop circulation fluidized bed reactor. In the current work it is utilized for the chemical looping combustion (CLC) process but the model can easily be modified for exploring some other chemical looping processes. The air reactor and the fuel reactor are operated in fast fluidization regime and simulated separately in a simultaneous mode. The connections between the two reactors are realized through time-dependent inlet-outlet boundary conditions. The model predictions are validated by comparison with experimental data reported in the literatures. Good agreement is observed between the experiments and simulations. Using this model, fluid dynamics and chemical process performance of the double loop reactor is investigated. The results show that the methane is rapidly consumed at a very short entrance section of the reactor and the axial distribution of the oxygen is more smooth. Higher reactant residence time and fuel reactor temperature increase the conversion of methane and oxygen. The methane conversion could reach 95% during the current study.

Analysis of operator splitting errors for near-limit flame simulations

High-fidelity simulations of ignition, extinction and oscillatory combustion processes are of practical interest in a broad range of combustion applications. Splitting schemes, widely employed in reactive flow simulations, could fail for stiff reaction–diffusion systems exhibiting near-limit flame phenomena. The present work first employs a model perfectly stirred reactor (PSR) problem with an Arrhenius reaction term and a linear mixing term to study the effects of splitting errors on the near-limit combustion phenomena. Analysis shows that the errors induced by decoupling of the fractional steps may result in unphysical extinction or ignition. The analysis is then extended to the prediction of ignition, extinction and oscillatory combustion in unsteady PSRs of various fuel/air mixtures with a 9-species detailed mechanism for hydrogen oxidation and an 88-species skeletal mechanism for n-heptane oxidation, together with a Jacobian-based analysis for the time scales. The tested schemes include the Strang splitting, the balanced splitting, and a newly developed semi-implicit midpoint method. Results show that the semi-implicit midpoint method can accurately reproduce the dynamics of the near-limit flame phenomena and it is second-order accurate over a wide range of time step size. For the extinction and ignition processes, both the balanced splitting and midpoint method can yield accurate predictions, whereas the Strang splitting can lead to significant shifts on the ignition/extinction processes or even unphysical results. With an enriched H radical source in the inflow stream, a delay of the ignition process and the deviation on the equilibrium temperature are observed for the Strang splitting. On the contrary, the midpoint method that solves reaction and diffusion together matches the fully implicit accurate solution. The balanced splitting predicts the temperature rise correctly but with an over-predicted peak. For the sustainable and decaying oscillatory combustion from cool flames, both the Strang splitting and the midpoint method can successfully capture the dynamic behavior, whereas the balanced splitting scheme results in significant errors.

Simultaneous improvement of exhaust emissions and fuel consumption by optimization of combustion chamber shape of a diesel engine

In order to achieve clean exhaust gas emissions and high fuel efficiency in diesel engines, a new combustion chamber concept called “egg-shaped piston bowl” was proposed and its effectiveness was validated by engine experiments using a single-cylinder research engine. Numerical simulations of combustion processes and exhaust gas emissions were carried out on different piston bowl geometries using GTT-CHEM code, which is a three-dimensional computational fluid dynamics code coupled with detailed chemical kinetics. In this code, a combustion model taking account of the auto-ignition process of a non-homogeneous mixture and a detailed phenomenological soot model was incorporated. In the detailed phenomenological soot model, particle inception from polycyclic aromatic hydrocarbons, surface growth/oxidation and particle coagulation processes were considered. In addition, to investigate the soot formation characteristics with different piston bowl geometries, experimental measurements by the two-color method were conducted with a constant-volume vessel under high-temperature and high-pressure conditions. As a result of the engine experiments and the numerical simulations, it was confirmed that simultaneous reduction in exhaust gas emissions and fuel consumption was able to be achieved by the egg-shaped piston bowl concept.

Towards Improving Simulations of Combustion Processes

This Special Issue highlights the progress made in addressing modelling issues relating to a range of combustion processes from MILD gaseous flames to droplets and the evolution of soot particles. ...

The technique for Simulation of Transient Combustion Processes in the Rocket Engine Operating with Gaseous Fuel “Hydrogen and Oxygen”

The article describes the method for simulation of transient combustion processes in the rocket engine. The engine operates on gaseous propellant: oxygen and hydrogen. Combustion simulation was performed using the ANSYS CFX software. Three reaction mechanisms for the stationary mode were considered and described in detail. Reactions mechanisms have been taken from several sources and verified. The method for converting ozone properties from the Shomate equation to the NASA-polynomial format was described in detail. The way for obtaining quick CFD-results with intermediate combustion components using an EDM model was found. Modeling difficulties with combustion model Finite Rate Chemistry, associated with a large scatter of reference data were identified and described. The way to generate the Flamelet library with CFX-RIF is described. Formulated adequate reaction mechanisms verified at a steady state have also been tested for transient simulation. The Flamelet combustion model was recognized as adequate for the transient mode. Integral parameters variation relates to the values obtained during stationary simulation. A cyclic irregularity of the temperature field, caused by precession of the vortex core, was detected in the chamber with the proposed simulation technique. Investigations of unsteady processes of rocket engines including the processes of ignition were proposed as the area for application of the described simulation technique.

Method of transient simulation of combustion processes in a low-thrust rocket engine operating on gaseous hydrogen and oxygen

The article describes a method of simulating combustion processes in a low-thrust rocket engine. The engine operates on gaseous propellants: oxygen and hydrogen. Transient simulation was performed using ANSYS CFX software. Three well-known mechanisms of oxygen and hydrogen combustion reactions for the stationary mode are considered and described in detail. A method of converting data on gas properties specified by coefficients of state equations into the NASA format was developed as one of the results of research. It was found that the initial component composition can be obtained fast by stationary simulation using an EDM combustion model. The difficulties connected with the application of the FRC combustion model, associated with a large scatter of reference data are revealed and described. A way of generation of a Flamelet-library with an ANSYS CFX integrated CFX-RIF generator is described. A method of simulation of transient combustion processes in a low-thrust rocket engine based on the Flamelet-library is proposed. Cyclical motion of the temperature field in the chamber resembling the precession of a vortex flow core was detected in the course of testing the method. The proposed method can be used to study this process and other transient processes in rocket engines.

Dependence of methane laminar flame propagation speed on the pressure and initial temperature

The paper presents the results that allowed obtaining the dependence of laminar flame propagation speed Sl on the equivalence ratio for a wide range of pressures and temperatures during methane combustion. A literature review was carried out to summarize the experimental data on the measurement of the Sl. The Sl was calculated using a kinetic mechanism GRI 3.0 within the required pressure and temperature range. The calculation results were generalized in the MATLAB software product to verify the Sl power dependencies on pressure and initial temperature. The results of calculation on the basis of the obtained approximating dependence were compared with the experimental data and results obtained by other authors. It was found that the exponents of power for the dependency on pressure and temperature are described not by constants or linear relations, but by second-degree equations on the fuel-air ratio. The results can be used in three-dimensional simulation of combustion processes and in calculations performed using engineering practices.

Evaluation of different turbulent combustion models based on tabulated chemistry using DNS of heterogeneous mixtures

This study used direct numerical simulations (DNSs) of combustion processes in turbulent heterogeneous mixtures for self-igniting partially-premixed configurations to assess the accuracy of partially-premixed turbulent combustion models that are based on the tabulation of chemistry progress in homogeneous reactors (HRs). DNS coupled with n-heptane/air detailed chemistry solving was considered as a reference result. Because the same detailed chemistry was used to generate the chemistry databases, the study was focused entirely on validating the modelling assumptions. Various HR-based tabulation models were tested: (1) the tabulated homogeneous reactor (THR) model, which is a direct exploitation of HR tabulation lacking any statistical information concerning mixture heterogeneity; (2) the presumed conditional moment (PCM) model, which includes a limited statistical description of the mixture and/or of the combustion advancement; (3) approximated diffusion flame (ADF) models, which consider the heterogeneous turbulent reactor as either a unique diffusion flame (simple ADF model formulation) or as a collection of flamelets with different strain rates (ADFχ model). The a priori response of the above mentioned models was compared with detailed chemistry DNS results. The main findings are as follows: (i) a direct use of HR tabulation (THR model) led to overly inaccurate results; (ii) an assumed independence between mixture fraction and progress variable was responsible for most PCM modelling failures in the context of turbulent heterogeneous self-ignited combustion; (iii) the presumed β-function of the progress variable distribution is likely to fail because of the complexity of autoignition kinetics; (iv) the best results were obtained with the ADF models; (v) a simple ADF formulation is preferable to ADFχ, which showed limitations in terms of accuracy concerning the distribution of the progress variable; (vi) all tested models provided an acceptable prediction of the autoignition delays, but only the ADF and ADFχ models are able to represent the temporal evolution of the progress variable.