Chemistry Combustion Model Research Articles

Tabulated Chemistry Combustion Model for Cost-Effective Numerical Simulation of Dual-Fuel Combustion Process

This study is dedicated to improving the efficiency of the flamelet-generated manifold (FGM) tabulated chemistry combustion modeling approach for predicting the combustion process in diesel-ignited internal combustion (IC) engines. The primary focus is on reducing table generation time and memory requirements. To accurately predict dual-fuel combustion processes, it is important to model both premixed and non-premixed combustion regimes. However, attempting to include both regimes in a single FGM lookup table leads to significant increases in the table size and generation time. In response, this work proposes a dual-table configuration, with each table dedicated to a specific regime. The solution is then interpolated from these tables based on the calculated combustion regime indicator during the computational fluid dynamics (CFD) simulation. This approach optimizes computational efficiency while ensuring an accurate representation of dual-fuel combustion. Additionally, to establish a cost-effective and accurate 3D CFD simulation workflow, the dual-table FGM methodology is coupled with the partially averaged Navier–Stokes (PANS) turbulence model. The feasibility of the proposed FGM methodology is tested utilizing six chemical kinetics mechanisms with different levels of detail. The results of this study demonstrated that the dual-table approach significantly accelerates table generation time and reduces memory requirements compared to a single table that includes both combustion regimes. Furthermore, 3D CFD simulation results of the dual-fuel combustion process are validated against available experimental data for three engine operating points. The in-cylinder pressure traces and rate of heat release obtained from the 3D CFD simulations employing the FGM PANS methodology show good agreement with experimental measurements, confirming the accuracy and reliability of this modeling approach.

Probing O2 dependence of hydroperoxy-butyl reactions via isomer-resolved speciation

Degenerate chain-branching mechanisms of n-alkanes are centered on the formation of hydroperoxy-alkyl radicals (̇QOOH), formed via ̇R + O2 reactions, and the ensuing competition between unimolecular decomposition and second-O2-addition. Quantitative measurements of partially oxidized intermediates formed via reactions of ̇QOOH provide critical constraints that are required for accurate modeling of combustion chemistry. To examine the influence of temperature and oxygen concentration on intermediates from unimolecular decomposition of ̇QOOH, isomer-resolved speciation measurements were conducted on n-butane oxidation at 835 Torr in a jet-stirred reactor (JSR) from 500 – 900 K. Resulting from negative-temperature coefficient behavior, cyclic ether formation peaked at two temperatures, 650 K and 800 K, which were selected for separate experiments to quantify the O2-dependence of species profiles using O2 concentrations of 4.2 · 1017 – 1.1 · 1019 molecules cm–3.Utilizing vacuum-ultraviolet absorption spectroscopy and electron-impact mass spectrometry, cyclic ether isomers were quantified separately, including explicit resolution of cis- and trans- isomers of 2,3-dimethyloxirane. Stereoisomers of 2-butene were also quantified explicitly. For all cyclic ethers, a common trend in O2-dependence emerged: species concentrations reach a maximum near 3.0 · 1018 molecules cm–3 (equivalence ratio of 0.5). Although quantitative disparities are evident, chemical kinetics modeling qualitatively reproduces the O2 dependence of species at 650 K. However, at 800 K, weak dependence on O2 is predicted, which is in contrast with the measurements. Two carbonyls, diacetyl and methyl vinyl ketone, were also quantified and follow similar dependence on [O2] and temperature as the cyclic ethers, which indicates some fraction forms via ̇QOOH-mediated reactions. The discrepancies between the measured and model-predicted species profiles indicate that sub-mechanisms for important intermediates may require additional elementary reactions, including stereochemical-specific reactions, to improve the fidelity of n-alkane combustion modeling.

Experimental and Modeling Study of Wall Film Effect on Combustion Characteristics of Premixed Flame in a Constant Volume Combustion Bomb

The primary objective of the present study was to investigate the impact of wall film on the combustion characteristics of premixed flames in internal combustion engines through the joint experimental and numerical techniques. The interaction between the premixed methane-air flame and n-dodecane film attached to the wall of a constant volume combustion bomb was experimentally examined. The flame propagation processes, as well as pressure evolution were quantitatively characterized. Then, computational fluid dynamic (CFD) simulation was performed incorporating the combustion chemistry model. To enable efficient simulation of the chemically reacting flow in engine chambers, a simplified modeling approach based on a two-step reaction scheme was developed. A compact reaction model for the selected model fuel n-dodecane was constructed and reduced to include 35 chemical species and 180 reactions. The flame propagation process of the premixed flame and its interaction with dry and wet walls was studied. The results showed that the propagation of the premixed flame could be divided into four stages, and the existence of the slit structure increased the instability of the flame structure in the near-wall region. The wall film tended to promote emissions, producing more unburned hydrocarbons, soot precursors and aldehydes.

Theoretical investigations on photodissociation dynamics of deuterated alkyl halides CD3CH2F

The product branching ratio between different products in multichannel reactions is as important as the over-all rate of reaction, both in terms of practical applications (e.g. models of combustion or atmosphere chemistry) in understanding the fundamental mechanisms of such chemical reactions. A global ground state potential energy surface for the dissociation reaction of deuterated alkyl halide CD3CH2F was computed at the CCSD(T)/CBS//B3LYP/aug-cc-pVDZ level of theory for all species. The decomposition of CD3CH2F is controversial concerning C−F bond dissociation reaction and molecular (HF, DF, H2, D2, HD) elimination reaction. Rice-Ramsperger-Kassel-Marcus (RRKM) calculations were applied to compute the rate constants for individual reaction steps and the relative product branching ratios for the dissociation products were calculated using the steady-state approach. At the different energies studied, the RRKM method predicts that the main channel for DF or HF elimination from 1,2-elimination of CD3CH2F is through a four-center transition state, whereas D2 or H2 elimination from 1,1-elimination of CD3CH2F occurs through a direct three-center elimination. At 266, 248, and 193 nm photodissociation, the main product CD2CH2+DF branching ratios are computed to be 96.57%, 91.47%, and 48.52%, respectively; however, at 157 nm photodissociation, the product branching ratio is computed to be 16.11%. Based on these transition state structures and energies, the following photodissociation mechanisms are suggested: at 266, 248, 193 nm, CD3CH2F→absorption of a photon→TS5→the formation of the major product CD2CH2+DF; at 157 nm, CD3CH2F→absorption of a photon→D/F interchange of TS1→CDH2CDF→H/F interchange of TS2→CHD2CHDF→the formation of the major product CHD2+CHDF.

Influence of thermal piston insulation on the indicated efficiency of SI-engines

High efficiency gasoline combustion engines with up to 50 % indicated efficiency are the target of current research work. To reach this goal, it’s essential to reduce all the combustion engine losses as much as possible. One major loss, with about 30 % of the total fuel energy, is the wall heat transfer loss. To reduce this loss, one solution is a temperature swing insulation, which is characterized by a low thermal conductivity and at the same time a low volumetric heat capacity. In order to analyze the thermal efficiency potential of different insulation materials, a thermal insulation model for one-dimensional engine process simulations has been developed and is presented in this paper. The insulation is discretized by a thermal node model and is coupled to an engine process simulation using the simulation tool GT-Power. The heat transfer and temperature swing behavior of the thermal insulation model is validated against 3D-CFD engine cycle simulations. A predictive detailed chemistry combustion model is used in 3D-CFD simulations to evaluate the influence of thermal insulations on the knocking tendency. Two different thermal insulation materials are investigated using the developed simulation model. One is yttria stabilized zirconia (YSZ) as a common thermal sprayed coating. The second material is produced by an electrolytic oxidation of the piston surface (anodizing). With thermal piston insulation, there is only a small increase in thermal efficiency in the range of 0.2 % to 0.6 % possible with both materials, whereby the potential increases at low speeds and medium loads. The reason can be found in the relative heat losses, which increases with a constant center of combustion and increasing load. An efficiency loss analysis shows that the exhaust losses increase by about two third of the reduced heat losses. Due to its lower volumetric heat capacity and similar heat conductivity, the anodized piston surface shows a thermal efficiency advantage compared to YSZ. The simulation results are finally validated by measurements conducted with a single-cylinder research engine for an YSZ coated piston surface as well as a hard anodized piston surface.

Construction of a skeletal multi-component diesel surrogate model by integrating chemical lumping and genetic algorithm

Towards high-fidelity combustion chemistry modeling of real diesel fuel, this study aims to construct a skeletal multi-component kinetic model with higher accuracy and heavy hydrocarbons (n-hexadecane, iso-cetane, n-octadecane, α-methylnaphthalene, decalin), which is feasible for engine computational fluid dynamics (CFD) applications. The developed skeletal model with 220 species and 1109 reactions is composed of lumped fuel-specific sub-mechanisms and a skeletal C0–C3 core mechanism derived from the well-validated detailed NUIGMech 1.1 mechanism. Chemical lumping integrated with skeletal reduction methods and reaction pathway analysis is used to develop compact fuel-molecule sub-models. Ignition delay and species concentration are then taken as targets simultaneously to optimize the original model automatically using genetic algorithm (GA) within given parameter ranges. Eventually, the optimized kinetic model is validated against various experimental results of pure components, their mixtures and real diesel fuels, including ignition delay times in both shock tubes and rapid compression machines, species concentration profiles in jet-stirred reactors, and laminar flame speeds in the counterflow configurations as well as actual engine data. In addition, it should be noted that due to the absence of test data on pure n-octadecane, the sub-model of n-octadecane is not directly validated in this work, but compared with measurements of real diesel. Overall, the simulation results are in good agreement with experiments under a wide range of engine-like conditions, suggesting that the present skeletal multi-component mechanism can be applied to mimic autoignition and oxidation of actual diesel. As such, this will provide a more accurate and robust combustion model for the development and optimization of advanced engines with high efficiency and ultra-low emissions.

Flamelet Versus Detailed Chemistry Large Eddy Simulation for a Liquid-Fueled Gas Turbine Combustor: A Comparison of Accuracy and Computational Cost

Abstract A Honeywell liquid-fueled gas turbine test combustor at idle conditions is numerically investigated in simcenterstar-ccm+ version 2020.3. This work presents large eddy simulation (LES) results using both the flamelet generated manifold (FGM) and detailed chemistry combustion models. Both take advantage of a hybrid chemical (HyChem) mechanism which has previously demonstrated very good accuracy for real fuels such as Jet-A with only 47 species. The objective of this work is to investigate the ability of FGM and detailed chemistry modeling to capture pollutant formation in an aero-engine combustor. Comparisons for NOx, CO, unburned hydrocarbons (UHC), and soot are made, along with the radial temperature profile. To fully capture potential emissions, a soot moment model and Zeldovich NOx model are employed along with radiation. A comparison of results with and without chemistry acceleration techniques for detailed chemistry is included. Then, computational costs are assessed by comparing the performance and scalability of the simulations with each of the combustion models. It is found that the detailed chemistry case with clustering can reproduce nearly identical results to detailed chemistry without any acceleration if CO is added as a clustering variable. With the Lagrangian model settings chosen for this study, the detailed chemistry results compared more favorably with the experimental data than FGM; however, there is uncertainty in the secondary breakup parameters. Sensitivity of the results to a key parameter in the spray breakup model is provided for both FGM and complex chemistry (CC). By varying this breakup rate, the FGM case can predict CO, NOx, and UHC equally well. The smoke number, however, is predicted most accurately by CC. The cost for running detailed chemistry with clustering is found to be about four times that of FGM for this combustor and chemical mechanism.

Simplified modeling combustion chemistry of neat and blended large hydrocarbon fuels with different functional groups

In the present study, a simplified modeling approach based on a two-step reaction scheme (TSRS) was developed to describe the high-temperature combustion chemistry of large hydrocarbon fuels. The characteristic reaction time scale analysis indicated a distinct two-step reaction property for the conversion of large hydrocarbon molecules. Along with the quasi-steady state assumption, TSRS utilized a seven-reaction sub-model to describe the fuel decomposition to a small group of intermediate products, and a detailed foundational fuel combustion chemistry model to describe the oxidation of these decomposed products. In the first half of this paper, the TSRS model was constructed for four fuel components with different functional groups, including n-heptane, iso-octane, methylcyclohexane, and n-butylbenzene, and validated sequentially by their speciation data, and global combustion properties of ignition delay time and laminar flame speed data. Sensitivity analysis and rate of production analysis revealed the primary decomposition paths in the TSRS model. Then, in the second half of the paper, algebraically blending the TSRS models of neat fuel components enabled the construction of surrogate fuel models for real fuels, including a two-component primary reference fuel (PRF), a three-component gasoline surrogate fuel (toluene-PRF), a four-component Chinese jet fuel (RP-3) surrogate, and a four-component diesel surrogate. Predictions from the TSRS-based surrogate models for real fuels were shown to be consistent with the speciation data as well as the global combustion properties, whenever available in the literatures, indicating the robustness and broad applicability of the TSRS approach.

Binary Diffusion Coefficients for Methane and Fluoromethanes in Nitrogen.

Binary gas-phase diffusion coefficients, of interest in physical models of atmospheric and combustion chemistry, have been measured in for the homologous series of refrigerant-related (fluoro)methanes: methane (), fluoromethane (), difluoromethane (), and trifluoromethane (). Values have been determined by reverse-flow gas chromatography, which has been previously demonstrated to provide accurate results over a wide range of temperatures. Coefficients were measured at temperatures of (300 to 550) K for all species and extending up to 650 K and 723 K for and , respectively, and down to 250 K for . We also performed measurements for in air at temperatures of (250 to 350) K, obtaining values the same as in within 0.3 %, well within our experimental uncertainty. We report the first measurements for and compare with the limited literature data for the other compounds. Our results agree broadly with earlier measurements in both and air. The greater temperature ranges reported in this work lead to temperature dependences that differ from most previous experiments, although they are consistent with several literature estimates and are similar to temperature exponents found for small hydrocarbons in . Comparison of the present work with a recent study that found different diffusion coefficients for methane when determined in a typical arrested flow apparatus and a novel "twin tube" method unaffected by sample adsorption shows much better agreement with the the arrested flow results over all common temperatures.

Numerical simulation of n-dodecane spray combustion based on OpenFOAM

For the purpose of providing the scientific insights to combustion characteristics of spray jet, numerical calculations of reacting and non-reacting spray cases are performed for ECN (engine combustion network) Spray A (n-dodecane spray combustion) which coupled finite chemistry combustion model PaSR and detailed chemical reaction kinetics based on OpenFOAM. The applicability and accuracy of the spray model is verified in the non-reacting spray case, and it is found that the predicted spray characteristics such as the penetration length of liquid and vapor and the mixture fraction are in good agreement with the test results. The two processes of low-temperature reaction and high-temperature ignition experienced by n-dodecane spray ignition are analyzed in reacting spray case, and it is found that the low-temperature reaction continues to exothermic before high-temperature ignition, and continues to proceed stably after high-temperature ignition, which promotes high-temperature ignition and flame stability. Finally, the effects of different fuel injection pressures on ignition delay time and flame lift-off length are studied.

Measurements of the laminar flame speed of premixed, hydrogen-air-argon stagnation flames

As the foundation for detailed hierarchical combustion chemistry models, the accuracy of the hydrogen oxidation mechanism is paramount to achieve truly predictive models. The recent introduction of new chemically termolecular reactions to this system suggests that our understanding of this fundamental chemistry could have initially been plagued with structural inaccuracies that have been carried along in the development of larger thermochemical mechanisms. Consequently, there is a need for additional independent experimental data in various experimental setups to assess the accuracy of model predictions. An atmospheric jet-wall stagnation-flame configuration is used in this work to measure the reactivity of premixed, lean-to-rich hydrogen-air flames diluted with argon. Mixtures with estimated adiabatic flame temperatures of ∼1800K are obtained by argon dilution to maintain the oxygen-nitrogen ratio while allowing for stable, laminar flames over the desired conditions. The accuracy of various thermochemical mechanisms available in the literature is assessed with direct comparisons of the velocity profiles in the stagnation configuration obtained through Particle Tracking Velocimetry to the solution of the quasi–1D flame simulation. Unstretched laminar flame speeds (SLo) are subsequently inferred using a direct comparison technique between the experiments and the simulations at multiple stretch values, similarly to a non-linear extrapolation to unstretched conditions. Significant discrepancies are observed between model predictions and experimental measurements, which supports the current efforts in model development. The inaccuracies in kinetic rates of the hydrogen oxidation model must first be resolved to avoid optimization and validation errors in the hierarchical development of increasingly complex hydrocarbon mechanisms.

Computational Study of Compartment Size Effects on Backdraft Intensity

A computational study was performed to evaluate the effects of compartment size on backdraft intensity. The compartment sizes were selected such that each direction was enlarged by a factor of 2, 2.5, 2.625, and 3 based on the reduced-scale compartment of a previous experimental study. A fire dynamics simulator was used for the computation, and a large eddy simulation and a mixing-controlled fast chemistry combustion model were adopted. Results revealed that the overall equivalence ratio defined by the amounts of fuel inside the compartment and oxygen induced from the opening had similar values at the moment when the air reached the inside wall. The fuel–air mixing inside the compartment was found to be achieved more rapidly with a decreased compartment size. The peaks of pressure and heat release rate inside the compartment increased with an increase in compartment size. However, these peaks were found to increase exponentially with an increase in the ratio of the compartment volume and opening size, and the correlation showed a very high R-squared value.

Evolution in size and structural order for incipient soot formed at flame temperatures greater than 2100 K

Soot formed in flames hotter than conventional combustion applications is expected to undergo unique formation processes and develop a carbon structure distinct from typical soot. A complementary experimental and modeling approach is reported here to assess flame temperature and equivalence ratio effects for soot formed in the higher-temperature regime (1950 K < Tf < 2250 K). Computations using three separate combustion chemistry models show that predictions of polycyclic aromatic hydrocarbon (PAH) concentration profiles for the higher-temperature flames are more sensitive to the choice in mechanism rather than specific flame conditions. As for material properties, the Raman signatures transition from a typical soot spectrum to features observed in disordered sp2 carbon materials. The defect distance extracted from the Raman bands nearly doubles from values typically reported for soot as the flame temperature exceeds 2200 K. Higher concentrations of gas-phase precursors may facilitate development of an ordered carbon structure as indicated by the relatively high defect distance observed for the highest equivalence ratio series. Particle size distributions measured by mobility sizing show size and yield of soot decreases with increasing flame temperature and the bimodal distribution falls within the ultra-fine range for all flame conditions. This is especially promising if the significant transformation in carbon structure inferred from the evolution in Raman spectra enables development of functional high-surface area sp2 carbon materials. Namely, the current observations indicate that the flame-formed carbon structure evolves towards high-defect sp2 carbon with size and carbon structure that can be tuned to some extent.

A Study on turbulence-combustion interaction and Sub-grid Scale model in the simulation of Methane pool fire using LES

In this paper, the effect of the combustion and turbulence sub-grid scale (SGS) model on the simulation of pool fire turbulence field has been studied in open source CFD software, OpenFOAM. Two combustion models of Eddy Dissipation Model (EDM) and infinite fast chemistry, with the one-equation and Smagorinsky SGS model, is evaluated for a large-scale pool fire. In general, fast kinetic-based combustion models predict excessive heat release rate. The mean squared of the velocity fluctuations is over-predicted. In this simulation, the turbulence models have no significant effect on the results. In fact, the effect of the combustion model is dominant. The EDM combustion model is more compatible when used with the one-equation SGS model and improves the results compared to other cases. In addition, the infinite fast chemistry combustion model is not a suitable model for fire simulation.

Numerical investigation of prediction performance of design fire curves for a tunnel fire

The prediction performance of design fire curves is numerically investigated for tunnel fire using the fire dynamics simulator (FDS). A large eddy simulation (LES) was adopted in the simulation of a previous 750 kW tunnel fire experiment. Based on the experimental heat release rate, t2-fire growth, quadratic and exponential design fire curves (DFCs) are mathematically constructed and adopted in the FDS simulation. The predictions of each DFCs are compared against the experimentally measured smoke temperature, smoke travel time, and carbon monoxide (CO) concentration. In addition, the prediction performance of the mixture fraction (MF) and mixing controlled fast chemistry (MCFC) combustion models, is compared. The simulation results of the MF and MCFC models are similar except for the CO concentration features. For the performance of the DFCs, t2-fire growth curve with the MF combustion model is the most effective combination, which demonstrated the most reasonable agreement with the experimental data.

Nucleation of soot: experimental assessment of the role of polycyclic aromatic hydrocarbon (PAH) dimers

Abstract The irreversible dimerization of polycyclic aromatic hydrocarbons (PAHs) – typically pyrene (C16H10) dimerization – is widely used in combustion chemistry models to describe the soot particle inception step. This paper concerns itself with the detection and identification of dimers of flame-synthesized PAH radicals and closed-shell molecules and an experimental assessment of the role of these PAH dimers for the nucleation of soot. To this end, flame-generated species were extracted from an inverse co-flow flame of ethylene at atmospheric pressure and immediately diluted with excess nitrogen before the mixture was analyzed using flame-sampling tandem mass spectrometry with collision-induced fragmentation. Signal at m/z = 404.157 (C32H20) and m/z = 452.157 (C36H20) were detected and identified as dimers of closed-shell C16H10 and C18H10 monomers, respectively. A complex between a C13H9 radical and a C24H12 closed-shell PAH was observed at m/z = 465.164 (C37H21). However, a rigorous analysis of the flame-sampled mass spectra as a function of the dilution ratio, defined as the ratio of the flow rates of the diluent nitrogen to the sampled gases, indicates that the observed dimers are not flame-born, but are produced in the sampling line. In agreement with theoretical considerations, this paper provides experimental evidence that pyrene dimers cannot be a key intermediate in particle inception at elevated flame temperatures.

Numerical Combustion Evaluation of Select Detailed Chemistry Mechanisms for Their Impact on Compression Ignition Diesel Engine Performance Prediction

The study focuses on the selection of detailed chemistry model for numerical combustion of compression ignition diesel engine. Three different established chemical reaction mechanisms of different chemistry resolution are considered to predict the macro performance characteristics. The numerical computation is performed on turbocharged 5.67L 130PS commercial vehicle diesel engine. The three chemical reactions mechanisms are used for engine performance prediction analysis viz. PSM Mechanism (having 121 species and 593 reactions), ERC Mech reaction mechanism model (having 61 species with 235 reactions) and Chalmers’ reaction mechanism model (having 42 species with 168 reactions) for analyses. The surrogate diesel fuel n-heptane is used in the combustion analysis. By making use of the three-chemistry model, conclusive results indicate significant differences in the computational runtime without much loss in the accuracy of the performance characteristics (expressed as the indicated mean effective pressure (IMEP)).

Scale-Resolving Simulation of a Propane-Fuelled Industrial Gas Turbine Combustor Using Finite-Rate Tabulated Chemistry

The scale-resolving simulation of a practical gas turbine combustor is performed using a partially premixed finite-rate chemistry combustion model. The combustion model assumes finite-rate chemistry by limiting the chemical reaction rate with flame speed. A comparison of the numerical results with the experimental temperature and species mole fraction clearly showed the superiority of the shear stress transport, K-omega, scale adaptive turbulence model (SSTKWSAS). The model outperforms large eddy simulation (LES) in the primary region of the combustor, probably for two reasons. First, the lower amount of mesh employed in the simulation for the industrial-size combustor does not fit the LES’s explicit mesh size dependency requirement, while it is sufficient for the SSTKWSAS simulation. Second, coupling the finite-rate chemistry method with the SSTKWSAS model provides a more reasonable rate of chemical reaction than that predicted by the fast chemistry method used in LES simulation. Other than comparing with the LES data available in the literature, the SSTKWSAS-predicted result is also compared comprehensively with that obtained from the model based on the unsteady Reynolds-averaged Navier–Stokes (URANS) simulation approach. The superiority of the SSTKWSAS model in resolving large eddies is highlighted. Overall, the present study emphasizes the effectiveness and efficiency of coupling a partially premixed combustion model with a scale-resolving simulation method in predicting a swirl-stabilized, multi-jets turbulent flame in a practical, complex gas turbine combustor configuration.

Quantifying uncertainty in kinetic simulation of engine autoignition

Combustion chemistry models have been developed with inherent uncertainties in them. Whether a model that is developed using fundamental combustion experiments is capable to reproduce practical combustion processes within typical levels of measurement uncertainty is an open question. This paper quantifies the uncertainty of engine autoignition simulation using the uncertainties in the selected chemical kinetic model and then minimizes the model prediction uncertainty using various experiments. The method adopts a deterministic framework of uncertainty quantification, termed bound-to-bound data collaboration, and applies it to simulate the autoignition of n-pentane in a standard octane rating experiment. The results show that simulation of the end-gas autoignition using a comprehensively tested n-pentane model coupled with a two-zone engine combustion model yields an uncertainty substantially higher than that of engine experiment (as indicated by the cycle-to-cycle variation of the autoignition timing measurement). In-cylinder thermochemical conditions are found to be less important than the kinetic parameters in determining the model uncertainty. The large model uncertainty can be reduced by constraining the simulation with consistent experimental data and their measurement uncertainties, including those from fundamental experiments that measure ignition delays, species concentrations, flame speeds, and more significantly from autoignition experiments in well-calibrated engines.

CFD Analysis of Supersonic Combustion at Mach 2 with K-E Turbulence Model

This In this paper combustion of hydrogen under unsteady and supersonic conditions has been presented. The combustor having an injector for injecting fuel parallel to the base. The main flow is also parallel to the base. Modeling of this supersonic combustion has been done using K-ε model with Finite rate chemistry combustion model. In supersonic combustion time available is very short for proper mixing. Intensity of heat release, duct geometry, injection techniques, and mixture (fuel + oxidizer) quality and flow regime are the predominating parameter which decides the flame stabilization. This numerical result demonstrates that flamelet approach is suitable in supersonic flows. Combustion characteristics for injected fuel and supersonic air flow in combustor are presented in this paper. The result shows that the mixing quality increases flame speed almost linearly. The stagnation temperature reaches up to 2420 k in the combustor.