Showing papers in "Combustion Science and Technology in 2010"

Effect of Ignition Location, Vent Size, and Obstacles on Vented Explosion Overpressures in Propane-Air Mixtures

Abstract: The authors present results of vented explosion tests using stoichiometric propane-air mixtures in a room-size enclosure 63.7 m3 in volume. The tests were focused on the effect of ignition location, vent size, and obstacles on explosion development and pressure buildup. The dependence of the maximum pressure generated on the experimental parameters was analyzed. It was found that the pressure maxima may be caused by pressure transients defined by the interplay of several factors, such as the maximum flame area and burning velocity in the chamber, and the overpressure generated by the external explosion. A simple model was proposed that allowed for the estimation of the maximum pressure for each of the main pressure transients. The model was found to agree with the experimental data within the experimental uncertainty.

Development of a Practical Soot Modeling Approach and Its Application to Low-Temperature Diesel Combustion

Abstract: The author's developed a practical soot model and implemented in the multidimensional computational fluid dynamics code, KIVA-3vr2 for use in low temperature diesel combustion simulations. The model framework is based on four fundamental steps: soot inception through a four-ring polycyclic aromatic hydrocarbon species, surface growth through acetylene, soot coagulation, and oxygen- and OH-induced soot oxidation. Diesel combustion was simulated by using a reduced n-heptane chemistry mechanism. A reduced polycyclic aromatic hydrocarbon chemistry mechanism was formulated from the literature and coupled with the n-heptane mechanism. Improvements were made in the chemistry mechanism for better predictions of ignition delay, liftoff length and soot precursor concentrations. The CHEMKIN-II code was used to solve the combustion chemistry. However, in order to reduce the computational time of the coupled soot and chemistry calculations, a semi-implicit solver was also implemented and used for the soot precursor sp...

Ignition and Combustion Characteristics of Nanoscale Al/AgIO3: A Potential Energetic Biocidal System

Abstract: The authors investigated the ignition and reaction of Al/AgIO3 thermites for potential use in biocidal applications. Rapid-heating wire experiments were performed to measure the ignition temperature and investigate the thermal decomposition of the oxidizer using a T-Jump/TOF Mass Spectrometer and an optical emission setup. Combustion experiments inside a constant-volume pressure cell were also carried out, and the relative performance was compared with other thermite systems. The ignition temperature in air at atmospheric pressure was found to be 1215 ± 40 K. The AgIO3 was found to significantly outperform CuO and Fe2O3 oxidizers in pressurization tests, and this is attributed to the enhanced gas release as the AgIO3 thermally decomposes to release iodine in addition to oxygen. The reacted product was collected to investigate the final state of the products. Transmission electron microscopy and X-ray diffraction were performed to show that the major Ag product species was AgI, and not elemental Ag and I2....

Numerical Investigation of Rotating Detonation Engine Propulsive Performance

Abstract: A series of 3- and 2-dimensional numerical simulations of a rotating detonation engine (RDE) are carried out with a 1-step chemical reaction model to investigate the RDE's propulsive performance. First, the performance is computed by a 3-dimensional simulation. After the initial instability dies down, the specific impulse and mass flux of RDE converge to constant values. Then, some simplified 2-dimensional cases are simulated. The following propulsive performance collusions are obtained: with the injection stagnation pressure increases, the mass flux increases linearly and the specific impulse decreases a little. With combustor length larger than a special value, specific impulse and mass flux change a little. The propulsive parameters obtained from the 3-dimensional simulation case agree with simplified 2-dimensional simulation cases.

Experimental Study of the Preheat Zone Formation and Deflagration to Detonation Transition

Abstract: The authors present experimental studies of the deflagration-to-detonation transition (DDT) in tubes with smooth and rough walls in stoichiometric hydrogen-oxygen and ethylene-oxygen mixtures. On the basis of experimental evidence, it is shown that formation of the preheat zone, where reaction is chemically frozen, promotes the transition to detonation if temperature and width of the preheat zone are above certain critical values. A sequence of high-speed Schlieren records permits an accurate determination of the minimal values of temperature and width of the preheat zone, leading to transition to detonation. The experimentally measured critical temperatures and widths of the preheat zone initiating restructuring of the flame and transition to detonation in hydrogen-oxygen and ethylene-oxygen mixtures are consistent with the developed theory.

Turbulent Spray Flames of Acetone and Ethanol Approaching Extinction

Abstract: This paper presents measurements of mean temperature, axial velocity, turbulence, and droplets fields in pilot-stabilized jet flames of dilute sprays where acetone or ethanol is used as liquid fuel. Laser-induced fluorescence (LIF) is employed to image hydroxyl radical OH which marks the existence of hot regions or reaction zones. Depending on the fuel used, droplets within the flow are delineated by imaging LIF from acetone or Mie scattering. As the jet velocity is increased, the flames gradually approach blow-off in a region further downstream from the stabilizing pilot. It is found that the mean velocity, turbulence, and droplet fields are somewhat similar for both ethanol and acetone flames, and these do not change much with increasing jet velocity, particularly when normalized with the relevant parameters. However, the temperature and reactive fields are varying and undergo departure indicative of nonpremixed to premixed flame behavior depending on the vapor pressure of the fuel and proximity to blow...

Validation of a turbulent flame speed model across combustion regimes

Abstract: A flame speed expression proposed recently is studied in detail and extensively validated in this study. This expression has no adjustable parameters, and its constants are closely tied to the physics of scalar mixing at small scales. In the weak turbulence limit, the flame speed expression recovers a linear dependence of the turbulent to laminar flame speed ratio, , on the normalized turbulence rms velocity, , in accordance with Damkohler's classical result. However, in the limit of intense turbulence, Damkohler's result gives a square-root dependence, while the new expression gives a combination of linear and square-root terms. Predictions of the new expression are compared to a wide range of experimental data of S T from various flame configurations and conditions, with the same values of the model constants. The quantitative comparisons are found to be very good with experimental data beyond the usually restricted range of of existing models. Predictions of S T for high-pressure turbulent flames, up t...

Kinetic modeling of the oxidation of ethanol and gasoline surrogate mixtures

Abstract: The kinetic characterization of the oxidation of ethanol–gasoline mixtures is of interest due mainly to its role in sustainable combustion processes. The aim of this paper is to revise and validate a kinetic mechanism of ethanol combustion inside a general scheme able to describe the pyrolysis and oxidation of hydrocarbons. Model predictions and experimental measurements are discussed and successfully compared across a wide range of operating conditions. This study moves from the detailed analysis of species profiles of ethanol oxidation in jet-stirred, flow reactors and laminar flames to global combustion properties (ignition delay times and laminar flame speeds) by referring to a large set of literature data; the analysis is then extended to the effect of ethanol on the combustion of ethanol–gasoline mixtures. The large experimental data set discussed in this paper includes very recent measurements and covers a wide range of operating conditions. The chemical effect of ethanol on the combustion properti...

Gas-Phase Reaction in Nanoaluminum Combustion

Abstract: The presence or absence of gas phase species during combustion of aluminum nanoparticles (n-Al) is a crucial observable in evaluating competing theories such as a diffusive oxidation mechanism and the melt dispersion mechanism. Absorption spectroscopy was used to probe the ground state of aluminum monoxide (AlO) and Al vapor in order to quantify the amount of Al and AlO present under conditions where these species were not observed in emission previously. Absorption measurements were made during combustion of nanoaluminum and micron-sized aluminum in a heterogeneous shock tube. AlO was detected in absorption at temperatures as low as 2000 K in n-Al combustion, slightly below the limit seen in micro-Al combustion. Al vapor was detected during n-Al combustion at temperatures as low as 1500 K, significantly lower than in micro-Al combustion, suggestive of a gas phase component. The detection limit for Al vapor was 1 × 1012 cm−3. The gas phase component was much weaker than that seen in 10 μm Al combustion. A...

Catalytic Activity of Nanometer-Sized CuO/Fe2O3 on Thermal Decompositon of AP and Combustion of AP-Based Propellant

Abstract: Nanometer-sized CuO, Fe2O3 and CuO/Fe2O3 were synthesized by a conventional solid-state reaction method. The obtained products were characterized by XRD and TEM. The catalytic activity of the products on ammonium perchlorate (AP) thermal decomposition was investigated by TG-DTA. The burning rate and pressure exponent of the propellant modified by the products CuO, Fe2O3 and CuO/Fe2O3 were measured by strand burner method, respectively. The experimental results showed that the obtained products play a catalytic role in the thermal decomposition of AP and combustion of AP-based propellant. The order of the catalytic performance of obtained products on AP thermal decomposition is CuO/Fe2O3 >CuO >Fe2O3. The catalytic activity of CuO/Fe2O3 is better than that of simplex CuO and Fe2O3, which attributes to the synergistic effect of combined catalyst. Compared with basic propellant, the burning rate of propellant modified by 1% CuO/Fe2O3 increases around 55%, whereas the pressure exponent is nearly invariable. A ...

Laminar Burning Velocities and Markstein Lengths of 2,5-Dimethylfuran-Air Premixed Flames at Elevated Temperatures

Abstract: Laminar burning velocities and Markstein lengths of 2,5-dimethylfuran (DMF)-air premixed mixtures at different initial temperatures and equivalence ratios were obtained using a constant volume combustion chamber and high-speed schlieren imaging system. The results indicate that both unstretched flame propagation speed and laminar burning velocity peak near the equivalence ratio of 1.2, and increase with increasing initial temperature. The peak unstretched flame propagation speed moves to the rich mixture side as the initial temperature increases, whereas the peak laminar burning velocity is unaffected by the variation of initial temperature. The Markstein length decreases with increasing equivalence ratio and increases with the increasing initial temperature. Based on the experimental data, a formula to calculate the laminar burning velocities of 2,5-DMF-air mixtures is provided.

Lean and Rich Premixed Dimethoxymethane/Oxygen/Argon Flames: Experimental and Modeling

Abstract: Experimental structures of two dimethoxymethane/oxygen/argon flames at equivalence ratios of phi = 0.24 and 1.72 have been studied by mass spectrometry. The detected species throughout the flame thickness were H-2, CH3, CH4, H2O, C2H2, CO, CH2O, CH3O, O-2, Ar, CO2, C2H4O2, and C3H8O2. The aim of this work was to extend an original model for ethylene combustion by building a sub-mechanism taking into account the formation and the consumption of oxygenated species involved in dimethoxymethane oxidation. By using kinetic data from the literature, the authors elaborated a new mechanism containing 480 reactions involving 90 chemical species in order to simulate these dimethoxymethane flames. The mechanism provides numerical results, which are in good agreement with experimental data for all species detected in both flames. Whatever the equivalence ratio of the flame, the two main degradation pathways of dimethoxymethane are the same: CH3OCH2OCH3 -> CH3OCH2OCH2 -> CH3OCH2 -> CH2O and CH3OCH2OCH3 -> CH3OCHOCH3 -> CH3OCHO -> CH3OCO -> CH3O -> CH2O, with the first being the fastest.

On the Role of Ambient Reactive Particles in the Mixing and Afterburn behind Explosive Blast Waves

Abstract: A hybrid two-phase numerical methodology is used to study the propagation of explosive blast waves from spherical charges of TNT and their interaction with an ambient dilute distribution of aluminum particles. The presence of these particles is found to cause perturbations at the contact surface between the inner detonation products and the outer shock-compressed air, which results in Rayleigh-Taylor instabilities at the contact surface. These instabilities grow in time, thereby creating a mixing layer characterized by enhanced mixing between the detonation products and air, resulting in afterburn. The afterburn energy release is observed to affect the pressure decay rate behind the blast wave and the speed and the strength of the secondary shock. The passage of the secondary shock through the mixing layer results in a Richtmyer-Meshkov instability, which is characterized by the creation of vorticity in the mixing layer through baroclinic torque effects. This phenomenon is observed to sustain the mixing p...

Effects of Mean Flow, Entropy Waves, and Boundary Conditions on Longitudinal Combustion Instability

Abstract: The development of a Linearized Euler Equation (LEE) model for analyzing high frequency longitudinal combustion instability is described. The model includes mean flow effects and is generalized for multiple domains as well as natural boundary conditions that deviate from acoustically perfect conditions. These effects are systematically evaluated. Calculated spatial mode shapes and resonant frequencies are compared to experimental measurements and good agreements are obtained. Demonstrative results using a prescribed unsteady heat release model are also analyzed. Observations made from analytical results include mean flow decreases resonant frequencies and shifts the antinode locations; effects of entropy wave and mean flow property changes are location-dependent; application of natural boundary conditions produces more resonant modes and shifts the nodal locations; and the primary effect of unsteady heat release is a change in the linear growth rate. The LEE model is shown to be a useful platform for deve...

Effect of Injection Pressure on Flame and Soot Characteristics of the Biodiesel Fuel Spray

Abstract: The authors studied the effect of injection pressure on nonevaporating spray and spray flame characteristics of biodiesel fuel injected by a common rail injection system in a constant volume combustion vessel. Two biodiesels, biodiesel from palm oil (BDFp) and biodiesel from cooked oil (BDFc) were investigated, including JIS#2 Diesel. Mie scattering technique was employed to investigate nonevaporating spray characteristics. High-speed direct photography and two-color pyrometry were applied for spray flame characteristics. Injection pressures of 100, 200, and 300 MPa and ambient environment typical of diesel engine were used. Nonevaporating spray result showed that biodiesel fuels give longer spray tip penetrations and narrower spray angles especially for BDFp. Integrated flame luminosity of BDFp and BDFc show lower values compared to that of diesel at injection pressure of 100 MPa, and integrated flame luminosity of BDFp and BDFc is even lower than that of diesel at injection pressures of 200 and 300 MPa....

Simplified Flame Models and Prediction of the Thermal Radiation Emitted by a Flame Front in an Outdoor Fire

Abstract: The authors proposed a comparison between 2 simplified flame models. The first flame model uses the radiant surface approach with a new analytical expression for the heat flux. The second one is derived from the Radiative Transfer Equation. The fire front has been considered as a line characterized by some geometric and physical parameters. Two assumptions are used to model the flame, either a radiant plane or a volumetric flame. The flame parameters have been identified from experiments using video records and applying an inverse method. These two models were tested against fires carried out in a fire tunnel and found to perform very well considering the complicate nature of the flame geometry and flame characteristics. The need to determine the heat flux from a large-scale fire has lead to make a number of assumptions. By means of the proposed modeling, the authors try to determine the extent to which the range of assumptions made disqualifies some simplified flame models from use.

Experimental and Numerical Investigation of a FLOX Combustor Firing Low Calorific Value Gases

Abstract: A prototype flameless oxidation (FLOX) gas turbine combustor has been investigated experimentally and numerically The combustor was operated with various Low Calorific Value gases At the outlet main component and emission measurements (CO and NO) have been performed The influence of several parameters (ie, fuel composition, outlet temperature, and nozzle diameter) on the emissions have been investigated Ultralow emissions (single digit) have been achieved Moreover, axial temperature profiles in the combustion chamber have been measured with a suction pyrometer The combustor has been simulated with a commercial CFD code (FLUENT 63) to gain insight in the combustion characteristics Using the Eddy Dissipation Concept model for turbulence-chemistry interaction in combination with the Reynolds Stress model for turbulence and two different chemistry mechanisms, the measured temperature profiles have been reasonably well reproduced In postprocessing mode different NO formation paths have been studied

Effects of Lewis Number on Scalar Dissipation Transport and Its Modeling in Turbulent Premixed Combustion

Abstract: The effects of Lewis number (Le) on scalar dissipation rate transport of the reaction progress variable have been studied using 3-dimensional DNS data of freely propagating turbulent premixed flames with global Lewis number ranging from 0.34 to 1.2. It has been found that the effects of dilatation rate become increasingly strong with decreasing Le, and is particularly strong for the Le ≪ 1 flames because of greater rate of heat release. Moreover, increasingly strong flame normal acceleration in flames with decreasing Le gives rise to countergradient transport for the turbulent flux of the scalar dissipation rate, whereas this flux exhibits gradient transport for flames with Le ≥ 1. This turbulent flux is observed to correlate with the behavior of the turbulent scalar flux and this behavior is used to propose an algebraic closure for the turbulent flux of the scalar dissipation rate. The modeling of nonunity Le effects on the unclosed terms arising from the density change across the flame front, the turbul...

Effects of Injector Recess and Chamber Pressure on Combustion Characteristics of Liquid–Liquid Swirl Coaxial Injectors

Abstract: Combustion characteristics such as combustion performance and combustion stability have been studied experimentally using a small liquid rocket thrust chamber with 19 liquid–liquid swirl coaxial injectors. Data were obtained from static pressure, temperature, and dynamic pressure sensors installed in propellant manifolds and the combustion chamber. While changing the recess length of the injector, characteristic velocity and pressure fluctuation data were collected and analyzed. In addition, chamber pressure was varied between 42 and 54 bar, which covers the sub- and supercritical pressures of oxygen. The results show that the longer recess length generally promotes combustion performance and the spray interaction between injectors in the multielement combustor increases the characteristic velocity. When the chamber pressure is above the critical pressure of oxygen, the recess length scarcely affects the pressure fluctuation. However, when the chamber pressure is below the critical pressure, the shift fro...

Modeling of Oxidation-Driven Soot Aggregate Fragmentation in a Laminar Coflow Diffusion Flame

Abstract: In this study, three different oxidation-driven soot aggregate fragmentation models with 1:1, 2:1, and 10:1 fragmentation patterns are developed and implemented into a laminar coflow ethylene/air diffusion flame, together with a pyrene-based soot model and a sectional aerosol dynamics model. It is found that the average degree of particle aggregation (n p ) in the soot oxidation region is not correctly predicted if oxidation-driven aggregate fragmentation is neglected; whereas the incorporation of aggregate fragmentation significantly improves the n p prediction in the soot oxidation region. Similar results are obtained using the 1:1 and 2:1 fragmentation patterns. However, as the pattern ratio increases to 10:1, appreciable difference in the predicted n p is observed. As the pattern ratio becomes larger, the fragmentation effect diminishes and the predicted n p approaches that of the original model neglecting fragmentation.

Gas diffusion in fractal porous media

Abstract: Gas diffusion in char pores or other fractal pores is anomalous diffusion that does not follow Fick's diffusion law. The authors studied gas diffusion in fractal porous media by simulating molecular movements in porous models. Through analyzing numerical results, gas diffusion equations in fractal pores have been presented. The effects of geometrical structures on pore diffusion can be described by three parameters: porosity, specific surface area, and fractal dimension. With these three parameters, the diffusion coefficient can be calculated. The steady-state diffusion equation is quantitatively determined so that it can be potentially used in modeling char combustion or other practical applications.

A shock tube and chemical kinetic modeling study of methy ethyl ketone oxidation

Abstract: Shock-tube ignition delay times for methy ethyl ketone (MEK; or 2-butanone) were measured at a reflected shock pressure of 1 atm (±2%) in the temperature range of 1250–1850 K at equivalence ratios of 0.5–2.0 for dilute mixtures in argon with fuel concentrations of 1.0%, 1.5%, and 2.0%. Rate constants for unimolecular fuel decomposition reactions were treated for falloff in pressure and temperature, with 9-parameter fits in the Troe formulism. A detailed chemical kinetic submechanism was developed and coupled to an existing C4 mechanism comprising 234 species and 1,369 reversible reactions. Model simulations show generally good agreement when compared to the available experimental data. MEK may be used as a fuel tracer, and thus further ignition delay time measurements were carried out by adding MEK to n-heptane in order to test the effect on ignition delay timing of blending these fuels together. It was found that autoignition characteristics of n-heptane remained unaffected by the presence of MEK fuel tr...

Oxidation of Ethylene and Propene in the Presence of CO2 and H2O: Experimental and Detailed Kinetic Modeling Study

Abstract: Ethylene and propene are major products of the thermal cracking of heavy oil. Under flameless combustion, they are oxidized in presence of large amounts of CO2 and H2O, which may affect their kinetics of oxidation. New experimental results for the kinetic of oxidation in a jet-stirred reactor (JSR) of ethylene and propene in the presence of CO2 and H2O were obtained (1 atm, 950–1450 K). Sonic probe sampling with online FTIR analyses and offline GC-TCD/FID analyses allowed the measurement of concentration profiles for the reactants and products. A detailed kinetic reaction mechanism was used to model the experiments. Good agreement with the data was obtained. Reaction paths analyses showed the important reactions influencing the kinetic of oxidation of the present fuel mixtures. Water tends to inhibit the combustion of the fuels, whereas CO2 has a small accelerating effect upon the oxidation of ethylene in fuel-rich conditions.

Characteristics of Aluminum Combustion Obtained from Constant-Volume Explosion Experiments

Abstract: 2Combustion of aluminum powders is studied using a constant volume explosion (CVE) experiment with varied powder mass loads and environment compositions. A simplified model of aerosol combustion in CVE experiment is proposed based on the assumption that the process is adiabatic. The model enables one to extract the information about the burning velocity and particle burn times from the experimental pressure traces. It is observed that at increased oxygen concentrations, the kinetics of Al combustion may be faster than that of gas phase combustion of methane. The burning velocities measured for Al aerosols compare well with those reported earlier for similar size Al powders. The burn times estimated using the proposed model are substantially longer than reported earlier for individual particles and low number density aerosols. The differences may be due to both interaction between burning particles and lack of correction for the difference in the ignition temperatures for particles of different sizes. The data processing also suggests that the flame quenching by the chamber wall results in incomplete combustion explaining the difference between the observed combustion pressures and those predicted by equilibrium thermodynamic calculations. Addition of methane in the oxidizing environment results in increased combustion temperatures and burning velocities for Al aerosol. At nearly stoichiometric Al powder loads, addition of methane also substantially reduces the particle burn time, while at the increased particle mass loads this effect is diminished.

Modeling the Effects of Thermal Expansion on Scalar Turbulent Fluxes in Turbulent Premixed Flames

Abstract: The thermal expansion induced by the chemical reactions taking place in a turbulent reactive flow affects the velocity field so strongly that velocity fluctuations and velocity gradients can be governed by chemistry rather than by turbulence. Moreover, thermal expansion is well known to be responsible for counter-gradient turbulent diffusion and flame-generated turbulence phenomena. In the present paper, a specific description of the velocity field is used, which allows to separate the influence of thermal expansion from the effects related only to the turbulent motion. Using this description, all the usual turbulent quantities are expressed in terms of two contributions: one due to thermal expansion and one due to turbulence. The theoretical analysis shows that only the contributions due to turbulence should be resolved by transport equations in which unclosed terms do not depend on thermal expansion. Deduced from this analysis, a relatively simple closure modelis proposed and successfully validated thro...

The Effects of Small-Scale Mixing Models on the Prediction of Turbulent Premixed and Stratified Combustion

Abstract: Reynolds-Averaged Navier-Stokes calculations of turbulent premixed and stratified flames in two different configurations are performed to assess the effect of small-scale mixing rate models. The small-scale mixing rate is commonly known as the scalar dissipation rate. The Libby–Williams model involving delta functions is used to calculate the mean reaction rate. The classical model for the scalar dissipation rate underpredicts the mixing rate and gives poor agreement with mean values of velocity, temperature, and species mass fractions. Two other recently proposed dissipation rate models give good predictions at various stratification levels. Further analysis shows that despite adequate mean predictions, there are substantial differences in the mixing rates, fuel mass fraction variance, turbulence kinetic energy, and turbulence frequency predicted by these models. Additionally, the turbulence quantities predicted by the models show opposite trends with increasing stratification. Further Direct Numerical S...

Statistical analysis of displacement speed in turbulent stratified flames: A Direct Numerical Simulation study

Abstract: Statistically planar turbulent stratified flames under different initial root mean square turbulent velocity fluctuation u′ levels are simulated for global equivalence ratios = 1.0 and = 0.7 using 3-dimensional compressible direct numerical simulations (DNS) with a modified single-step Arrhenius-type chemistry. For the simulations of stratified flames, a sinusoidal variation of equivalence ratio is introduced in the unburned reactants ahead of the flame. The simulation parameters are chosen in such a manner that the combustion situation belongs to the thin reaction zones regime in all cases. The DNS data has been used to analyze the statistical behavior of the displacement speed S d and its components (i.e., the reaction rate component S r , the normal molecular diffusion component S n , the tangential diffusion component S t , and the component arising due to reactant inhomogeneity S ξ) and their curvature and tangential strain rate dependence. The mean behavior of displacement speed S d and its ...

A Priori Direct Numerical Simulation Assessment of Algebraic Models of Variances and Dissipation Rates in the Context of Reynolds-Averaged Navier-Stokes Simulations for Low Damköhler Number Partially Premixed Combustion

Abstract: Statistically planar turbulent premixed and partially premixed flames for different initial turbulence intensity are simulated for global equivalence ratio ⟨φ⟩ = 0.7 and 1.0 using three-dimensional simplified chemistry based Direct Numerical Simulations (DNS). For the simulations of partially premixed flames a bimodal distribution of equivalence ratio variation about the prescribed value of ⟨φ⟩ is introduced in the fresh reactants. The simulation parameters are chosen in such a manner that the combustion situation in all the cases represents the thin reaction zones regime with global Damkohler number smaller than unity. The DNS data has been used to analyze the statistics of the variances , covariances (where Y, ξ and c are the fuel mass fraction, mixture fraction, and reaction progress variable, respectively, and tilde and double prime represent the Favre mean and Favre fluctuation of the relevant quantities, respectively), scalar dissipation rates (i.e., and ) of active scalar variances, and the cross-s...

Thermal and Kinetic Impact of CO, CO2, and H2O on the Postoxidation of IC-Engine Exhaust Gases

Abstract: The thermal and kinetic impact of the residual species CO, CO2, and H2O on hydrocarbon (HC) oxidation chemistry was investigated numerically. The case of pure dilution by N2 was tested against a dilutant composed of CO, CO2, and H2O in proportions corresponding to internal combustion (IC)-engine Postoxidation conditions (at the end of the expansion stroke and throughout exhaust). The impact of each residual species was tested individually, as well as in combination with others. Attention was given to the thermal impact, kinetic impact and third-body effects of each residual. In the cases of CO2 and H2O, a negative thermal Cp -effect in competition with an accelerating kinetic impact due to third-body reactions was observed. The influence of CO on HC-oxidation is restricted to its direct participation in oxidizing reactions, and its thermal impact is negligible compared to N2. CO2 and H2O have a negative thermal impact compared to N2, resulting from their increased heat capacities. Kinetically, they intera...

Detonation Limit Thresholds in H2/O2 Rotating Detonation Engine

Abstract: The rotating detonation engine (RDE) is a new engine system using detonation, which may provide a higher performance and smaller and simpler design in comparison with the pulse detonation engine (PDE) and other traditional engines. However the research on RDE stands just at the first step now. The authors perform a numerical analysis to understand about RDE in terms of features of rotating detonation and its propagation limit. The lower threshold pressure of detonation limit was 2.6 MPa and the upper threshold pressure of detonation limit was 7.1 MPa. The engine performance analysis shows that the maximum mixture based specific impulse (I spm ) was about 440 s, which is comparable with that of the present typical rocket engine.