Calculated Ignition Delay Times Research Articles

Investigation of aluminum particle ignition dynamics in various propellant environments

The ignition delay of aluminum particles can be profoundly influenced by the agglomeration and combustion characteristics of solid propellants. In this experimental study, the ignition of individual aluminum particles in nitrate ester plasticized polyether (NEPE) and hydroxyl‑terminated polybutadiene (HTPB) propellant atmospheres was examined using laser ignition tests and high-speed photography. Focus was directed at the effects of the atmospheric composition, pressure, and aluminum particle size (500, 800 and 1000 µm). It was observed that the non-homogeneous reaction heat generation and convective heat exchange rates during particle ignition could be increased by increasing the CO2 content or ambient temperature, resulting in a shorter ignition delay time. This explains why aluminum particles tended to burn more efficiently in nitrate ester plasticized polyether than in hydroxyl‑terminated polybutadiene. In addition, it was found that the ignition delay time decreased with increasing pressure and was inversely proportional to the particle size squared. An ignition model for aluminum particle ignition in a multi-component atmosphere was developed and validated to describe the temperature change and energy transfer during ignition. The calculated ignition delay times were found to be within 5% of the experimental values. The model also showed that increasing the ambient temperature was more effective than increasing the CO2 content at enhancing ignition, and that CO2 was more effective than O2, which was itself more effective than H2O. Overall, this study provides useful insight into the ignition characteristics of aluminum particles in different propellant environments. The results could be used to develop more effective propellant formulations, optimize combustion processes, and improve safety in the handling and use of aluminum-based propellants.

Modeling of a Reduced Hybrid H2–Air Kinetic Scheme Integrating the Effect of Hypersonic Reactive Air with Supersonic Combustion

A hybrid H2–air kinetic scheme of 11 species and 15 reactions is developed, which is capable of simulating the high-temperature air reaction flows and H2–O2 combustion flows respectively or simultaneously. Based on the Gupta scheme, the mole fraction varying with a Mach number at specific conditions is analyzed, and the weakly-ionized 7-species 7-reaction scheme is selected. The effect of nitrogenous species on the H2–O2 combustion is analyzed by a zero-dimensional simulation of steady-state and unsteady-state combustion under specified conditions, and the selected dominant nitrogenous reaction N + OH = NO + H is distinguished by the production rate of the nitrogenous species. The thermodynamic properties are verified by comparison using the NIST–JANAF database. The reaction rate coefficients of the dominant reaction of the hybrid kinetic scheme distinguished by a sensitivity analysis are corrected. The proposed kinetic scheme is validated by a zero-dimensional calculation of the ignition delay time and two-dimensional computational fluid dynamics (CFD) simulation with finite-rate chemistry on the shock-induced sub-detonative and super-detonative combustion. The ignition delay time of the hybrid kinetic scheme is almost in the middle between the Shang scheme and Jachimowski scheme, and all the calculated ignition delay times are acceptably greater than the experiments due to the errors of the experiments and numerical models. The clearly captured bow shock wave and combustion front using the hybrid kinetic scheme and Shang scheme are almost the same, which is strongly consistent with the schlieren image. In addition, a good agreement of the flow characteristics and mass fraction of the species along the stagnation line is also obtained, which indicates the accuracy and reasonableness of the hybrid kinetic scheme to simulate hybrid H2–air reactive flows.

Laminar Flame Speeds and Ignition Delay Times of Gasoline/Air and Gasoline/Alcohol/Air Mixtures: The Effects of Heavy Alcohol Compared to Light Alcohol

The oxidation of gasoline and gasoline/alcohol blends is studied in a shock tube and a spherical reactor. A commercial oxy-free gasoline and two alcohols (ethanol and iso-pentanol) were used in this study. The spherical reactor experiments were conducted at an initial temperature of 483 K, initial pressure of 0.1 MPa, and equivalence ratios from 0.65 to 1.36. Ignition delay times were measured behind reflected shock waves. The shock tube experiments were conducted at 2 MPa over a temperature range from 955 to 1284 K and for two equivalence ratios (0.5 and 1). The experimental measurements indicate that replacing ethanol by iso-pentanol on a gasoline/alcohol blend results in flame speeds which are closer to the ones of a commercial gasoline at nearly stoichiometric conditions (an in-engine applications). On the other hand, the ignition delay times are more affected by the presence of iso-pentanol than the ethanol case. Two different surrogate fuels composed of n-heptane, iso-octane, and toluene were also tested against the newly obtained experimental results (oxy-free gasoline and mixtures with ethanol) using kinetic modeling with a reduced model (Cai, L.; Pitsch, H. Combust. Flame 2015 162, 1623–1637). Although a good agreement between real fuel and surrogate properties was observed for the laminar flame speeds, discrepancies were obtained between the measured and calculated ignition delay times especially in the lower temperature range of our study. Additional simulation analyses on the ignition delay times were performed with a different chemical kinetic model (detailed LLNL model for gasoline surrogates) and a more complex four-component surrogate. The results show a considerable improvement in the prediction capabilities of the ignition properties of the oxy-free gasoline and the oxy-free gasoline + ethanol mixtures. The ignition delay time data are also in agreement with the correlations provided in the literature for gasoline fuels and their surrogates.

Experimental and Numerical Analysis on Two-Phase Induced Low-Speed Pre-Ignition

The root cause of the initial low-speed pre-ignition (LSPI) is not yet clarified. The literature data suggest that a two-phase phenomenon is most likely triggering the unpredictable premature ignitions in highly boosted spark-ignition engines. However, there are different hypotheses regarding the actual initiator, whether it is a detached liquid oil-fuel droplet or a solid-like particle from deposits. Therefore, the present work investigates the possibility of oil droplet-induced pre-ignitions using a modern downsized engine with minimally invasive endoscopic optical accessibility incorporating in-cylinder lubrication oil detection via light-induced fluorescence. This setup enables the differentiation between liquid and solid particles. Furthermore, the potential of hot solid particles to initiate an ignition under engine-relevant conditions is analyzed numerically. To do so, the particle is generalized as a hot surface transferring heat to the reactive ambient gas phase. The gas-phase reactivity is represented as a TRF/air mixture based on RON/MON specifications of the investigated fuel. The chemical processes are predicted using a semi-detailed reaction mechanism, including 137 species and 633 reactions in a 2D CFD simulation framework. In the optical experiments, no evidence of a liquid oil droplet-induced pre-ignition could be found. Nevertheless, all observed pre-ignitions had a history of flying light-emitting objects. There are strong hints towards solid-like deposit LSPI initiation. The application of the numerical methodology to mean in-cylinder conditions of an LSPI prone engine operation point reveals that particles below 1000 K are not able to initiate a pre-ignition. A sensitivity analysis of the thermodynamic boundary conditions showed that the particle temperature is the most decisive parameter on the calculated ignition delay time.

Experimental investigation of auto-ignition of ethylene-nitrous oxide propellants in rapid compression machine

Considering the available experimental investigations of auto-ignition behaviors of N2O-C2 hydrocarbons propellants are limited in high-temperature regime, in the work the ignition delay times for N2O-C2H4 propellants have been measured under the conditions of TC = 885–940 K, PC = 2.5–4.3 MPa, φ = 1.05 and 1.35 using the rapid compression machine experiments. Then the relational expression between ignition delay time and condition factors is derived as lgτig=11.781000/Tc-0.26Pc-0.83φ-9.41 by linear fitting. The expression can be used to predict ignition delay times of N2O-C2H4 propellants in practice. Moreover, the calculated ignition delay times by three kinetic models are compared with experimental data. The results show that these models can well predict ignition behaviors at high temperature regime, but fail at low-temperature regime. Through temperature sensitivity analysis, at high-temperature regime the N2O decomposition reaction has the highest sensitivity coefficient and dominated the overall reaction. While at low-temperature regime, the oxidation reactions of N2O and hydrocarbons become more important steps. For better prediction of low-temperature ignition behaviors, the low-temperature oxidation mechanism of N2O and hydrocarbons needs further development, and the kinetic parameters of the highly sensitive reactions should be improved.

A Novel Dual Fuel Reaction Mechanism for Ignition in Natural Gas–Diesel Combustion

In this study, a reaction mechanism is presented that is optimized for the simulation of the dual fuel combustion process using n-heptane and a mixture of methane/propane as surrogate fuels for diesel and natural gas, respectively. By comparing the measured and calculated ignition delay times (IDTs) of different homogeneous methane–propane–n-heptane mixtures, six different n-heptane mechanisms were investigated and evaluated. The selected mechanism was used for computational fluid dynamics (CFD) simulations to calculate the ignition of a diesel spray injected into air and a natural gas–air mixture. The observed deviations between the simulation results and the measurements performed with a rapid compression expansion machine (RCEM) and a combustion vessel motivated the adaptation of the mechanism by adjusting the Arrhenius parameters of individual reactions. For the identification of the reactions suitable for the mechanism adaption, sensitivity and flow analyzes were performed. The adjusted mechanism is able to describe ignition phenomena in the context of natural gas–diesel, i.e., dual fuel combustion.

Influences of isomeric butanol addition on anti-knock tendency of primary reference fuel and toluene primary reference fuel gasoline surrogates

The anti-knock tendency of blends of butanol isomers and two gasoline surrogates (primary reference fuels and toluene primary reference fuels) was studied on a single-cylinder cooperative fuel research engine. The effects of butanol molecular structure (n-butanol, i-butanol, s-butanol and t-butanol) and butanol addition percentage on fuel research octane numbers were investigated. The experimental results revealed that butanol addition to either PRF80 or TPRF80 increased research octane numbers, and the research octane numbers of fuel blends showed higher linearity with the molar percentage than with the volumetric percentage of butanol addition. Furthermore, the research octane number boosting effects of butanol isomers were observed to change with the fuel compositions, that is, i-butanol >s-butanol >n-butanol >t-butanol for primary reference fuels and i-butanol >s-butanol >t-butanol >n-butanol for toluene primary reference fuels. In addition, butanol/primary reference fuel blends exhibited higher research octane numbers than butanol/toluene primary reference fuel blends. We thereafter tried to elucidate the underlying fuel combustion kinetics for the observed anti-knock quality of different butanol/gasoline surrogate blends. It was found that the measured research octane numbers of fuel blends showed the best correlation with the calculated ignition delay times at the thermodynamic condition of 770 K and 2 MPa, and the reaction sensitivity analysis in auto-ignition at this condition revealed that the H-abstraction reactions of butanol isomers by OH radical suppressed fuel reactivity, thus elevating the fuel research octane numbers when butanol was added to the gasoline surrogates. Compared with the butanol/primary reference fuel blends, the positive sensitive reactions related to n-heptane were of higher importance, while the inhibitive effects of sensitive reactions related to butanol and iso-octane decreased for the toluene primary reference fuel/butanol blends, thus leading to lower research octane numbers of the toluene primary reference fuel/butanol blends than those of the butanol/primary reference fuel blends.

Shock-tube study of dimethyl ether ignition by high-voltage nanosecond discharge

A shock tube with a discharge cell was used to experimentally analyze the kinetics of dimethil ether (DME) ignition in DME:O2:Ar and DME:O2:Ar:He mixtures at temperatures from 1075 to 1860 K. We measured ignition delay time in lean and stoichiometric mixtures after a reflected shock wave. Measurements were made in the mixtures activated by a high-voltage nanosecond discharge and without discharge plasma. The dominant mechanisms of DME ignition were studied on the basis of a numerical simulation of the discharge and ignition stages. We calculated the densities of chemically active species generated in the discharge and used these data to model ignition. The calculated ignition delay times agreed reasonably with the measured data for autoignition and plasma-assisted ignition. The limiting processes during the discharge and ignition were shown using sensitivity analysis. It was demonstrated that the partial replacement of Ar with He in the mixtures studied allowed the same values of plasma-assisted ignition delay times at much lower gas temperatures being opposite to ignition without plasma where the delay time was not sensitive to the replacement of Ar with He. Calculations showed that this is explained by an increased specific discharge energy spent on the excitation of DME, O2 and Ar, whereas the excitation of He was negligible. It followed from the calculations that electron-impact ionization of DME molecules is of great importance for the production of active species in the discharge phase and consequently for ignition with plasma. The electron-impact ionization cross section of DME is poorly known and its variation influences the calculated ignition delay time. In addition, at reduced gas temperatures, the effect of plasma nonuniformity is important for shock-tube studies.

Effects of Vibrational Excitation on Nanosecond Discharge Enhanced Methane–Air Ignition

A zero-dimensional model of nonequilibrium plasma-assisted methane–air ignition at atmospheric pressure is presented to study the effects of vibrationally excited species on ignition enhancement. It is found that the vibrationally excited species , , and especially can be generated efficiently when the reduced electric field strength is below 100 Td in a stoichiometric methane–air mixture. The results show that vibrationally excited species could not effectively enhance ignition via kinetic pathways due to their fast relaxation, but instead via thermal pathways through gas heating. Despite this, the thermal enhancement is much less effective than the kinetic effects due to plasma, indicating that the production of vibrationally excited species consumes the energy deposited in the plasma, and thus limits the production of more active particles, such as O, , and . A sensitivity analysis is conducted to further understand the detailed chemistry of the ignition enhancement involving vibrational excitation. The results show the reactions and have significant inhibitive effects on ignition enhancement in discharge conditions with a fixed plasma energy. The reactions involving the production of O and show promotive effects in enhancing ignition because they accelerate the radical production through chain branching reactions. Finally, the calculated ignition delay times at different temperatures show that the ignition enhancement by nanosecond discharge and the promotive effect of N are more significant at low temperatures.

Development of a surrogate fuel mechanism for application in two-stroke marine diesel engine

A reduced n-tetradecane-toluene mechanism was developed as a surrogate fuel for marine diesel engines. The new mechanism includes 85 species and 317 reactions. The mechanism was used in a computational fluid dynamics model to investigate the performance of marine diesel engine. The new mechanism was validated with experimental data from experiments with a shock tube, flow reactor, jet-stirred reactor and marine diesel engine. The effect of toluene content on the performance of marine diesel engines was also investigated. The results showed that the calculated ignition delay times of n-tetradecane and toluene species were consistent with the experimental data. The errors in the mole fractions of main middle species of toluene were in an acceptable range. The calculated in-cylinder pressure of the marine diesel engine was consistent with the experimental data. The calculated quantity of NOx was also close to the experimental data. The physical properties of toluene significantly affected the performance of the marine diesel engine. The n-tetradecane-toluene mechanism including 30% mass fraction toluene is most suitable as a surrogate fuel for a marine diesel engine, considering the comparisons of calculated and experimental data of power, brake specific fuel consumption, and the quantities of NOx and CO2.

Investigation of the effect of correlated uncertain rate parameters via the calculation of global and local sensitivity indices

Applications of global uncertainty methods for models with correlated parameters are essential to investigate chemical kinetics models. A global sensitivity analysis method is presented that is able to handle correlated parameter sets. It is based on the coupling of the Rosenblatt transformation with an optimized Random Sampling High Dimensional Model Representation method. The accuracy of the computational method was tested on a series of examples where the analytical solution was available. The capabilities of the method were also investigated by exploring the effect of the uncertainty of rate parameters of a syngas–air combustion mechanism on the calculated ignition delay times. Most of the parameters have large correlated sensitivity indices and the correlation between the parameters has a high influence on the results. It was demonstrated that the values of the calculated total correlated and final marginal sensitivity indices are independent of the order of the decorrelation steps. The final marginal sensitivity indices are meaningful for the investigation of the chemical significance of the reaction steps. The parameters belonging to five elementary reactions only, have significant final marginal sensitivity indices. Local sensitivity indices for correlated parameters were defined which are the linear equivalents of the global ones. The results of the global sensitivity analysis were compared with the corresponding results of local sensitivity analysis for the case of the syngas–air combustion system. The same set of reactions was indicated to be important by both approaches.

A six-component surrogate for emulating the physical and chemical characteristics of conventional and alternative jet fuels and their blends

Conventional and alternative jet fuels, such as petroleum-derived Jet-A, coal-derived IPK, and natural-gas-derived S-8, display significant chemical and physical fuel property differences that influence their ignition characteristics. The current work addresses the need for surrogate mixtures capable of emulating the various properties of these fuels and their select blends, which are often used within compression ignited engines for acceptable ignition behavior. A six-component surrogate palette is proposed with species that are readily available within recent kinetic mechanisms, including n-dodecane, n-decane, iso-cetane, iso-octane, decalin, and toluene. The use of these species allows for a seamless compositional transition between the neat target jet fuels and their blends. The surrogate optimizer, which includes various correlations and models to estimate properties of model mixtures, is used to determine the surrogate composition that best matches target fuel properties. For an accurate ignition quality prediction during the optimization, a non-linear Derived Cetane Number regression equation is generated from Ignition Quality Tester experiments of 76 surrogate component mixtures. The newly formulated surrogates and their blends successfully capture the wide range of properties present within the target fuels, including temperature-dependent physical properties such as density, viscosity, specific heat, and volatility, along with experimental ignition delays obtained from a constant volume spray chamber. Kinetic modeling with a detailed mechanism showed that predicted ignition delay times are in good agreement with shock tube and rapid compression machine ignition delay experiments. A sensitivity analysis with variations in the composition of the Jet-A surrogate showed that its calculated ignition delay times are most sensitive to the composition of n-dodecane among the four Jet-A surrogate constituents over the range of temperatures and pressures examined.

Shock Tube Measurement of Ethylene Ignition Delay Time and Molecular Collision Theory Analysis

In this study, 75% and 96% argon diluent conditions were selected to determine the ignition delay time of stoichiometric mixture of C2H4/O2/Ar within a range of pressures (1.3–3.0 atm) and temperatures (1092–1743 K). Results showed a logarithmic linear relationship of the ignition delay time with the reciprocal of temperatures. Under both two diluent conditions, ignition delay time decreased with increased temperature. By multiple linear regression analysis, the ignition delay correlation was deduced. According to this correlation, the calculated ignition delay time in 96% diluent was found to be nearly five times that in 75% diluent. To explain this discrepancy, the hard-sphere collision theory was adopted, and the collision numbers of ethylene to oxygen were calculated. The total collision numbers of ethylene to oxygen were 5.99×1030 s−1cm−3 in 75% diluent and 1.53×1029 s−1cm−3 in 96% diluent (about 40 times that in 75% diluent). According to the discrepancy between ignition delay time and collision numbers, viz. 5 times corresponds to 40 times, the steric factor can be estimated.

Calculations of thermal ignition time of hydrogen–air mixtures taking into account quantum corrections

The effect of quantum corrections to the rate constants of chemical reactions on the time of thermal ignition of hydrogen-containing mixtures is studied. It is shown that, at high pressures (30–100) atm and temperatures in the range of (700–900) K, accounting for the quantum corrections to the initiation reaction H2 + O2 → 2OH brings the data on the calculated ignition delay times of the hydrogen-containing mixture into agreement with the previously published results of measurements.

Study of ignition delay time and generalization of auto-ignition for PRFs in a RCEM by means of natural chemiluminescence

An investigation of the effects of contour conditions and fuel properties on ignition delay time under Homogeneous Charge Compression Ignition (HCCI) conditions is presented in this study. A parametric variation of initial temperature, intake pressure, compression ratio, oxygen concentration and equivalence ratio has been carried out for Primary Reference Fuels (PRFs) in a Rapid Compression Expansion Machine (RCEM) while applying the optical technique of natural chemiluminescence along with a photo-multiplier. Additionally, the ignition delay time has been calculated from the pressure rise rate and also corresponding numerical simulations with CHEMKIN have been done. The results show that the ignition delay times from the chemical kinetic mechanisms agree with the trends obtained from the experiments. Moreover, the same mechanism proved to yield consistent results for both fuels at a wide range of conditions. On the other hand, the results from natural chemiluminescence also showed agreement with the ignition delay from the pressure signals. A 310nm interference filter was used in order to detect the chemiluminescence of the OH∗ radical. In fact, the maximum area and peak intensity of the chemiluminescence measured during the combustion showed that the process of auto-ignition is generalized in the whole chamber. Moreover, the correlation of peak intensity, maximum area and ignition delay time demonstrated that natural chemiluminescence can also be used to calculate ignition delay times under different operating conditions. Finally, the area of chemiluminescence was proved to be more dependant on the fuel and ignition delay time than on the operating conditions.

Autoignition characteristics of laminar lifted jet flames of pre-vaporized iso-octane in heated coflow air

The stabilization characteristics of laminar non-premixed jet flames of pre-vaporized iso-octane, one of the primary reference fuels for octane rating, have been studied experimentally in heated coflow air. Non-autoignited and autoignited lifted flames were analyzed. With the coflow air at relatively low initial temperatures below 940K, an external ignition source was required to stabilize the flame. These lifted flames had tribrachial edge structures and their liftoff heights correlated well with the jet velocity scaled by stoichiometric laminar burning velocity, indicating the importance of the edge propagation speed on flame stabilization. At high initial temperatures over 940K, the autoignited flames were stabilized without requiring an external ignition source. These autoignited lifted flames exhibited either tribrachial edge structures or mild combustion behaviors depending on the level of fuel dilution. Two distinct transition behaviors were observed in the autoignition regime from a nozzle-attached flame to a lifted tribrachial-edge flame and then to lifted mild combustion as the jet velocity increased at a certain fuel dilution level. The liftoff data of the autoignited flames with tribrachial edges were analyzed based on calculated ignition delay times. Analysis of the experimental data suggested that ignition delay time may be much less sensitive to initial temperature under atmospheric pressure conditions as compared with predictions.

Experimental and Kinetic Modeling Study of Ignition Characteristics of Chinese RP-3 Kerosene

The ignition delay times of gas-phase Chinese RP-3 kerosene/O2/Ar mixtures were measured by monitoring pressure and electronically excited OH chemiluminescence signals behind reflected shock waves in a chemical shock tube. The experiments were performed over the temperature range of 1100–1600 K, at pressures of 0.1 MPa, 0.2 MPa, and 0.3 MPa, and for equivalence ratios of 0.5, 1.0, and 1.5. The effects of temperature, pressure, and equivalence ratio on the ignition delay time were also investigated. The results show that a linear relationship exists between the reciprocal of temperature and the logarithm of the ignition delay times, and an increase in temperature results in a decrease in the measured ignition delay times at all conditions. Furthermore, with equivalence ratio decreasing or pressure increasing, the measured ignition delay times are decreasing. A new surrogate fuel consists of n-decane (65 vol%), toluene (10 vol%), and propylcyclohexane (25 vol%) for Chinese RP-3 kerosene was presented and a reaction mechanism consists of 150 chemical species and 591 elemental reactions of this surrogate fuel was developed. Comparisons of the calculated ignition delay times of this surrogate fuel using this reaction mechanism with the experimental ignition delay times of Chinese RP-3 kerosene show excellent agreement.

Ignition of ethanol-containing mixtures excited by nanosecond discharge above self-ignition threshold

The kinetics of ignition in lean and stoichiometric C2H5OH:O2:Ar mixtures by a high-voltage nanosecond discharge are studied experimentally and numerically for gas temperatures above self-ignition threshold. Autoignition delay time and ignition delay after a high-voltage nanosecond impulse discharge are measured using reflected shock-wave technique. It is shown that the additional excitation by the discharge plasma leads to an order of magnitude decrease in ignition delay. Discharge processes are simulated on the basis of the measured time–resolved discharge characteristics. The densities of atoms, radicals and excited and charged particles produced in the discharge phase are calculated and used as initial conditions for chemical modeling. Calculated ignition delay times agree well with measurements with and without the discharge plasma. Calculations show that the effect of the discharge plasma on ignition of the ethanol-containing mixtures is primarily associated with active species production in the discharge phase; the role of fast gas heating during the discharge and in its afterglow is relatively small. A method is suggested to compare the effect of nonequilibrium pulse discharge plasma on ignition in different fuel–air and fuel-oxygen mixtures above self-ignition temperatures. It is shown that this effect is more profound at low gas temperatures when the thermal production of initial radicals is not efficient. Due to O2 dissociation in the discharge phase, the influence of nonequilibrium discharge plasma on ignition is more pronounced for fuels with high activation energy of thermal dissociation (like H2 and CH4). The role of N2 in favoring plasma-assisted ignition owing to additional O2 and fuel dissociation is demonstrated.

Experimental and Kinetic Study on Ignition Delay Times of Di-n-butyl Ether at High Temperatures

Ignition delay times of di-n-butyl ether (DBE)/oxygen mixtures diluted with argon were measured behind reflected shock waves for the pressures between 1.2 and 4 bar, the temperatures between 1100 and 1570 K, and the equivalence ratios of 0.5, 1.0, and 1.5. A recently developed DBE model was employed to simulate the autoignition process of the homogeneous mixture. Comparisons between the measured and calculated ignition delay times indicate that the model yields fairly good agreement under all test conditions. Results show that the ignition delay time increases with the decrease of the pressure and the increase of the dilution ratio. The ignition delay time demonstrates a strong negative dependence upon the equivalence ratio at high temperatures, and the difference among the ignition delay times tends to decrease when the temperature is decreased. Sensitivity analysis reveals the importance of H-abstraction reactions and decomposition of α fuel radicals in the ignition process of DBE. Reaction pathway anal...

Kinetic Simulation of Combustion Process in the Combustor of the Aero-Engine

The use of detailed chemical reaction mechanisms of aviation fuels is still very limited in analyzing the combustion process concerning complex multidimensional fluid dynamics issues. In this work, a reduced chemical kinetic mechanism containing 210 elemental reactions (including 92 reversible reactions and 26 irreversible reactions) and 50 species was introduced and studied in the kinetic simulation of the ignition and combustion of n-decane (n-C10H22) at various combustion regimes. Moreover, it was validated with the experimental results obtained from both premixed flame of a flat-flame burner and n-C10H22 shock-tube ignition. The results show that the calculated ignition delay time of fuel n-C10H22 in the shock-tube under typical conditions viz. a pressure of 12 or 50 bar and corresponding equivalence ratio at 1.0 or 2.0, as well as the calculated mole fractions of the main reactants and products of fuel n-C10H22 in the premixed combustion process, agree very well with the experimental data. The combustion processes in the single flame tube of a tube annular combustor were simulated through coupling this reduced reaction mechanism of surrogate fuel n-C10H22 and one step reaction mechanism of surrogate fuel C12H23 into the computational fluid dynamics (CFD) software, and this combustion process was also experimentally studied. It is found that the reduced reaction mechanism exhibits clear advantages in simulating the combustion processes and certain species formation in the single flame tube over the one step reaction mechanism. In particular, the temperature radial distribution at the outlet of the single flame tube computed by using reduced reaction mechanism of surrogate fuel n-C10H22 is found to be more reasonable and agreed better with the experimental data than that computed by one step reaction mechanism of surrogate fuel C12H23.