Shock Tube Ignition Delay Times Research Articles

Laminar flame speeds of pentanol isomers: An experimental and modeling study

Long chain alcohols such as 1- and iso-pentanol are foreseen as a suitable replacement for ethanol, due to more favorable physical properties (higher energy density, higher boiling point and lower hygroscopicity). The present study presents high accuracy laminar flame speed measurements for iso-pentanol/air and 1-pentanol/air mixtures, at initial temperatures of 353 K, 433 K and 473 K, 1 bar pressure and equivalence ratios ranging from 0.7 to 1.5. Comparisons with previous measurements from the literature are also presented and the observed deviations are discussed in detail. The updated kinetic mechanism for alcohols combustion from the CRECK group at Politecnico di Milano is discussed and used for modeling purposes. For a more complete validation of the oxidation mechanism at high temperature conditions, modeling results are also compared with shock tube ignition delay times from the literature. This study extends the presently sparse and uncertain experimental database for high molecular weight alcohols oxidation in laminar flames, providing high accuracy and reliable experimental data of use for alcohols oxidation mechanism development and improvement.

Shock tube ignition delay times and methane time-histories measurements during excess CO2 diluted oxy-methane combustion

The combustion of methane in air results in large amounts of CO2 and NOX emissions. In order to reduce the NOX emissions, one possible solution is the oxy-methane combustion with large CO2 dilution so that the combustion products can be reduced mainly to CO2 and H2O. However, there are very few studies on the chemical kinetics of oxy-methane combustion in a CO2 diluted environment. In this study, methane time-histories, CH* emission profiles, and pressure time-histories measurements were conducted behind reflected shock waves to gain insight into the effects of CO2 dilution of the gas mixtures on the ignition of methane. The measurements were carried out for mixtures of CH4, CO2 and O2 in argon bath gas at temperatures of 1577–2144 K, pressures of 0.53–4.4 atm, equivalence ratios (Φ) of 0.5, 1, and 2, and CO2 mole fractions (XCO2) of 0, 30, and 60%. The laser absorption measurements were conducted using a continuous wave distributed feedback interband cascade laser (DFB ICL) centered at 3403.4 nm. The results showed the decrease of activation energy and the increase of ignition delay time as the amount of CO2 dilution was increased. However, the changes were minor and within the experimental uncertainties of the measurements. Also, the results were compared to the predictions of two different natural gas mechanisms: GRI 3.0 and AramcoMech 1.3 mechanisms. In general the predictions were reasonable when compared to the experimental data; however, there were discrepancies at some conditions. Three different influences of CO2 addition to the argon bath gas in regards to chemistry, collision efficiencies, and heat capacities were examined. In addition, the present study included experimentally obtained correlations for absorption cross sections of methane for its P(8) line in the v3 band in argon bath gas with and without carbon-dioxide dilutions at temperatures between 1200 < T < 2000 K and pressures between 0.7 < P < 1.2 atm.

Comparison Between RCCE and Shock Tube Ignition Delay Times at Low Temperatures

The rate-controlled constrained-equilibrium (RCCE) method is a reduction technique based on local maximization of entropy or minimization of a relevant free energy at any time during the nonequilibrium evolution of the system subject to a set of kinetic constraints. In this paper, RCCE has been used to predict ignition delay times of low temperatures methane/air mixtures in shock tube. A new thermodynamic model along with RCCE kinetics has been developed to model thermodynamic states of the mixture in the shock tube. Results are in excellent agreement with experimental measurements.

Development of a skeletal multi-component fuel reaction mechanism based on decoupling methodology

A new coupled bio-diesel surrogate and primary reference fuel (PRF) oxidation skeletal mechanism has been developed. The bio-diesel surrogate sub-mechanism consists of oxidation sub-mechanisms of Methyl decanoate (MD), Methyl 9-decenoate (MD9D) and n-Heptane fuel components. The MD and MD9D are chosen to represent the saturated and unsaturated methyl esters respectively in bio-diesel fuels. Then, a reduced iso-Octane oxidation sub-mechanism is added to the bio-diesel surrogate sub-mechanism. Then, all the sub-mechanisms are integrated to a reduced C2–C3 mechanism, detailed H2/CO/C1 mechanism and reduced NOx mechanism based on decoupling methodology. The final mechanism consisted of 68 species and 183 reactions. The mechanism was well validated with shock-tube ignition delay times, laminar flame speed and 3D engine simulations.

Mixed butanols addition to gasoline surrogates: Shock tube ignition delay time measurements and chemical kinetic modeling

The demand for fuels with high anti-knock quality has historically been rising, and will continue to increase with the development of downsized and turbocharged spark-ignition engines. Butanol isomers, such as 2-butanol and tert-butanol, have high octane ratings (RON of 105 and 107, respectively), and thus mixed butanols (68.8% by volume of 2-butanol and 31.2% by volume of tert-butanol) can be added to the conventional petroleum-derived gasoline fuels to improve octane performance. In the present work, the effect of mixed butanols addition to gasoline surrogates has been investigated in a high-pressure shock tube facility. The ignition delay times of mixed butanols stoichiometric mixtures were measured at 20 and 40 bar over a temperature range of 800–1200 K. Next, 10 vol% and 20 vol% of mixed butanols (MB) were blended with two different toluene/n-heptane/iso-octane (TPRF) fuel blends having octane ratings of RON 90/MON 81.7 and RON 84.6/MON 79.3. These MB/TPRF mixtures were investigated in the shock tube conditions similar to those mentioned above. A chemical kinetic model was developed to simulate the low- and high-temperature oxidation of mixed butanols and MB/TPRF blends. The proposed model is in good agreement with the experimental data with some deviations at low temperatures. The effect of mixed butanols addition to TPRFs is marginal when examining the ignition delay times at high temperatures. However, when extended to lower temperatures (T < 850 K), the model shows that the mixed butanols addition to TPRFs causes the ignition delay times to increase and hence behaves like an octane booster at engine-like conditions.

Experimental and kinetic modeling study of the shock tube ignition of a large oxygenated fuel: Tri-propylene glycol mono-methyl ether

Tri-propylene glycol monomethyl ether (TPGME) is an important oxygenated fuel additive that can be used to reduce soot in diesel engines. However, a validated chemical kinetic model that incorporates the low- to high-temperature chemistry, needed to simulate ignition in a diesel engine is not available for TPGME. In addition, no fundamental experimental data are available that can be used to validate a TPGME mechanism. In this study, a surrogate chemical kinetic model for TPGME that includes low- and high-temperature chemistry has been developed, and shock tube ignition delay time data has been acquired for its validation at 0.25% TPGME for temperatures in the range of 980–1545K, at pressures of 10 and 20atm, and at equivalence ratios of φ=0.5, 1.0 and 2.0. The predictions from the model have been compared to the experimental measurements with good agreement. Under the experimental conditions investigated in the shock tube, TPGME was found to be consumed by molecular elimination reactions and also H-atom abstraction by Ḣ atoms and by ȮH and HȮ2 radicals. In performing sensitivity analyses it was found that the ignition of TPGME is most sensitive to reactions involving propene. Considering how the sensitivity analyses change with pressure, the most sensitive reactions involved Ḣ atoms at 10atm and HȮ2 radicals at 20atm. With respect to the effect of equivalence ratio, reactions involving Ḣ atoms are relatively more sensitive under fuel-rich conditions while those involving HȮ2 radicals are relatively more sensitive under fuel-lean conditions. Further experimental work is needed to enable validation of the model under low-temperature conditions. TPGME was compared to n-heptane which has similar ignition properties based on Cetane Number. Predictions showed that TPGME has a higher overall reactivity compared to n-heptane. In addition, TPGME is shown to produce significantly less soot precursor species when TPGME predictions are compared to n-heptane.

A comprehensive experimental and modeling study of 2-methylbutanol combustion

2-Methylbutanol (2-methyl-1-butanol) is one of several next-generation biofuels that can be used as an alternative fuel or blending component for combustion engines. This paper presents new experimental data for 2-methylbutanol, including ignition delay times in a high-pressure shock tube and premixed laminar flame speeds in a constant volume combustion vessel. Shock tube ignition delay times were measured for 2-methylbutanol/air mixtures at three equivalence ratios, temperatures ranging from 750 to 1250K, and at nominal pressures near 20 and 40bar. Laminar flame speed data were obtained using the spherically propagating premixed flame configuration at pressures of 1, 2, and 5bar. A detailed chemical kinetic model for 2-methylbutanol oxidation was developed including high- and low-temperature chemistry based on previous modeling studies on butanol and pentanol isomers. The proposed model was tested against new and existing experimental data at pressures of 1–40atm, temperatures of 740–1636K, equivalence ratios of 0.25–2.0. Reaction path and sensitivity analyses were conducted for identifying key reactions at various combustion conditions, and to obtain better understanding of the combustion characteristics of larger alcohols.

On the Rational Interpretation of Data on Laminar Flame Speeds and Ignition Delay Times

This article examines a seemingly trivial issue, namely, the apparently large scatter found for the laminar flame speeds of fuel-rich mixtures as compared to those of lean mixtures. Using the hydrogen/air flame speed at atmospheric pressure as an example, it is demonstrated that this perceptive notion is based on rather uninformed data presentation. It is shown that the cause for the notion has little to do with the data itself, but it is the result that the flame speed data are customarily plotted against the equivalence ratio, which by its asymmetric definition, compresses the data for lean mixtures and expands the data for rich ones. When plotting the flame speed against the symmetrized equivalence ratio defined as ≡ φ/(1 + φ), it can be readily shown that the flame speed data have, in fact, similar uncertainties across the entire range of stoichiometric mixtures tested thus far. A statistical analysis of an extensive set of flame speed data further illustrates the above point, namely, a nearly invariant confidence interval across the same range of stoichiometry. The aforementioned result, coupled with a similar statistical analysis performed for a representative set of shock-tube ignition delay time, highlights the importance of the systematic treatment of the uncertainty in these global, yet fundamental combustion property measurements in aiding reaction model development and testing. For this purpose, an impact factor is proposed for combustion experiments, by combining the sensitivity of the response to rate parameters with the inherent uncertainty of the experiment. It is demonstrated that with the exception of some extreme cases, the impact factors of the flame speed and shock tube ignition delay data are quite close to each other, making both indispensable for model testing. Overall the study illustrates that as a quantitative science, fundamental combustion property measurements must consider inherent experimental uncertainty and require a careful analysis of the uncertainty in order to yield useful results.

Experimental and kinetic modeling study of the low- and intermediate-temperature oxidation of dimethyl ether

Recent experiments on low-temperature oxidation of dimethyl ether (DME) at atmospheric pressure reveal much lower fuel conversion than the predictions of all published models. Consistent with previous measurements, the present work on DME oxidation in a laminar flow reactor between 400 and 1160K at atmospheric pressure also confirmed this behavior. To reduce the gap between model predictions and experimental results, both regarding key oxygenated species and fuel conversion, an extended and updated kinetic model of DME oxidation was developed from the widely used model of Z. Zhao, M. Chaos, A. Kazakov, F.L. Dryer, Int. J. Chem. Kinet. 40 (2008) 1–18. The development of the model focused on the reaction sequences that affect the low-temperature oxidation reactivity. In particular, the reactivity of DME oxidation in the low-temperature regime and at atmospheric pressure can now be predicted. This is possible upon the inclusion of an additional, chemically-activated pathway of CH3OCH2 reaction with O2, as well as of the new decomposition chemistry of OCH2OCHO radical, investigated theoretically in this work. The present model was examined against species concentrations in DME oxidation from low to intermediate temperatures and shock tube ignition delay times. It shows satisfactory performance in reproducing the respective literature data.

An ignition delay and kinetic modeling study of methane, dimethyl ether, and their mixtures at high pressures

The development of accurate chemical kinetic models capable of predicting the combustion of methane and dimethyl ether in common combustion environments such as compression ignition engines and gas turbines is important as it provides valuable data and understanding of these fuels under conditions that are difficult and expensive to study in the real combustors. In this work, both experimental and chemical kinetic model-predicted ignition delay time data are provided covering a range of conditions relevant to gas turbine environments (T=600–1600K, p=7–41atm, ϕ=0.3, 0.5, 1.0, and 2.0 in ‘air’ mixtures). The detailed chemical kinetic model (Mech_56.54) is capable of accurately predicting this wide range of data, and it is the first mechanism to incorporate high-level rate constant measurements and calculations where available for the reactions of DME. This mechanism is also the first to apply a pressure-dependent treatment to the low-temperature reactions of DME. It has been validated using available literature data including flow reactor, jet-stirred reactor, shock-tube ignition delay times, shock-tube speciation, flame speed, and flame speciation data. New ignition delay time measurements are presented for methane, dimethyl ether, and their mixtures; these data were obtained using three different shock tubes and a rapid compression machine. In addition to the DME/CH4 blends, high-pressure data for pure DME and pure methane were also obtained. Where possible, the new data were compared with existing data from the literature, with good agreement.

Ignition of alkane-rich FACE gasoline fuels and their surrogate mixtures

Petroleum derived gasoline is the most used transportation fuel for light-duty vehicles. In order to better understand gasoline combustion, this study investigated the ignition propensity of two alkane-rich FACE (Fuels for Advanced Combustion Engines) gasoline test fuels and their corresponding PRF (primary reference fuel) blend in fundamental combustion experiments. Shock tube ignition delay times were measured in two separate facilities at pressures of 10, 20, and 40bar, temperatures from 715 to 1500K, and two equivalence ratios. Rapid compression machine ignition delay times were measured for fuel/air mixtures at pressures of 20 and 40bar, temperatures from 632 to 745K, and two equivalence ratios. Detailed hydrocarbon analysis was also performed on the FACE gasoline fuels, and the results were used to formulate multi-component gasoline surrogate mixtures. Detailed chemical kinetic modeling results are presented herein to provide insights into the relevance of utilizing PRF and multi-component surrogate mixtures to reproduce the ignition behavior of the alkane-rich FACE gasoline fuels. The two FACE gasoline fuels and their corresponding PRF mixture displayed similar ignition behavior at intermediate and high temperatures, but differences were observed at low temperatures. These trends were mimicked by corresponding surrogate mixture models, except for the amount of heat release in the first stage of a two-stage ignition events, when observed.

Constrained-Equilibrium Modeling of Methane Oxidation in Air

Rate-controlled constrained-equilibrium method has been further developed to model methane/air combustion. A set of constraints has been identified to predict the nonequilibrium evolution of the combustion process. The set predicts the ignition delay times of the corresponding detailed kinetic model to within 10% of accuracy over a wide range of initial temperatures (900 K–1200 K), initial pressures (1 atm–50 atm) and equivalence ratios (0.6–1.2). It also predicts the experimental shock tube ignition delay times favorably well. Direct integration of the rate equations for the constraint potentials has been employed. Once the values of the potentials are obtained, the concentration of all species can be calculated. The underlying detailed kinetic model involves 352 reactions among 60 H/O/N/C1-2 species, hence 60 rate equations, while the RCCE calculations involve 16 total constraints, thus 16 total rate equations. Nonetheless, the constrained-equilibrium concentrations of all 60 species are calculated at any time step subject to the 16 constraints.

Assessment of Chemical Kinetic Modeling for Silane/Hydrogen Mixtures in Hypersonic Applications

An assessment of the ignition characteristics of several silane/hydrogen combustion models under conditions that are relevant to hypersonic combustion applications is presented. Numerical predictions of silane/hydrogen ignition characteristics are compared to experimental measurements of explosion limits and shock-tube ignition delay times. Furthermore, the ignition properties of silane/hydrogen mixtures are evaluated at conditions extracted from representative streamlines calculated in a computational-fluid-dynamics simulation of a model scramjet configuration tested at the Alliant Techsystems/General Applied Science Laboratory at Mach 10. It is found that the analyzed silane chemical kinetic models are extremely sensitive to temperature and pressure at key combustor conditions. Moreover, the presence of many inconsistencies between experiments and chemical models show that the current knowledge of silane combustion pathways is not sufficient to perform accurate computational-fluid-dynamics simulations of hypersonic combustors. The uncertainties associated with many silane/hydrogen experiments suggest that new accurate measurements at relevant conditions are needed to improve the predictive properties of silane models.

Global Reduced Model for Conventional and Alternative Jet and Diesel Fuel Autoignition

A global reduced model for the autoignition of conventional petroleum-derived and alternative, hydroprocessed and Fischer–Tropsch, jet and diesel fuels is presented. The model is based on a seven-step model from the literature (Zheng, J.; Miller, D. L.; Cernansky, N. P. A Global Reaction Model for the HCCI Combustion Process, SAE Paper 2004-01-2950, 2004) and includes steps to predict oxidation and autoignition in the three temperature regimes of interest to engine applications, the high-, low-, and negative-temperature-coefficient (NTC) regimes. Here we have included dependence of reaction rate parameters on the derived cetane number (DCN) to predict the influence of fuel variability on autoignition and optimized the reduced model to best fit target shock tube ignition delay time data for jet and diesel fuels. The standard deviation between model predictions for ignition delay and the target shock tube data set is ±21% and the model captures all experimental trends for ignition delay variation with DCN, temperature, pressure, and fuel–air equivalence ratio in all temperature regimes. Comparisons to experimental ignition delay time data not contained in the target data set show model–experiment deviation similar to the comparisons with the target data, with global standard deviation of ±20–30% and differences of at most a factor of 2. The model comparisons with shock tube data suggest that the model is suitable for autoignition prediction for fuels containing large quantities of aliphatic compounds with DCN = 30–80 for 650–1300 K, 8–80 atm, and fuel–air equivalence ratios of 0.25–1.5.

Ignition delay times of very-low-vapor-pressure biodiesel surrogates behind reflected shock waves

Ignition delay times for a variety of low-vapor-pressure biodiesel surrogates were measured behind reflected shock waves, using an aerosol shock tube. These fuels included methyl decanoate (C11H22O2), methyl laurate (C13H26O2), methyl myristate (C15H30O2), methyl palmitate (C17H34O2), and a methyl oleate (C19H36O2)/Fatty Acid Methyl Ester (FAME) blend. Experiments were conducted in 4% oxygen/argon mixtures with the exception of methyl decanoate which was studied in 1% and 21% oxygen/argon blends. Reflected shock conditions covered initial temperatures from 1026 to 1388K, pressures of 3.5 and 7.0atm, and equivalence ratios from 0.3 to 1.4. Arrhenius expressions describing the experimental ignition delay time data are given and compared to those derived from applicable mechanisms available in the literature. Graphical comparisons between experimental data and mechanism predictions are also provided. Experiments of methyl laurate, methyl myristate, and methyl palmitate represent the first shock tube ignition delay time measurements for these fuels. Finally, experiments with methyl palmitate represent, to the authors’ knowledge, the first neat fuel/oxidizer/diluent gas-phase shock tube experiments involving a fuel which is a waxy solid at room temperature.

A shock tube and laser absorption study of ignition delay times and OH reaction rates of ketones: 2-Butanone and 3-buten-2-one

Ketones are potential biofuel candidates and are also formed as intermediate products during the oxidation of large hydrocarbons or oxygenated fuels, such as alcohols and esters. This paper presents shock tube ignition delay times and OH reaction rates of 2-butanone (C2H5COCH3) and 3-buten-2-one (C2H3COCH3). Ignition delay measurements were carried out over temperatures of 1100–1400K, pressures of 3–6.5atm, and at equivalence ratios (Ф) of 0.5 and 1. Ignition delay times were monitored using two different techniques: pressure time history and OH absorption near 306nm. The reaction rates of hydroxyl radicals (OH) with these two ketones were measured over the temperature range of 950–1400K near 1.5atm. The OH profiles were monitored by the narrow-line-width ring-dye laser absorption of the well-characterized R1(5) line in the OH A–X (0, 0) band near 306.69nm. We found that the ignition delay times of 2-butanone and 3-buten-2-one mixtures scale with pressure as P−0.42 and P−0.52, respectively. The ignition delay times of 3-buten-2-one were longer than that of 2-butanone for stoichiometric mixtures, however, for lean mixtures (Ф=0.5), 2-butanone had longer ignition delay times. The chemical kinetic mechanism of Serinyel et al. [1] over-predicted the ignition delay times of 2-butanone at all tested conditions, however, the discrepancies were smaller at higher pressures. The mechanism was updated with recent rate measurements to decrease discrepancy with the experimental data. A detailed chemistry for the oxidation of 3-buten-2-one was developed using rate estimation method and reasonable agreements were obtained with the measured ignition delay data. The measured reaction rate of 2-butanone with OH agreed well with the literature data, while we present the first high-temperature measurements for the reaction of OH with 3-buten-2-one. The following Arrhenius expressions are suggested over the temperature range of 950–1450K: kC2H5COCH3+OH=6.78×1013exp(-2534/T)cm3mol-1s-1kC2H3COCH3+OH=4.17×1013exp(-2350/T)cm3mol-1s-1

A comprehensive experimental and modeling study of iso-pentanol combustion

Biofuels are considered as potentially attractive alternative fuels that can reduce greenhouse gas and pollutant emissions. iso-Pentanol is one of several next-generation biofuels that can be used as an alternative fuel in combustion engines. In the present study, new experimental data for iso-pentanol in shock tube, rapid compression machine, jet stirred reactor, and counterflow diffusion flame are presented. Shock tube ignition delay times were measured for iso-pentanol/air mixtures at three equivalence ratios, temperatures ranging from 819 to 1252K, and at nominal pressures near 40 and 60bar. Jet stirred reactor experiments are reported at 5atm and five equivalence ratios. Rapid compression machine ignition delay data was obtained near 40bar, for three equivalence ratios, and temperatures below 800K. Laminar flame speed data and non-premixed extinction strain rates were obtained using the counterflow configuration. A detailed chemical kinetic model for iso-pentanol oxidation was developed including high- and low-temperature chemistry for a better understanding of the combustion characteristics of higher alcohols. First, bond dissociation energies were calculated using ab initio methods, and the proposed rate constants were based on a previously presented model for butanol isomers and n-pentanol. The model was validated against new and existing experimental data at pressures of 1–60atm, temperatures of 650–1500K, equivalence ratios of 0.25–4.0, and covering both premixed and non-premixed environments. The method of direct relation graph (DRG) with expert knowledge (DRGX) was employed to eliminate unimportant species and reactions in the detailed mechanism, and the resulting skeletal mechanism was used to predict non-premixed flames. In addition, reaction path and temperature A-factor sensitivity analyses were conducted for identifying key reactions at various combustion conditions.

An experimental and modeling study of the low- and high-temperature oxidation of cyclohexane

The experimental study of the oxidation of cyclohexane has been performed in a jet-stirred reactor at temperatures ranging from 500 to 1100K (low- and intermediate temperature zones including the negative temperature-coefficient area), at a residence time of 2s and for dilute mixtures with equivalence ratios of 0.5, 1, and 2. Experiments were carried out at quasi-atmospheric pressure (1.07bar). The fuel and reaction product mole fractions were measured using online gas chromatography. A total of 34 reaction products have been detected and quantified in this study. Typical reaction products formed in the low-temperature oxidation of cyclohexane include cyclic ethers (1,2-epoxycyclohexane and 1,4-epoxycyclohexane), 5-hexenal (formed from the rapid decomposition of 1,3-epoxycyclohexane), cyclohexanone, and cyclohexene, as well as benzene and phenol. Cyclohexane displays high low-temperature reactivity with well-marked negative temperature-coefficient (NTC) behavior at equivalence ratios 0.5 and 1. The fuel-rich system (ϕ=2) is much less reactive in the same region and exhibits no NTC. To the best of our knowledge, this is the first jet-stirred reactor study to report NTC in cyclohexane oxidation. Laminar burning velocities were also measured by the heated burner method at initial gas temperatures of 298, 358, and 398K and at 1atm. The laminar burning velocity values peak at ϕ=1.1 and are measured as 40 and 63.1cm/s for Ti=298 and 398K, respectively. An updated detailed chemical kinetic model including low-temperature pathways was used to simulate the present (jet-stirred reactor and laminar burning velocity) and literature experimental (laminar burning velocity, rapid compression machine, and shock tube ignition delay times) data. Reasonable agreement is observed with most of the products observed in our reactor, as well as the literature experimental data considered in this paper.

Shock Tube and Chemical Kinetic Modeling Study of the Oxidation of 2,5-Dimethylfuran

A detailed kinetic model describing the oxidation of 2,5-dimethylfuran (DMF), a potential second-generation biofuel, is proposed. The kinetic model is based upon quantum chemical calculations for the initial DMF consumption reactions and important reactions of intermediates. The model is validated by comparison to new DMF shock tube ignition delay time measurements (over the temperature range 1300-1831 K and at nominal pressures of 1 and 4 bar) and the DMF pyrolysis speciation measurements of Lifshitz et al. [ J. Phys. Chem. A 1998 , 102 ( 52 ), 10655 - 10670 ]. Globally, modeling predictions are in good agreement with the considered experimental targets. In particular, ignition delay times are predicted well by the new model, with model-experiment deviations of at most a factor of 2, and DMF pyrolysis conversion is predicted well, to within experimental scatter of the Lifshitz et al. data. Additionally, comparisons of measured and model predicted pyrolysis speciation provides validation of theoretically calculated channels for the oxidation of DMF. Sensitivity and reaction flux analyses highlight important reactions as well as the primary reaction pathways responsible for the decomposition of DMF and formation and destruction of key intermediate and product species.

Experimental and modeling study on the oxidation of Jet A and the n-dodecane/iso-octane/n-propylbenzene/1,3,5-trimethylbenzene surrogate fuel

Jet A POSF 4658 and n-dodecane/iso-octane/n-propylbenzene/1,3,5-trimethylbenzene (2nd generation surrogate) oxidation experiments were conducted in a shock tube at high pressures and at fuel lean and rich conditions to verify if the formulated surrogate fuel emulates the combustion characteristics of the jet fuel. A model was developed for the 2nd generation surrogate using an existing 1st generation surrogate model (consisting of n-decane/iso-octane/toluene) as the base model and sub-models for n-propylbenzene and 1,3,5-trimethylbenzene were included from the literature. The experimental work on both the Jet A and 2nd generation surrogate was performed in a heated high-pressure single pulse shock tube at equivalence ratios of 0.46, 1.86 and 0.47, 1.85, respectively. Experimental data were obtained over the temperature range of 879–1733K, a pressure range of 16–27atm, and reaction times from 1.34 to 3.36ms. The mole fractions of the stable species were determined using gas chromatography and mass spectroscopy. Comparing the Jet A and the 2nd generation surrogate experiments showed that the surrogate fuel emulates the decay of O2, and the formation of CO, CO2, and C1–C3 intermediate species within experimental errors. The modeling results of the 2nd generation surrogate model compared against the experimental data showed good agreement with the mole fractions of CO, CO2, C1–C3 intermediate species and the decay of the surrogate fuel and oxygen. Comparison of the modeling results for O2 decay to the 2nd generation surrogate experiments and pure 1,3,5-trimethylbenzene oxidation experiments revealed that the surrogate fuel model is capable of predicting O2 decay with a greater degree of accuracy in the 2nd generation surrogate experiments than in that of pure 1,3,5-trimethylbenzene experiments. This suggests that the radical pool formed due to the non-aromatics species during the consumption of 2nd generation surrogate fuel components prior to the formation of CO and CO2 could contribute to the initial decay of O2 at lower temperatures and thereby results in better prediction by the model, which includes both non-aromatics and aromatics chemistry, of O2 decay and formation of CO and CO2. Flow reactor simulations of the 2nd generation surrogate fuel experiments showed the surrogate model captures the overall trends of the decay of O2 and the formation of CO, CO2, and H2O. Additionally, simulated shock tube ignition delay times above 750K were within a factor of two when compared to experimental ignition delay times.