Dependence Of Ignition Delay Time Research Articles

Numerical study of heat and mass transfer during ignition of thermal decomposition products of a coal particle

A numerical research was executed for macroscopic regularities determination of heat and mass transfer processes under the conditions of phase transformation and chemical reaction at the ignition of vapour coming from fabrics impregnated by typical combustible liquid into area at the local power supply. Limit conditions of heterogeneous system fabric - combustible liquid - oxidant ignition at the heating of single metal particle was established. Dependences of ignition delay time on temperature and rates of local power source were obtained. The mathematical modeling of interrelated processes of heat and mass transfer and chemical reacting was carried out at ignition of single coal particles with different sizes from 0.05 mm to 0.5 mm in air flow heated to moderate temperatures (T<500 K). A physical model of ignition process describes the more common scheme of investigating phenomena (Figure 1).

Shock-Tube Experiments and Kinetic Modeling of 2-Methylfuran Ignition at Elevated Pressure

Ignition delays of 2-methylfuran were measured behind reflected shock waves over a wide range of experimental conditions: equivalence ratios from 0.25 to 2.0, average pressures from 1.25 to 10.65 bar, temperatures from 1120 to 1700 K, and oxygen concentrations up to 20%. Results show that the ignition delay decreases with increasing the pressure and decreasing the dilution ratio. For a given dilution ratio, there exists a crossover in the ignition delay time dependence upon the equivalence ratio and the crossing point shifts to the higher temperature at a higher pressure. The measured ignition delays of 2-methylfuran show good agreement with the previous data at atmospheric pressure. The 2-methylfuran model NUI_MF2 well predicts the ignition delays of 2-methylfuran at 1.25 bar but gives the underprediction when pressures are elevated to 4.25 and 10.65 bar. Sensitivity analysis identifies the importance of the reactions involving the n-butadienyl radical (C4H5-n) in the ignition process of 2-methylfuran. Better prediction on ignition delay times is achieved by perturbing the rate constants of β-scission reactions for the C4H5-n radical, and these perturbations do not affect the primary fuel consumption flux based on the reaction pathway analysis.

Blending effects on ignition delay times of methyl octanoate/n-nonane/methylcyclohexane

Ignition delay times were measured behind reflected shock waves under highly dilute conditions (99% Ar) for 10 ternary blends of methyl octanoate, n-nonane, and methylcyclohexane (MCH), using a Design of Experiments approach, namely an L9 array. Measurements were obtained over a wide range of temperature (1258<T (K)<1630), pressure (1.5<P (atm)<9.5), and equivalence ratio (ϕ=0.5, 1.0, 2.0). The series of experiments focused on the effects of variation in relative fuel volume fractions to assess respective influence of hydrocarbon class (i.e. methyl ester, n-alkane, cycloalkane) on ignition delay times of blended fuel. The L9 array utilized for the design of the experimental test matrix led to the development of an empirical ignition delay time correlation which was then employed for a broad series of calculations examining the effects of fuel-ratio variation. Results of the calculations show that addition of methyl octanoate to blends of n-nonane and MCH lowers the power-law pressure dependence of ignition delay times of such blends (the latter two species share similar dependence on pressure). The correlation also shows MCH as the most dominant of the three fuels in the blends studied with respect to controlling ignition delay time, a finding supported by ignition delay time-sensitivity calculations. Calculation of blending effects, defined herein as deviation from neat-fuel behavior, using the correlation indicated several key features of the studied blends. First, for fixed MCH concentration in a ternary blend, correlation calculations revealed an insensitivity of ignition delay time to variation in the ratio of methyl octanoate to n-nonane for all conditions. Second, blending effects on ignition delay times depend strongly on blend composition and on experimental conditions (pressure, equivalence ratio, temperature), indicating fuel- and condition-specific complexities, although were generally more pronounced at lower temperature. Third, of the three experimental conditions varied, ignition delay times of fuel blends exhibited the most sensitivity to equivalence ratio. To support experimental results, the study also involved compilation of a detailed chemical kinetics mechanism (4815 reactions, 1082 species) by integrating pertinent reaction chemistry from two independently validated mechanisms into a base model for n-nonane oxidation from a previous study by the authors. Model-based calculations indicate that under stoichiometric conditions near 10atm, blending effects are negligible above 1350K yet become increasingly significant towards lower temperature. Lastly, to assess the importance of blending effects, ignition delay times of fuel blends measured experimentally were compared against times calculated using a linear combination method (i.e. superposition of constituent-fuel ignition delay times). In general, superposition of neat-fuel trends cannot be utilized to reproduce ignition trends of the fuel blends herein, highlighting the importance of and continued need for blended-fuel studies.

Further study on the ignition delay times of propane–hydrogen–oxygen–argon mixtures: Effect of equivalence ratio

Using a shock tube facility, measurements on ignition delay times of propane/hydrogen mixtures (hydrogen fraction XH2 is from 0% to 100%) were conducted at equivalence ratios of 0.5, 1.0 and 2.0. Results show that when XH2 is less than 70%, ignition delay time shows a strong Arrhenius temperature dependence, and the ignition delay time increases with the increase of equivalence ratio. When XH2 is larger than 95%, the ignition delay times do not retain an Arrhenius-like temperature dependence, and the effect of equivalence ratio is very weak when the hydrogen fraction is further increased. Numerical studies were made using two selected kinetic mechanisms and the results show that the predicted ignition delay times give a reasonable agreement with the measurements under all test conditions. Both measurements and predictions show that for mixtures with XH2 less than 70%, the ignition delay time is only moderately decreased with the increase of XH2, indicating that hydrogen addition has a weak effect on the ignition enhancement. Sensitivity analysis reveals the key reactions that control the simulation of ignition delay time. Further investigation of the H-atom consumption is made to interpret the ignition delay time dependence on equivalence ratio and XH2.

Measurements and kinetic study on ignition delay times of propane/hydrogen in argon diluted oxygen

Measurements on ignition delay times of propane/hydrogen mixtures in argon diluted oxygen were conducted for hydrogen fractions in the fuel mixtures (XH2) from 0 to 100%, pressures of 1.2, 4.0 and 10 atm, and temperatures from 1000 to 1600 K using the shock-tube. Results show that for XH2 less than 70%, ignition delay time shows a strong Arrhenius temperature dependence and it decreases with the increase of pressure, while for XH2 larger than 90%, there is a crossover pressure dependence of the ignition delay time with increasing temperature. Numerical studies were made using the selected kinetic mechanisms and results show that the predicted ignition delay time gives a reasonable agreement with the measurements. Both measurements and predictions show that for XH2 less than 70%, the ignition delay time is only moderately decreased with the increase of XH2, indicating that hydrogen addition has weak effect on ignition enhancement. Sensitivity analysis reveals the key reactions that control the simulation of ignition delay time. Kinetic study is made to interpret the ignition delay time dependence on pressure and XH2.

Autoignition of Methyl Decanoate, a Biodiesel Surrogate, under High-Pressure Exhaust Gas Recirculation Conditions

The autoignition of methyl decanoate, a standalone biodiesel surrogate or surrogate component, is studied under high-pressure exhaust gas recirculation (EGR) conditions relevant to internal combustion engines. Ignition delay times were determined in reflected-shock experiments using measured pressure and electronically excited OH chemiluminescence for stoichiometric methyl decanoate/air/EGR mixtures containing 0–60% EGR at 900–1300 K and 20 and 50 atm. Ignition delay time dependence upon pressure and EGR fraction was found to obey τ ∝ P–0.8 and τ ∝ (1 – EGR %/100)−1 for the conditions studied. Experimental results are compared to three comprehensive kinetic models for methyl decanoate oxidation from the recent literature: Herbinet et al. (Herbinet, O.; Pitz, W. J.; Westbrook, C. K.Combust. Flame 2008, 154, 507−528 and Herbinet, O.; Pitz, W. J.; Westbrook, C. K.Combust. Flame 2010, 157, 893–908), Glaude et al. (Glaude, P. A.; Herbinet, O.; Bax, S.; Biet, J.; Warth, V.; Battin-Leclerc, F.Combust. Flame 2010...

Ignition Delay Time and Laminar Flame Velocity for a Combined Laser–Microwave Ignition

An analysis of the ignition delay time dependence on microwave energy input time, electric field strength, and discharge energy at high-pressure conditions is presented for a combined laser-microwave ignition. The existence of a saturation power effect at high-pressure conditions is predicted. An analytical formula for a laminar flame velocity is obtained for a case of the reaction rate dependence on vibrational temperature.

Ethane ignition and oxidation behind reflected shock waves

Several diluted C 2H 6/O 2/Ar mixtures of varying concentrations and equivalence ratios ( 0.5 < ϕ < 2.0 ) were studied at temperatures between 1218 and 1860 K and at pressures between 0.57 and 3.0 atm using a shock tube. The argon dilution ranged from 91 to 98% by volume. Reaction progress was monitored using chemiluminescence emission from OH ∗ and CH ∗ at 307 and 431 nm, respectively. The dependence of ignition delay time on temperature, activation energy, and reactant concentrations is given in a master correlation of all the experimental data. The overall activation energy was found to be 39.6 kcal/mol over the range of conditions studied. For the first time in a shock-tube C 2H 6 oxidation study, detailed species profile data and quantitative OH ∗ time histories were documented, in addition to ignition delay times, and compared against modern detailed mechanisms. Because of the comprehensive scope of the present study and the high precision of the experimental data, several conclusions can be drawn that could not have been reached from earlier studies. Although there is some discrepancy among previous ethane oxidation data, the present work clearly shows the convergence of ignition delay time measurements to those herein and the remarkable accuracy of current kinetics models over most of the parameter space explored, despite the variation in the literature data. However, two areas shown to still need more measurements and better modeling are those of higher pressures and fuel-rich ethane–air mixtures. After appropriate OH ∗ and CH ∗ submechanisms are added, two modern chemical kinetics mechanisms containing high-temperature ethane chemistry are compared to the data to gauge the current state of C 2H 6 oxidation modeling over the conditions of this study. The reproduction of the OH ∗ and CH ∗ profiles, together with τ ign predictions by these models, are compared against the profiles and ignition times found in the experimental data. The models are then used to identify some key reactions in ethane oxidation and CH formation under the conditions of this study.

Shock tube ignition measurements of iso-octane/air and toluene/air at high pressures

Ignition delay times were measured in a shock tube for iso-octane/air and toluene/air at conditions similar to those found in homogeneous charge compression ignition (HCCI) engines. Initial reflected shock conditions spanned the following ranges: temperature 855–1269 K, pressure 14–59 atm, and equivalence ratios ϕ of 0.5 and 1 in synthetic air. Ignition delay times were measured using sidewall pressure via piezo-electric transducers and confirmed with OH* and CH* emission measurements. The iso-octane ignition delay times are in excellent agreement with existing measurements by Fieweger et al. [Proc. Combust. Inst. 25 (1994) 1579; Combust. Flame 109 (1997) 599] and modeling by Ogink and Golovitchev [SAE Technical Paper Series, 2001, Paper No. 2001-01-3614]. No comparable high-pressure data exist for toluene/air, and modeling by Pitz et al. [U.S. Sections of the Combustion Institute 2nd Joint Spring Meeting, 2001, Paper 253] and Dagaut et al. [Fuel 81 (2002) 173] significantly over-predicts the toluene/air ignition delay times at ϕ = 1. The large pressure range of the current measurements permits determination of the pressure dependence of ignition delay time at the temperatures and pressures of direct interest in HCCI engine simulations. Detailed examination of the pressure–time profiles shows evidence of significant pre-ignition energy release in both the iso-octane/air and toluene/air systems. Using current detailed mechanisms, the rate of this energy release is not correctly predicted either in iso-octane/air or toluene/air at temperatures above 850 K.

The Ignition and Oxidation of Tetrahydrofuran: Experiments and Kinetic Modeling

The ignition of tetrahydrofuran (THF) has been studied in a single-pulse shock tube under reflected shock wave conditions while the oxidation of THF was studied in a high-pressure jetstirred reactor (JSR). The present experiments cover a wide range of conditions: 2–10atm, 0.5≤ ≤2.0, 800–1800K. The ignition delays of THF, measured in a shock tube, have been used to propose an overall representation for the dependence of ignition delay time on the concentration of each component in the ignitable gas mixture: τall=10-14.4 exp (19590/T5)[c4h8O]0.272[O2 -0.984[AR]-0.189(units:s, mole/dm3, K). Concentration profiles of the reactants, stable intermediates and products of the oxidation of ThF were measured in a JSR. A numerical model, consisting of a detailed kinetic reaction mechanism with 484 reactions (most of them reversible) of 71 species, describes the ignition of THF in reflected shock waves and its oxidation in a jet-stirred reactor. We observed a fairly good agreement between the experimental results and the computations. Detailed kinetic modeling enabled identification of the major reaction paths and sensitive kinetic parameters.

The Ignition and Oxidation of Tetrahydropyran: Experiments and Kinetic Modeling

The ignition and the oxidation of tetrahydropyran have been studied in a single-pulse shock tube under reflected shock wave conditions, and also in a high-pressure jet-stirred reactor(JSR) These experiments cover a wide range of conditions: 2-10 atm, 0.5 ≤ 𝛗 ≤ 2.0,800- 1700 K. The ignition delays of tetrahydropyran measured in a shock tube have been used to propose an overall representation for the dependence of ignition delay time on the concentrations of each component in the ignitable gas mixture: τ all= 10−13.6 exp (15360/T5) [C5H10O] 0.0026[O2] −0.868 [Ar] 0.0274 (units: s, mole/dm3, K). Concentration profiles of the reactants, stable intermediates and products of the oxidation of tetrahydropyran were measured in a JSR. A numerical model, consisting of a detailed kinetic reaction mechanism with 507 reactions (most of them reversible) of 72 species describes the ignition of tetrahydropyran in reflected shock waves and its oxidation in a jetstirred reactor. A fairly good agreement between the experimental results and the model was observed. Detailed kinetic modeling identified the major reaction paths.

The ignition of oxetane in shock waves and oxidation in a jet-stirred reactor: An experimental and kinetic modeling study

The ignition and oxidation of oxetane have been studied in a single-pulse shock tube under reflected shock wave conditions and also in a jet-stirred reactor (JSR). These experiments cover a wide range of conditions: 1–10 atm, 0.5 ≤ φ ≤ 2.0, 800–1780 K. The ignition delays of oxetane measured in a shock tube have been used to propose an overall dependence of ignition delay time on the concentrations of each component in the gas as: τ = 10 −13.5 exp( 13389 T 5 )[C 3H 6O] −0.36[O 2] −0.59[Ar] 0.088 (units: seconds, moles per cubic decimeters, and Kelvin). Concentration profiles of the reactants, intermediates, and products of the oxidation of oxetane were measured in a JSR. A numerical model, consisting of a detailed kinetic reaction mechanism with 423 reactions (most of them reversible) of 63 species describes the ignition of oxetane in reflected shock waves and its oxidation in a jet-stirred reactor. Fairly good agreement between the observations and the model was obtained. The major reaction paths have been identified through detailed kinetic modeling.

Convective combustion of ordered porous structures

The authors study the ignition and convective combustion kinetics of a powdered condensed solid fuel in an ordered planar grid of capillary channels with diffusion into the channels of incandescent combustion products. Their results indicate that conditions for stable ignition of the grid depend primarily on pressure, the channel cross sectional area, and the total channel volume. Ignition and combustion were photographed; a full description of the combustion chamber used in the experiment is given. They conclude that an explanation of the strong reciprocal dependence of ignition delay time on channel size in a range less than 0.06 square mm. will require further experimentation.

Chemical aspects of the autoignition of hydrocarbonair mixtures

Some aspects of the chemistry of knock in internal combustion engines have been examined within the context of a model of autoignition of hydrocarbonair mixtures at high pressure. The basic model follows an earlier one developed by workers at Shell Research Ltd., which has been refined and extended using reactions and rate parameters which are compatible with the expanding body of kinetics information on the type of elementary processes involved. This model was able to predict moderately well the temperature, fuel, and O 2 dependence of ignition delay time observed in previous experiments in a rapid compression machine, thus providing further support for the validity of the knock mechanisms. Fuel-structure dependent parameters were identified, and first indications of a rational basis for the stability ranking of alkane fuels with respect to autoignition have been found.