Ignition Delay Times Of Mixtures Research Articles

Jet ignition characteristics of ammonia-hydrogen passive pre-chamber: Emphasis on equivalence ratio and hydrogen/ammonia ratio

Ammonia-hydrogen blend fuels offer the potential for zero-carbon emissions in internal combustion (IC) engines. To improve combustion performance, considerable attention has been focused on pre-chamber jet ignition technologies. Passive pre-chamber featuring a simple structure can be installed in the spark plug hole without modifying the cylinder head. However, the jet ignition characteristics of ammonia-hydrogen passive pre-chambers are not fully understood, and there is a lack of visualized evidence on how critical parameters (e.g., equivalence ratio and hydrogen/ammonia ratio) impact ignition processes. This work investigated the effects of equivalence ratio and hydrogen/ammonia ratio on ammonia-hydrogen jet ignition characteristics in a rapid compression machine with passive pre-chamber. High-speed photography and instantaneous pressure acquisition were employed to capture detailed ignition and combustion evolutions. Results show that under low hydrogen/ammonia ratio conditions, there exists a combustion regime with noticeable fluctuations in jet penetration, indicating degenerate ignition performance. As the hydrogen/ammonia ratio increases from 0 % to 20 %, the ignition delay time of mixtures in the main chamber is reduced by 70 %, suggesting an improved overall ignition performance. Regarding the equivalence ratio, more pronounced effects on jet ignition and flame propagation are identified under lean-burning conditions. For mixtures at the hydrogen/ammonia ratio of 20 %, as the equivalence ratio increases from 0.6 to 0.8 and from 0.8 to 1.0, the decay rates for 10 %–90 % combustion duration are 82.5 % and 20.6 %, respectively. Besides, with the increase of equivalence ratio, flame initiation is shifted from the jet head to the side surface. The role of hydrogen/ammonia ratio and equivalence ratio is different, with the former modifying mixture reactivity while the latter affecting ignition energy.

Influence of the Composition and Particle Sizes of the Fuel Mixture of Coal and Biomass on the Ignition and Combustion Characteristics

The work determines the characteristics of the processes of thermal decomposition and combustion when heating coal, cedar needles, and their mixtures with different fuel particle sizes. Based on the results of thermal analysis, the following characteristics were determined: the temperature at which the coke residue ignition occurs, the temperature at which the combustion process is completed, and the combustion index. An analysis was carried out of the interaction between the fuel mixture components on the characteristics of their combustion for compositions (50% coal and 50% biomass) with a particle size of 100–200 μm and 300–400 μm. The combustion kinetic parameters of individual solid fuels and their mixtures containing 50% coal and 50% biomass are compared. The activation energy for coal combustion was 60.3 kJ mol−1, for biomass 24.6 kJ mol−1, and for mixture 42.5 kJ mol−1. The co-combustion of coal and biomass has a positive effect on the main combustion characteristics of solid fuels. Fuels with particle sizes of 100–200, 200–300, and 300–400 μm were studied at temperatures of 500–800 °C under heating conditions in a heated airflow. Using a hardware-software complex for high-speed video recording of fast processes, the ignition delay times were determined, the values of which for the considered fuels vary in the range from 0.01 to 0.20 s. Adding 50 wt% biomass with particle sizes of 100–200, 200–300, and 300–400 μm to coal reduces the ignition delay times of mixtures by 55, 41, and 27%, respectively. The results obtained can become the basis for the conversion and design of modern power plants operating on solid fuel mixtures to co-combust coal with biomass.

Scaling-effect of explosion in H2/CH4/air mixtures

The scaling-effect of mixture explosion is an unresolved issue in explosion science. In this work, we carry out experimental measurements of explosion characteristics using hydrogen/methane/air (H2/CH4/air) mixtures in two tubes with lengths of 1.5 m and 60 m. The explosion overpressure of the mixtures increases exponentially with hydrogen mole fractions in the small tube, as expected. In contrast, explosion overpressure increases rapidly, causing detonation when hydrogen is added to the mixtures. Comparing measurements in both tubes, the explosion overpressure exhibits a clear scaling-effect dependence on the tube size. The scaling-effect cannot be explained by the aspect ratio (AR) of the tube. The analysis of the hotspot size, which is correlated with the ignition delay time of mixtures, is the critical factor governing the scaling-effect of explosion seen in a large tube.

Investigation of a High Karlovitz, High Pressure Premixed Jet Flame with Heat Losses by LES

ABSTRACT Large-eddy simulations (LES) are presented for a lean preheated high pressure jet flame experiment for which detailed in situ data is available, using a finite rate chemistry (FRC) approach in a gas-turbine model combustor at high Karlovitz number. The impact of the different combustion models on the flame stabilization in the simulation is investigated and the predicted carbon monoxide (CO) and nitric oxide (NO x ) emissions are analyzed. For the FRC approach, the DRM19 reaction mechanism and a new inhouse skeletal mechanism are applied. The more detailed DRM19 mechanism is extended to include OH* species, the new skeletal mechanism includes CO and NO x reaction paths. An industry relevant tabulated chemistry approach is assessed on the ability to predict this lifted flame, where the flamelet tables are calculated from the detailed GRI-3.0 reaction mechanism. A dynamic thickened flame approach is applied to resolve the flame on the numerical grid including a model for the turbulence chemistry interaction. Adiabatic and non-adiabatic simulations are compared, where the impact of heat losses due to chamber cooling and thermal radiation are considered. Velocities, temperatures, fuel mass fractions and CO and NO x mass fractions at different axial locations are in good agreement to the experiments when heat losses are considered. The significant flame lift was correctly predicted by the FRC approach with DRM19 chemistry when non-adiabatic boundary conditions were applied. This provides evidence that the flame is stabilized by flame propagation assisted by auto ignition and that ignition-delay times of mixtures composed of fresh and burnt gases need to be captured by the applied models.

Shock Tube and Kinetic Study on the Effects of CO2 on Dimethyl Ether Autoignition at High Pressures

First-stage and overall ignition delay times of dimethyl ether (DME) were measured in a high-pressure shock tube for various mixtures containing high amounts of CO2. The data are available for DME/air mixtures diluted with 40% CO2 as well as for the mixture of DME and oxidizer containing 20.5% O2 and 79.5% CO2. As a reference, data were also collected for mixtures containing the corresponding amounts of N2. Measurements were conducted for pressures of 15, 35, and 50 bar and a range of temperatures (744–1316 K). For the DME/air mixture diluted with CO2, the equivalence ratio was varied in the range of 0.5–2.0. The results demonstrate that CO2 dilution has a strong effect on ignition delay times in the NTC (negative temperature coefficient) region. The kinetic study that was conducted showed that this phenomenon can be attributed to a thermal effect resulting from the high heat capacity of CO2. In low and high temperature ranges, the effect of CO2 is less pronounced. Additionally, a chemical effect was identified. At high temperatures this effect can be attributed mostly to the influence of CO2 on third-body reactions and leads to slight acceleration of ignition. Various chemical-kinetic models available were evaluated with respect to their accuracy in prediction of ignition delay times for mixtures containing DME and large amounts of CO2.

Shock-tube studies of Sarin surrogates

To further refine the existing high-temperature combustion chemistry mechanisms of Sarin surrogates or to develop new ones, the ignition delay times of mixtures containing various Sarin surrogates have been studied in the authors’ laboratory, namely dimethyl-methylphosphonate, diethyl-methylphosphonate (DEMP), and triethylphosphate, and the results are compared for the first time herein. They were each measured in a heated shock tube, with the DEMP-related ignition delay times being the new data reported in this paper. The Sarin surrogates were studied in neat mixtures with oxygen or seeded to baseline mixtures of hydrogen or methane at around 1.5 atm. Noticeable differences were observed between the ignition delay times of the three simulants, whether sole or mixed with a fuel. Comparisons of OH* time histories obtained from each surrogate highlight the similarities and differences in chemical structure among the different compounds. In mixtures with oxygen and Ar, the three surrogates present similar ignition delay times below 1380 K, whereas the ignition delay time results rapidly diverge above this temperature. When the surrogates were added into $$\hbox {H}_{2}/\hbox {O}_{2}$$ or $$\hbox {CH}_{4}/\hbox {O}_{2}$$ mixtures, large changes in the reactivity of the mixtures were observed. These changes in reactivity are however dependent on the surrogate, for each fuel investigated.

A detailed chemical kinetics for the combustion of H2/CO/CH4/CO2 fuel mixtures

A genetic algorithm (GA) was proposed and validated for the optimal extraction of a sub-mechanism for H2/CO/CH4/CO2 mixtures from the detailed Aramco1.3 chemical kinetics mechanism (Metcalfe et al., 2013), which was developed for C1–C5 hydrocarbons and oxygenated fuels. Ninety ignition delay time data involving mixtures containing H2, CO, CH4, CO2, N2, and H2O at wide range of experimental conditions were chosen as optimization targets to guide the GA, so that the final reduced mechanism was able to fully describe the combustion characteristics of syngas and biogas fuel mixtures. The final reduced mechanism for H2/CO/CH4/CO2 fuel mixtures comprised of 72 species and 290 reactions (reduced from 325 species and 2067 reactions), and it was extensively validated against experimental results, such as measured ignition delay times and laminar flame speeds, over a wide range of operating conditions. The excellent agreement between the reduced mechanism and Aramco1.3 mechanism in predicting the combustion properties of H2/CO/CH4/CO2 mixtures with maximum relative error values of only 0.9% and 2.75%, respectively for the ignition delay time and laminar flame speed results, indicates that the proposed reduced mechanism can be used for predicting the combustion characteristics of biogas and syngas fuel mixtures. Furthermore, it was observed that the reduced mechanism shows excellent agreement with the Aramco1.3 mechanism in predicting the ignition delay time of mixtures with added ethane and propane. Therefore, the proposed reduced mechanism represents the most up-to-date detailed chemical kinetics mechanism for biogas and syngas fuel mixtures, and it can also be used for predicting the combustion properties of natural gas with impurities such as ethane and propane. The reduced mechanism agreed so well with the Aramco1.3 mechanism in predicting the combustion properties of H2/CO/CH4/CO2 mixtures, where both mechanisms performed identically in over predicting the ignition delay time for H2/CO/CO2, CO2, H2/CO/CH4, and H2/CO/CH4/CO2/H2O mixtures at several experimental conditions. These observations were also reported by Lee et al. (2015), where they proposed two new rate constants for H+O2(+CO2)=HO2(+CO2) and CH4+OH=CH3+H2O to reconcile the discrepancies observed. These two new rate constants were assessed in this study by incorporating the modified rate constants into the 290Rxn mechanism (referred as 290Rxn-V1), where it was found that the modified rate constants did improve the ignition delay time predictions. However, the two proposed rate constants did not improve the predictions of the laminar flame speed for mixtures with a high CO2 content at high equivalence ratios (ϕ>1.2). Therefore, optimization of the rate constants in the 290Rxn mechanism is highly recommended to further improve its agreement with experimental data for biogas and syngas fuel mixtures.

Ignition and combustion of isopropyl nitrate

The ignition delay times for mixtures of isopropyl nitrate (IPN) with air and argon are measured in a rapid-injection reactor at a pressure of 1 atm and in a shock tube at 2–3 atm. It is shown that the ignition delay time τ of mixtures in which heat is largely released due to oxidation by the oxygen contained in the IPN molecule is determined by the unimolecular decomposition of IPN over the entire temperature range covered (500–730 K). For mixtures in which heat is mainly produced by oxidation reactions involving air oxygen, the ignition delay time at high temperatures is controlled by secondary reactions of oxidation of the hydrocarbon moiety of the IPN molecule, leading to an increase in τ by more than an order of magnitude. Liquid IPN burns in a nitrogen atmosphere only at pressures above 40 atm, at a linear rate of ~4 mm/s. The measured flame temperatures are in close agreement with the respective values calculated using a thermodynamic code.

Experimental and Kinetic Study on Ignition Delay Times of Liquified Petroleum Gas/Dimethyl Ether Blends in a Shock Tube

In this study, ignition delay times of liquified petroleum gas (LPG)/dimethyl ether (DME) (LPG consists of C3H8 and C4H10 in this work) were measured in a shock tube at different DME blending ratios (0%, 10%, 30%, and 50%), pressures (5, 10, and 15 atm), temperatures (1100–1500 K), and equivalence ratios (0.5, 1.0, and 1.5). The chemical kinetic mechanism of LPG/DME was established based on Lawrence Livermore National Laboratory’s C1–C4 chemical kinetic mechanism (Combust. Flame 1998, 114, 192–213) and Zhao’s DME chemical kinetic mechanism (Int. J. Chem. Kinet. 2008, 40, 1–18), and its predictions agree well with experimental data. A sensitivity analysis and a reaction pathway analysis were conducted using CHEMKIN-PRO to study the impact of DME addition on the ignition and combustion process. The experimental results show that the ignition delay times of LPG/DME change linearly with increasing DME blending ratios. The sensitivity analysis shows that the number of major promoting reactions for mixtures increases, including H-abstraction and decomposition of CH3OCH3, while the sensitivity factors of the H-abstraction and the decomposition of C3H8 (reactions R115, R120, and R125) decrease with increasing DME blending ratios. The reaction pathway analysis indicates that the H-abstraction reactions play a dominant role, and the contribution rate of OH to H-abstraction increases, while that of H-radical decreases slightly in the oxidation of C3H8 and C4H10 with the increasing proportion of DME in the LPG/DME mixtures. Further analysis shows that although the growth rate of H before ignition is LPG100 > LPG50 > DME, reaction R22 in the oxidation process of mixtures makes OH accumulate rapidly in a short time, resulting in a much higher peak concentration of OH than that of H; therefore, the ignition delay times of mixtures are shorter than those of neat LPG.

An experimental and kinetic modeling study of the pyrolysis and oxidation of n-C3[sbnd]C5 aldehydes in shock tubes

Due to the increasing interest in the use of biofuels for energy production, it is of great importance to better understand the combustion and thermal decomposition characteristics of species such as aldehydes. These are known to be key intermediate products of transport fossil and bio-fuels combustion and are also dangerous pollutants emitted from combustion in internal combustion engines and from gasification of biomasses. In this study, an experimental and kinetic modeling investigation of propanal, n-butanal and n-pentanal pyrolysis and oxidation in two shock tube facilities was carried out. Experiments were performed in a single pulse shock tube to determine the speciation profiles of the fuels and intermediate species under pyrolysis conditions for mixture of pure propanal/n-butanal/n-pentanal (3%)–Ar (97%), at averaged reflected pressure of 1.9atm and at reflected shock temperatures of 972–1372K. Additionally, ignition delay times for mixtures of pure propanal/n-butanal/n-pentanal (1%)–O2/Ar were measured in the temperature range 1136–1847K, at pressures of 1 and 3atm, and at equivalence ratios of 0.5, 1.0 and 2.0.A comprehensive sub-mechanism for the high temperature kinetics of the three aldehydes was developed. This scheme was then coupled with NUIG (National University of Ireland, Galway) and POLIMI (Politecnico di Milano) C0C4 kinetic schemes. The inclusion of the aldehydes sub-mechanism in two different kinetic environments, required modifications for the H-abstraction reactions, due to different rate rules in use in the two kinetic environments, and due to differences in the C0C4 kinetic schemes. Both of the models were validated and showed good agreement with the new experimental data. The mechanisms are also satisfactorily compared with ignition delay times, speciation profiles and laminar burning velocities previously published in literature. Reaction pathways and sensitivity analyses were also performed to highlight the important reaction steps involved in the pyrolysis and oxidation processes. The major differences between the models and the experiments have to be attributed to the chemistry of the smaller species, more than to aldehyde specific reactions. This work further highlights the relevant role of the C0C4 sub-mechanism, mainly in terms of a unification process that needs to start from the smaller species chemistry in order to obtain an unambiguous description of any fuel investigated.

A comprehensive experimental and detailed chemical kinetic modelling study of 2,5-dimethylfuran pyrolysis and oxidation

The pyrolytic and oxidative behaviour of the biofuel 2,5-dimethylfuran (25DMF) has been studied in a range of experimental facilities in order to investigate the relatively unexplored combustion chemistry of the title species and to provide combustor relevant experimental data. The pyrolysis of 25DMF has been re-investigated in a shock tube using the single-pulse method for mixtures of 3% 25DMF in argon, at temperatures from 1200 to 1350K, pressures from 2 to 2.5atm and residence times of approximately 2ms.Ignition delay times for mixtures of 0.75% 25DMF in argon have been measured at atmospheric pressure, temperatures of 1350–1800K at equivalence ratios (ϕ) of 0.5, 1.0 and 2.0 along with auto-ignition measurements for stoichiometric fuel in air mixtures of 25DMF at 20 and 80bar, from 820 to 1210K.This is supplemented with an oxidative speciation study of 25DMF in a jet-stirred reactor (JSR) from 770 to 1220K, at 10.0atm, residence times of 0.7s and at ϕ=0.5, 1.0 and 2.0.Laminar burning velocities for 25DMF-air mixtures have been measured using the heat-flux method at unburnt gas temperatures of 298 and 358K, at atmospheric pressure from ϕ=0.6–1.6. These laminar burning velocity measurements highlight inconsistencies in the current literature data and provide a validation target for kinetic mechanisms.A detailed chemical kinetic mechanism containing 2768 reactions and 545 species has been simultaneously developed to describe the combustion of 25DMF under the experimental conditions described above. Numerical modelling results based on the mechanism can accurately reproduce the majority of the experimental data. At high temperatures, a hydrogen atom transfer reaction is found to be the dominant unimolecular decomposition pathway of 25DMF. The reactions of hydrogen atom with the fuel are also found to be important in predicting pyrolysis and ignition delay time experiments.Numerous proposals are made on the mechanism and kinetics of the previously unexplored intermediate temperature combustion pathways of 25DMF. Hydroxyl radical addition to the furan ring is highlighted as an important fuel consuming reaction, leading to the formation of methyl vinyl ketone and acetyl radical. The chemically activated recombination of HȮ2 or CH3Ȯ2 with the 5-methyl-2-furanylmethyl radical, forming a 5-methyl-2-furylmethanoxy radical and ȮH or CH3Ȯ radical is also found to exhibit significant control over ignition delay times, as well as being important reactions in the prediction of species profiles in a JSR. Kinetics for the abstraction of a hydrogen atom from the alkyl side-chain of the fuel by molecular oxygen andHȮ2 radical are found to be sensitive in the estimation of ignition delay times for fuel–air mixtures from temperatures of 820 to 1200K.At intermediate temperatures, the resonantly stabilised 5-methyl-2-furanylmethyl radical is found to predominantly undergo bimolecular reactions, and as a result sub-mechanisms for 5-methyl-2-formylfuran and 5-methyl-2-ethylfuran, and their derivatives, have also been developed with consumption pathways proposed. This study is the first to attempt to simulate the combustion of these species in any detail, although future refinements are likely necessary.The current study illustrates both quantitatively and qualitatively the complex chemical behaviour of what is a high potential biofuel. Whilst the current work is the most comprehensive study on the oxidation of 25DMF in the literature to date, the mechanism cannot accurately reproduce laminar burning velocity measurements over a suitable range of unburnt gas temperatures, pressures and equivalence ratios, although discrepancies in the experimental literature data are highlighted. Resolving this issue should remain a focus of future work.

着火促進を目的とした誘電体バリア放電の超音速流における動作特性

The authors developed a method to produce nonequilibrium plasma by dielectric barrier discharge (DBD) in supersonic flow and investigated the possibility for using it as an ignition enhancement technique in a high speed engine, such as a scramjet engine. The discharge characteristics were investigated by varying applied voltage and the flow Mach number. It was revealed from direct photographs that the discharges got stronger and the volume got larger as flow Mach number increased. Estimated discharge power indicated that nonequilibrium plasma could be generated by considerably small energy in comparison with thermal plasma such as a plasma jet torch, which is a typical thermal plasma. The emissions from several excited molecules and atoms were confirmed by spectroscopic measurement of the plasma. Ignition delay analysis revealed that the effect of ozone (O3) addition to shorten the ignition delay time of mixture is almost equal to those of O or H radicals.

Ignition delay times of low-vapor-pressure fuels measured using an aerosol shock tube

Gas-phase ignition delay times were measured behind reflected shock waves for a wide variety of low-vapor-pressure fuels. These gas-phase measurements, without the added convolution with evaporation times, were made possible by using an aerosol shock tube. The fuels studied include three large normal alkanes, n-decane, n-dodecane and n-hexadecane; one large methyl ester, methyl decanoate; and several diesel fuels, DF-2, with a range of cetane indices from 42 to 55. The reflected shock conditions of the experiments covered temperatures from 838 to 1381 K, pressures from 1.71 to 8.63 atm, oxygen concentrations from 1 to 21%, and equivalence ratios from 0.1 to 2. Ignition delay times were measured using sidewall pressure, IR laser absorption by fuel at 3.39 μm, and CH * and OH * emission. Measurements are compared to previous studies using heated shock tubes and current models. Model simulations show similar trends to the current measurement except in the case of n-dodecane/21% O 2/argon experiments. At higher temperatures, e.g. 1250 K, the measured ignition delay times for these mixtures are significantly longer in lean mixtures than in rich mixtures; current models predict the opposite trend. As well, the current measurements show significantly shorter ignition delay times for rich mixtures than the model predictions.

Experimental study of the ignition of n-hexane- and n-decane-based surrogate fuels

Surrogate fuels on the basis of mixtures of n-hexane, n-decane, and benzene are fuels alternative to petroleum motor fuels, similar to the former in thermodynamic and kinetic properties. The fact the surrogate fuels are composed of a limited number of components makes it possible to develop both detailed and global kinetic mechanisms of their ignition in mixtures with oxidizers. In turn, the possibility of the kinetic modeling of the ignition of such fuels over wide temperature and pressure ranges is of critical importance for the numerical modeling of combustion-to-detonation transition phenomena. An experimental method for measuring ignition delay times of mixtures of air with liquid fuels with low vapor pressure under normal conditions is developed and tested. In the present work, the ignition of stoichiometric mixtures of air with n-hexane, n-decane, and surrogate fuels composed of 20% n-hexane and 80% n-decane, 20% benzene and 80% n-decane, and 9.1% n-hexane, 18.2% benzene, and 72.7% n-decane is experimentally investigated in a static reactor. The ignition delay time is determined by recording pressure oscillograms at temperatures of 530–1030 K and pressures of 1–9 atm.

Shock-tube study of the autoignition of n-heptane/toluene/air mixtures at intermediate temperatures and high pressures

The ignition delay times of mixtures containing 35% n-heptane and 65% toluene by liquid volume at room temperature (i.e., 28% n-heptane/72% toluene by mole fraction) were determined in a high-pressure shock tube in the temperature range 620 ⩽ T ⩽ 1180 K at pressures of about 10, 30, and 50 bar and equivalence ratios, ϕ, of 0.3 and 1.0. The equation τ / μs = 9.8 × 10 −3 exp ( 15 , 680 K / T ) ( p / bar ) −0.883 represents the data for ϕ = 0.3 in the temperature range between 980 and 1200 K. At lower temperatures no ignition was found at 10 bar within the maximum test time of 15 ms, whereas for 50 bar, a reduced activation energy was observed. A pressure coefficient of −1.06 was found for the data with ϕ = 1.0 . No common equation for the data at ϕ = 1.0 could be found analogous to that for ϕ = 0.3 because the ignition delay times show no Arrhenius-like behavior. A comparison with ignition delay times of n-heptane/air and toluene/air for ϕ = 1.0 and 30 bar shows that the values of the mixture of the two components are between the values of the single substances. Furthermore, the results confirm the negative temperature coefficient behavior found for the mixtures at 30 and 50 bar, similar to n-heptane/air. A comparison for the other pressure and equivalence ratio values of this study was not possible because of the lack of data for pure toluene. These experimental data have been used in the development of a chemical kinetics model for toluene/ n-heptane mixtures as described in a companion paper.

Chemical Kinetic Mechanism for High Temperature Oxidation of Butane Isomers

Ignition delay times of mixtures of n-C4H10 and i-C4H10 (1.0% C4H10 and Φ = 0.72 diluted in Ar) have been measured behind reflected shock waves by monitoring time histories of UV emission and press...

Modeling of n-Heptane and Iso-Octane Oxidation in Air

A simplified kinetic mechanism is presented for 1006 reactions involving 134 chemical species of that 23 include nitrogen atoms that describes the combustion of n-heptane, iso-octane, and their mixtures in air. The submechanism for the C 5 -C 8 species is directly derived from the earlier presented mechanisms for the combustion of methane, ethane, propane, and butane in air. The following experimental data taken from the literature and obtained by means of shock-tube experiments have been chosen to validate the mechanism: the pyrolysis of i-C 8 H 1 8 and the ignition delay times of mixtures of n-C 7 H 1 6 and i-C 8 H 1 8 with air, respectively. The comparisons have yielded good agreement for the initial temperature T 0 varying between 650 and 1200 K, the initial pressure P 0 ranging from 0.65 to 4.5 MPa, and the fuel-to-oxygen ratio Φ ranging from 0.5 to 2.

The high temperature oxidation of pyrrole and pyridine; ignition delay times measured behind reflected shock waves

The ignition delay times for mixtures of pyrrole and oxygen and pyridine and oxygen were measured behind reflected shock waves, using argon as a diluent. Ignition delay times, defined with respect to pressure rise, were measured for mixtures comprising of 0.5–1.0% fuel and 1.5–14.5% oxygen, between 200 and 560 kPa within the temperature regime of 1100–1800 K. Results for the ignition times for the compounds studied can be fitted to the following global regression equations (times in s, concentrations in mol cm –3): t=10 −12.8 exp 17,510 T 5 [Pyrrole] 0.59[O 2] −1.32[Ar] −0.02 t=10 −13.0 exp 18,250 T 5 [Pyridine] 0.31[O 2] −1.00[Ar] 0.04 The results for these high temperature oxidation experiments are discussed in relation to the thermal decomposition of these compounds as well as being compared and contrasted with previous benzene ignition studies.

96/05225 Determination of ignition delay times in mixtures of ethylene oxide, oxygen, and argon behind a reflected shock

The Australian Permian cratonic Cooper and Galilee Basins contain extensive deposits of inertinite-rich coals. In contrast, the contiguous foreland Sydney and Bowen Basins are dominated by vitrinite-rich coals. Inertinite in the cratonic basin coals is mainly botanically unstructured fragmentary inertodetrinite. In the foreland basin coals, semifusinite is the dominant inertinite maceral.Microlithotypes in the cratonic basin coals are characteristically finely banded. Sulfur and ash contents are low by world standards, < 1% and < 10% by weight, respectively. The cratonic basins also contains several exceptionally thick coals, which reach 50 m in places. These coals are everywhere inertinite-rich.The cratonic basin coals accumulated in freshwater mires, where low subsidence rates led to extensive oxidation of the peat. Subaerial and probably subaqueous oxidation took place due to water table fluctuations. There is no evidence that these inertinite-rich coals were formed from a unique flora or under climatic conditions different from vitrinite-rich Permian coals.

Determination of ignition delay times in mixtures of ethylene oxide, oxygen, and argon behind a reflected shock

The detonation of mixtures of ethylene oxide, oxygen, and argon has been studied in a shock tube and also using computer modeling from 950 to 1220 K at 100 torr. The emission from OH at 306.4 nm from behind the reflected shock was measured to monitor ignition delay times. Using a mechanism of 88 elementary reactions, involving 30 chemical species, ignition delay times were computed. The simulation and sensitivity analysis confirmed that the isomerization of ethylene oxide to acetaldehyde is the main chain-initiation step.