摘要:

A comparison is made between measured species concentrations in a spark ignition engine and predictions from a numerical model using detailed chemical kinetics. Gas samples are extracted from the end gas at times just prior to autoignition of n-butane/air oriso-butane/air mixtures. Concentration histories of stable species are ohtained through gas chromatographic analysis. A detailed chemical kinetics model is used to predict species concentrations in an idealized end gas. The chemical reactions leading to formation of the relevant species are identified. The relative distribution of intermediate products predicted by the model is in good agrrement with the experimental measurements. Chemical kinetic differences between autoignition of n-butane, a straight chain hydrocarbon, and iso-butane. a branched chain hydrocarhon. are discussed.

ISSN:0010-2202    

DOI:10.1080/00102208608923923

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Molecular beam mass spectrometry has been used to determine temperature and species concentrations in the discharge plume of a pulsed plasma jet igniter. Laser schlieren photographs of the plume/sampling cone interaction reveal that the molecular beam sampling has negligible effect on jet fluid mechanics up to the time of impingement, and temperature and species measurements indicate that at later times the gas is sampled from within the plume. The temperature in an atmospheric pressure jet of nitrogen ranged from a maximum of 50,000 K to ambient temperature. Peak nitrogen atom concentration at the detector was found to range from 5 percent. 2 mm from the igniter, to less than 100 ppm at 14 mm.

ISSN:0010-2202    

DOI:10.1080/00102208608923924

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The ignition characteristics of the turbulent element produced by a pulsed plasma source are modelled using a simple Arrenhius reaction rate formulation and the entrainment hypothesis. It is shown that critical ignition conditions depend on the heat content of the combustible mixture and the ratio of the energy and momentum injected by the plasma source. The model indicates formation times of the order of milliseconds during which times extinguishing cases cannot easily be distinguished from combusting cases. During this time the chemical reactions are controlled by the turbulent mixing alone. This furnishes a tentative explanation of anomalously long ignition "delay" times sometimes observed with pulsed plasma jet ignition systems. Experimental observations confirm the broad features of the theoretical model, in particular the validity of the similarity assumptions and the scaling factors predicted for the element behavior.

ISSN:0010-2202    

DOI:10.1080/00102208608923925

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The ignition efficiency of methane-oxygen-argon mixtures was measured with plasma jet ignition over a range of equivalence ratios. Several plasma feed gases, including the mixture to be ignited, were used as the plasma feed. Measurements were made at different stages of filling of the plasma cavity with the plasma feed in order to separate the effect of plasma composition from the effect of local mixture alteration by the feed gas. Methane. acetylene, propane, and hydrogen as plasma feeds resulted in the highest ignition efficiencies in the leanest mixtures. Oxygen, nitrogen, and helium also produced an increase in the ignition efficiency over that obtained with no feed, although the effect was less for these feeds than with the fuels. Although the local charge alteration at the igniter exit was greatly reduced, if not eliminated, in these experiments compared to many plasma jet experiments previously reported, the results are qualitatively quite similar. This suggests that either local charge alteration has not been completely eliminated, or that the plasma products of the fuels are as effective in igniting the lean mixtures as is a mixture enriched in the ignition region by the fuel itself.

ISSN:0010-2202    

DOI:10.1080/00102208608923926

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

A computational study of the chemical kinetic effects of oxygen addition on the process of soot formation from hot acetylene is reported. The results, which are supported by trends observed in shock-tube experiments, reveal that the reaction pathway to soot identified previously for acetylene pyrolysis remains essentially unchanged in an oxidative environment. The main effects of oxygen are: (1) promotion of fuel decomposition, which alters the initiation route to soot; (2) supplementary rapid production of hydrogen atoms in the initial, small-molecule reactions, which drives the concentration of hydrogen above the equilibrium value with respect to H2and thus enhances polymeric growth of polycyclic aromatics; (3)oxidation of aromatic radicals by molecular oxygen, which removes them from the polymeric growth. The computational results indicate a crucial need for kinetic studies of high temperature reactions between molecular oxygen and hydrocarbon radicals.

ISSN:0010-2202    

DOI:10.1080/00102208608923927

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Flow reactor data from the oxidation of n-propylbenzene near 1060 K are analyzed to deduce the reactions involved in removing the n-propyl group. Three major routes are found: (i) abstraction of a hydrogen from the propyl group followed by decomposition of the radical and oxidative reactions, (ii) displacement of the propyl group by a radical species, and (iii) direct cleavage of the sidechain followed by the oxidation of the benzyl radical. The reaction sequences beginning with the abstraction of primary and benzylic hydrogens from the propyl group show a strong analogy to results for the oxidation of propane. However, the products predicted based on the analogy to propane for the abstraction of secondary hydrogens from the propyl group were not detected in significant quantities. The absence of expected products led to the recognition that a rapid phenyl shift isomerization of the beta-phenyl propyl radical occurs prior to the decomposition of the radical.

ISSN:0010-2202    

DOI:10.1080/00102208608923928

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The HTP technique makes it possible to study the kinetics and mechanisms of elementary reactions of important combustion-related free radicals over wide temperature ranges. It utilizes standard flash photolysis methods to generate the radicals and resonance fluorescence diagnostics to follow their time-dependent concentrations, from which kinetic and mechanistic information is derived. The use of a single technique to explore the kinetics of reactions over wide temperature ranges gives high confidence in the experimentally determined temperature dependences and provides a precise data base for both theoretical and empirical extrapolation of kinetic parameters to other temperatures of interest. Results obtained in HTP studies of the reactions O+CH3, H+H2O, OH+CH4, and OH+C6H6are discussed.

ISSN:0010-2202    

DOI:10.1080/00102208608923929

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The dependence of the rate coefficients of gas—phase oxidation reactions of monatomic and diatomic refractory species on temperature is discussed. Examples given pertain primarily to Al and B species reactions in the 300–1900 K range. These reactions show a wide variety of ln k(T) vs. T—1behavior patterns. It is shown that, because of this variety, it is not yet possible to make reliable predictions regarding reactions for which no experimental data on temperature dependence are available. However, some guidance is given toward making preliminary estimates. Quantitative kinetic data on the reactions are given and the importance of their thermochemistry is discussed. The experimental method (HTFFR) used to obtain these data is briefly reviewed.

ISSN:0010-2202    

DOI:10.1080/00102208608923930

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Hydroxyl radical (OH) density profiles as a function of height above the surface of a flat-flame burner have been determined for propane-air flames at three fuel-air equivalence ratios (0.63, 1.17, and 1.45) and for two total gas flow velocities at the richest equivalence ratio. The experiments have been performed using both absorption spectroscopy and laser-induced-fluorescence (LIF) imaging. The absorption and fluorescence profiles are in good agreement. Superequilibrium OH densities are observed near the flame zone with decay toward equilibrium occurring in the post-flame gases. An apparent second order kinetic dependence of this OH decay has been verified for the 𝚽 = 1.17 flame. The rate constant for the irreversible consumption of acetylene by OH has been determined to be 1.2(+0.3)x 10-12cm3/molecule-sec in the burned gas from the richest flame for temperatures of 1620-1700 K. The data suggest that the methyl radical is an important ultimate product formed in this reaction. The observed CO decay rate in the burned gas, measured by a quartz probe, is consistent with the OH density determination in the lean (𝚽= 0.63) flame.

ISSN:0010-2202    

DOI:10.1080/00102208608923931

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor