摘要:

Net heat release, knock characteristics and temperature were derived from in-cylinder pressure and end-gas CARS measurements for different fuels in a single-cylinder engine. The maximum net heat release rate resulting from the final phase of autoignition is closely associated with knock intensity. Aromatic fuels have lower maximum heat release rates and lower knock intensities than expected from their octane number when compared to paraffinic fuels; this is observed even when there is significant heating of the end-gas from pre-flame reactions. Leaner mixtures have tower combustion rates so that pressure development is slowed and hence ignition needs to be more advanced to get knock to occur as frequently as in a richer mixture. However, for a given frequency of knock occurrence, there is no significant difference in peak net heat release rates and hence in knock intensities for different mixture strengths.

ISSN:0010-2202    

DOI:10.1080/00102209508951924

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We have obtained quantitative LIF measurements of NO concentration in the postflame zone of a series of flat, laminar, premixed CH4/O2/N2flames (0.5 ≤ φ ≤ 1.6) at pressures ranging from l-14.6atm. The temperatures of the flames were 1660-J 960 K, indicating that prompt NO was the primary pathway for NO formation in the majority of these flames. In addition, we have modeled many of the experimental flames using the chemical reaction mechanism of Glarborg-Miller-Kee as modified by Drake and Blint (GMK-DB). This model accurately predicts the behavior of NO with increasing pressure and shows reasonable quantitative agreement for many of the flames at pressures ≤ 6.1 atm. At pressures greater than 6.1 atm, inaccuracies in the predicted temperature field preclude good quantitative agreement between the modeled and measured NO concentrations. Detailed NO measurements in ultra-lean (φ = 0.55−0.8) flames showed higher NO emissions with increasing pressure, a result consistent with kinetic modeling of these lean flames via the GMK-DB mechanism.

ISSN:0010-2202    

DOI:10.1080/00102209508951925

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We have studied the oxidation of allene in a rich ( φ = 1.5), low-pressure H2/O2/Ar flame to which one percent altene was added. Temperatures were measured by thermocouple and by OH laser-induced fluorescence. Stable species profiles were determined from mass spectrometer measurements using a quartz microprobe, and OH concentrations were determined using LIF. The experiments were analyzed with the aid of a chemical kinetic model. Significant quantities of methane and acetylene are formed early in the flame as a consequence of recombination of propargyl with hydrogen atoms,

ISSN:0010-2202    

DOI:10.1080/00102209508951926

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The structure of the hydrogen-air counterflow diffusion flame is investigated by Damkohler-n umber asymptotics. Attention is restricted to flowfield strain times smaller than dissociation times but larger than the characteristic chemical time of three-body recombination reactions, thereby placing the system on the upper, vigorously burning branch of the characteristic S-curve of peak temperature as a function of strain time without equilibrium broadening. Under these conditions, it is shown that the reactants can coexist only within a thin reaction zone separating two radical-free equilibrium regions. First, the equations for the counterflow mixing layer in the two outer equilibrium regions are solved in the classical Burke-Schumann limit by the introduction of appropriate conserved scalars that account for variable transport coefficients and variable Schmidt numbers, different for different species. Then, the reaction zone is investigated with scaling that identifies the relevant reduced Damkohler number. While the solutions in the outer zones are peculiar to the counterflow configuration because of their convective-diffusive character, the reactive-diffusive nature of the reaction zone at leading order enables its structure in transformed coordinates to be expressed independently of the geometrical configuration. Matching the solutions from the inner reaction region with those from the outer equilibrium regions yields the first-order asymptotic solution to the problem, which compares favorably with results obtained by numerical integration of the full conservation equations with detailed chemistry and transport descriptions. In particular, the reason that the maximum radical concentration and temperature deficit vary linearly with the one-third power of the strain rate is explained.

ISSN:0010-2202    

DOI:10.1080/00102209508951927

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Different knitted silica-fibre supported metal oxides (oxides of Co, Ni, Mn, Cr) and various combinations of them, platinum-activated cobalt and nickel oxide catalysts as well as noble metal (Pt, Pd) catalysts were prepared. The catalysts were tested for their activity in propane and natural gas combustion in a continuous flow tube reactor at temperature range of 423-823 K and GHSV of 23900 and 47800 h−1. High combustion efficiencies were obtained by the metal oxides and platinum activated metal oxides. Co3O4was found to be the most active single metal oxide catalyst in propane combustion. The low temperature activity of metal oxide was strongly improved by use of platinum as an activator. The propane combustion over Pd/SiO2was found to be structure sensitive under our experimental conditions. The dependence of the rate of propane combustion over noble metal containing catalysts was found to be zero order with respect to oxygen and one with respect to propane. The reaction orders over metal oxides were fractional (0 < n,m < 1). The catalysis were more active in propane than in natural gas combustion. NiO and Pd were found to be the most active catalysts in natural gas combustion. The activity pattern of the prepared catalysts in complete oxidation of propane and natural gas is reported. The catalysts were characterized by O2-TPD and the chemisorption of propane, carbon monoxide and hydrogen.

ISSN:0010-2202    

DOI:10.1080/00102209508951928

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In the present paper the two-colour technique is applied to study the in-cylinder soot volume fraction evolution in a Direct Injection Diesel engine. A preliminary analysis of the theoretical uncertainty involved in performing the two-colour soot emission measurements is carried out. It is found that, with interference filters at 600 and 1000 nm, and reducing the data with the appropriate numerical algorithm, the total accuracy about soot temperature and volume fraction-values is confined respectively under ± 57 K and ± 30%. The in-cylinder measurements are performed at fixed engine angular speed and injected fuel mass, varying the injection timing and the fuel quality. Employing the two-colour pyrometry technique the following results can be obtained: a) the fuel cetane number controls the soot loading of paraffinic fuels; b) at a fixed level of cetane number (up to 58) the fuel aromatic content strongly influences the engine soot loading amount, but, at a further increase of cetane number (over 62), any significant difference between fuel sooting behaviour with different aromatic content vanishes; c) for aromatic fuels at the cetane level 50 and 58 the sum of di- and tri- aromatics is a candidate to be a better indicator of fuei sooting tendency with respect to the total fuel aromatic content

ISSN:0010-2202    

DOI:10.1080/00102209508951929

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We extend the classical stability analyses of Landau, Darrieus and Markslein to flames propagating in gases that are seeded with fine inert particles, and account for the resufting radiative exchanges. Our main assumptions are that: i) the Zel'dovich number based upon the flame-speed sensitivity to reaction temperature can be considered large; ii) the two-phase mixture is a one-velocity,one-temperature continuous medium; iii) radiation follows the Eddington equation; iv) radiant exchanges are weak, yet non negligible; v) the flame front is optically very thin but local curvature effects can be accounted for via a Markstein length that is proportional to the actual front thickness,

ISSN:0010-2202    

DOI:10.1080/00102209508951930

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

NO formation in laminar partially premixed ethane-air flames is investigated as a function of the amount of air introduced into the central fuel tube of an annular co-flow burner. The NO emission index at the exhaust is determined by chemiluminescent detection while the local NO number density is measured by laser-saturated fluorescence. The measurements are taken in flames with an overall equivalence ratio of 0.5, fuel-tube equivalence ratios varying from 1.1-10, and a fixed fuel flowrate of 0.15 slpm. Local NO number densities are measured as a function of both radial position and height above the burner. An intermediate dual-flame pattern is identified which minimizes the NO emission index. NO production is found to occur primarily between an inner premixed and an outer nonpremixed flame front, which constitutes the dual-flame structure. These results suggest that the optimum bumer-lube equivalence ratio occurs because of a compromise between prompt and thermal formation of NO in the predominantly premixed and nonpremixed flame regions, respectively.

ISSN:0010-2202    

DOI:10.1080/00102209508951931

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Fast-time instabilities refer to dynamics that may develop within the reaction zone of a flame, where the chemical kinetic time scales are very brief. Premixed flames with order one heat losses and diffusion flames with order one reactant leakage are known to possess this instability when the Lewis number is one (Peters, 1978). Work by Stewart (1986) indicates that the instability should also arise for adiabatic flames with Lewis numbers exceeding one. Recent work in reverse smouldering combustion (Lozinski and Buckmaster, 1994) requires an examination of the combined effect of heat losses and Lewis numbers well below unity. Because of the general nature of the results, they are presented here. The numerical computations reveal that while heat losses tend to destabilize the flame, small Lewis numbers have a countervailing stabilizing effect, suppressing the instability for an order one range of heat losses. This plays a key role in selecting the physically significant solution to the reverse smouldering combustion model (Lozinski and Buckmaster, 1994). The instability is one-dimensional; an examination of higher dimensions reveals no new instabilities arising for reasonable parameter values.

ISSN:0010-2202    

DOI:10.1080/00102209508951932

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The conditional moment closure (CMC) method constitutes an alternative approach in the modelling of turbulent reacting systems. In the present study, the CMC formulation is introduced for turbulent premixed combustion and the transport equation for the conditional mass fraction is derived. It appears that the key points for these methods consist in the modelling of the conditional scalar dissipation rate and mean velocity. In order to provide information concerning these two quantities, an existing data base for direct numerical simulations (DNS) of three-dimensional turbulent premixed flames is used. From the DNS, the effects of the Damköhler and Lewis numbers on the conditional means are presented and discussed. It appeal's that the conditional mean scalar dissipation remains unaffected by the turbulent mixing in the reaction zone. However, at low Damköhler numbers, the gradients of the mean progress variable are steeper in the preheat zone of the instantaneous flame fronts leading to a higher dissipation rate. The conditional mean velocity is found to evolve almost linearly through the turbulent flame brush, as expected from the mean pressure gradient that arise from the overall heat release. A noticeable negative slip velocity associated with the wrinkling of the turbulent flame is observed in the simulations. It is also found that there is no significant change in the axial velocity through the instantaneous flame front. This suggests that the flame adjusts itself so that it can provide dilatation without axial acceleration in the instantaneous flame front. The probability density function of the progress variable exhibits a strongly bimodal shape, but the peak corresponding to the fresh gas side is broader. Turbulent fluxes for the mean progress variable are derived from the DNS and, contrary to previous studies, no counter-gradient diffusion is observed in these simulations.

ISSN:0010-2202    

DOI:10.1080/00102209508951933

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor