摘要:

Mean and rms values of the axial and swirl velocity components obtained by a laser Doppler anemometer in a model can-type gas turbine combustor under isothermal and combusting flow conditions are reported. The results show that the combustor swirl is characterised by a solid body rotation near the axis and a free vortex flow in regions close to the combustor wall. Combustion strengthens and contracts the primary vortex, accelerates the flow in stream-wise direction and increases the rms of velocity fluctuations. Although the effect of air-fuel ratio on velocity characteristics is relatively weak in the primary zone where the interaction of fuel momentum with the swirler flow causes some changes in primary vortex structure, it becomes steadily more pronounced with downstream distance.

ISSN:0010-2202    

DOI:10.1080/00102208608923900

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

A consistent means to establish the flame coordinate for oblique premixed turbulent flames based on the use of conditioned statistics of two velocity components is described. The flame coordinate is used to transform the conditioned velocity data for comparison with the predictions of the Bray-Moss-Libby (BML) model of turbulent combustion, assess the modeling assumptions and calculate one of the empirical constants. The most significant change in the flame statistics after transformation is that the Reynolds stress in the flame is found to be at the same level as in the incident flow. The Favre averaged turbulence intensities and scalar transport derived from experimental measurements are in qualitative agreement with previously reported experimental and numerical results. The results also support the BML second order closure technique for the third order covariances. However, the values of the empirical constant computed from experimental data do not lend strong support to a sub-model for the change in the conditioned statistics.

ISSN:0010-2202    

DOI:10.1080/00102208608923901

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

An experimental study of the oxidation of propane in the temperature range 563–743 K. was carried out using a static reactor. The oxidation mechanism was found to undergo a transition from a low temperature reaction regime (T<600K) to that of an intermediate temperature regime ( T> 650 K) separated by a region of negative temperature coefficient (600-650 K). In the lower temperature regime alkylperoxy radicals are formed and become the dominant radical species. These can react in several ways, the most important of which leads to the formation of hydroperoxides. Hydroperoxides were determined to be the main chain branching intermediates responsible for the acceleration of the reaction and for the formation of cool flames. At the intermediate temperatures hydroperoxyl radicals are dominant and lead to hydrogen peroxide, which is the main branching intermediate in this regime. These conclusions are based in large measure upon the hydrocarbon products formed which consist mainly of oxygenated species at the lower temperatures and lower alkanes and alkenes at the intermediate temperatures. The negative temperature coefficient and the change in mechanism are due to the competition between reactions involving the addition of Oa to the alkyl radical forming the alkylperoxy radical and reactions involving the abstraction of hydrogen from the alkyl radical by Oa to form the conjugate alkene and the hydroperoxyl radical. The effect of increasing the reaction vessel surface-to-volume ratio was to enhance heterogeneous termination, resulting in longer reaction times. Comparison of the reaction products from vessels with different surface-to-volume ratios showed there to be no significant effect of surface on the main reaction paths of the mechanism. Some aspects of the mechanism at these temperatures are compared to those in the high temperature regime (T>1000K).

ISSN:0010-2202    

DOI:10.1080/00102208608923902

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The width ( δ ) of a laminar flame is often characterized as a basic property of the flame and is sometimes used in turbulent combustion models to categorize the turbulence scale of the mixture. From computed flame speeds and temperature profiles of C3H8/Oa/Ns (ø=1) flames we have determined widths, using definitions based on ( dT*sol;dx)max, Q (the heat release rate) and r (the characteristic chemical time) and characteristic distances have been determined from the transport properties of the burned (δb) and unburned (δu) gases. The flame widths are compared via the transport properties, (A/Cp), of the gas mixtures in the flame where A is the thermal conductivity and Cpis the heat capacity. A derived or approximate transport property for the flame widths is defined by the product of the mass flow rate (Mƒ) and the flame width. The functional dependence of these flame widths is compared by varying the Na fraction and initial mixture temperature. Both the set of Na fractions and mixture temperatures show the same range of flame speeds (40–350 cm/sec), but exhibit very different flame width values and dependence. The values of the derived transport properties from the ( dT/dx) max definition approximate the transport properties of the burned gas mixture (ST∼2*SI,) while those from the characteristic chemical time approximate the transport properties of the unburned gas mixture (δt;∼$). However, the values of the derived transport property based on the half-width of the heat release rate gives physically unreasonable transport properties in excess of either the burned or the unburned gases. These calculated flame widths differ significantly in absolute value and show a non-linear dependence on dilution. Although flame speeds for increasing mixture temperature and for differing dilutions are similar, the flame widths calculated for increasing mixture temperatures decrease only slightly compared to those for decreasing dilutions. These definitions of flame width, although given the same name, do not describe similar flame properties. The flame width definition based on the temperature gradient is proposed to be the proper specification of a laminar length scale because it is based on the physically measurable temperature profile and because it incorporates the effects of both heat release and transport which determine the temperature profile.

ISSN:0010-2202    

DOI:10.1080/00102208608923903

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

ISSN:0010-2202    

DOI:10.1080/00102208608923904

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

A comparison of predicted and experimental HC emissions at high rates of exhaust gas recirculation (EGR), indicates that partial burning is responsible for significant changes in HC emission trends under otherwise normal, non-misfiring engine operating conditions. Ion-probe experiments show a measurable fraction of engine cycles in which the flame did not completely propagate across the chamber whenever HC emissions were high. A simple semi-empirical model is proposed to predict HC emissions from partial burning based on measured burn rate parameters.

ISSN:0010-2202    

DOI:10.1080/00102208608923905

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor