In an experimental study the effects of varied oxygen concentrations in the oxidizer gas on resulting flow fields, combustion products and general behavior of pulverized coal swirl flames under oxy-fuel conditions have been investigated. Experiments were carried out in a small scale down-fired cylindrical combustion chamber equipped with an annular swirl burner. Studied flames had a constant power output of 40 kWth and O2/CO2 oxidizer gas mixtures with O2 concentrations ranging from 23 to 33 vol%. Detailed two-dimensional flow field measurements are obtained from laser Doppler anemometry (LDA). Velocity profiles (Mean and RMS) have been obtained for all conditions investigated and serve as basis for identification of flow field characteristics. Velocity RMS values are provided as supplementary material. To complement flow field measurements, in-flame gas composition measurements were also conducted using a sampling probe combined with infrared gas absorption analysis via Fourier-transform infrared (FTIR) spectrometry. The results obtained show increased velocities, particularly along the main vortex for flames with increased oxygen contents, while lower velocities are found to occur inside the recirculation regions. The opposite occurs with lower O2 concentrations, showing significantly reduced velocities in the main vortex, but stronger recirculation than the high oxygen counterparts. This effect is attributed to a modification of the swirl level introduced by the expansion of product gases. Measured NO and CO in-flame concentrations showed significant variations under different O2 concentrations in the oxidizer. 相似文献
Recent studies have demonstrated stable generation of power from pure ammonia combustion in a micro gas turbine (MGT) with a high combustion efficiency, thus overcoming some of the challenges that discouraged such applications of ammonia in the past. However, achievement of low NOx emission from ammonia combustors remains an important challenge. In this study, combustion techniques and combustor design for efficient combustion and low NOx emission from an ammonia MGT swirl combustor are proposed. The effects of fuel injection angle, combustor inlet temperature, equivalence ratio, and ambient pressure on flame stabilization and emissions were investigated in a laboratory high pressure combustion chamber. An FTIR gas analyser was employed in analysing the exhaust gases. Numerical modeling using OpenFOAM was done to better understand the dependence of NO emissions on the equivalence ratio. The result show that inclined fuel injection as opposed to vertical injection along the combustor central axis resulted to improved flame stability, and lower NH3 and NOx emissions. Numerical and experimental results showed that a control of the equivalence ratio upstream of the combustor is critical for low NOx emission in a rich-lean ammonia combustor. NO emission had a minimum value at an upstream equivalence ratio of 1.10 in the experiments. Furthermore, NO emission was found to decrease with ambient pressure, especially for premixed combustion. For the rich-lean combustion strategy employed in this study, lower NOx emission was recorded in premixed combustion than in non-premixed combustion indicating the importance of mixture uniformity for low NOx emission from ammonia combustion. A prototype liner developed to enhance the control and uniformity of the equivalence ratio upstream of the combustor further improved ammonia combustion. With the proposed liner design, NOx emission of 42?ppmv and ammonia combustion efficiency of 99.5% were achieved at 0.3?MPa for fuel input power of 31.44?kW. 相似文献
The focus of this study lies on turbulent incompressible swirling flows with high swirl intensity. A systematic parameter study is conducted to examine the sensitivity of the mean velocity field in a swirl chamber to changes in the Reynolds number, swirl intensity and channel outlet geometry. The investigated parameter range reflects the typical kinematic flow conditions found in heat transfer applications, such as the cooling of the turbine blade known as cyclone cooling. These applications require a swirl intensity, which is typically much higher than necessary for vortex breakdown. The resulting flows are known as flow regime II and III. In comparison to flow regime I, which denotes a swirling flow without vortex breakdown, these flow regimes are characterized by a subcritical behavior. In this context, subcritical means that the flow is affected by the downstream channel section. Based on mean velocity field measurements in various swirl chamber configurations, it is shown that flow regime III is particularly sensitive to these effects. The channel outlet geometry becomes a determining parameter and, therefore, small changes at the outlet can produce entirely different flow patterns in the swirl chamber. In contrast, flow regime II, as well as flow regime I and axial channel flows, are much less sensitive to changes at the channel outlet. The knowledge about the sensitivity of the flow in different flow regimes is highly relevant for the design of a cyclone cooling system. Cooling systems employing flow regime III can result in a weakly robust flow system that may change completely over the operating range. As a remedy, the swirl intensity needs to be decreased so that flow regime III cannot be reached, which, however, reduces the maximum achievable heat transfer in the cooling system. Alternatively, the flow has to transition back from flow regime III to flow regime II or I before the flow leaves the swirl chamber. Two practical methods are presented. These findings can be directly applied in the design processes of future cyclone cooling systems, and other applications of swirling flow. 相似文献
The production of prompt neutrinos in the beam dump experiment is explained in a cluster model, by postulating the emission
of strange clusters in hadron collisions, besides the usual non-strange clusters. The low mass strange clusters can decay
only by the weak interaction. The leptonic and semi-leptonic decay modes of these clusters give rise to prompt neutrinos.
A prediction of the model is that the ratios <ve>/π+ at PS energies would be the same as SPS energies. 相似文献
The paper presents large eddy simulations of co-annular swirling jets into an open domain. In each of the annuli a passive
scalar is introduced and its transport is computed. If the exit of the pilot jet is retracted strong coherent flow structures
are generated which substantially impact on the transport and mixing of the scalars. Average and instantaneous fields are
discussed to address this issue. A conditional averaging technique is devised and applied to velocity and scalars. This allows
to quantify the impact of the coherent structures on the mixing process. 相似文献
Numerical studies have been made on co-flow non premixed methane air flame in a cylindrical micro combustor with heat recirculating wall. An optimum Peclet number Peopt based on air flow velocity has been observed at which the flame location from the combustor inlet is minimum and the rate of heat recirculation to fresh charge is maximum. The optimum Peclet number is almost independent of the outer wall Nusselt number NuE and the thermal conductivity ratio ks/kg. The rate of heat recirculation shows contrasting increasing and decreasing trends with NuE, depending upon whether Pe < Peopt or Pe >Peopt respectively.
A higher limit of Peclet number for flame blow-off and a lower limit of Peclet number for flame extinction have been identified for a given global equivalence ratio and given values of NuE, ks/kg and t/D (the ratio of wall thickness to tube diameter). The upper Pe limit decreases sharply with NuE, while the lower Pe limit is almost uninfluenced by both NuE and ks/kg. Heat diffusion and chemical reaction in the gas phase are found to be the dominant processes of exergy destruction. The second law efficiency shows a minimum value around 30% at an optimum value of Peclet number where flame stand-off becomes minimum. 相似文献