Effect of the configuration of the rear wall of the cavity on combustion in a supersonic combustor

Results of an experimental study of a supersonic combustor with a solid (continuous) and discrete (discontinuous) rear wall of the cavity are reported. The tests are performed in a short-duration wind tunnel with an attached pipeline at the entrance Mach number of 3, total temperatures of 2550–3140 K, and static pressures of 178–195 kPa. Heated kerosene is used as a fuel. Data on ignition conditions and kerosene combustion efficiency are obtained for different cavity configurations. The drag of internal elements of the combustor, which form recess stabilizers, is estimated. An overall advantage of the combustor with a discrete rear wall of the cavity over a solid rear wall is demonstrated.     

Effect of steam addition pathways on NO reduction characteristics in a can-type spray combustor

Steam addition effect on NO reduction in kerosene spray combustion was investigated experimentally. Three steam addition pathways (Case-1, Case-2 and Case-3) were arranged to find out the effective way of steam addition. In Case-1, steam was directly introduced into the fuel spray. In Case-2, it was pre-mixed with combustion air and introduced into the combustor. In Case-3, it was introduced through side holes of the combustor. NO, O₂, CO, CO₂, and temperature distributions in the combustor were analyzed for these steam pathways. It was clearly observed that the maximum temperature was reduced and high temperature region in the combustion chamber became narrow with steam addition. As a result, the effects of NO reduction in Case-1 and Case-2 were stronger than that in Case-3. It was considered that the suppression of NO formation in just after ignition region was necessary to reduce NO emission from the combustor.     

Continuous spin detonation of a coal-air mixture in a flow-type plane-radial combustor

Regimes of continuous spin detonation of coal particles in an air flow in a flow-type plane-radial combustor 500 mm in diameter are studied. The tested substance is fine-grained cannel coal from Kuzbass having a particle size of 1–7 µm and containing 24.7% of volatiles, 14.2% of ashes, and 5.1% of moisture. A certain amount of hydrogen is added for coal transportation into the combustor and promotion of the chemical reaction on the surface of solid particles. To reduce air pressure losses in channels connecting the manifold and the combustor, their cross section is increased to limiting values (25 cm²), whereas the combustor exit diameter is reduced. The angle of the air flow direction and the combustor geometry are also varied. The minimum pressure difference in the air injection channels (16%) is reached with stability of continuous spin detonation in the combustor being retained. The domain of continuous spin detonation regimes in the coordinates of the fuel flow rate and specific flow rate of the mixture is constructed. The results of studying detonation burning of solid fuels can find applications in power engineering, chemical industry, and environmental science, in particular, contamination by combustion products.     

Development of a catalytically assisted combustor for a gas turbine

A catalytically assisted low NO_x combustor has been developed which has the advantage of catalyst durability. This combustor is composed of a burner section and a premixed combustion section behind the burner section. The burner system consists of six catalytic combustor segments and six premixing nozzles, which are arranged alternately and in parallel. Fuel flow rate for the catalysts and the premixing nozzles are controlled independently. The catalytic combustion temperature is maintained under 1000°C, additional premixed gas is injected from the premixing nozzles into the catalytic combustion gas, and lean premixed combustion at 1300°C is carried out in the premixed combustion section. This system was designed to avoid catalytic deactivation at high temperature and thermal or mechanical shock fracture of the honeycomb monolith. In order to maintain the catalyst temperature under 1000°C, the combustion characteristics of catalysts at high pressure were investigated using a bench scale reactor and an improved catalyst was selected for the combustor test. A combustor for a 20 MW class multi-can type gas turbine was designed and tested under high pressure conditions using LNG fuel. Measurements of NO_x, CO and unburned hydrocarbon were made and other measurements were made to evaluate combustor performance under various combustion temperatures and pressures. As a result of the tests, it was proved that NO_x emission was lower than 10 ppm converted at 16% O₂, combustion efficiency was almost 100% at 1300°C of combustor outlet temperature and 13.5 ata of combustor inlet pressure.     

波瓣喷嘴燃烧室燃烧特性的数值模拟

建立了波瓣式燃油多点喷射燃烧室模型,考察了波瓣诱发涡系对燃烧室燃烧特性的影响。采用文献的多点喷射燃烧室实验的空载、30%载荷、巡航与起飞4种工况,对波瓣喷嘴燃烧室内的流场涡系结构、燃烧多物量场及燃烧特性进行了数值模拟。结果表明,不同油气质量比下随空气质量流量增加,每个工况下的流向涡、正交涡等无量纲涡量逐渐增大,出口温场品质逐渐提高,NOx排放逐渐降低,燃烧效率和出口温度场改善。波瓣喷嘴燃烧室实验台的水流模型实验结果验证了模型计算结果的正确性。     

Coal combustion characteristics in a fluidized bed combustor with a draft tube

The effects of gas velocity to draft tube (3–6 U_m), bed temperature (800–900°C) and excess air ratio (0–30%) on the total entrainment rate, overall combustion efficiency and heat transfer coefficient have been determined in an internally circulating fluidized bed combustor with a draft tube. The total entrainment rate increases with an increase in gas velocity to draft tube, but decreases with increasing bed temperature and excess air ratio. The overall combustion efficiency increases with increasing excess air ratio, but decreases with increasing gas velocity to draft tube. The overall combustion efficiency obtained in internally circulating fluidized beds was found to be somewhat higher than that in a bubbling fluidized bed combustor.     

Mixing and combustion in a shallow coal-limestone fluidized bed combustor

A model based on the Monte Carlo approach was developed to simulate the mixing and combustion behavior of a shallow coal-limestone fluidized bed combustor. The model involved the coupling of two sub-models: a combustion sub-model based on the two-phase concept of fluidization and a mixing sub-model based on our previously developed dynamic mixing model. The combustion sub-model considered both the volatile and char combustion. It assumed that the combustor consisted of three distinct phases, i.e., jet, bubble and emulsion, with combustion occurring only in the emulsion phase. The mixing sub-model considered the upward or downward movement of a coal particle in the bed as being governed by certain probability laws; these laws were, in turn, affected by the bubbling hydrodynamics. In all, the combustor simulation model took into consideration the effects of coal feed rate, coal size distribution, limestone size, air flow rate and combustor temperature on the combustor behavior. The simulation results included the dynamic response of coal concentration profile, coal size distribution, coal particle elutriation rate as well as the mixing status between the coal and limestone particles.     

Combustion characteristics of a two-stage swirl-flow fluidized bed combustor

In order to investigate the combustion characteristics of a two-stage swirl-flow fluidized bed combustor, combustion experiments of low-grade anthracite coal were performed. Experimental parameters were the fluidizing air velocity, coal feed rates, bed temperature, stoichiometric air ratio, swirl nozzle diameter and rotational diameter. The experimental results showed that, due to the swirl flow, the elutriation rates of fines were lower than those of the single-stage fluidized bed combustor. The combustible contents of the ash in the outflow streams were also reduced. Therefore, the combustion efficiency of the two-stage swirl-flow fluidized bed combustor was 20% greater than that of the single-stage fluidized bed combustor under the same operating conditions.     

Simulation of gas-particle turbulent combustion in a pulverized coal-fired swirl combustor

A particle stochastic trajectory model for turbulence-particle reaction interactions is proposed and formulated in the present paper. This model provides the basis for a comprehensive model of pulverized coal combustion. It is applied to the simulation of gas-particle turbulent flow and combustion in a pulverized coal-fired swirl combustor. The results are compared with the measured test data and those obtained by the particle stochastic trajectory model without considering turbulence-particle reaction interactions. The predicted gas temperature and species concentrations in the upstream region of the combustor are improved by utilizing the model with turbulence-particle reaction interactions.     

Experimental and numerical studies of mixing and flame stability in a micro-cyclone combustor

A 30-W-class micro-cyclone combustor was developed as a heat source for a 1-W thermoelectric power generator (TPG). Methane gas was used as a fuel instead of liquefied fuel in this feasibility study for convenience. The combustion stability of the combustor was measured, and the flame shapes were visualized experimentally. Numerical simulations were performed to examine the details of the flame structure and flame stabilization mechanism inside the micro-cyclone combustor. The micro-cyclone combustor burned the supplied fuel stably inside the combustion chamber in the range where the combustor generated 30 W of heat energy. The mixing and flow characteristics of non-reacting and reacting flows in the combustor were examined using the simulation results. The mixing of the fuel with air in a non-reacting flow field was enhanced by increasing the equivalence ratio for a fixed fuel flow rate. For non-reacting flow, a recirculation region and a small negative axial velocity region near the injection ports were formed. The recirculation region became wider with decreasing equivalence ratios. For reacting flows, however, the recirculation region disappeared and the only small negative axial velocity region was formed near the fuel injection ports. The flame was stabilized inside the combustor because the flame base was anchored near the negative axial velocity region near the fuel injection ports.     

凹槽稳焰的超音速燃烧室内混合和燃烧特性分析

采用数值计算方法分析超声速气流流过安装凹槽稳定器的燃烧室气动机理和边界层对混合和燃烧的影响。复杂的激波、膨胀波结构和激波边界层的作用有利于气流混合;同时,凹槽内的低速回流区不断和主流气体发生质量动量交换,可以起到点火和火焰稳定的作用。     

Performance evaluation of a pilot scale vortexing fluidized bed combustor

To understand vortexing fluidized bed combustor (VFBC) performances, an investigation was carried out in a 0.45 m diameter and 4.45 m height pilot scale VFBC. Rice husks, corn, and soybean were used as the biomass feedstock and silica sand serving as the bed material. The bubbling bed temperature was controlled by using water injected into the bed. The experimental results show that the excess air ratio is the dominant factor for combustion efficiency. The in-bed combustion proportion increases with the primary air flow rate and bed temperature, and decreases with the volatile/fixed carbon ratio. The stability constant is proposed to describe the inertia characteristics of the vortexing fluidized bed combustor. The experimental results indicate that the stability of the VFBC increases with bed weight and primary air flow rate, but decreases with bed temperature.     

Numerical analysis of combustion of a hydrogen–air mixture in an advanced ramjet combustor model during activation of O<Subscript>2</Subscript> molecules by resonant laser radiation

This paper presents a numerical study of the combustion of a hydrogen–air mixture in a model ramjet combustor with separate hydrogen and air supply during activation of O₂ molecules by resonant laser radiation at a wavelength of 762.3 nm and 193.3 nm. The calculation is made using the parabolized Navier–Stokes equations taking into account chemical reactions, laser irradiation, and the nonuniformity of air parameters at the combustor inlet due to the complex gas-dynamic structure of the flow in the air intake. It is shown that the combustion completeness at the combustor outlet can be increased by a factor of 2.8 by redistributing the hydrogen supply through the system of fuel tank pylons. Further increase in the combustion completeness can be obtained by exposure of a narrow flow region to resonant laser radiation, more effectively at a wavelength of 193.3 nm. The combination of laser exposure with hydrogen supply redistribution increases the combustion efficiency by a factor of more than 4.7 compared to the base case. In this case, this provides a 95% increase the longitudinal force component in the portion of the internal engine duct that provides a positive contribution to the thrust. Estimation of the energy efficiency of using laser radiation shows that the laser energy input required to achieve this effect is 40–80 times (depending on the fuel supply method) less than the increase in the chemical energy (compared to the case of no laser exposure) released due to fuel combustion.     

Test results of a catalytic combustor for a gas turbine

A catalytically assisted low NO_x combustor has been developed which has the advantage of catalyst durability. Combustion characteristics of catalysts at high pressure were investigated using a bench scale reactor and an improved catalyst was selected. A combustor for multi-can type gas turbine of 10 MW class was designed and tested at high-pressure conditions using liquefied natural gas (LNG) fuel. This combustor is composed of a burner system and a premixed combustion zone in a ceramic type liner. The burner system consists of catalytic combustor segments and premixing nozzles. Catalyst bed temperature is controlled under 1000°C, premixed gas is injected from the premixing nozzles to catalytic combustion gas and lean premixed combustion is carried out in the premixed combustion zone. As a result of the combustion tests, NO_x emission was lower than 5 ppm converted at 16% O₂ at a combustor outlet temperature of 1350°C and a combustor inlet pressure of 1.33 MPa.     

Test results of a catalytically assisted combustor for a gas turbine

A catalytically assisted ceramic combustor for a gas turbine was designed and tested to achieve low NO_x emissions. This combustor is composed of a burner and a ceramic liner. The burner consists of an annular preburner, six catalytic combustor segments and six premixing nozzles, which are arranged in parallel and alternately. In this combustor system, catalytic combustion temperature is controlled under 1000 °C, premixed gas is injected from the premixing nozzles to the catalytic combustion gas and lean premixed combustion over 1300 °C is carried out in the ceramic liner. This system was designed to avoid catalyst deactivation at high temperature and thermal shock fracture of the ceramic honeycomb monolith of the catalyst. A 1 MW class combustor was tested using LNG fuel. Firstly, NO_x emissions from the preburner were investigated under various pressure conditions. Secondly, two sets of honeycomb cell density catalysts and one set of thermally pretreated catalysts ware applied to the combustor, and combustion tests were carried out under various pressure conditions. As a result, it was found that the main source of NO_x was the preburner, and total NO_x emissions from the combustor were approximately 4 ppm (at 16% O₂) at an adiabatic combustion temperature of 1350 °C and combustor inlet pressure of 1.33 MPa.     

Development of can-type low NOx combustor for micro gas turbine (fundamental characteristics in a primary combustion zone with upward swirl)

A low NO_x combustor for kerosene-fueled micro gas turbine based on a new concept was proposed, and the combustion characteristics of the prototype combustor were investigated. The new concept combustor consisted of primary and secondary combustion zones, and they were connected by a throat. A swirler was set between the primary and secondary combustion zones. In order to enhance the recirculation of burned gas in the primary combustion zone, the combustion air was introduced through the swirler and forced to flow upward to the combustor bottom, from where fuel spray was supplied through a nozzle. An optimum configuration of the primary combustion zone such as length of primary zone, swirler vane angle, diameter of throat, etc. were investigated to achieve high combustion stability and low emission in wide ranges of fuel flow rate and excess air ratio. The optimum value of each part in the primary combustion zone was found out by measuring fundamental combustion characteristics such as lean combustion limit, flame luminosity, exhaust gas composition and combustion gas temperature.     

Development of a low NOx catalytic combustor for a gas turbine

Catalytic combustion is an advanced combustion technology and is effective as a NO_x control for a 1300°C class gas turbine for power generation, but the catalyst reliability at high temperatures is still insufficient. To overcome this difficulty, catalytic combustors combined with premixed combustion were designed. In this concept, it is possible to obtain combustion gas at a temperature of 1300°C while keeping the catalyst bed temperature below 1000°C. Catalyst segments are arranged alternately with premixing nozzles for the mixing of catalytic combustion gas and fresh premixture. An air bypass valve was fitted to this combustor for extending the range of stable combustion. As a result of the atmospheric combustion tests, NO_x emission was lower than 5 ppm, combustion efficiency was almost 100%, and high combustion efficiency was obtained in the range of 900–1300°C of the combustor exit gas temperature. A full-pressure combustion test is planned to prove the combustor performance.     

Combustion of Liquid and Gaseous Fuels in a Supersonic Combustor

Results of an experimental study of a full scramjet model operating on kerosene, which was performed in an IT-302M hotshot wind tunnel based at the Institute of Theoretical and Applied Mechanics of the Siberian Division of the Russian Academy of Sciences, and an experimental study of a model operating on hydrogen, which was performed in a hotshot wind tunnel with fire heating based at the China Aerodynamic Research and Development Center, are reported. The tests were performed for Mach numbers 5 and 6 for flow parameters close to in-flight conditions. An optimal system for kerosene injection under these conditions was determined, and the thrust characteristics of the engine model were examined. The possibility of controlling kerosene combustion in tests in the short-duration wind tunnel was analyzed, and special features of fuel ignition in a short combustor were considered. Intense combustion of kerosene was achieved with upstream injection of more than 3% of hydrogen, which allowed obtaining effective thrust. The distributions of static pressure and force characteristics of the model in the case of kerosene and hydrogen combustion were compared.     

Heat fluxes to combustor walls during continuous spin detonation of fuel-air mixtures

Pioneering measurements of heat fluxes to the walls of flow-type combustors of different geometries were performed in regimes of continuous spin detonation of fuel-air mixtures under unsteady heating. These heat fluxes are compared with those observed in the regime of conventional turbulent combustion in the same combustor. Air is used as an oxidizer, and acetylene or hydrogen is used as a fuel. For identical flow rates of the fuel, the heat fluxes to the combustor walls in regimes of continuous spin detonation and conventional combustion are close to each other; their mean steady values are ≈1 MW/m² (≈0.5% of the enthalpy flux of the products over the channel cross section). In both detonation and combustion regimes, the maximum heat fluxes penetrate into the walls in the mixing region (where the heat release occurs). In the case of detonation, regenerative cooling of the combustor walls by the flow of the fresh mixture occurs in the heat-release region (region of propagation of the detonation-wave front). The regeneration becomes less effective in the downstream direction because of the shorter time of contact between the walls and the cold mixture and a longer time of contact between the walls and the hot products. More intense heating persists downstream of the front, where the regeneration ceases, but the temperature of the products is high. The character of heating of the wall in the region of rotation of the front of spin detonation waves depends on the number of these waves: the zone of the maximum heat release becomes narrower with increasing number of waves. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 1, pp. 80–88, January–February, 2009.