Vortex Combustor Research Articles

Effects of swirling motion on the cavity flow field and combustion performance

An investigation has been carried out through experimental and simulation analyses to evaluate the cold flow field and combustion performance of a novel trapped vortex combustor that incorporates swirling motion. The cavity is an annular region, and the swirling flow (swirl number is 0.0, 0.6, 0.8, 1.0, and 1.2) is in the central axis of the cavity region. The technique of particle image velocimetry (PIV) is employed to investigate the flow field, with a specific focus on the swirling flow configurations within cavities. Additionally, it serves as a reference point for verifying and enhancing simulation methods. Methane is being subjected to combustion experiments at atmospheric pressure, where the fuel is only introduced into the cavity region and the air used is at a temperature of 300 K. The results show that: the cavity vortices are squeezed due to the swirl jet dumping into the cavity region as a result of the overwhelmingly increased centrifugal forces with the strong swirling flow. Additionally, the vortices' tangential velocity within the cavity area undergoes a significant rise under the influence of swirling flow, ultimately leading to a prolonged residence time. A significant increase in turbulence intensity of cavity vortices is also achieved when the swirl number is increased. For combustion results, the average temperature of the cavity increases with an increase in the cavity rear flow equivalence ratio (Φr); as the Φr further increases, the temperature reduces. The maximum temperature is approximately 1600 K for the mainstream with a swirling flow, and it is about 1200 K for no swirling flow. Finally, the rich/lean blowout limit is extended when the swirl number increases.

Physics of flame evolution following spontaneously combusting hydrogen emerging from a tube into the unconfined space

Unexpected self-ignition flame resulting from accidental release of pressurized hydrogen can induce a jet flame after it flows into the unconfined space. The flame evolution in the near-field region of the tube exit is important for the formation of jet flame. This paper presents a study on the physics for the evolution of spontaneously combusting hydrogen flame near the tube exit. Effects of release pressure and tube length are explored. Results show that the flame evolution is controlled by both the shock wave and vortex formed in the near-field region around the nozzle. Although two different types of flame evolution can be formed, both of them undergo the same four stages: initial flame, flame under the effect of shock wave, flame under the effect of vortex and stable combustion. The initial location of the vortex in the two types is different, which is the reason for the presence or absence of the flame separation phenomenon. If the vortex is formed inside the flame, flame separation is induced. In addition, two types of flame can transform into each other depending on the tube length. A hybrid flame can be clearly identified in the transition region in which the tube length varies from 300 mm to 700 mm. It has also been found that the flame in the transition region has features of both types and is easy to be extinguished.

Effect of a passive control strategy on lean ignition and blowout performance of a gas turbine combustor

In this study, a radial strut is designed in the mainstream channel of a trapped vortex combustor (TVC) to improve the mixing between cavity products and mainstream air. This improves combustion efficiency and uniformity of outlet temperature distribution. However, a certain amount of mainstream flow is entrained into the cavity owing to the blockage of the radial strut; this entrainment deteriorates the ignition and blowout performance. To resolve this problem, a passive control strategy using a vertical jet is proposed to restrain the entrainment of mainstream flow into the cavity. Experimental results indicate that compared with the conventional TVC, the proposed strategy significantly improves the ignition and blowout performance. To gain insight into the experimental results, Reynolds-averaged Navier-Stokes-based simulations with a validation methodology were conducted to simulate the flow field and fuel distribution characteristics of the cavity. The simulation results demonstrate that the passive control strategy can effectively restrain the mainstream air entrained in the cavity. The improved ignition and blowout performance provided by passive control strategy can be attributed to the formation of a desirable flow structure with two vortices and high local fuel equivalence ratio inside the cavity.

An experimental study of a bidirectional vortex combustor with two-stage air supply

An experimental study of a bidirectional vortex combustor with two-stage air supply

Combined combustion of pulverized coal and liquid fuel in a low power vortex burner

In this work we study the process of co-combustion of pulverized coal fuel (coal grinded up to 100 microns) and liquid (diesel) fuel in a new low power burner, where coal-air mixture is fed tangentially together with secondary air, and liquid fuel is atomized by a high velocity steam jet. Temperature profiles and composition of intermediate combustion products along the vertical axis of the burner have been studied. The heat release (power) and the gas composition of final combustion products have been measured. This allowed us to demonstrate the principal possibility of combined combustion of coal dust and diesel fuel in a compact laboratory burner.

ВЛИЯНИЕ ИНТЕНСИВНОСТИ КРУТКИ ВОЗДУХА В ВИХРЕВЫХ ГОРЕЛКАХ НА ВЫДЕЛЕНИЕ ОКСИДОВ АЗОТА В ПРОМЫШЛЕННЫХ ТРУБЧАТЫХ ПЕЧАХ

An important task in the design and operation of industrial furnaces is to reduce the formation of harmful substances, in particular, nitrogen oxides (NOx), directly at the source of their occurrence. One of the promising methods of reducing the concentration of NOx in the gas emissions of furnaces is the use of vortex burners with a twist of the flow, providing better mixing of combustion products, thereby reducing the maximum local temperatures in the furnace and equalizing the temperatures over the working volume. However, the available information on the effect of vortex formation on the intensity of nitrogen oxides release is extremely contradictory – depending on the design of the burners and the furnace, the twist of the flow can both increase and decrease the formation of nitrogen oxides. Moreover, single burners have been studied at least in some way from the point of view of NOx release, but their interaction with each other in large-volume furnaces has not been practically investigated and requires additional study. By numerical experiments conducted on the basis of the mathematical model developed by us, it is shown that the smallest release of nitrogen oxides is ensured by the use of burners with a twist of the air flow (oxidizer), as well as their combination with two-stage combustion when the burners are located in the same horizontal plane. It is shown that the combined use of these two methods reduces the release of nitrogen oxides in the furnace by more than a factor of ten.

Combustion of pulverized coal fuel in a spray vortex burner

Combustion of pulverized coal fuel in a spray vortex burner

Numerical modelling of heat transfer processes in coal-fired vortex furnace with bottom-port secondary blowing: ecological performance comparison for two types of coal fuel

The work is devoted to numerical 3D modelling of aerodynamics and pulverized-coal combustion processes in a novel vortex furnace of a boiler unit for thermal power stations. A prospective retrofitting design of this furnace, featuring additional tangential blowing at the bottom part of the vortex combustion chamber, has been studied. The firing regimes using two types of siberian coal (black coal, brown coal) are considered. Numerical results for the studied combustion regimes in the modified vortex furnace are presented, including the fields of velocity, temperature, species and dispersed phase concentrations, and the comparative analysis of NOx emissions for two types of coal.

Effect of the Specific Features of the Torch Aerodynamics on the Integrated Efficiency of the Multifuel Boiler

This scientific paper gives the literature review emphasizing that the overwhelming majority of the operated boilers are equipped with vortex burners. These burners are characterized by an increased NOx formation, low operation reliability of screen tubes and convective heating surfaces, small maneuverability range and insufficient economical indicators. The defining role of the aerodynamic organization of the furnace processes affecting the operation efficiency of the boilers was shown for the case of the combustion of the energy fuels of a different type. Hence, the problems of an increased reliability, maneuverability, environmental safety and economical operation of the boilers are rather topical. The above problems faced by Ukraine today have been essentially exacerbated due to the fact that most boilers of the thermal power plants have a depleted resource and the production of new boilers (especially high power boilers) was actually stopped. The use of vortex burners with the traditional counter layout on the two opposite furnace walls is peculiar for the overwhelming majority of modern high power boilers in Ukraine and abroad. In this case, the central zone of the furnace is designed to provide the collision of the burner torches of opposite walls and a high-temperature burning core is created. In the case of gas –oil boilers, the availability of the high-temperature core results in an intensified formation of the thermal nitrogen oxides and a decreased operation reliability of the metal of furnace screens. The torch throw onto the side furnace walls during the combustion of fuel oil results in an essential decrease of the operation reliability of the screen tubes due to a high-temperature hydrogen sulfide corrosion. This paper highlights the issues of the effect of the specific features of the torch aerodynamics on the integrated efficiency of the boiler operation and the optimization of the layouts for the combustion of energy fuels in the multifurnace boilers for further reconstruction of the boilers to reduce the emission of harmful substances, increase reliability and economicity of their operation and enlarge the steam load carrying range.

Flow and Combustion Characteristics of Wave Rotor–Trapped Vortex Combustor System

Breaking through the limit of conventional compression and combustion, wave rotor and trapped vortex combustors are able to improve the thermal efficiency of gas turbines. Detailed two-dimensional numerical simulations based on Ansys Fluent were performed to study the flow and combustion characteristics of the wave rotor–trapped vortex combustor system. The calculated pressure characteristics agree with the experimental results giving a relative error for average pressure of 0.189% at Port 2 and of 0.672% at Port 4. The flow stratification characteristics and the periodic fluctuations were found to benefit the zonal organized combustion in the trapped vortex combustor. For the six cases of different rotor speeds, as the rotor speed increased, the oxygen mass fraction at the combustor inlet rose and then fell. The proportion of exhaust gas recirculation fell at first and then rose, and the combustion mode became unstable with the dominant frequencies of the fluctuations increasing.

A Development of Meso-Scale Vortex Combustion for a Micro Power Generator Based on a Thermoelectric Generator

The development of portable electronic devices has increased; this development needs to be accompanied by the development of reliable power sources. In this study, two different vortex combustor sets were used in conjunction with a thermoelectric generator to determine their energy output. This study focuses on the development of a meso-scale vortex combustor to obtain the electric energy for a micro power generator; different materials and different vortex designs are analyzed. Numerical and experimental methods have been used to analyze the development of the vortex combustor. A horizontal vortex combustor made from stainless steel had higher wall temperature and voltage output measurements. To analyze the energy output for the micro power generator, a single TEG and double TEG are analyzed; according to the results, a double TEG with a water-cooled system has the highest electric power compared with the other results.

Analysis and performance assessment of the use of ammonia-based nano additive for lean combustion

In recent years, considerable progress has been made in exploring new applications of fuel additives to reduce emissions. Reduction of total nitrogen oxide (NOx) emissions can be achieved by decreasing the flame temperature by using fuel emulsified with water and/or using ammonia-based nano additives such as urea. The use of water as part of the hydrocarbon fuel is also one of the prospective directions in the development of new types of fuel systems. For the preparation of emulsified fuel, it is desirable to achieve greater stability of the emulsified fuel with minimum expenditure of chemicals and energy, so that the emulsified fuel can be used for a longer period. The paper analyzed the influence of nano-dispersed urea particles, water, and surfactant (Span 80/Tween 80) on the combustion stability and emission characteristics of aviation fuel. The experimental campaign was conducted on a test stand (a 300kW liquid vortex combustor of 300 kW) consisting of a cylindrical combustion chamber with four optical windows and equipped with high-precision pressure sensors, thermocouples, and an exhaust gas analyzer for acquiring emissions. The experimental campaign was conducted at a constant fuel/air ratio (Φ). One of the main focus is related to the stability of the emulsion. Chemiluminescence imaging was performed to characterize the effects of the additive on flame emissions. In addition, a statistical and spectral analysis was performed using the pressure sensor for instability analysis. Exhaust gas analysis was performed both with the additive described above and without additive for a constant Φ condition. The analysis was performed for NOx, carbon monoxide (CO) and carbon dioxide (CO2) and oxygen (O2).

Acoustic vibrations of a gas with an inhomogeneous distribution of the speed of sound along the pipe

In this paper, the pulsating combustion of a premixed propane-butane fuel with air in a vortex combustion chamber is considered. The conclusion of the refined frequency equation is made. The characteristic of the mixture supply system is given.

Investigation of performance in a cylindrical trapped vortex combustor with swirler

Investigation of performance in a cylindrical trapped vortex combustor with swirler

An experimental study of syngas combustion in a bidirectional swirling flow

The paper reports on the results of an experimental study of methane and syngas combustion as well as their co-firing in a bidirectional swirling flow. The results confirmed that the bidirectional flow structure provides a significant decrease in the lean blow-off equivalence ratio as well as that of emissions of main pollutants. The combustion intensification becomes more evident when using syngas is as fuel. The composition of the used syngas is as follows (by volume): H2 - 29.42%; CO - 14.32%; CH4 - 3.8%; N2 - 49.11%; H2O - 3.35%. In this case, the lean blow-off is achieved at ϕ < 0.1, NOx emission is halved, while CxHy and CO emissions become 20 times less compared to pure methane combustion. However, according to experimental results, the co-combustion of syngas (volume fraction Vsyn = 15%) and methane is the most appropriate fuel utilization mode. It provides blow-off and emission properties similar to those for combustion of pure syngas, whereas energy consumption for its production is much lower. Moreover, unlike hydrocarbon fuel combustion, that of syngas in a bidirectional swirling flow is characterized by the presence of density stratification. This is accompanied by the flame formation at significantly different locations in the combustion chamber at lean and “ultra-lean” modes of operation. Hydrogen combustion most likely to occur in the core region at near-blow-off modes ϕ < 0.1, whereas normal ‘operating modes in the range 0.2 = ϕ ≤ 0.4 result in the formation of a conical flame surface where CH4 and CO combustion occurs. These new results with respect to the flame structure as well as blow-off and emission properties make it possible to consider bidirectional vortex combustors for application in modern gas turbine power plants in order to meet the strict environmental and energy requirements.

Energy-ecological assessment of the boiler equipment modernized with the jet-niche technology

The results devoted to the issues of energy-ecological assessment of industrial boiler equipment with jet-niche combustion technology are given in the paper. The basic principles underlying this technology include: rational distribution of fuel in the oxidant stream; stable adjustable structure of fuel, oxidant and combustion products; self-regulation of the fuel mixture composition in the zone of the torch stabilization when the unit load changes. As of today, a large number of industrial gas-burning equipment has been modernized by jet-niche technology, including: boilers, furnaces, dryers, metallurgical facilities, etc. The results of industrial implementation of the technology allowed to accumulate a significant amount of technical information and gave the possibility of preliminary environmental assessment during the modernization of gas combustion equipment. As practice shows, at the present stage the main direction of the technology improvement is to enhance its environmental performance. The influence of the main regime and technical parameters of fire equipment on its emission indicators is established in the paper. Possibilities for reducing nitrogen oxides by primary technological methods, the simplest and most effective of which is the introduction of recirculation gases into the furnace space, have been identified. According to the results of the analysis of emission indicators of the modernized fire equipment with a capacity of 0.5–60 MW, data to estimate the emission indicators of low and medium power boilers depending on the main influencing factors, namely, unit size, excess air ratio and boiler load were obtained. The influence of the introduction of recirculation gases into the furnace space on the level of nitrogen oxides concentration is also taken into account. The efficiency of application of the recirculation gases introduction scheme into the primary air flow in comparison with combustion technologies based on vortex burners is shown. According to the results of the industrial experiment, the energy efficiency of the proposed measures was established on the example of the dependences of efficiency on the load of boilers PTVM-50 and KVGM-20.

Experimental and numerical study on the influence of pneumatic parameters on the flow structure in trapped vortex combustor

Flow field of combustors have been commonly used to help understand the combustion characteristics. In this study, the experimental and numerical investigation was carried out combined to study the effect of pneumatic parameters, such as the main stream Mach number, pressure ratio, and temperature, on the flow structure in a trapped vortex combustor This study aimed to investigate the influence of pneumatic parameters on the vortex center position and area of primary and secondary vortices in the cavity, and also study the distribution of axial and radial velocity in the cavity obtained by changing the inlet airflow temperature. The flow fields in the combustor cavity with the variation of main stream Mach number and pressure ratio were obtained by using Particle Image Velocimetry The results show that, a double-vortex pattern can be generated and tightly locked inside the cavity. Furthermore, the flow structure is significantly influenced by pressure ratio ( rp = 0.97–1.07) instead of mainstream Mach number (Ma = 0.13–0.17). Under the same Mach number, the location of vortex center in the main stream plane is moved with the appearance of the temperature gradient. Meanwhile, the velocity profiles indicate that the axial velocity is reduced as the temperature increase. This study provides a design guideline for combustion with the main stream and second stream, and also offers important reference value for the analysis of combustion performance in cavity.

A Study of Walls Thermal Conditions for a Bidirectional Vortex Combustor

Bidirectional vortex combustors are among the most efficient devices in terms of pollutants emission, fuel residence time, an extended range of stable operation. Despite many papers devoted to flow structure in the bidirectional chamber, their heat transfer and wall temperature distributions are not well-studied experimentally as well as most available calculation results are based on adiabatic or isothermal wall conditions. The present paper reports on new experimental and numerical results on flow and flame structures and surface temperature distributions obtained for a combustor with a toroidal vortex chamber. These results show a strong effect of the combustor operation mode and geometry configuration on its thermal conditions. Based on experimental validation, a reliable numerical approach for fluid dynamics, combustion, and heat transfer simulations in the bidirectional vortex chamber is suggested. This approach could assist in determining the most efficient parameters of the bidirectional combustor in terms of energy and environmental indicators as well as wall thermal conditions and service life.

Development of technology for obtaining coal-water fuel

The object of the study is coal sludge and coal fines of the Shubarkol deposit and the Kuznetsk coal basin (Republic of Kazakhstan) for the production of coal-water fuel, which allows replacing liquid and gaseous expensive products. The resulting fuel (after treatment of coal seams and burial) from industrial waste should not harm the environment, which requires certain economic investments. For crushing coal and coal sludge in the crushing and grinding unit, an electrohydroimpulse device for fine grinding of materials was used, consisting of a control unit with a protection system, a pulse capacitor and a high-voltage generator (capacitor bank capacity 0.75 µF, pulse discharge voltage 15–30 kV, length of the interelectrode distance 7–10 mm). After grinding, fine coal particles rise to the surface of the water, and impurities settle at the bottom of the device, which allows enriching the product (flotation). Surface structures and coal fraction sizes were obtained using a Tescan Mira 3 scanning electron microscope. The main characteristics of coal-water fuel during vortex combustion were: the diameter of the fraction 0–250 microns – 63–74 %, process water – 36–24 %, special additive – 1–2 %. Coal-water fuel is similar to liquid fuel, and when transferring heat-generating plants to combustion of suspension, no significant changes in the design of boilers (units) are required. This makes it easy to mechanize and automate the processes of receiving, feeding and burning fuel, and the vortex combustion technology at a temperature of 950–1,050 °C guarantees fuel efficiency of more than 97 %. The given optimal parameters of electrohydroimpulse technology when introduced into production will allow not only grinding, but also enriching the coal product

Experimental and Numerical Study of the Flammability Limits in a CH4/O2 Torch Ignition System

The current work is devoted to studying combustion initiation inside the methane-oxygen torch igniter for a hybrid rocket motor. The ignition system can generate a wide range of power and oxidizer-to-fuel ratios. It has a self-cooled vortex combustion chamber with one fuel jet injector and one circumferential vortex oxidizer injector. The system adjusts the mass flow rates of the propellants through the control valves and organizes cooling of the wall and flame stabilization. Experimental analysis of the ignition limits was investigated on the laboratory test bench. The propellants’ pressure and mass-flow rates, combustion temperature, ignition delay, and spark frequency were controlled during the tests. The authors executed a series of tests with different propellants’ mass flow rates. As a result, the region of stable ignition was found as well as the regions of ignition failure or unreliable ignition. A previously validated numerical model was used to analyze the flow in the reliable ignition region and the ignition failures region. Several numerical simulations of the transient three-dimensional chemically reacting flow were implemented. Consequently, the ignition delay and the thermal impact on the combustion chamber wall were determined numerically. Results of the simulations were compared with theoretical and experimental data showing good correspondence.