Combustor Structure Research Articles

Experimental investigation into effects of combustor structure on characteristics of rotating detonation of cracked kerosene gas

This study examines the influence of the structure of the combustor on the propagation of rotating detonation waves (RDWs) of cracked kerosene gas (CKG) by using oxygen-rich air, with mass fractions of oxygen of 36% and 48%, as the oxidant while maintaining stable values of the state parameters of CKG. The experimental results showed that the structure of the combustor played a key role in the initiation and stable propagation of CKG, and suitable values of its width and the width of its outlet promoted the stable self-sustained propagation of the RDWs. Combustors of 8 and 14 mm width failed to initiate with 36% oxygen-rich air and without blockage ratio. In the combustors of 20 and 26 mm width, as the blockage ratio increased, the modes of propagation of the RDW included a single stable RDW, intermittent single RDW, and four, six, and eight counter-rotating RDWs. With the further increase in the blockage ratio, the reflected shock wave at the end of the combustor was enhanced, resulting in an increase in the number of RDW wave heads. As a result, the height of the fresh fuel layer was decreased, the mixing time was decreased and led to a decrease in the RDW velocity. The increase in the width of the combustor was conducive to the radial and axial diffusion of fuel and oxidizer in the combustor, which led to an obvious increase in the propagation velocity of RDW. In the 26 mm width combustor, the maximum RDW velocity is 1769 m/s.

Thermodynamic and entropy generation analyses of Telsa-valve structured meso-scale combustors fuelled with hydrogen for thermophotovoltaic applications

The present work numerically examed the effects of hydrogen volume flow rates (Qv) and equivalence ratios (Φ) on thermal performances of meso-scale combustors structured with Tesla-vale type flow channels. Four distinct Tesla-valve configurations are implemented and then subsequently compared. The reverse-flow Tesla valve with counter-flow combustor (RC) structure shows a remarkable improvement of 72.6 % to the combustor wall temperature at Qv = 100 mL/min. The diodicity (Di) of the Tesla valve is found to be increased with a higher Qv, and a lower Φ contributes to a higher Di. Besides, Di is decreased when Φ goes up, stabilizing at Φ = 0.9. The reverse-flow Tesla valve exhibits a more uniform pressure distribution and entropy production than the forward-flow Tesla valve. At Φ = 0.9, the hydrogen-to-air ratio maximized heat release, producing the highest entropy. Tesla-valve structured combustors demonstrate near complete combustion before Φ reaching 0.9, the combustion efficiency (ηcombustion) is gradually decreased after Φ getting to 1.0. The RC construction achieved maximum combustion efficiency under conditions of insufficient oxygen. This present study demonstrates the feasibility of enhancing thermal and overall performances of meso-scale combustors structured with Tesla-valve channels, and revealing the key parameters effects on the combustion characteristics in these combustors.

Effects of liquid-fuel temperature on rotating-detonation-wave propagation

The utilization of liquid fuel will greatly expand the application scope of rotating detonation engines, and there are still great challenges to achieve high-performance liquid-fuel rotating detonation operation. In this paper, aviation kerosene was used as the liquid fuel to investigate the effects of fuel temperature on the propagation characteristics of rotating detonation waves in two combustor structures: annular and cavity. An electric heating tape was employed to heat the kerosene up to 390 K. The results demonstrate that increasing the temperature of kerosene enhances its atomization efficiency, leading to a marked enhancement in the peak pressure and propagation stability of detonation waves. Moreover, the duration required to establish a detonation wave is notably reduced, as low as 11.2 ms. Furthermore, the detonation wave velocity increases with fuel temperature, with significantly higher velocities observed in the cavity combustor structure compared to the annular combustor structure. In the cavity combustor, the detonation wave velocity can reach up to 74 % of the theoretical CJ value. The results verify the feasibility of improving the rotating-detonation performance via increasing liquid-fuel temperature, which can provide reference for the engineering application of rotating detonation.

Influence of cyclone combustor structure on the motion behaviors of solid fuel particles

A coarse-grained computational fluid dynamics-discrete element method (CFD-DEM) was established to investigate the influence of cyclone combustor structure on the motion behaviors of solid fuel particles. Four structural parameters, i.e., primary inlet number (Pn), secondary inlet number (Sn), secondary inlet location (SL), and guide blade angle (α), were examined. Compared to the base structure with a single primary inlet, the addition of extra primary inlet, secondary inlet, or diversion structure elevates the global parcel location. Increasing Pn and Sn decreases the average parcel residence time, while augmenting SL and α generally lengthens it. Meanwhile, increasing Pn, Sn, and SL or decreasing α broadly reduces the wall parcel-hold ratio. Furthermore, the inclusion of secondary inlet and diversion structure increases the probability of small parcels occurring in the near-wall zone. These observations are helpful for optimizing the design and operation of cyclone combustors.

Structure effect of wall cooling channel on liquid metal heat transfer in aero-engines

In this study, a model of the cooling channel and an experimental system for heat transfer involving liquid metal are studied, to investigate the influence of the wall cooling channel structure of combustor on the heat transfer process. The error between the experimental and simulated outcomes fall is within 3 %, suggesting that the accuracy of the simulation is satisfactory. The simulation results found that the temperature non-uniformity coefficient can be reduced by 13 % and 7 % through adjusting the aspect ratio under the heat flux of 3 MW/m2 and 1.5 MW/m2 respectively, and the wall temperature of gas side can be reduced by 89 K and 47 K respectively. A smaller aspect ratio is favorable for homogenizing the liquid metal temperature distribution. Longer widths, however, can lead to horizontal thermal stratification, which can be unfavorable for heat transfer. With an aspect ratio and rib thickness of about 0.5 and 0.4 mm, respectively, the cooling channel outlet has the lowest non-uniformity coefficient of temperature and enthalpy, which is conducive to the improvement of the wall energy recovery rate. The optimal cooling channel effectively improves the thermal stratification in channel, and provides theoretical guidance for the suitable application of liquid metal to the combustor wall cooling channel.

Investigation of swirler effect on combustion and exergy efficiency of hydrogen/chlorine combustor based on entropy generation analysis

Inefficient reagent reaction limits the development of compact combustion-based HCl synthesis production. To address this issue, a non-premixed HCl synthesis combustor that combines a swirler at the hydrogen channel with a porous nozzle at the chlorine channel is proposed. A three-dimensional non-premixed combustion model is used to investigate the effects of this combustor structure on the combustion efficiency, exergy efficiency, and pressure loss coefficient. The entropy generation analysis is employed to evaluate multiple irreversible losses for different structures and flow states. Through experimental validation and numerical simulation analysis, the effects of the swirler installation, inlet flow rate, and H2/Cl2 equivalence ratio on the combustion and heat transfer characteristics are investigated. The results demonstrate that the combustor with the swirler and porous nozzle improves exergy efficiency, leading to higher HCl purity and a reduced flame height for faster reactions under low-flow states. Chemical reactions contribute to over 96 % of entropy generation during combustion, with the swirler reducing total entropy by approximately 5 %. Optimal heat transfer effects and minimized entropy generation are achieved when the swirler is installed below the combustor spray hole. The installation of the swirler can increase the exergy efficiency of the H2/Cl2 combustor to approximately 43.73 %.

Performance seeking control method for minimum pollutant emission mode for turbofan engine

The research shows that the impact of aero-engine pollutant emission on the environment cannot be ignored. In addition to fuel type and combustor structure, aero-engine exhaust pollutants are also related to engine operating conditions and control systems. In this context, taking CO and NOx as the main exhaust pollutants of the engine as the research object, a performance optimization control method of the minimum pollutant emission mode of the engine is proposed. Firstly, the CO and NOx emission characteristics of the engine under different operating conditions at sea level are calculated by CFD numerical simulation method, and the engine component-level model applicable to all flight envelope and all conditions is established according to the characteristic data. Secondly, in order to improve computational efficiency, an airborne model with high accuracy and real-time performance is established through the deep neural network. Compared to the component-level model, the average relative error of each performance parameter is less than 0.5 %, and the real-time performance is improved by about 12 times. Finally, the optimization principle of the minimum pollutant emission mode is discussed. The feasible sequential quadratic programming (FSQP) algorithm is selected, and the fuel quantity and throat area of the tail nozzle are taken as control variables. Numerical simulations are performed in the typical mission envelope. Simulation results show that the CO emission index decreases by 5 % and the NOx emission index decreases by more than 6.5 % through performance optimization control of the minimum pollutant emission mode under the premise of ensuring constant engine thrust and meeting other constraints.

Numerical simulation and improvement of combustor structure in 3D printed sand recycling system

Abstract In this paper, a new combustor with an output of 5 t/h is designed based on a computational particle fluid dynamics (CPFD) model. The flow field simulation is combined with the combustion simulation to analyze the internal two-phase flow, temperature field, and combustion products. The combustor structure was optimized. The simulation results show that the recovery efficiency of the waste sand and the energy utilization of the combustor can be improved under the original structure. The sand bed has a significant effect on flow field characteristics. The increase in particle temperature in the combustor increases the efficiency of waste sand recovery by increasing the height of the sand bed by 50 mm. The utilization rate of natural gas is increased and the economic efficiency is improved. The feasibility of the CPFD method can simulate the flow field characteristics inside the combustor very effectively.

Numerical investigations on the performance of a hydrogen-fueled micro planar combustor with tube outlet for thermophotovoltaic applications

As the practical application of the micro thermophotovoltaic system is limited by its low output power and energy conversion efficiency, optimizing the structure of micro combustor to enhance the thermal performance of micro combustors is an effective method. In this work, the tube outlet is proposed to enhance the heat transfer between the burned gas and combustor wall. A three-dimensional model including fluid flow, heat transfer and combustion is constructed to investigate effects of tube length, tube diameter and solid wall materials on the performance of a hydrogen-fueled micro planar combustor with tube outlet. The findings show that the tube outlet can effectively improve mean outer wall temperature and outer wall temperature uniformity of micro planar combustor, and the energy output and energy conversion efficiency of MTPV system, but the pressure loss is higher. The energy output and energy conversion efficiency of MTPV system is increased with the reduction of tube length and the increment of tube diameter, while the pressure loss is slowly decreased. Moreover, when nickel is used as the solid wall material, the energy output and energy conversion efficiency of MTPV system can reaches to 6.14 W and 3.54%, respectively.

Combustion instability of ethanol and n-heptane fuels under different combustor geometries

Combustion instability has become one of the most significant challenges faced in designing modern industrial gas turbines and aero-engines. In this study, the influence of combustor structure on the combustion instability of ethanol and n-heptane is explored by adjusting the plenum length (200–550 mm) and the swirler vane angle (60° and 75°). The ethanol combustion instability maps show that the oscillation frequency increases as the equivalence ratio and plenum length decrease with the stabilization range of n-heptane being broader. The maximum pressure pulsation amplitudes of ethanol and n-heptane during combustion instabilities are close to 495 and 415 Pa, respectively. The flow field temperature measurements show that the fuel properties change the flame shape and temperature distribution in the combustor, thus potentially affecting the intensity of the oscillations. Short, compact ethanol flames and more uneven temperature distribution are more likely to lead to unstable combustion. This work provides more experimental observations on the effects of fuel properties and combustion configuration on combustion stability.

Study of Diesel Spray Impinging Ignition and Combustion Characteristics Under Variable Ambient Densities Based on the Visualization Experiment

Abstract The application of turbocharged intercooler direct injection (DI) diesel engine in large diesel vehicle transportation and construction machinery will be indispensable for a long time in the future. The extreme condition of the plateau has become a hotspot in the research of diesel combustion. When the diesel engine works on the cold-start or low-load/low-speed condition, the problems of combustion and emission caused by abnormal supercharging of a turbocharger are apparent. The development of the miniaturization of diesel engines can effectively avoid liquid-wall impingement. However, the low density of the plateau will bring inevitable combustion modes, such as impinging ignition and combustion. This study summarized the relationship among spray, fuel–air mixing, ignition, soot formation, and ambient density under the condition of impinging ignition and nonliquid spray impingement, providing a reference for the further research and improvement of diesel engine combustor structure design. The effect of ambient density change on diesel spray mainly weakens radial air entrainment in the fuel injection. There was apparent impinging ignition at 11.37 g/m3 density, and the ignition time delay was 0.2 ms longer than that at 16.07 g/m3, corresponding to the 0 m altitude. Under high altitude with more significant density, the combustion is more intense under higher temperature. However, the larger flame diffusion area under low density leads to the larger soot distribution area and more considerable soot generation.

Numerical Study on the Effect of Jet on the Operation of Powder Fuel Scramjet

Metal powder fuel has high energy and volume calorific values, and it is an excellent power fuel for hypersonic aircraft in the future. However, metal powder has poor flow characteristics and is difficult to be effectively mixed with air when supersonic air is injected. The mixing degree of fuel and air is an important factor to the efficiency of the engine. One way to solve this problem is to introduce a jet (the primary jet) upstream of the powder fuel inlet to improve the mixing degree of fuel and increase the residence time. In this study, a doublehole jet two-dimensional scramjet combustor structure was established, the effects of different initial jet conditions on the performance of scramjets was studied and analyzed. The results show that the introduction of the primary jet can effectively improve the mixing degree of the powdered fuel and air in the combustion chamber, prolong the residence time of the particles in the combustion chamber and improves the combustion efficiency of the metal powder. However, both the combustion efficiency of the metal powder fuel and engine thrust increase and then decrease when the mass flow rate of the primary jet increases.

Experimental studies on a high performance thermoelectric system based on micro opposed flow porous combustor

This study proposes an opposed flow porous micro combustor structure that provides stable combustion in a 2 mm combustion chamber under high inlet power of propane/air. The results showed that the combustor fully meet the temperature requirements of thermoelectric module, which it can provides over 600 K to thermoelectric devices; And the unique structure of opposed flow intake can improve the flame stability under wider flammable range and enhance the system power density, but the thermal efficiency of combustor is limited due to the heat leakage from intake cavities. The thermal efficiency of this combustor rises dramatically when the inlet power reaches more than 20 W, at the same time, the efficiency of the heat loss on the combustor surface drops sharply. The customized thermoelectric module and heat sink are adopted into this study. Meanwhile, the experimental study is arranged to verify the power density and overall conversion efficiency of combustion-based micro thermoelectric system. In conclusion, the thermoelectric system in this study achieves the power density of 0.18 W/cm3 while maintaining the overall conversion efficiency of 4.27%.

Effects of Injector Spray Angle on Performance of an Opposed-Piston Free-Piston Engine

A free-piston engine is a novel internal combustion engine which has the advantages of a variable compression ratio and multi-fuel adaptability. This paper focuses on numerical simulation for combustion process and spray angle optimization of an opposed-piston free-piston engine. The working principle and spray-guided central combustor structure of the engine are discussed. A three-dimensional computational fluid dynamic model with moving mesh is presented based on the tested piston motion of the prototype. Calculation conditions, spray models, and combustion models were set-up according to the same prototype. The effects of spray angle on fuel evaporation rate, mixture distribution, heat release rate, in-cylinder pressure, in-cylinder temperature, and emissions were simulated and analyzed in detail. The research results indicate that the performance of the engine was very sensitive to the spray angle. The combustion efficiency and the indicated thermal efficiencies of 97.5% and 39.7% were obtained as the spray angle reached 40°.

Numerical analysis of heat recuperation in micro-combustors using internal recirculation

Heat recuperation in micro-combustors used as a radiation source for micro-thermophotovoltaic devices is an important mechanism to increase system efficiency and improve flame stability. A novel combustor structure is proposed to improve the heat transfer from the combustion gases to the combustor outer wall using an internal recirculation region filled with porous media. Numerical results indicate that the temperature difference in the recirculation region can be reduced up to 10 times using metal foams as porous media, which significantly increase the outer wall temperature. Different porous media and recirculation positions were investigated and it was found that the average radiation emission efficiency, for different inlet velocities, can be increased up to 24% in comparison with combustors without recirculation and up to 18% in comparison with combustors with open-channel recirculation (no porous media). The performance improvement is more significant for higher inlet velocities, with increases up to 40%.

Large Eddy Simulation of Combustion and Heat Transfer in a Single Element GCH4/GOx Rocket Combustor

The single element GCH4/GOx rocket combustion chamber developed at the Technische Universitat Munchen has been computed using Large Eddy Simulation. The aim of this work is to analyze the flow and combustion features at high pressure, with a particular focus on the prediction of wall heat flux, a key point for the development of reusable engines. The impact of the flow and flame, as well as of the model used, on thermal loads is investigated. Longitudinal distribution of wall heat flux, as well as chamber pressure, have been plotted against experimental data, showing a good agreement. The link between the heat released by the flame, the heat losses and the chamber pressure has been explained by performing an energetic balance of the combustion chamber. A thermally chained numerical simulation of the combustor structure has been used to validate the hypothesis used in the LES.

Combustion Characteristics Analysis of Improved Combustor Structure of Micro Turbine Engine

In order to improve the performance of micro combustor, the 60 slots of the original combustor were modified into 120 slots for the MIT 6-wafer micro-combustor. The performance of the micro combustor with the improved and original design was compared through numerical simulation, and stable operating ranges was studied. It was found that the improved combustor can stabilize the flame under the condition of higher fuel/air mixture mass flow rate.

Numerical Investigation of Fuel Distribution Effect on Flow and Temperature Field in a Heavy Duty Gas Turbine Combustor

Abstract Multiple-swirlers structure is commonly adopted for combustion design strategy in heavy duty gas turbine. The multiple-swirlers structure might shorten the flame brush length and reduce emissions. In engineering application, small amount of gas fuel is distributed for non-premixed combustion as a pilot flame while most fuel is supplied to main burner for premixed combustion. The effect of fuel distribution on the flow and temperature field related to the combustor performance is a significant issue. This paper investigates the fuel distribution effect on the combustor performance by adjusting the pilot/main burner fuel percentage. Five pilot fuel distribution schemes are considered including 3 %, 5 %, 7 %, 10 % and 13 %. Altogether five pilot fuel distribution schemes are computed and deliberately examined. The flow field and temperature field are compared, especially on the multiple-swirlers flow field. Computational results show that there is the optimum value for the base load of combustion condition. The pilot fuel percentage curve is calculated to optimize the combustion operation. Under the combustor structure and fuel distribution scheme, the combustion achieves high efficiency with acceptable OTDF and low NOX emission. Besides, the CO emission is also presented.

Study on the Structure of Combustor for Model Stirling Engine Using CFD Analysis

Study on the Structure of Combustor for Model Stirling Engine Using CFD Analysis

Flow field characteristics analysis and combustion modes classification for a strut/cavity dual-mode combustor

Experimental and numerical study of a strut/cavity dual-mode combustor has been conducted in this paper. Under different fuel equivalence ratio and allocation proportion conditions, the pressure distribution and flow field structure of combustor show distinct characteristics. For strut fuel injecting at a low equivalence ratio, the luminosity images show that combustion zone distributes in the shear layer behind the strut. The wall fuel injecting before strut would change the starting point of pressure rising. Based on the flow field structure, the dual-mode combustor operation process is classified into three combustion modes, including scramjet mode, weak ramjet mode and strong ramjet mode. Because of a strong interaction of the shock wave with the boundary layer, weak ramjet mode has a stronger isolator compression effect and higher combustion efficiency than scramjet mode. With heat release increasing, the thermal throat formation is an indication of the strong ramjet mode, which has a subsonic gap in the isolator. Further, by judging the pressure from dominant pressure sensor before the strut, the three different combustion modes could be classified. Comparing the specific impulse of combustor, it has an obvious distinction in the different combustion modes.