Numerical simulation of plasma-assisted combustion of methane-air mixtures in combustion chamber

A two-dimensional mathematical model was developed to investigate the effects of dielectric barrier discharge （DBD） plasma on CH4-air mixtures combustion at atmospheric pressure. Considering the physical and chemical processes of plasma-assisted combustion （PAC）, plasma discharge, heat transfer and turbulent were simultaneously coupled into simulation of PAC. This coupling model consists of DBD kinetic model and methane combustion model. By comparing simulations and the original reference＇s results, a high-accuracy of this model was validated. In addition, the effects of PAC actuation parameters on combustion characteristics were studied. Numerical simulations show that with an inlet airflow velocity of 10 m s-1, a CH4-air mixtures＇ equivalence ratio of 0.5, an applied voltage of 10 kV, a frequency of 1200 kHz, compared to conventional combustion （CC）, the highest flame temperature rises by 32 K; outlet temperature distribution coefficient drops by 2.3%; the maximum net reaction rate of CH4 and H20 increase by 11.22% and 12.80% respectively; the maximum CO emission index decreases by 14.61%; the mixing region turbulence mixing time reduces by 89 ms.

Effect of Swirl Preset Vorticity on Combustion Performance of Lobe Nozzle Combustor Chamber

To improve the combustor performance of multi-point injection combustion,lobe nozzle design was applied to the aero-engine model combustor,by presetting the swirl through a certain twisted angle of the edge of the lobe outlet.Numerical simulation in combination with modelling test is used in this paper.The effects of swirl vorticity presetting onto the vortex structure,the characteristics of combustion temperature field,the combustor exit temperature field quality,the combustion efficiency,and the NOx emissions of multi-point injection combustion chamber are investigated.Compared with the conventional vortex flow at the lobe outlet edge,the results of numerical simulation and water modelling test of the swirl vorticity presetting show that the swirl presetting can efficiently enhance the range and intensity of the lobe-induced vorticities.Besides,it can improve the uniformity of the combustion temperature in the combustor chamber,together with the reduced emissions of the pollutant NOx.Moreover,compared with the conventional lobe nozzle chamber,the swirl vortex presetting can effectively improve its combustion performance.The flow simulation test results demonstrate the fluid vortex structure in the combustion chamber and validate the simulation results.

Application of Reaction-Bonded Silicon Carbide in Manufacturing of Spacecraft Combustion Chamber

Silicon carbide (SiC) ceramics is a good structural ceramics material, which have a lot of excellent properties such as superior high-temperature strength up to a temperature of 1 350 ℃, chemical stability, good resistance to thermal shock and high abrasion resistance. The silicon carbide ceramics material has so far been used widely for manufacturing various components such as heat exchangers, rolls, rockets combustion chamber. Sintering of ceramics structural parts have many technological method, the reaction-bonded is one of important sintering technology of ceramics structural parts. The preparation of reaction-bonded silicon carbide (RBSC) is based on a reaction sintering process, whereby a compacted body of α-SiC and carbon (graphite) powders is heated in contact with liquid silicon or gas silicon, which impregnates the body, converting the carbon (graphite) to β-SiC which bonds the original alpha grain. This process is characterized by low temperature and a short time sintering, and being appropriate to the preparation of large size and complex-shaped components, and so on. Besides, during compacting process of reaction sintering, it can maintain a stable dimension of ceramics parts. Therefore, the method of reaction-bonded silicon carbide ceramics has been identified as a technology suitable for producing complicated and highly exact dimensions’ ceramics parts. In this paper, the method of reaction-bonded silicon carbide was applied to the manufacturing of a complex-shaped spacecraft combustion chamber of SiC ceramics. SiC and carbon powder of 4～30 μm were chosen as the raw materials, green compacts containing appropriate wt.% carbon were formed using the mold press method, sintering was performed in a graphite electric furnace under an argon atmosphere. It was introduced in detail that the technological parameters and technological flow of reaction sintering silicon carbide ceramics. At the same time, physical and mechanical experiments such as bending strength, coefficient of thermal expansion, coefficient of thermal conductivity, gastight property, heat resisting property etc. have been carried out. The results demonstrated that spacecraft combustion chamber made from reaction sintering of silicon carbide ceramics is feasible and the results of experiment is satisfactory. The strength of high-temperature structural parts made by reaction sintered SiC varied with silicon content; Under the this article testing condition, the optimum silicon content is 10.5% for the part investigated. The method of reaction sintered SiC ceramics is suitable for manufacturing of complicated spacecraft parts with a working temperature of 1 500 ℃.

Fundamental Laws of Physics and Calculation of Heat Transfer in Combustion Chambers of Gas-Turbine Plants

The laws of heat radiation from black body, the laws of Stefan-Boltzmann, Planck, and Wien are fundamental laws of physics. All in all, a little more than 30 fundamental laws of physics, studied by pupils and students worldwide were disclosed. Scientific disclosure of fundamental laws influences mainly power technology, fuel and energy resources saving. In the late XIX century the laws of heat radiation from gas volumes and the laws of Makarov were disclosed. Since the radiation laws from blackbody are fundamental laws of physics, then the laws of heat radiation from gas volumes are fundamental laws of physics. Effect of using laws of heat radiation from gas volumes on fuel saving, reduction of development pressure on the environment in many countries of the world is shown. Calculation results from heat transfer in combustion chamber of gas-turbine plant are described. The torch in a combustion chamber is modeled by cylindrical gas volumes. Fluxes data from the torch and convective fluxes of cooling air are confirmed by measuring data from chamber-wall temperature.

Effect of Gasoline Property on Formation of Intake Valve and Combustion Chamber Deposits

The cleanliness of gasoline is related to its components and properties.All commercial gasoline builds up deposits on the engine's injector,intake valve and combustion chamber,which can significantly lower the engine performance and influence exhaust gas emissions.In this study,the intake valve deposits (IVD) and combustion chamber deposits (CCD) produced from combustion of fuel containing 21 v%—42 v% of aromatics and 8 v%—31 v% of olefins have been studied using Ford engine tests,and the characteristics of deposits were studied by IR spectroscopy,TGA and elemental analysis instrument.The test results have shown that deposit formation depends on the fuel composition,especially the aromatic content in the fuel.It is also observed that there are differences in the values of IVD and CCD measured by IR spectrometry and elemental analyses.

Application of the porous medium combustion technology in the chamber reheating furnaces at Baosteel

The design of the porous medium combustion （PMC） system which has been applied to chamber reheating furnaces is presented in this study and its main application effects are described in detail. Porous medium materials are mainly ceramic ball sucked granular bed porous media and foam ceramic porous media. This study investigates the foam ceramic porous medium and a schematic diagram of the combustion inside this porous medium. The PMC takes a solid medium as its main heat exchange way, thus greatly improving the heat transfer efficiency. Judging from the application effects,the following conclusions have been made： the PMC technology can save more than 25% of energy with remarkable effects; the furnace temperature uniformity can be significantly enhanced; the porous media combustion technology can make the heating furnace design in a more compact way, reduce the time for heating up the furnace, improve the heating rate and reduce energy consumption.

The Impact of Flexible Element Inside of Intake Canal on Kinematics of Load in Combustion Chamber

The results of analysis of technical possibilities to increase engine efficiency were presented in this article. This problem was connected with kinematics properties of air inflow to the combustion chamber. The possibilities of intake airflow modulation have a positive impact on combustion process, level of engine usable parameters and emission. This issue was presented on the results of experimental research. Results of baseline research gave information about the flow resistance. On the basis of results of experimental research, conclusions were formulated.

Full Cycle Cold Flow Analysis of the Effect of Twin Swirl Combustion Chamber Design in a Diesel Engine

New designs and adaptation methods are experimented to ensure compliance to ever increasing emissions and efficiency requirements of modern diesel engines. Piston head structure which influences the mixing rate and timing of the fuel within in the combustion chamber is known to enable increase in combustion efficiency and thus lower emission rates. In this paper, computation analysis of flow within a diesel engine cylinder with a twin swirl combustion chamber design throughout a full cycle is presented. The results obtained indicate that the effect of the twin swirl combustion chamber on the cold flow conditions is noteworthy and further analysis together with experiments may reveal information that may prove to be useful in further new designs.

Influence of Combustion Chamber Design Parameters and Intake Environments on Spark Ignition Engine Performance and Exhaust Gas Emission

In the present paper, the effect of the combustion chamber design parameters on the improvement of combustion efficiency (the heat generated inside the combustion chamber) and the enhancement in the pollution rates (heat emissions) from a four-stroke, spark-ignition engine has been studied experimentally and theoretically. Two different programs, Gaseq and Ansys, were used to simulate the effect of the combustion chamber shape, turbulent kinetic energy, intake temperature, intake pressure, parity ratio, compression ratio, and engine speed on reducing specific fuel consumption in the engine, reducing carbon dioxide emissions, and increasing overall engine efficiency. The results showed increasing the intake temperature increased the amount of heat produced in the combustion chamber. This leads to increases in the overall efficiency of the engine, but leads to increasing the carbon dioxide and nitrogen oxide emissions. Increasing the intake pressure has a positive effect on the combustion temperature and pressure, but it has a negative effect on carbon dioxide and nitrogen oxides. Raising the pressure ratio improved the overall efficiency of the engine by increasing the combustion heat, but increasing specific fuel consumption and emissions. Also, increasing the engine speed above the permissible limit has an adverse effect on the spraying speed due to the piston speed being higher than the flame speed, which leads to a reduction in the engine brake torque. An increase in the compression ratio leads to higher fluid pressure and output capacity, but combustion methods occur. An increase in the kinetic energy of the turbulence leads to good combustion. A bowl in a piston has the highest rate of rotation and rotation compared to flat and hemispherical pistons. That is, the design of the cylinder head of this type leads to an improvement in the combustion efficiency and thus the efficiency of the engine.

Experimental Tests on a Pre-Heated Combustion Chamber for Ultra Micro Gas Turbine Device: Air/Fuel Ratio Evaluation

Current portable power generators are mainly based on internal combustion engine since they present higher values of efficiency comparing to other engines;the main reason why internal combustion engine is not convenient for micro power generation (5 - 30 kW) is because of their heaviness. Micro and ultra micro gas turbine devices, based on a micro compressor and a micro turbine installed on the same shaft, are more suitable for this scope for several reasons. Micro turbine systems have many advantages over reciprocating engine generators, such as higher power density (with respect to size and weight), extremely low emissions and few, or just one, moving part. Those designed with foil bearings and air-cooling operate without oil, coolants or other hazardous materials. Micro turbines also have the advantage of having the majority of their waste heat contained in their relatively high temperature exhaust. Micro turbines offer several potential advantages compared to other technologies for small-scale power generation, including: a small number of moving parts, compact size, lightweight, greater efficiency, lower emissions, lower electricity costs, and opportunities to utilize waste fuels. The object of this study is the experimental tests on a stand-alone gas turbine device with a pre-heated combustion chamber (CC), to validate the fuel consumption reduction, compared to an actual and commercial device, used on air models.

Combustion Characteristics in Growth Chamber for Verneuilgrown Rutile Crystal

Combustion characteristics of three-tube burner in growth chamber for preparation of single crystal by the Verneuil method were investigated,and the effects of nozzle structure and flow rate on the surface temperature of molten cap were analyzed.The results showed that hydrogen flowed out from the nozzle diffused with inner and outer oxygen,and two flame produced in the center and near the wall of growth chamber.The surface temperature of molten cap were gradually reduced from the center outward.The temperature of molten cap decreased gradually with increasing the nozzle aperture of inner oxygen,and varied slightly with the diameter of hydrogen and outer oxygen nozzle.The temperature of molten cap decreased gradually with increasing the flow rate of inner and outer oxygen,while increased with the flow rate of hydrogen.

Optimizing Spray and Combustion in Diesel Engine by Multidimensional Numerical Simulation

The calculation of spray and combustion in diesel engines is described by using the softwares FIRE and BOOST. The application of the resulting computational method to the simulation of fuel spray and breakup, mixture formation and combustion in a heavy duty diesel is presented. According to detailed insight into the governing processes provided by the simulation results, various aspects of the dependence of the spray propagation and combustion on the chamber geometry and spray angle are discussed. Then, global cylinderaveraged pressure traces are extracted from the space and time resolved field quantities and compared to incylinder pressure measurements. Finally, an optimized configuration of the chamber geometry and spray angle with a new injection rate of higher injection pressure is proposed.

Improving Designs of CA6DF2 Series Diesel Combustion System

The technical improvements are made based on the former CA6110 diesel engine to meet the requirements of Euro Ⅱ emission standards. The performance and emission for CA6DF1 and CA6DF2 are all met the demand of design by improving the fuel, combustion and supercharging systems. The injection system adopts high-pressure pump-pipe-injector injection system. To enhance the injection pressure, the methods of augmenting plunger diameter, decreasing the nozzle hole diameter and reducing the inner diameter of the high-pressure fuel pipe are adopted. The design of combustion chamber and the match of inner fuel distributions with air motion are based on a great deal of experimental database and some simple computer-aided methods, which ensure the optimization of performance and provide the guide for experimental development.

Experimental Study of MHD-Assisted Mixing and Combustion Under Low Pressure Conditions

In order to reveal the mechanism of MHD-assisted mixing, and analyse the major parameters which influence the effect of MHD-assisted mixing, experiments of MHD-assisted mixing are carried out with a non-premixed butane-air combustion system. The evolvement of the discharge section and the effect of MHD-assisted mixing on combustion are investigated by changing the magnetic flux density and airflow velocity. The results show that the discharge area not only bends but also rotates around the centered wire electrode, which are mainly caused by the Lorentz force. Moreover, the highest curvature occurs near the centered wire electrode.The discharge localizes near the surface of the wire electrode and annular electrode when there is no ponderomotive force. However, if the ponderomotive force is applied, the discharge happens between these two electrodes and it gradually shrinks with time. The discharge area cannot localize near the annular electrode, which is due to the increase of energy loss in the airflow.When the airflow velocity exceeds a certain value, the discharge section becomes unstable because the injected energy cannot maintain the discharge. The rotation motion of the discharge section could enlarge the contact surface between butane and air, and is therefore beneficial for mixing and combustion. Magnetic flux density and airflow velocity are critical parameters for MHD-assisted mixing.

Influence of Internal Combustion Engine Parameters on Gas Leakage through the Piston Rings Area

In this work, the influence of internal combustion engine parameters (cylinder-piston clearance, piston head height, the first segment position, gap of the first piston ring and gap of the second piston ring, piston rings’ axial clearance, intake valve debit coefficient) gas leakage from the combustion chamber through the piston rings’ area was investigated. This influence was studied by making an initial forming operation over gas leakage in the analyzed area.

Optimization of Combustion Characteristics and Fuel Injection Timing of a New Type Dual-Pit Combustor Rotary Engine

In order to improve the performance of the rotary engine,this paper has designed a new type of dual-pit rotary engine combustion chamber structure,and compares the combustion and emission characteristics with the rotary engine with a traditional combustion chamber.The existence of the dual-pit combustion chamber strengthens the overall vortex intensity in the cylinder,effectively promotes the mixing process of fuel and air in the cylinder,the maximum combustion pressure in the cylinder increased by 8.6%,significantly increases the diffusion combustion speed,and significantly improves the dynamic performance of the rotary engine.On this basis,the effects of fuel injection timing parameters on fuel distribution,combustion and emission characteristics were studied.Fuel distribution is more even and dispersed during injection in the later stage of compression.When the fuel injection timing was 105°BTDC in the middle of the compression phase,the matching effect of fuel distribution law and ignition scheme was the best.When the injection timing was 75°BTDC and 85°BTDC in the late compression stage,the mass fraction of NOx remained at a low level.The correlation between soot generation and the change of fuel injection timing was weak.When the injection time was 85°BTDC,the soot generation remained at a relatively high level.

双进气道结构下带凹腔补燃室燃烧特性数值研究

针对导弹应用固体冲压发动机补燃室的掺混燃烧问题,通过一次燃气的气相燃烧模型和硼燃料的KING燃烧模型,探究了双侧90°和双侧180°进气条件下带凹腔补燃室(后倾角范围为90°~150°)的温度场和流场分布情况.阐述了凹腔旋流效应及其对燃烧过程和燃烧产物的影响,进行了燃烧性能量化分析.数值结果表明:双侧180°进气条件下凹腔增大了燃料和空气的掺混空间,凹腔截面出现4个大对冲旋涡,掺混更加均匀,有利于燃烧组织,有效燃烧空间更大,补燃室出口总燃烧效率达到85%.双侧90°进气条件下凹腔截面形成逆时针单向旋涡,燃烧集中在狭小空间,对燃烧过程不利,补燃室出口总燃烧效率仅为55%.凹腔后倾角由90°提高到120°时,燃料和空气的掺混空间增大,促进了燃烧过程.凹腔后倾角继续提高到150°,凹腔空间增大改善燃烧的作用微弱.

乙烯富燃燃气旋转爆轰波传播特性实验研究

本文以乙烯与氧气燃烧产生的富燃燃气作为燃料,空气为氧化剂,开展了乙烯富燃燃气旋转爆轰波传播特性实验研究。探究了不同传播模态下旋转爆轰波传播特性以及传播模态的影响因素,对不同模态下的时频特性、传播速度及起爆延迟时间等参数进行了对比分析。研究表明:乙烯富燃燃气传播模态及工作当量比区间与一次燃烧产物有关。在单波模态中,当量比为0.67时,获得爆轰波最大传播速度为1347.4 m/s。空气质量流量增加,乙烯富燃燃气旋转爆轰波传播模态向多波模态发展,爆轰波波头数目增加会导致爆轰波传播速度下降。同种传播模态下,起爆延迟时间随着空气流量增加而缩短。

双喷油器大角度喷雾碰撞模拟与试验研究

为提高柴油机升功率,高功率密度(HPD)柴油机采用双喷油器.但在高温环境(1200K)下,过多的燃油量不仅增加了燃烧当量比,而且缩短了滞燃期,使燃油未充分雾化就开始着火,从而导致燃烧恶化现象.组织喷雾碰撞能一定程度上促进油气混合、缓解燃烧恶化,目前碰撞喷雾相关研究中喷雾的碰撞角度较小,且主要针对喷雾雾化.为进一步提高超高功率密度柴油机的燃烧效率,本文基于可视化定容燃烧弹(CVCC)探究了双喷油器大角度碰撞喷雾(90°、120°、150°、180°)的雾化和碳烟生成特性,并利用Star-ccm+软件对喷雾碰撞进行了模拟.研究发现,任意角度喷雾碰撞的动能损失均可以通过180°对撞喷雾的动能损失预测,并基于此提出喷雾碰撞的动能损失模型.实验表明,随碰撞角度增加,碰撞后喷雾区域湍动能增强,雾化改善,燃烧品质提升,碳烟峰值减小,碳烟氧化速度加快.

掺氢天然气管道阀室泄漏爆炸规律研究

将一定比例的氢气掺入天然气中并通过现有天然气管道进行输送是大规模输氢的有效方式。氢气点火能量低,爆炸范围广,扩散燃烧速度快,掺氢天然气发生燃烧爆炸事故的危害性较常规天然气更大。为探究掺氢天然气管道阀室发生泄漏后的燃烧爆炸规律,采用计算流体力学软件FLACS对受限空间内输气管道法兰连接处破损后混合气体的泄漏、扩散、燃烧、爆炸过程进行了模拟研究。结果表明:气体泄漏后爆炸时混合气体中氢气含量越高,泄漏后气云点火时间越长,爆炸的强度及危害程度越大;顺风向气云爆燃强度显著强于逆风向气云燃爆强度;不同阀室结构会产生不同强度的爆炸超压,泄爆墙对降低阀室燃爆危害的作用有限,露天阀室和棚式阀室结构产生的爆炸危害较小。