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.

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 ℃.

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.

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.

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.

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.

Optimization of aero-engine combustion chambers with the assistance of Hierarchical-Kriging surrogate model based on POD downscaling method

In view of the long calculation cycle,high processing test and cost of the traditional aero-engine combustion chamber design process,which restricts the engine optimization design cycle,this paper innovatively proposes a surrogate model for the performance of aero-engine combustion chambers based on the POD-Hierarchical-Kriging method.Through experiments,the predicted results of the POD-Hierarchical-Kriging model are compared and analyzed with the calculated results of the one-dimensional program,and the root mean square error of the predicted values of combustion efficiency and total pressure loss is 0.0064%and 0.1995%,respectively.The accuracy of the POD-Hierarchical-Kriging model is compared with the cubic polynomial model,the basic Kriging model and the Hierarchical-Kriging model.It verifies the feasibility and accuracy of the POD-Hierarchical-Kriging model for the prediction of performance of aero-engine combustion chambers.The global sensitivity analysis method is applied to obtain the influence effect of design variables on the performance.Then,a multi-objective optimization method based on the NSGA-II algorithm is studied,and finally the optimal set of Pareto solutions is obtained and analyzed,which can be used to guide the optimal design of aero-engine combustion chambers and accelerate the progress of aero-engine development.

Design and analysis of annular combustion chamber of a low bypass turbofan engine in a jet trainer aircraft

The design of an annular combustion chamber in a gas turbine engine is thebackbone of this paper.It is specifically designed for a low bypass turbofan engine in a jettrainer aircraft.The combustion chamber is positioned in between the compressor and turbine.lt has to be designed based on the constant pressure,enthalpy addition process.The presentmethodology deals with the computation of the initial design parameters from benchmarking ofreal-time industry standards and arriving at optimized values.It is then studied for feasibilityand finalized.Then the various dimensions of the combustor are calculated based on differentempirical formulas.The air mass flow is then distributed across the zones of the combustor.The cooling requirement is met using the cooling holes.Finally the variations of parameters atdifferent points are calculated.The whole combustion chamber is modeled using Siemens NX8.0,a modeling software and presented.The model is then analyzed using various parametersat various stages and levels to determine the optimized design.The aerodynamic flowcharacteristics is simulated numerically by means of ANSYS 14.5 software suite.The air-fuelmixture,combustion-turbulence,thermal and cooling analysis is carried out.The analysis isperformed at various scenarios and compared.The results are then presented in image outputsand graphs.

Thermal and elemental analysis of the combustion chamber deposits in a large-scale two-stroke marine diesel engine

It is of significance to understand the chemical content of carbon deposits in the large-scale two-stroke(LSTS) marine diesel engine because of adverse effect on the engine performance, oil consumption and emissions. In this work, two different combustion chamber deposits in an LSTS marine diesel engine were studied using thermogravimetry analysis(TGA), elemental analysis(EA) and synchrotron X-ray fluorescence(SXRF). One was on the piston top and the other on the piston land, termed PTCD and PLCD, respectively. For the PTCD sample, the 97% residue in the TGA and 1.4% carbon content in the EA indicated the main compositions of PTCD were metal salts or oxides and ashes, significantly different from the previous findings of the highest carbon content in deposits from the small four stroke engines. The different chemical content between PTCD and PLCD implied higher thermal load in the LSTS marine diesel engine led to a nearly complete thermal decomposition of PTCD. The higher calcium content in PTCD and PLCD indicated the additives of cylinder oil should be the main source of metal content of PTCD and PLCD. Calcium distribution in the SXRF results was indicative of the potential layered structure in PTCD and PLCD. In addition, the appearance of iron on the surface against the piston in PTCD and PLCD indicated iron oxides formation between carbon deposit and piston materials.

Thermal Activation of the Combustion Chamber of a Reciprocating Internal Combustion Engine

The dominant feature of the work of many specialists on the design of the internal combustion engine is to achieve the possible lowest fuel consumption, which is the most convenient measure of the efficiency of the thermodynamic cycle. From the very beginning of this heat machine, there are many of solutions that are better or worse fit to the global development trend. In this paper, the authors suggest the possibility closer to the optimal solution by introducing structural active zones, where the task is instantaneous(during one cycle) heat transfer to the skin layer on elements of the combustion chamber and to transfer part of the recovered heat to the next cycle, reaching a growth effect of the useful efficiency by 10% to 20%. The solution is different from the ones used by the fact that it is only partially insulating barrier, and the main goal is focused on supporting the next thermal cycle by which it is possible to affect as mentioned above. This paper describes the idea of the functioning of the active combustion chamber and pointed out the technical capabilities of its creation.

Development and Test of Combustion Chamber for Stirling Engine Heated by Natural Gas

The combustion chamber is an important component for the Stifling engine heated by natural gas. In the paper, we develop a combustion chamber for the Stifling engine which aims to generate 3-5 kWe electric power. The combustion chamber includes three main components： combustion module, heat exchange cavity and thermal head. Its feature is that the structure can divide ＂combustion＂ process and ＂heat transfer＂ process into two appar- ent individual steps and make them happen one by one. Since natural gas can mix with air fully before burning, the combustion process can be easily completed without the second wind. The flame can avoid contacting the thermal head of Stifling engine, and the temperature fields can be easily controlled. The designed combustion chamber is manufactured and its performance is tested by an experiment which includes two steps. The experi- mental result of the first step proves that the mixture of air and natural gas can be easily ignited and the flame burns stably. In the second step of experiment, the combustion heat flux can reach 20 kW, and the energy utiliza- tion efficiency of thermal head has exceeded 0.5. These test results show that the thermal performance of com- bustion chamber has reached the design goal, The designed combustion chamber can be applied to a real Stifling engine heated by natural gas which is to generate 3-5 kWe electric power.

Development of a fan-stirred constant volume combustion chamber and turbulence measurement with PIV

A fan-stirred combustion chamber is developed for spherically expanding flames,with P and T up to 10 bar and 473 K,respectively.Turbulence characteristics are estimated using particle image velocimetry(PIV)at different initial pressures(P=0.5-5 bar),fan frequencies(ω=0-2000 r/min),and impeller diameters(D=100 and 114 mm).The flame propagation of methanol/air is investigated at different turbulence intensities(u′=0-1.77 m/s)and equivalence ratios(f=0.7-1.5).The results show that u′is independent of P and proportional toω,which can be up to 3.5 m/s at 2000 r/min.L_(T)is independent of P and performs a power regression withωapproximately.The turbulent field is homogeneous and isotropic in the central region of the chamber while the inertial subrange of spatial energy spectrum is more collapsed to-5/3 law at a high Re_(T).Compared to laminar expanding flames,the morphology of turbulent expanding flames is wrinkled and the wrinkles will be finer with the growth of turbulence intensity,consistent with the decline of the Taylor scale and the Kolmogorov scale.The determined S_(L)in the present study is in good agreement with that of previous literature.The S_(L)and S_(T)of methanol/air have a non-monotonic trend with f while peak S_(T)is shifted to the richer side compared to S_(L).This indicates that the newly built turbulent combustion chamber is reliable for further experimental study.

Numerical Investigation of the Flow inside the Combustion Chamber of a Plant Oil Stove

Recently a low cost cooking device for developing and emerging countries was developed at KIT in cooperation with the company Bosch und Siemens Hausger^ite GmbH. After constructing an innovative basic design further development was required. Numerical investigations were conducted in order to investigate the flow inside the combustion chamber of the stove under variation of different geometrical parameters. Beyond the performance improvement a further reason of the investigations was to rate the effects of manufacturing tolerance problems. In this paper the numerical investigation of a plant oil stove by means of RANS simulation will be presented. In or- der to reduce the computational costs different model reduction steps were necessary. The simulation results of the basic configuration compare very well with experimental measurements and problematic behaviors of the ac- tual stove design could be explained by the investigation.

Testing Procedure for Laboratory Scale Semi Cryogenic Combustion Chamber of LPRE with Problems Faced and Lessons Learned

Design, development, and testing of LPRE(Liquid Propellant Rocket Engine) are difficult and expensive tasks. Prior to full-scale design, it is indispensable to optimize important parameters at sub-scale. Propellants flow rates are low for a sub-scale or laboratory scale combustion chambers. It is hard to satisfy chamber cooling and chill feed lines quickly with low flow rates of propellants. This paper proposes a detailed procedure for testing of a laboratory scale semi-cryogenic combustion chamber. Many tests were conducted with a small scale adjustable length combustion chamber. The injection head of the chamber was interchangeable. Liquid-liquid pressure swirl injector and like impinging injectors were used with two different injection heads. Liquid oxygen and kerosene were used as oxidizer and fuel, respectively. Oxidizer to fuel mixing ratio was 0.29-0.45 and the total propellant mass flow rate was 0.06-0.1 kg/s. Problems were faced during testing, including, explosion in the combustion chamber, fuel injector blockage, unstable combustion, incomplete chilling and blockage of cooling water channel, etc. A detailed procedure is designed on the basis of the lessons learned which was experimentally proved.

Mathematical Models Developed by Zone Method Considering Non-Gray Radiation Properties of Gas in Combustion Chamber

Water vapour and carbon dioxide as the main products in combustion chamber have strong non-gray radiation properties. Multidimensional mathematical models were developed by zone method considering the non-gray radiation properties of gas in combustion chamber. Edwards exponential wide band model （EBWM） was adopted to calculate the non-gray radiation properties of gas, and the three-point Gauss-Legendre integral formula was used to calculate direct radiation exchange areas. Reflected radiation heat fluxes were obtained by Gauss elimination method, and energy balance equations were solved by main variable correction method. An example was given to validate the developed models, and further investigation of effects of flame distribution on heat transfer was carried on.

直流燃烧室内气体辐射换热特性研究

As one of the core components of aero-engine,the thermal protection scheme of combustion chamber has an important impact on its service life.In order to improve the design level of high-performance combustion chamber,the radiation heat transfer characteristics of combustion chamber are studied by experimental method.The following results are obtained:1)With the increase of oil-gas ratio,the gas temperature increases first and then tends to be stable,the radiant heat flow increases gradually,the convective heat flow increases gradually and then tends to be stable,and the proportion of radiant heat flow remains basically unchanged;2)With the increase of the inlet temperature,the gas temperature increases gradually,the radiant heat flow,especially in the flame barrel head area,increases significantly,the convective heat flow remains basically unchanged,and the proportion of radiant heat flow increases significantly;3)With the increase of the combustion chamber pressure,the gas temperature increases gradually.When the combustion chamber pressure is low,the radiant heat flow increases sharply with the increase of the pressure;When the combustion chamber pressure is high,the radiant heat flow increases slowly with the increase of the pressure.The convective heat flow gradually decreases and tends to be stable,and the proportion of radiant heat flow gradually increases and tends to be stable.This study is of great significance to improve the calculation accuracy of radiant heat flow of combustion chamber and the reliability design of thermal protection scheme of combustion chamber.

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.

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.

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.