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 chemica...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.展开更多
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 resi...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 ℃.展开更多
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 (h...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.展开更多
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 convenie...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.展开更多
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 ti...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.展开更多
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 position...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.展开更多
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 f...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.展开更多
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 differen...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.展开更多
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 radiati...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.展开更多
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,...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.展开更多
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 butan...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.展开更多
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 ...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.展开更多
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 propose...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.展开更多
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 rota...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.展开更多
Numerical computation of turbulent strongly-swirling flows in combustors is presented. Turbulence models examined are based on the transport equations of the Reynolds stresses, i.e., the second moment closures. The pa...Numerical computation of turbulent strongly-swirling flows in combustors is presented. Turbulence models examined are based on the transport equations of the Reynolds stresses, i.e., the second moment closures. The particular flows in question include confined as well as free swirling situations where the swirl number is large. It is indicated that the second-moment closure models offer an effective means for predicting strongly swirling flows. In particular, the isotropization of production and convection (IPC) model gives the best overall performance. The study directly serves for the improvement of combustor design.展开更多
This paper summarizes the current situation of China’s industrial hazardous waste treatment,the disposal technology and the characteristics of rotary kiln incineration system,analyzes the refractory lining design of ...This paper summarizes the current situation of China’s industrial hazardous waste treatment,the disposal technology and the characteristics of rotary kiln incineration system,analyzes the refractory lining design of rotary kiln incineration system in China,and puts forward optimization suggestions according to the process characteristics.展开更多
The author describes the fundamental laws of physics, the laws of thermal radiation of ionized and non-ionized gas volumes. Based on open laws, a modern theory of heat transfer and methods for calculating heat transfe...The author describes the fundamental laws of physics, the laws of thermal radiation of ionized and non-ionized gas volumes. Based on open laws, a modern theory of heat transfer and methods for calculating heat transfer in electric arc and flare metallurgical furnaces, furnaces of steam boilers, and combustion chambers of gas turbine plants of power plants have been developed. The use of scientific discovery makes it possible to create innovative electric arc steel-smelting furnaces, flare heating furnaces, and combustion chambers in which the consumption of electricity and fuel is reduced, productivity and service life are increased, and the amount of harmful emissions into the environment is reduced.展开更多
The ignition tendency of diesel fuels is highly sensitive to ambient conditions and fuel properties.In this study,the ignition characteristics of different diesel surrogate fuels with the same derived cetane numbers(D...The ignition tendency of diesel fuels is highly sensitive to ambient conditions and fuel properties.In this study,the ignition characteristics of different diesel surrogate fuels with the same derived cetane numbers(DCN)were measured and compared in varied thermodynamic and oxidizing environments.The combustion pressures,heat release rates,ignition delays,and combustion delays of the test fuels were compared.The experimental results showed that the diesel surrogate fuels with the same DCNs exhibit similar ignition propensity at standard DCN test conditions.Further,for the test conditions of high cetane fuels,high ambient temperatures,and suficient oxygen concentrations,surrogate fuels with the same DCN have similar ignition behaviors,and using the DCN to evaluate fuel ignition tendency is appropriate.However,for the test conditions of low cetane fuels,low ambient temperatures,and reduced oxygen concentrations,different ignition behaviors are observed for the surrogate fuels with the same DCN,so at these conditions using DCN as the evaluation index for fuel ignition tendency may lead to higher uncertainty.展开更多
Natural gas engines have become increasingly important in transportation applications,especially in the commercial vehicle sector.With increasing demand for high efficiency and low emissions,new technologies must be e...Natural gas engines have become increasingly important in transportation applications,especially in the commercial vehicle sector.With increasing demand for high efficiency and low emissions,new technologies must be explored to overcome the performance limitations of natural gas engines such as limits on lean or dilute combustion,unstable combustion,low burning velocity,and high emissions of CH_(4) and NO_(x).This paper reviews the progress of research on natural gas engines over recent decades,concentrating on ignition and combustion systems,mixture preparation,the development of different combustion modes,and after-treatment strategies.First,the features,advantages,and disadvantages of natural gas engines are introduced,following which the development of advanced ignition systems,organization of highly turbulent flows,and the preparation of high-reactivity mixtures in spark ignition engines are discussed with a focus on pre-chamber jet ignition,combustion chamber design,and H_(2)-enriched natural gas combustion.Third,the progress in natural gas dual-fuel engines is highlighted,including the exploration of new combustion modes,the development of novel pilot fuels,and the optimization of combustion control strategies.The fourth section discusses after-treatment systems for natural gas engines operating in different combustion modes.Finally,conclusions and future trends in the development of high-efficiency and clean combus-tion in natural gas engines are summarized.展开更多
The ceramic insulators of spark plugs in gasoline engines are especially prone to damage when deto-knock occurs.To under-stand the damage process and mechanism,the present work investigated the impact resistance of ce...The ceramic insulators of spark plugs in gasoline engines are especially prone to damage when deto-knock occurs.To under-stand the damage process and mechanism,the present work investigated the impact resistance of ceramic insulators using detonation waves as impact sources.A test device that generates detonation waves was developed,representing a novel means of evaluating the knock resistance of ceramic insulators.Various impact types and detonation intensities were employed,and detonation initiation and propagation at peak pressures greater than 100 MPa were assessed using synchronous high-speed direct photography and pressure measurements.The test results demonstrate that ceramic insulators tend to break at the base of the breathing chamber when damaged by a single high peak pressure detonation wave impact.In contrast,multiple low pressure impacts eventually break the insulator into multiple fragments.The data also show that the positioning of a ground electrode upstream of the ceramic insulator greatly increases the resistance of the ceramic to the detonation impact.A two-dimensional computational fluid dynamics simulation coupled with a chemical kinetics analysis demonstrated that this improved resistance can be ascribed to a reduced peak pressure that appears after the detonation wave diffracts from the electrode prior to contacting the ceramic insulator.展开更多
基金supported by National Natural Science Foundation of China(No.51436008)
文摘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.
文摘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 ℃.
文摘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.
文摘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.
文摘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.
文摘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.
文摘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.
基金supported by the National Natural Science Foundation of China(Grant No.52076171).
文摘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.
基金Item Sponsored by National Basic Research Program of China (2006CB601203)
文摘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.
基金National Science and Technology Major Project of China(No.2017-Ⅲ-0003-0027)。
文摘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.
基金supported by National Natural Science Foundation of China(No.11372352)the Mechanism Research on Near Electrode Thermal-Electromagnetic-Flow of High Temperature Supersonic MHD Generation(No.51306207)Natural Science Foundation of Shaanxi Province of China(No.2015JM5184)
文摘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.
文摘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.
基金Sichuan Science and Technology Program(Grant No.2023YFG0336).
文摘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.
基金National Natural Science Foundation of China No.51976083 and the Qing Lan Project.
文摘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.
文摘Numerical computation of turbulent strongly-swirling flows in combustors is presented. Turbulence models examined are based on the transport equations of the Reynolds stresses, i.e., the second moment closures. The particular flows in question include confined as well as free swirling situations where the swirl number is large. It is indicated that the second-moment closure models offer an effective means for predicting strongly swirling flows. In particular, the isotropization of production and convection (IPC) model gives the best overall performance. The study directly serves for the improvement of combustor design.
文摘This paper summarizes the current situation of China’s industrial hazardous waste treatment,the disposal technology and the characteristics of rotary kiln incineration system,analyzes the refractory lining design of rotary kiln incineration system in China,and puts forward optimization suggestions according to the process characteristics.
文摘The author describes the fundamental laws of physics, the laws of thermal radiation of ionized and non-ionized gas volumes. Based on open laws, a modern theory of heat transfer and methods for calculating heat transfer in electric arc and flare metallurgical furnaces, furnaces of steam boilers, and combustion chambers of gas turbine plants of power plants have been developed. The use of scientific discovery makes it possible to create innovative electric arc steel-smelting furnaces, flare heating furnaces, and combustion chambers in which the consumption of electricity and fuel is reduced, productivity and service life are increased, and the amount of harmful emissions into the environment is reduced.
基金supported by the National Natural Science Foundation of China(Grant No.52022058)the Shanghai Science and Technology Committee(Grant No.19160745400)。
文摘The ignition tendency of diesel fuels is highly sensitive to ambient conditions and fuel properties.In this study,the ignition characteristics of different diesel surrogate fuels with the same derived cetane numbers(DCN)were measured and compared in varied thermodynamic and oxidizing environments.The combustion pressures,heat release rates,ignition delays,and combustion delays of the test fuels were compared.The experimental results showed that the diesel surrogate fuels with the same DCNs exhibit similar ignition propensity at standard DCN test conditions.Further,for the test conditions of high cetane fuels,high ambient temperatures,and suficient oxygen concentrations,surrogate fuels with the same DCN have similar ignition behaviors,and using the DCN to evaluate fuel ignition tendency is appropriate.However,for the test conditions of low cetane fuels,low ambient temperatures,and reduced oxygen concentrations,different ignition behaviors are observed for the surrogate fuels with the same DCN,so at these conditions using DCN as the evaluation index for fuel ignition tendency may lead to higher uncertainty.
基金This work is supported by the Key Program of National Natural Science Foundation of China(21761142012)the National Key Research and Development Program of China[2016YFB0101402][2017YFE0102800].
文摘Natural gas engines have become increasingly important in transportation applications,especially in the commercial vehicle sector.With increasing demand for high efficiency and low emissions,new technologies must be explored to overcome the performance limitations of natural gas engines such as limits on lean or dilute combustion,unstable combustion,low burning velocity,and high emissions of CH_(4) and NO_(x).This paper reviews the progress of research on natural gas engines over recent decades,concentrating on ignition and combustion systems,mixture preparation,the development of different combustion modes,and after-treatment strategies.First,the features,advantages,and disadvantages of natural gas engines are introduced,following which the development of advanced ignition systems,organization of highly turbulent flows,and the preparation of high-reactivity mixtures in spark ignition engines are discussed with a focus on pre-chamber jet ignition,combustion chamber design,and H_(2)-enriched natural gas combustion.Third,the progress in natural gas dual-fuel engines is highlighted,including the exploration of new combustion modes,the development of novel pilot fuels,and the optimization of combustion control strategies.The fourth section discusses after-treatment systems for natural gas engines operating in different combustion modes.Finally,conclusions and future trends in the development of high-efficiency and clean combus-tion in natural gas engines are summarized.
基金This work was supported by National Natural Science Foundation of China(Grant Nos.91541206 and 51706121)China Postdoctoral Science Foundation(Grant No.2017T100076).
文摘The ceramic insulators of spark plugs in gasoline engines are especially prone to damage when deto-knock occurs.To under-stand the damage process and mechanism,the present work investigated the impact resistance of ceramic insulators using detonation waves as impact sources.A test device that generates detonation waves was developed,representing a novel means of evaluating the knock resistance of ceramic insulators.Various impact types and detonation intensities were employed,and detonation initiation and propagation at peak pressures greater than 100 MPa were assessed using synchronous high-speed direct photography and pressure measurements.The test results demonstrate that ceramic insulators tend to break at the base of the breathing chamber when damaged by a single high peak pressure detonation wave impact.In contrast,multiple low pressure impacts eventually break the insulator into multiple fragments.The data also show that the positioning of a ground electrode upstream of the ceramic insulator greatly increases the resistance of the ceramic to the detonation impact.A two-dimensional computational fluid dynamics simulation coupled with a chemical kinetics analysis demonstrated that this improved resistance can be ascribed to a reduced peak pressure that appears after the detonation wave diffracts from the electrode prior to contacting the ceramic insulator.