Numerical Study on Effect of Non-uniform CMAS Penetration on TGO Growth and Interface Stress Behavior of APS TBCs

The penetration of CaO-MgO-Al_(2)O_(3)-SiO_(2)(CMAS)is one of the most significant factors that induce the failure of air-plasma-sprayed thermal barrier coatings(APS TBCs).The direct penetration of CMAS changes the thermal/mechanical properties of the top coat(TC)layer,which affects the thermal mismatch stress behavior and the growth of thermally grown oxide(TGO)at the TC/bond coat(BC)interface,thereby resulting in a more complicated interface stress state.In the present study,a two-dimensional global model of APS TBCs with half of the TC layer penetrated by CMAS is established to investigate the effect of non-uniform CMAS penetration on the interface stress behavior.Subsequently,a local model extracted from the global model is established to investigate the effects of interface morphologies and CMAS penetration depth.The results show that non-uniform CMAS penetration causes non-uniform TGO growth in APS TBCs,which consequently causes the stress behavior to vary along the interface.Furthermore,the CMAS pen-etration depth imposes a significant effect on the TC/TGO interface stress behavior,whereas the interface roughness exerts a prominent effect on the stress level at the BC/TGO interface under CMAS penetration.This study reveals the mechanism associated with the effect of non-uniform CMAS penetration on the interface stress behavior in APS TBCSs.

Transient and Steady Spray Characteristics of Soybean Oil/2,5-Dimethylfuran Blended Fuel in an Underwater Stirling Engine

The reduction of oxygen consumption is a key factor to improve the energy density of underwater Stirling engine.A series of fundamental experiments are carried out to elucidate the spray characteristics of soybean oil/2,5-dimethylfuran(DMF)blended fuel in an underwater Stirling engine.Spray characteristics such as spray penetration,spray angle,spray area,and light intensity level under low injection and ambient pressures are obtained using image post-processing method.The results show that the effects of injection pressure,ambient pressure,and nozzle diameter on the transient spray characteristics of underwater Stirling engine are similar to those of diesel engine.However,in the steady spray process,the injection pressure has little effect on spray near angle,and the spray far angle increases with the increase of the injection pressure.Compared with the spray far angle at injection pressure of 3 MPa,the spray far angle at 5 MPa and 7 MPa increased by 11.38%and 18.14%respectively.The addition of DMF can obviously improve the atomization of soybean oil/DMF blended fuel.The spray angle of blended fuel in transient process increases with the increase of the DMF concentration.The spray near angle has exceeded that of diesel(46.21°)when the DMF volume fraction exceeds 25%.The spray far angle is equivalent to that of diesel when the DMF volume fraction reaches 75%.Moreover,the spray with gas ejection no longer keeps conical,the droplet diameter distribution is more dispersed,and the droplet diameter is smaller.

Pre-chamber turbulent jet ignition of methane/air mixtures with multiple orifices in a large bore constant volume chamber: effect of air-fuel equivalence ratio and pre-mixed pressure

Liquefied natural gas (LNG), mainly composed of methane, is in progress to substitute diesel fuel in heavyduty marine engine for practical, economic, and environmental considerations. However, natural gas is relatively difficult to be ignited in a large bore combustion chamber. A combustion enhancement technique called prechamber turbulent jet ignition (TJI) can permit combustion and flame propagation in a largebore volume. To investigate the effect of air-fuel equivalence ratio and pre-mixed pressure on pre-chamber TJI of methane/air mixtures with multiple orifices in a large bore volume, experimental tests and computational simulations were implemented to study the discharge of hot turbulent jets from six orifices of the pre-chamber. Different initial pressures and air-fuel equivalence ratios were considered to analyze the characteristics of TJI. The asymmetry of the turbulent jet actuated from six different orifices were found due to the asymmetric orientation of the spark plug, resulting in the inhomogeneous distribution of combustion in the constant volume chamber, which should be considered seriously in the marine engine design. Besides,as the premixed pressure increases, it has more effect on the flame propagation and plays a more important role, as it further increases.

Formation and transformation of volatile nanoparticles from a diesel engine during exhaust dilution

A classic H 2 SO 4-H 2 O binary homogeneous nucleation model coupled to an aerosol dynamics model,suitable for studying the formation and transformation of volatile nanoparticles (VNPs) during diesel engine exhaust dilution,has been developed.Using the H 2 SO 4-H 2 O binary homogeneous nucleation model,the nucleation ratio and molecular cluster size were calculated.The effect of aerosol dynamic processes on VNP number size distributions was studied.The effects of fuel sulfur content (FSC) and sampling conditions in the laboratory on VNP number size distributions were also calculated.Our simulations demonstrated that nucleation increased the cluster number concentration and that FSC,temperature and humidity significantly affected the nucleation ratio and molecular cluster size.Coagulation promoted the evolution of cluster-particle size distributions from monodisperse to polydisperse.Soot present in the exhaust can suppress the formation of VNPs.FSC and sampling conditions,like the primary dilution temperature,the primary dilution relative humidity,residence time and the primary dilution ratio have significant effects on VNP number size distributions.

基于航改三轴燃气轮机的湿空气透平循环建模与分析（英文）

由于航改三轴燃气轮的排气温度很低,传统的联合循环技术并不适用于三轴燃气轮机。湿空气透平(HAT)循环不需要高温余热,因此,为航改燃气轮机提供了一种新的选择。然而由于单轴燃气轮机结构更加简单,现有的HAT循环试验电站都是基于单轴燃气轮机设计的,而将航改燃气轮机改造为HAT循环依然缺乏充分的研究。本文提出了一种基于航改燃气轮机的HAT循环模型,详细介绍了基于模块化建模的饱和器、燃气轮机和换热器的建模方法,并通过对国产某航改三轴燃气轮机的仿真验证了该方法的准确性。仿真结果表明,在不改变燃气轮机尺寸和运行特性的前提下,直接转变为HAT循环后,由于注入水的缘故,系统无法达到原有的额定透平进口温度。但是,当HAT循环运行在额定功率时,系统效率依然可以提高0.16%。此外,仿真结果还表明,当考虑燃气轮机改型后,HAT循环效率的提升非常显著。文章结果对基于多轴燃气轮机,特别是航改燃气轮机的HAT循环设计与分析提供了参考。

一种基于通用传热传质系统的新型饱和器的动态建模方法（英文）

饱和器是湿空气透平(HAT)循环最重要的部件之一,也是HAT循环与其他燃气轮机循环最重要的区别。由于缺少相关商业运行的经验,热力系统建模与仿真,特别是对饱和器的建模、仿真工作,对HAT循环系统设计、优化有着至关重要的意义。传统饱和器模型通常是基于传热传质理论,该理论需要精确的传热系数和传质系数来保证模型的准确性。本文提出了一种利用基于冷却塔模型的通用传热传质系数来描述小型HAT循环系统中饱和器的建模方法。通过与仿真结果的比较表明,该模型可以很好地预测饱和器在低压低温条件下的内部湿度和温度的动态分布特性。

The effect of catalyst layer design on catalyst utilization in PEMFC studied via stochastic reconstruction method

Catalyst utilization is an important determinant of proton exchange membrane fuel cell performance,and increasing the catalyst utilization is one of the most critical approaches to reducing the catalyst loading in PEMFC.4-phase stochastic reconstruction method based on the variable-resolution Quartet Structure Generation Set(QSGS)algorithm is utilized to elucidate the influence of different parameters of electrode preparation,including the porosity,the dispersion degree of carbon agglomerate,ionomer content,and carbon support size,on the catalyst utilization in the catalyst layer.It was found that there exist optimal values for the porosity,dispersion degree of carbon agglomerate,ionomer content,and carbon support sizes in CLs and any deviations from these optimal values would lead to transport issues of electron,proton and mass within CLs.Taking electron,proton and mass transport into consideration simultaneously,the optimal Pt utilization is 46.55%among 48 cases in this investigation,taken at the carbon support diameter of 40 nm,the porosity of 0.4,the agglomerate spatial density of 25μm^(−3) and I/C at 0.7.The selection of porosity,ultrasonic dispersion technique and ionomer content for conventional electrode preparation requires compromises on mass,electron and proton transport,leading to catalyst utilization in CLs hardly exceeding 50%.Therefore,the next generation of catalyst layer design and preparation technology is desired.

DECISION OF SAMPLE SIZES IN EXPERIMENTS OF TURBULENT FLOW BASED ON WAVELET ANALYSIS

By making the wavelet analysis in both time and frequency aspect and statistical analysis, a method was proposed to decide sample sizes in the experiments of turbulent flows. With an example of analyzing the turbulent kinetic energy in a turbulent boundary layer, this method was proved to be practicable.

Prediction of the effective thermal conductivity of packed bed with micro-particles for thermochemical heat storage

The heat transfer property of the powder bed greatly affects the performance of a thermochemical heat storage system. Therefore, an accurate evaluation of effective thermal conductivity(ETC) is a key for developing thermochemical heat storage systems. This paper focuses on the ETCs of commonly used porous thermochemical materials, such as Mg O/Mg(OH)2and Ca O/Ca(OH)2powders, as well as the corresponding composites with embedded metal foams. Random sphere-like particles packing(RSPP)method is proposed to reconstruct the microstructures of the powder and micro-scale generation method and computed tomography are adopted for the metal foams. Energy transport equations through porous media are solved by the lattice Boltzmann method(LBM) to obtain ETC. Results obtained using RSPP-LBM method agree with experimental data better than other existing methods. For thermochemical heat storage, the variation of ETC during chemical reactions is numerically predicted. Metal foam-embedded thermochemical materials are also studied to evaluate the enhancing effects of the metal foams. Results show that ETC of the powders is dominated by the gas phase, whereas that of the metal foam composites is dominated by the metal phase.

Applicability of high dimensional model representation correlations for ignition delay times of n-heptane/air mixtures

It is difficult to predict the ignition delay times for fuels with the two-stage ignition tendency because of the existence of the nonlinear negative temperature coefficient (NTC) phenomenon at low temperature regimes. In this paper, the random sampling-high dimen-sional model representation (RS-HDMR) methods were employed to predict the ignition delay times of n-heptane/ air mixtures, which exhibits the NTC phenomenon, over a range of initial conditions. A detailed n-heptane chemical mechanism was used to calculate the fuel ignition delay times in the adiabatic constant-pressure system, and two HDMR correlations, the global correlation and the stepwise correlations, were then constructed. Besides, the ignition delay times predicted by both types of correlations were validated against those calculated using the detailed chemical mechanism. The results showed that both correlations had a satisfactory prediction accuracy in general for the ignition delay times of the n-heptane/air mixtures and the stepwise correlations exhibited a better performance than the global correlation in each subdo-main. Therefore, it is concluded that HDMR correlations are capable of predicting the ignition delay times for fuels with two-stage ignition behaviors at low-to-intermediate temperature conditions.

The use of phase-change cooling strategy in proton exchange membrane fuel cells:A numerical study

Thermal management is considered a critical issue in proton exchange membrane fuel cells(PEMFCs),since it not only influences the cell performance but also impacts PEMFC’s reliability and durability.With the ever-increasing power density of PEMFC,traditional cooling approaches including air cooling and water cooling become difficult to meet the demand for highpower heat dissipation.Therefore,phase-change cooling is proposed for fuel cell application in this work,and the potential advantages are discussed and demonstrated via a mathematical model incorporating phase-change heat transfer.The thermal management performance is evaluated by temperature uniformity,maximum temperature difference,and the cooling capacity to compare the difference between phase-change cooling and traditional methods,which demonstrates that phase-change cooling owns a greatly improved thermal management performance.In addition,a simple method to broaden the operating temperature of phase-change cooling based on one certain coolant is offered,which is pressurizing in the coolant channel to regulate the boiling temperature that could further improve the application feasibility of phase-change cooling strategy in fuel cells.

An experimental study on the spray characteristics of diesel-dimethyl ether (DME) blended fuels by phase doppler anemometry

This paper presents an experimental study on the spray characteristics of diesel-dimethyl ether (DME) blended fuels by phase doppler anemometry (PDA). Blended fuels with DME mass fractions of 15%, 30% and pure diesel fuel were used to evaluate the effect of the DME concentration on the spray pattern, droplet size and velocity. The data for spray velocity vector and droplet size field were obtained. The experimental results reveal that the micro-explosive function exists in the jet of diesel-dimethyl ether (DME) blended fuels and the radial velocity of the blended fuels spray is larger than that of conventional diesel fuel spray near the nozzle exit. At the downstream part of the spray, the radial velocity and its attenuation rate of blended fuels are much more uniform and smaller than those of pure diesel spray. At the centerline of the spray, the attenuation rates of all spray axial velocities are similar. With the in- crease of DME concentration in the fuel, the spray angle and the exit velocity increase and the droplet size deceases.

An in-situ DRIFTS study in the reaction between NO_x and soot on BaAl_2O_4

The interactions between NO, O2 and their mixture on BaAl2O4, as well as the reaction of NOx with soot in the presence of O2, have been investigated using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). NO adsorption produces only nitrites species in the absence of O2. NO2 ad- sorption produces nitrates species besides nitrites species. The produced nitrites will further react with O2, O-su rf and O l2-att ice to form nitrates. The reaction of NOx with soot begins with the reaction of ni- trates with soot oxygenated complex (C(O)), which is regarded as the key and rate determining step. A reaction pathway is proposed for the catalyzed reaction of NOx with soot in the presence of O2.

Experimental study of stratified lean burn characteristics on a dual injection gasoline engine

Due to increasingly stringent fuel consumption and emission regulation,improving thermal efficiency and reducing particulate matter emissions are two main issues for next generation gasoline engine.Lean burn mode could greatly reduce pumping loss and decrease the fuel consumption of gasoline engines,although the burning rate is decreased by higher diluted intake air.In this study,dual injection stratified combustion mode is used to accelerate the burning rate of lean burn by increasing the fuel concentration near the spark plug.The effects of engine control parameters such as the excess air coefficient(Lambda),direct injection(DI)ratio,spark interval with DI,and DI timing on combustion,fuel consumption,gaseous emissions,and particulate emissions of a dual injection gasoline engine are studied.It is shown that the lean burn limit can be extended to Lambda=1.8 with a low compression ratio of 10,while the fuel consumption can be obviously improved at Lambda=1.4.There exists a spark window for dual injection stratified lean burn mode,in which the spark timing has a weak effect on combustion.With optimization of the control parameters,the brake specific fuel consumption(BSFC)decreases 9.05%more than that of original stoichiometric combustion with DI as 2 bar brake mean effective pressure(BMEP)at a 2000 r/min engine speed.The NO_(x) emissions before threeway catalyst(TWC)are 71.31%lower than that of the original engine while the particle number(PN)is 81.45%lower than the original engine.The dual injection stratified lean burn has a wide range of applications which can effectively reduce fuel consumption and particulate emissions.The BSFC reduction rate is higher than 5%and the PN reduction rate is more than 50%with the speed lower than 2400 r/min and the load lower than 5 bar.

Dynamic simulation of gas turbines via feature similarity-based transfer learning

Since gas turbine plays a key role in electricity power generating,the requirements on the safety and reliability of this classical thermal system are becoming gradually strict.With a large amount of renewable energy being integrated into the power grid,the request of deep peak load regulation for satisfying the varying demand of users and maintaining the stability of the whole power grid leads to more unstable working conditions of gas turbines.The startup,shutdown,and load fluctuation are dominating the operating condition of gas turbines.Hence simulating and analyzing the dynamic behavior of the engines under such instable working conditions are important in improving their design,operation,and maintenance.However,conventional dynamic simulation methods based on the physic differential equations is unable to tackle the uncertainty and noise when faced with variant real-world operations.Although data-driven simulating methods,to some extent,can mitigate the problem,it is impossible to perform simulations with insufficient data.To tackle the issue,a novel transfer learning framework is proposed to transfer the knowledge from the physics equation domain to the real-world application domain to compensate for the lack of data.A strong dynamic operating data set with steep slope signals is created based on physics equations and then a feature similarity-based learning model with an encoder and a decoder is built and trained to achieve feature adaptive knowledge transferring.The simulation accuracy is significantly increased by 24.6%and the predicting error reduced by 63.6%compared with the baseline model.Moreover,compared with the other classical transfer learning modes,the method proposed has the best simulating performance on field testing data set.Furthermore,the effect study on the hyper parameters indicates that the method proposed is able to adaptively balance the weight of learning knowledge from the physical theory domain or from the real-world operation domain.

Micro Morphology of Soot Particles Sampled from High Pressure Jet Flames of Diesel from Direct Coal Liquefaction

Diesel from direct coal liquefaction(DDCL) is a new type of engine alternative energy. But its hydrocarbon composition and physicochemical properties are quite different from those of Petro diesel. In this study, a premixed constant volume combustion chamber(CVCC) system with soot particle sampling devices was built. The soot particles in the spray flame were sampled and photographed by thermophoresis probe and transmission electron microscope(TEM). An automatic processing code based on Matlab software was developed to process the TEM images and extract the micro morphology parameters of the soot particles. This study has systematically studied the effects of sampling location, injection pressure, ambient density and oxygen concentration on the micro morphology of soot particles. The ambient density refers to the initial gas density in the CVCC. The results showed that various morphologies and sizes of soot particles coexisted in the upstream of the spray flame. During the evolution of soot particles from upstream to downstream in the flame, the size of soot aggregates gradually decreased, while the maturity of soot aggregates increased. With the increase of injection pressure, ambient density and oxygen concentration, the average sizes of soot aggregates and primary soot particles decreased, but the fractal dimensions of soot aggregates increased gradually. Under the same combustion condition and in-flame sampling location, the average projection area, gyration radius and primary soot diameter of soot aggregates produced by DDCL were significantly lower than those of Petro diesel. The structure of soot particles from DDCL was more compact than that of Petro diesel.

Multi-stage ammonia production for sorption selective catalytic reduction of NO_(x)

Sorption selective catalytic reduction of nitrogen oxides(NO_(x))(sorption-SCR)has ever been proposed for replacing commercial urea selective catalytic reduction of NO_(x)(urea-SCR),while only the single-stage sorption cycle is hitherto adopted for sorption-SCR.Herein,various multi-stage ammonia production cycles is built to solve the problem of relative high starting temperature with ammonia transfer(AT)unit and help detect the remaining ammonia in ammonia storage and delivery system(ASDS)with ammonia warning(AW)unit.Except for the singlestage ammonia production cycle with MnCl2,other sorption-SCR strategies all present overwhelming advantages over urea-SCR considering the much higher NO_(x) conversion driven by the heat source lower than 100℃ and better matching characteristics with low-temperature catalysts.Furthermore,the required mass of sorbent for each type of sorption-SCR is less than half of the mass of AdBlue for urea-SCR.Therefore,the multifunctional multi-stage sorption-SCR can realize compact and renewable ammonia storage and delivery with low thermal energy consumption and high NO_(x) conversion,which brings a bright potential for efficient commercial de-NO_(x) technology.

Experimental Investigations on NO_(x) Emission and Combustion Dynamics in an Axial Fuel Staging Combustor

Axial Fuel Staging(AFS)technology is an advanced low-emission combustion method in modem gas turbine,which divides the combustor into two axially arranged combustion zones.For revealing the characteristics of axial staged combustion,an industrial-grade combustor was designed and built.The distribution of temperature and velocity field in the combustor was presented with numerical simulation.And an Atmospheric Combustor Test Rig for axial staged combustion was built.The flow resistance characteristics of the combustor were measured at first.Then the effects of the equivalent ratio and the preheating temperature on the pollutant emission and combustion instability were investigated.The results show that the total pressure recovery coefficient in cold state is always above 98%;starting the secondary combustion at low load can reduce NO emissions by 50%,and can suppress the combustion oscillation amplitude of the combustor.At the design point with φ=0.62 and preheating temperature=400°C,NO emission and CO emission are 15.68 and 4.22 mg/m^(3)(@15%O_(2)).

Evaluation on the Fuel Economy of Automated Vehicles with Data-Driven Simulation Method

With more commercialized automated vehicles(AVs)shortly entering the market,evaluating their fuel economy has become an important topic.The traditional fixed-profile test methods only indicate the effect of powertrain efficiency on fuel economy and cannot reflect the influences of control algorithms or driving behaviors on fuel consumption under real-world traffic conditions.Therefore,a data-driven simulation method for evaluating the real driving fuel economy of automated vehicles is developed.It utilizes naturalistic driving data to reconstruct test cycles.This method can inspect the performance of automated vehicle control algorithms under realistic traffic conditions in terms of fuel economy.The naturalistic driving data collected on urban expressways and freeways were used to model the longitudinal driving scenarios.Then,the fuel consumption of automated and human-driven vehicle was evaluated under the simulated scenarios via the Monte Carlo integration approach.It was found that the fuel consumption rate of the automated vehicle was 11.944 L/100 km under the car-following scenarios.The human-driven vehicle had a fuel consumption rate of 10.124 L/100 km under the same traffic conditions.The tested automated vehicle control algorithm is tuned to achieve better performance in terms of safety and travel efficiency and hence it tends to maintain a relatively steady time headway to the leading vehicle.It applies more frequent accelerating/braking cycles and higher average speed compared to typical human drivers.These characteristics lead to a higher fuel consumption rate of the automated vehicle.The presented method provides an accurate and efficient way to analyze the fuel economy performance of automated vehicles under practical conditions.This method can easily be scaled for large-scale traffic flow analyses.It can also be used to study the effects of human driving styles on fuel economy.

Molecular simulation on carbon dioxide capture performance for carbons doped with various elements

Among the different types of CO_(2)capture technologies for post-combustion,sorption CO_(2)capture technology with carbon-based sorbents have been extensively explored with the purpose of enhancing their sorption perfor-mance by doping hetero elements due to the rapid reaction kinetics and low costs.Herein,sorption capacity and selectivity for CO_(2)and N 2 on carbon-based sorbents doped with elements such as nitrogen,sulfur,phosphorus,and boron,are evaluated and compared using the grand canonical Monte Carlo(GCMC)method,the universal force field(UFF),and transferable potentials for phase equilibria(TraPPE).The sorption capacities of N-doped porous carbons(PCs)at 50℃were 76.1%,70.7%,50.6%,and 35.7%higher than those of pure PCs,S-doped PCs,P-doped PCs,and B-doped PCs,respectively.Its sorption selectivity at 50℃was approximately 14.0,nearly twice that of pure PCs or other hetero-element-doped PCs.The N-doped PCs showed the largest sorption heat at 50℃among all the PCs,approximately 20.6 kJ·mol^(−1),which was 9.7%−25.5%higher than that of the pure PCs under post-combustion conditions.Additionally,with the product purity of 41.7 vol.%−75.9 vol.%for vacuum pressure swing sorption,and 53.4 vol.%−83.6 vol.%for temperature swing sorption,the latter is more suitable for post-combustion conditions than pressure-swing sorption.