Large eddy simulations were performed for film cooling on scaled-up C3X turbine vane at the nominal blowing ratio of M=0.5~1.5, and the Reynolds number, Re=3000, based on the mainstream inlet velocity and hole diameter. On the pressure surface, large-scale coherent structures including hairpin vortexes and horseshoe vortexes are generated in film-cooling flow fields. Hairpin vortexes promote the mixture between hot mainstream and coolant jet and degrade cooling performance. The anti-entrainment of horseshoe vortexes improves the lateral-covering capability of coolant jet in the near-field region and results in the formation of a pair of low-temperature strips wrapped around the hole at high blowing ratio. On the suction surface, the transition of the boundary layer takes place in the downstream of cascade throat but in the upstream of the discharged hole, plenty of broken vortexes dominate film-cooling flow fields. The distribution of turbulent kinetic energy also indicates that the coolant jet from the suction surface generates higher turbulent intensity than that from the pressure surface. For pressure signals for film cooling on the suction surface, small-scale and random fluctuation takes the dominant role. For pressure signals for film cooling on the pressure surface, a dominant frequency corresponding to Strouhal number St≈2.1 both exists at low and high blowing ratios. The film-cooling system on the suction surface exhibits a higher random degree than that on the pressure surface.

Due to concerns over CO₂ emissions and higher efficiency requirements future power generation systems with stationary gas turbines are projected to utilize carbon-free fuels such as ammonia and hydrogen at increasingly high pressure ratios and turbine inlet temperatures. This raises concerns whether conventional approaches for estimating the working fluid properties and for heat balance calculations are appropriate under such conditions. Herein, we therefore investigate the effect of several simplifying assumptions for the working fluid and the combustion scheme often made. We find that at high temperatures and equivalence ratios chemical reactions during the expansion of the gas should be considered, in particular at equivalence ratios close to unity. The extent to which chemical reactions occur during expansion in the turbine requires further investigations, as it could have severe consequences for the heat balances and output calculation of the turbine, as well as the concentration of pollutants such as NO_x in the exhaust gas.

Urea Selective Catalytic Reduction (urea SCR) system is widely used for diesel engine to reduce the emission of NO_x by NH₃ which is provided by a hydrolysis of urea water. Concentration distribution of NH₃ in an exhaust pipe is an important factor for improvement of the SCR efficiency and prevention of NH₃ slip and urea deposit. Therefore, it is necessary to measure two-dimensional (2D) concentration of NH₃ in detail. The purpose of this study is to develop the real-time two cross-sectional measurements technology of NH₃ concentration using the computed tomography-tunable diode laser absorption spectroscopy (CT-TDLAS). Theoretical NH₃ concentration distribution which was reconstructed by CT agreed to CFD results and quadruple pipe’s results showed good resolution by 14th order reconstruction. Therefore, this method has enough resolution and accuracy for measuring the concentration distribution of NH₃. And this method was employed in a bent pipe model demonstrated a urea SCR system. The experimental results of two cross-sectional 2D concentration of NH₃ show differences of the concentration distribution of NH₃ each cross-section and flow pattern like swirl flow. It was found that CT-TDLAS was an effective method to measure concentration distribution of NH₃ and observe characteristics of flow. In addition, observing flow pattern enable to validate CFD results, and it helps to improve efficiency of after treatment system.

Cooling technology plays an important role on the safe operation of hydro-generator. The natural circulation evaporative cooling system of hydro-generator stator busbar was proposed in China, which has the advantages of safety, energy-saving and high-efficiency and can meet better the requirements of generator cooling, compared with the traditional cooling technologies. In this paper, the thermal-hydraulic characteristics of this new cooling system under different loop heights were studied theoretically and experimentally, revealing the intrinsic relationship between the loop height and the system cooling performance. The increase of loop height can cause the mass flow rate increases gradually, enhancing the self-driven force and cooling capacity of system, and also makes the ratio of two phase region decrease and the system pressure increase, resulting in the rise of the wall temperature of the stator busbar. Hence the loop height should be selected optimally to ensure the adequate cooling capacity of system and the good cooling effects. Compared with the temperature of stator busbar by using the air cooling technology, it’s shown that those by utilizing evaporative cooling technology can be reduced greatly, indicating that this new cooling system has great potential of application for larger capacity hydro-generator. The results in this paper can also provide some reference for other two-phase natural circulation systems.

This study focuses on the application of OH planar laser-induced fluorescence (OH-PLIF) in high-pressure rocket combustion conditions, up to 7.0 MPa. The signal to noise ratio of PLIF degrades in high-pressure combustion owing to effects such as line broadening and interference from intense chemiluminescence. The OH(2,0) band excitation method was applied to obtain the OH(2,1) fluorescence emitted near 290 nm and filter out the intense OH(0,0) band chemiluminescence emitted near 308 nm. The gaseous H₂/O₂ (GH₂/GO₂) jet diffusion flame was formed using a recessed coaxial shear injector. The GH₂/GO₂ injection Reynolds number, Re (Re_H2/Re_O2 ≈ 2320/22800–4660/45600), was varied to examine the variation of the flame structure and reaction zone thickness under each pressure condition P_c, and Re injection condition. In addition, the variation of the experimentally derived full width at half maximum (FWHM) of the radial OH distribution, δ_OH, with the Damköehler number, Da, was compared with that of the simulated FWHM of the OH mole fraction, δ_OH-SIM. The OH distribution was clearly observed in the instantaneous PLIF image while eliminating the intense OH chemiluminescence even in the highest pressure condition of 7.0 MPa, which is a pressure higher than any of the previous OH-PLIF studies conducted on rocket combustion. The flame structure showed the typical characteristics of a turbulent jet diffusion flame and depended on Re rather than on the chamber pressure P_c. The variation of δ_OH with Da corresponded qualitatively with δ_OH-SIM and showed the characteristics of flame stretch in the vicinity of the injector.

Time-domain (TD) pulse laser is employed as the measurement laser to solve the inverse problem of radiative heat transfer and phase change in the participating medium. The finite volume method and an improved stochastic particle swarm optimization (ISPSO) algorithm are employed as the direct and inverse problem algorithms, respectively. Moreover, an optimal selection principle of the TD dimensionless boundary temperature measurement signals based on the principle component analysis (PCA) approach is proposed to improve the retrieval accuracy in retrieving the Stefan number St and the conduction to radiation parameter N. Results show that the TD dimensionless boundary temperature measurement signals obtained within dimensionless time selected within [0.05t_p*, 0.8t_p*] helps with the improvement in the retrieval accuracy. Moreover, compared with the SPSO algorithm, the ISPSO can avoid local optima and improve convergence accuracy, and reasonable results can be obtained even with 5% random measurement errors. As a whole, the present methodology provides a reliable and effective technique to study the inverse problem of radiative heat transfer and phase change in participating medium.

The HCCI engine can be a possible potential engine technology that gives high performance with fewer dangerous exhaust emissions. In HCCI engines, low-temperature combustion of lean, highly premixed charge effectively reduces the NO_X and soot. The HCCI combustion allows utilization of a wide variety of fuels and provides higher thermal efficiency like conventional diesel. However, there are several practical challenges observed in HCCI combustion which limits HCCI engine operations to part-load conditions only. These challenges are; combustion phase control, abnormal pressure rise, and high levels of HC and CO emissions, cold start and homogeneous charge preparation, etc. The thermal and fuel stratification strategies, coupled to combustion phase control are introduced to address these issues. This paper reviews the methods to achieve the in-cylinder thermal and fuel stratifications, implementation with combustion phasing control parameters such as fuel injection timings, intake temperature, DI ratio, and EGR rate, and their effects on engine performance, and emissions.

Conjugate heat transfer in a microtube gas flow with constant wall temperature boundary condition is studied numerically, taking into consideration the effects of the shear work, axial conduction rarefaction, pressure work and viscous dissipation. Analytical solutions for the case with non-zero Brinkman number are also obtained. The effect of the tube wall thickness and the wall thermal conductivity on Nusselt number, inner wall heat flux, bulk gas temperature, inner wall temperature and other heat transfer characteristics are analyzed. Comparisons with the standard zero wall thickness case are also presented. The results illustrate the significance of the wall heat conduction on the thermal entrance length and the heat transfer characteristics in the microtube in the thermally developing and the fully developed flow regions, and show the deviation from those with zero wall thickness. The analysis shows that in the thermally fully developed region, the Nusselt number and the heat flux at the inner wall are however, not influenced by the tube wall heat conduction. Heat exchange between the gas and the wall is shown to take place only in the thermal entrance region.

This paper concerns with effect of scaling on performance of MILD combustor when increasing its geometry and thermal throughput from the 0.58 MW prototype to its scaled-up versions of 5.8 MW. The constant velocity (CV) and constant residence time (CRT) scaling approaches were used in this work. Their performances were simulated with a numerical model for MILD combustion which was thoroughly validated against existing experimental data. It was found that despite MILD condition could be successfully maintained with both scaling approaches up to the scaling factor of 10, the effect of CV scaling could lead to elevated NO_X emission due to increase in flow retention time in hot environment. The results were also discussed in term of Damköhler number. Despite of promising technology of MILD combustion for low-NO_X emission, care must be taken on NO_X emission level when scaling up with large scale factor under the CV criteria. As for the CRT criteria with increasing inlet velocity with the scale factor, the fuel and air supply pressure should be considered as a constrain when scaling up with large scale factor.

The model of the energy storage tank based on multiple tubes with phase change material was established. The influence of the tube circle diameter and the inner annulus temperature on the heat storage performance of the tube bundle in the concentric circle was studied by numerical simulation. The results show that the increase of the tube circle diameter (Ф) can significantly improve the heat storage efficiency, and the increase in inner wall temperature (T_w) can make the heat storage time significantly shorter, but with the tube circle diameter (Φ) increases, the effect of T_w on shortening the heat storage time is gradually weakened. In addition, the dimensionless criterion equation of the liquid fraction function (f) at different tube circle diameters is presented too. Furthermore, based on the variation of the mean Nu with Fo, the heat transfer mechanism of the melting process of the PCM can be divided into four stages: (1) heat conduction dominates stage; (2) natural convection dominates stage; (3) natural convection begins to transform into heat conduction stage; and (4) heat conduction dominates again.

We evaluated the ideal limits of performance (power and efficiency) of heat engines operated with external heat sources along with their engine speed and compression ratio, using the method of adjoint equations based on variational principle. It is known that the power and efficiency of heat engines are maximum when the finite-time heat-transfer from/to the heat sources occurs isothermally, and such an engine is called Curzon–Ahlborn (CA) engine, so we derived a formula to express the temperature in the isothermal process of the CA engine as functions of the rate constant (or time constant) of either expansion or compression of the volume of the working fluid during that process. Using this formula, we found that the CA engine has the maximum of compression ratio and the slowest limit of engine speed for each compression ratio while at each compression ratio the thermal efficiency becomes greater with increasing engine speed and at each engine speed the efficiency increases with increasing compression ratio. These characteristics indicate the ideal performance envelope of the heat engines operated with external heat sources.