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A configuration for a dual-duct rotating detonation aero-turbine engine (DRDATE) is proposed. With the isolator and mixer arranged upstream and downstream from the rotating detonation combustor (RDC) respectively, the compatibility between turbomachinery and RDC can be realized. The conventional single annular RDC is replaced with a multi-annular RDC to expand the stable operation range of the RDC. A low-order analytical model of the rotating detonation process is presented, and comparisons between the results calculated by this model and the CFD solvers show reasonable agreement. Thereafter, a performance simulation model of the DRDATE is established, and further the variations in the overall performances with design parameters under three different flight conditions are investigated. The results demonstrate that, there exists an optimum compressor pressure ratio π opt that maximizes the specific thrust and an optimum pressure ratio π opt ′ that maximizes the thermal efficiency for the DRDATE. With an increase in the compressor and turbine polytropic efficiency and turbine inlet temperature, both π opt and π opt ′ increase monotonically. Comparisons between the DRDATE and conventional turbine engine reveal that, the former exhibits a major improvement in overall performance at low compressor pressure ratios, while the improvement decreases continuously with an increase in the pressure ratio. Moreover, as the turbine inlet temperature increases, the specific thrust improvement increases and the fuel consumption performance improvement decreases monotonically.

In this research, n-hexane flashing jets discharged from two-hole GDI injectors were studied numerically with different superheat levels and inter-hole angles. The mutual interaction between under-expanded flashing jets was discussed in terms of its effect and mechanism. It was found that under certain conditions, the jets deflected towards each other and merged into one jet which moved along the central axis, indicating the occurrence of spray collapse. The spray collapse is ascribed to the pressure drop in the central area between the two jets, which is an effect of the low-pressure cores within individual jets. The pressure drop in the central area is mainly determined by two effects, i.e. the intensity and volume of the low-pressure cores in individual jets, and the formation of the secondary cell which protects the central area from being affected by the ambience. In the transitional stage from non-collapse to fully-collapse, the pressure drop was enhanced with the rise of superheat level or the decrease of inter-hole angle, and the extent of spray collapse increased. Besides, unique shock structures similar to those of under-expanded gaseous twin-jets were formed at high superheat levels, which consist of two primary cells and a secondary cell.

Nitrous oxide fuel blend propellants have great potential to be used in rocket engine, and investigations on the fundamental combustion characteristics of such propellants are therefore necessary to control flashback and develop their chemical kinetics mechanism. Laminar burning velocities (LBVs) of C2H4/N2O flames are measured by using spherical expansion flames in this paper at 0.5–2.0 atm and 280 K. The present method for upper and lower limits of effective flame radius is reasonable for the experimental stretched flame speeds can be fitted very well with the flame stretch rates. The LBVs of C2H4/N2O flames are smaller than those of C2H4/N2/O2 flames (same N/O ratio as N2O) at conditions near stoichiometric ratio, while they are larger than those at other conditions especially at fuel-rich side. The LBVs of C2H4/N2O flames are not sensitive to the pressure in the measured range. Two kinds of sub-mechanisms are applied for detailed chemical kinetics mechanisms of C2H4/N2O reactions, which are USC Mech II-2 for hydrocarbon reactions as well as GRI 3.0 mechanism and San Diego mechanism for nitrogen oxide reactions respectively. Eight key elementary reactions are chosen based on the sensitivity analysis, and the effects of their available rate constants from literatures on the LBVs are tested. Modified mechanisms for C2H4/N2O reactions are therefore proposed by replacing the rate constants of these key elementary reactions, which predicts well for LBVs of hydrocarbon/N2O flames. Sensitivity analyses are performed for C2H4/N2O flames at different equivalence ratios, it is found that the N2O decomposition is a dominant reaction in conditions near stoichiometric ratio, while it is the codominant and nondominant reaction in fuel-lean and fuel-rich conditions respectively. Furthermore, the reaction pathways of oxidizers consumption in C2H4/N2O flames and C2H4/N2/O2 flames are analyzed, and the observations on the LBVs of these two flames in the experiment can be well explained through the reaction pathways and their relative changes under fuel-lean, stoichiometric and fuel-rich conditions.

Pulsating instabilities in hydrogen/air double-flame partially premixed counterflow flames are numerically investigated with detailed chemistry and transport. The whole stability map on the equivalence ratio-strain rate plane is obtained. With the increase of the equivalence ratio or strain rate, there are two transitions for combustion patterns from stable to unstable, and to stable again. For the one transition presented at the smaller equivalence ratio and strain rate, it is similar to that in the pure premixed flame. After this transition, the flames do not extinguish with the increase of equivalence ratio or strain rate, but transit from unstable to stable. For the second transition appeared at the larger equivalence ratio and strain rate, the effects of equivalence ratio and strain rate on the pulsating instability are completely contrary to those in pure premixed flames. The effective activation energy of the premixed flame of partially premixed flame predicted by a new method is applied to calculate the Zeldovich number. Then the first transition is proved to satisfy Sivashinsky-like criterion, but the critical value is larger than that for pure premixed flame due to the heat transfer between premixed and non-premixed flames. It means that the pulsating instability is more difficult to happen in partially premixed flames. From the first transition to the second transition along the equivalence ratio or strain rate, though the premixed flame becomes weaker, the increase degree of heat transfer from non-premixed flame to premixed flame is much larger than the decrease degree of max heat release of the premixed flame due to decrease of distance and increase of temperature difference of two flames, which induces the premixed flame stable again. The second transition is therefore controlled by the heat transfer between two flames.

In this paper, n-hexane flashing jets discharged from a single-hole gasoline direct injector (GDI) were studied numerically with the adoption of diffuse Eulerian framework and the homogeneous relaxation model (HRM). The fuel temperature ranged from 30 to 130 °C, and the ambient pressure varied from 20 to 101 kPa. The results showed that considerable vaporization started at the counter bore and a liquid core existed near the nozzle exit. Due to drastic vaporization, the pressure within the liquid core increased so the two-phase flow became under-expanded. Violent expansion then occurred and a low-pressure region was formed, which is believed as the origin of the spray collapse under flashing conditions for multi-hole GDI injectors. At high superheat levels, shock wave structures similar to those in highly under-expanded gaseous jets were identified. However, the transonic position located at some distances from the nozzle rather than at the throttle. Besides, vapor fraction played the dominant role in the onset of expansion, while the expansion was ended by the pressure difference between the two sides of the Mach disk.

The successful application of hierarchically porous structure in environmental treatment has provided new insights for solving environmental problems. Hierarchically structured semiconductor materials were considered as promising photocatalysts for NO oxidation in gas phase. Multi-shelled ZnO microspheres (MMSZ) were controllably shaped with hierarchically porous structures via a facile hydrothermal route using amino acid (N-Acetyl- d -Proline) as template and post-calcination treatment. Symmetric Ostwald ripening was used to explain the morphological evolution of hierarchical nanostructure. MMSZ was proved highly efficient for oxidizing NO (400 ppb) in gas phase under UV light irradiation with a much higher photocatalytic removal rate (77.3%) than that of the as-obtained ZnO crystals with other hierachically porous structures, owing to its higher photocurrent intensity. Such greatly enhanced photocatalytic activity can be assigned to the enhanced crystallinity of ZnO, mesopores and unique multi-shelled structure. Enhanced crystallinity promotes photogenerated charges under light irradiation. Mesoporous porosity can ensure enough light scattering between the shells. Multi-shelled structure endows ZnO with higher specific surface area and high frequency of multiple light reflection, resulting in more exposed active sites, higher light utilization efficiency, and fast separation efficiency of photogenerated charge carriers. The experimental results demonstrated that the photogenerated holes (h+) are the main active species. Hierarchically structured ZnO is not only contributed to directly use solar energy to solving various problems caused by atmospheric pollution, but also has potential applications in energy converse and storage including solar cells, lithium batteries, water-splitting, etc.

A configuration is presented for the rotating detonative airbreathing combined cycle engine with compatibility between the turbomachinery and rotating detonation combustor being realized. Two propulsion units are merged to achieve three different operating modes, which provides a favorable propulsion choice for advanced full range and trans-aerosphere vehicles. For the vehicle taking off from the ground, the engine operates at turbojet mode until the thrust demand could not be satisfied. Then the ramjet unit ignites and the operating mode turns into transition mode, during which the ratio of the thrust generated by ramjet unit to the total thrust increases with an increase in M a 0 . When the ratio reaches 1.0, the engine transforms into the ramjet mode. Thereafter, a mode transition strategy with the thrust and freestream mass flowrate remaining constant is proposed for the combined cycle engine, based on the steady state characteristics of turbine and ramjet units. Furthermore, the parametric performance simulation model of the engine is developed to verify the potential performance improvements generated by the application of rotating detonation technology, and analyze the application characteristics of the mode transition strategy formulated in this study. It is shown the lower initial Mach numbers of mode transition result in higher values of equivalent specific thrust but lower values of equivalent specific impulse during the transition mode. For the detonative combined cycle engine, the minimum value of initial Mach number of mode transition is below 2.0, which is much lower than that of the conventional turbine based combined cycle engine. Therefore, the performance during transition mode is expected to be improved with the application of rotating detonation technology.

A new method for the inlet condition is proposed for the high-accuracy numerical simulation of supersonic reacting mixing layer by considering the conservation of mass, momentum and energy in the mixing process of two freestreams at the inlet. This method can ensure that all parameters at the inlet are compatible. Based on the inlet condition obtained from this method, direct numerical simulations of air/hydrogen supersonic reacting mixing layers are carried out, and the effect of the inlet condition is examined by comparing with that based on traditional inlet conditions. It is shown that the commonly used inlet conditions can lead to abnormal distributions of density and product of gas constant and temperature at the inlet, subsequently causing unreasonable results or even divergence in computation. These problems are avoided by using the proposed compatible inlet condition. The predicted profiles and flowfield are more reasonable, demonstrating the advantages of the proposal.

We investigate passive scalar mixing in spatially developing supersonic shear layer flows formed by two planar streams by means of large eddy simulation. After validation of the numerical procedures employing a high-order hybrid WENO/compact scheme by comparing the results of simulation with the results obtained from a well characterized experimental case, the effects of the convective Mach number, M c , flow velocity ratio, r = U 1 / U 2 , and fluid density ratio, s = ρ 1 / ρ 2 , between Stream 1 and Stream 2 on passive scalar mixing are considered by examining the variation of mixing layer thickness and the mixing efficiency represented by the transport of the passive scalar. M c is specified from 0.2 to 0.8. The evolution of large-scale coherent structures is well reproduced, with vortices undergoing rolling up, pairing, merging, and breaking up. The mixing layer thickness and mixing efficiency both decrease as M c increases. As s increases, the mixing layer thickness increases, and the mixing efficiency of an entrained fluid decreases. As r increases, the mixing layer thickness decreases while the mixing efficiency increases. While the present results are not applicable to the examination of micro-mixing properties, which require assessment by experimental methods or high computing cost direct numerical simulation, they are useful for evaluating the effects of different flow parameters on macro-performance, which is equally important for scramjet combustor design and evaluation in engineering.

Super knock induced by pre-ignition in highly boosted spark ignition engines can cause very high peak pressure, which may lead to severe engine damage. Although it is difficult to investigate the mechanism of super-knock due to its inherent randomness, the very high peak pressure implies that super knock may relate to detonation. In this study, a tube-like one-dimensional constant volume bomb, which simplifies the geometry of a real engine's combustion chamber near top dead center, was used to better understand the fundamental phenomenon underlying super knock. H 2 /O 2 mixture was used to maintain reaction intensity even at lower pressure than that in real highly boosted engines. Simultaneous high speed shadowgraphy and pressure measurement were conducted to study the effects of initial pressure and temperature on combustion mode and flame propagation. By comparing the frequencies of super knock pressure oscillation in the boosted engine and after-detonation pressure wave in the constant volume bomb, a relation can be found between the super knock and detonation. The experimental results also show that the detonation tendency of H 2 /O 2 mixture in the constant volume bomb increases with increasing initial pressure but decreases with increasing initial temperature, indicating that the mixture density i.e. energy density plays an important role in detonation onset.

To determine the mechanism of interaction between a pressure wave and a propagating flame during knock, normal combustion and knock are numerically modeled in a simplified one-dimensional hydrogen-fueled spark ignition engine. The heat release rate of the flame front during knock abruptly increases when the pressure wave propagates through the reaction zone. The pressure wave in the diffusion zone perturbs temperature and thus causes thermal runaway at positions with low temperature and high reactant concentra

The effects of Soret diffusion on premixed syngas/air flames at normal and elevated temperatures and pressures are investigated numerically including detailed chemistry and transport. The emphasis is placed on assessing and interpreting the influence of Soret diffusion on the unstretched and stretched laminar flame speed and Markstein length of syngas/air mixtures. The laminar flame speed and Markstein length are obtained by simulating the unstretched planar flame and positively-stretched spherical flame, respectively. The results indicate that at atmospheric pressure the laminar flame speed of syngas/air is mainly reduced by Soret diffusion of H radical while the influence of H 2 Soret diffusion is negligible. This is due to the facts that the main reaction zone and the Soret diffusion for H radical (H 2 ) are strongly (weakly) coupled, and that Soret diffusion reduces the H concentration in the reaction zone. Because of the enhancement in the Soret diffusion flux of H radical, the influence of Soret diffusion on the laminar burning flux increases with the initial temperature and pressure. Unlike the results at atmospheric pressure, at elevated pressures the laminar flame speed is shown to be affected by the Soret diffusion of H 2 as well as H radical. For stretched spherical flame, it is shown that the Soret diffusion of both H and H 2 should be included so that the stretched flame speed can be accurately predicted. Similar to the laminar flame speed, the Markstein length is also reduced by Soret diffusion. However, the reduction is found to be mainly caused by Soret diffusion of H 2 rather than that of H radical. Moreover, the influence of Soret diffusion on the Markstein length is demonstrated to decrease with the initial temperature and pressure.

Based on the fractional volume of fluid (VOF), a pure Eulerian model for defining and capturing the gas/liquid interface is developed in this paper. This model can describe gas/liquid interface in high refinement, which is better than the original VOF methodology. To validate the proposed model and the algorithm, the computational code is employed to predict the flow performance in a cylindrical swirl injector under cold-flow condition, and the predicted results agree well with experimental measurements. Furthermore, the proposed model is used to simulate gas-liquid reacting flows inside a gas/liquid coaxial swirl injector operating in a hot environment. The turbulent combustion process is simulated with the [email protected] model. The numerical simulation is carried out under actual operating condition of the coaxial injector. The injector performances, such as liquid film thickness, liquid film injection velocity, spray angle, pressure drop, are obtained based on the detailed information of the internal flow field. The predicted results also show that droplets are shed from the liquid film in the recess cup of the coaxial injector because of the large velocity gradient between the gas and liquid streams, and a burning area, which is characterized by high temperature, is present inside the injector.