Hao Tang

High gravity (high-g) combustion can significantly increase flame propagation speed, thereby potentially shortening the axial length of aero-engines and increasing their thrust-to-weight ratio. In this study, we utilized the large eddy simulation model to investigate the combustion characteristics and flame morphology evolution of premixed propane–air flames in a channel with a backward-facing step. The study reveals that both the increase in centrifugal force and flow velocity can enhance pressure fluctuations during combustion and increase the turbulence intensity. The presence of centrifugal force promotes the occurrence of Rayleigh–Taylor instability (RTI) between hot and cold fluids. The combined effects of RTI and Kelvin–Helmholtz instability (KHI) enhance the disturbance between hot and cold fluids, shorten the fuel combustion time, and intensify the dissipation of large-scale vortices. The increase in fluid flow velocity can raise the flame front’s hydrodynamic stretch rate, thereby enhancing the turbulence level during combustion to a certain extent and increasing the fuel consumption rate. When a strong centrifugal force is applied, the global flame propagation speed can be more than doubled. Within a certain range, the increase in high-g field strength can enhance the intensity of RTI and accelerate the transition of RTI to the nonlinear stage.

Liquid atomization is a very complex issue, involving multiple length and time scales over several orders of magnitude. To better understand the atomization characteristics of the main injection in a lean premix prevaporize (LPP) combustor, a volume of fluid (VOF)–particle conversion algorithm Lagrangian particle tracking (LPT) coupled approach was proposed to simultaneously reproduce the primary and secondary breakup processes. A VOF model with an adaptive mesh refinement strategy was used to resolve the liquid disintegration on a large scale. The small liquid structures qualified as droplets were transformed into discrete particles based on particle conversion criteria. Next, these particles were tracked using the LPT method to simulate the secondary breakup process. The proposed coupled method used in the Eulerian/Lagrangian framework was validated against liquid jet in crossflow experimental data. The numerical results achieved good agreement with the experimental data. Finally, the proposed method was used to predict the atomization characteristics of the main injection in an LPP combustor under various aerodynamic conditions. Qualitative and quantitative information about liquid deformation and spray characteristics were obtained, which varied depending on the aerodynamic parameters.

The combustion of fuel under intense volumetric forces has the potential to enhance the velocity of flame propagation. To investigate the influence of volumetric forces on the combustion process and the characteristics of flame propagation within fuel, this research paper conducted a numerical analysis of a two-dimensional rotating pipe subjected to varying volumetric forces. The findings reveal that, within a specific range, an augmentation in volumetric forces progressively elevates both the global and localized speeds of flame propagation. The primary rationale behind the heightened flame propagation speed under intense volumetric forces lies in the fact that the increase in such forces facilitates an enlargement of the interface area between the burned and unburned gases. This, in turn, fortifies the transfer of heat and the chemical reaction rate between the two, effectively shortening the duration of combustion and augmenting the speed of flame propagation. At exceedingly low volumetric forces, the pressure wave generated by combustion in the pipe exerts a certain influence on the speed of flame propagation and the progression of the flame.

A numerical simulation of the detonation propagation process of acetylene-air under fuel-rich conditions is carried out using a reduced acetylene reaction model. The loose coupling method is used to solve the conservation equations with source terms. The flow is solved explicitly using a gas kinetic scheme, and the chemical reactions are solved implicitly. The numerical results show that the oxidation reaction is the chain initiation in the self-sustained detonation propagation process in rich acetylene. The self-decomposition reaction of acetylene provides the energy to maintain the coupling between the shock wave and the chemical reaction zone. The results show that the initial induced reaction is still an oxidation reaction due to the low activation energy of the oxidation reaction under the condition of low oxygen content. The intensity of the transverse wave is affected by the acetylene concentration. The post-detonation disturbance of temperature is mainly affected by the strength of the tail of transverse wave and the area of the unreacted pocket. With the increase of acetylene concentration, the self-decomposition process of acetylene increases the intensity of the transverse wave tail and improves the degree of temperature homogenization. This creates a formation-fragmentation-regeneration cycle of polycyclic aromatic hydrocarbons. This process changed the branching ratio of polycyclic aromatic hydrocarbons with different structures and delayed the formation of polycyclic aromatic hydrocarbons. When the acetylene concentration is low, the region where the dominant temperature after detonation is 1500 ~ 2500 K provides a favorable environment for the growth of polycyclic aromatic hydrocarbons.

The detailed chemical reaction mechanism of high temperature pyrolysis is constructed through the comparison of various current reaction mechanisms and sub‐models. This mechanism can better predict the formation of polycyclic aromatic hydrocarbons. Through path analysis, the interrelationship of the growth mechanisms of polycyclic aromatic hydrocarbons is expounded. And the important contribution pathways of five‐membered/six‐membered rings at high temperatures are investigated. Through component flux analysis and sensitivity analysis, the results show that the main formation path of the external five‐membered ring is the acetylene addition of naphthalene. Its stability decreases with increasing temperature and is the main introduction route of molecular curvature during low temperature pyrolysis. However, the embedded five‐membered ring obtained by benzene cycloaddition is less affected by temperature and is the most important chemical reaction process introduced by high temperature molecular curvature. The hydrogen abstraction acetylene addition mechanism still plays a dominant role at different temperatures and is a classical pathway for the formation of six‐membered rings. By cooperating with multiple reaction mechanisms, the formation mechanism of polycyclic aromatic hydrocarbons at different temperatures can be well predicted.

The efficient utilization of energy in rich fuel detonation processes and the effective control method of soot are important topics in combustion research. In this paper, we numerically study the detonation wave behavior of acetylene–air systems in rich fuel condition by using a reduced reaction mechanism. The non-stiff terms of the governing equations are solved explicitly using the gas kinetic scheme, and the stiff terms are solved implicitly. Our results show that the acetylene pyrolysis is the dominant reaction process. The oxidation reaction is exploited to initiate the reaction induction process, providing the required energy to overcome the potential energy barrier. The secondary detonation structure is due to the stable interaction of the transverse waves and the combined action of the vinyl reaction system, thus effectively improve the energy release rate and providing a powerful solution for the fuel-rich high-energy release of advanced heat engines. The area of the unreacted pocket increases with the acetylene concentration, resulting in an irregular wave-front and detonation cell. The reflected shock wave impacting on the wall induces the secondary reaction of the detonation products. The concentration of polycyclic aromatic hydrocarbons decreases significantly and regenerates near the wall. Our approach provides an effective tool for controlling detonation soot and the preparation of carbon particles.

A numerical study was conducted to verify and validate a new solver, named hyperReactingSodFoam, based on the OpenFOAM toolbox. This study mainly focuses on verification of solver’s computational capability to compute hypersonic flows involving shock-induced combustion, and its applications. This investigation is limited to inviscid flow and incorporates Minmod limiter to achieve total variation diminishing property. Analysis of a practical case was conducted by simulate and validate hypersonic blunt body projectile experiments at Mach 6.46 and 4.18. Likewise, to demonstrate the wider applicability of solver, a standing detonation in an oblique detonation wave engine combustor with a sharp as well as a blunted wedge geometry was studied. It was observed that, for a given flow condition and combustor geometry, a sharp wedge has a better mass-weighted average pressure recovery comparative to the blunted wedge. However, blunted wedge geometry provides a better picture of the detonation phenomenon as a practical wedge will have finite bluntness. In addition, the concept of the detonation induction length becomes less relevant for a blunted wedge.

Li-ion batteries are widely used in electric vehicles for their superior performance. To investigate a simple and efficient method for the Li-ion power batteries, the cold plate with four types of structures A, B, C, and D were established, respectively. Subsequently, the effects of micro-channel thickness and width on the cooling performance of battery thermal management systems were analyzed by using a numerical simulation method. The results show that with the increases of the micro-channel thickness, the maximum temperature (Tmax) of the cold plate is gradually increased under structures A, B, and C, while it is gradually decreased under structure D. The standard deviation of temperature (T?) of the cold plate of structure A was less affected by the change of the micro-channel thickness. Under structures B, C, and D, the temperature uniformity of the cold plate can be well maintained when the micro-channel thickness was 1.0 [mm]. With the increase of the micro-channel width, the Tmax and T? of the cold plate are gradually increased in all cases, while the ?P from the inlet to outlet is gradually decreased. The temperature uniformity of the cold plate is well maintained by structure C. The decreasing amount and changing range of ?P caused by the change of micro-channel width is smaller than caused by the change of the thickness.

High-g combustor (HGC) is a significant branch of the ultracompact combustor, an innovative gas turbine combustor with the ability to shorten the combustor length and improve engine efficiency. To improve the feasibility of the HGC concept, a new HGC was designed to substitute the conventional combustor of a KJ66 small turbine engine. The KJ66 was modified to fit an instrumentation system and test bench to conduct relative experiments. Based on the experiment results, design iterations were conducted relying on simulation methods. The design iteration was comprised of six primary configurations, of which the first four configurations focused on establishing an appropriate high-centrifugal environment to accelerate primary combustion, while the last two modifications focused on improving overall combustion performance. In configuration 4, a pinwheel-shaped swirl inlet was designed to successfully create the high-g environment and balance the flow distribution while bringing insignificant total pressure loss. One modification of configuration 4 was a grid inlet design that divided the inlet channel into several subchannels to constrain the inlet flow and establish an ideal high-g environment. The other modification was a divergent mainstream channel to encourage the dilution process and improve the exit temperature profile. The final design could save at least 1/3 of combustor length while maintaining the same level of performance as the original combustor. Further, the engine was predicted to save at least 12% of the total engine weight and improve at least 14% of the engine thrust-to-weight ratio.