High Heat Release Research Articles

Direct numerical simulation of turbulent premixed ammonia and ammonia-hydrogen combustion under engine-relevant conditions

The combustion characteristics of ammonia and ammonia-hydrogen fuel blends under spark-ignited turbulent premixed engine-relevant conditions were investigated by means of direct numerical simulation and detailed chemistry. Several test cases were investigated for an outwardly expanding turbulent premixed flame configuration covering pure ammonia and ammonia-hydrogen fuel blends with 10% and 15% hydrogen content by volume for different equivalence ratio values of 0.9, 1.0 and 1.1. The results showed that the fuel-lean flames exhibit strong wrinkled structures at flame front compared to stoichiometric and fuel-rich flames. The heat release rate plots indicate that adding hydrogen into ammonia improves the reactivity of the flame and enhances the combustion process. The scatter plots of heat release rate versus local curvature coloured by NO formation, show that high heat release rate values occur in the concave structures and low heat release rate values occur in the convex structure, which is consistent with NO distribution. The highest turbulent burning velocity values were found for the fuel-lean cases due to more wrinkled flame front with lower effective Lewis number compared to fuel-rich cases. The results show a bending effect for the ratio between turbulent to laminar burning velocities with respect to hydrogen addition at all equivalence ratios with 10% hydrogen addition into ammonia exhibiting a highest value for the burning velocity ratio. Two distinct flame structures (concave and convex) were analysed in terms of local equivalence ratio based on the elements of N and O as well as H and O. They revealed an opposite distribution of NO formation normal to the flame front within concave and convex structures. Elementary chemical reactions involved in NO formation have shown that hydrogen addition into ammonia influences the reactivity of certain specific chemical reactions.

Effects of high‐energy multicore ferrocene‐based catalysts on the thermal decomposition of ammonium perchlorate

AbstractThree high‐energy multicore ferrocene‐based catalysts containing energy bonds (C═N, N–N) (EMFcs), EMFcs‐1, EMFcs‐2, and EMFcs‐3, were designed and synthesized to reduce the high temperature decomposition (HTD) temperature and increase the heat release of ammonium perchlorate (AP) as well as improve anti‐migration performance for the development of composite solid propellants. The theoretical calculation of the highest occupied molecular orbital (EHOMO), the lowest unoccupied molecular orbital (ELUMO), and the electrostatic potential (ESP) were performed to explore the electronic structure of EMFcs (1–3) and predict their catalytic performance on AP. The chemical structures were confirmed by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), ultraviolet (UV), and elemental analysis, and the oxidation ability was evaluated by cyclic voltammetry (CV). The catalytic performance of obtained catalysts was verified by differential scanning calorimetry‐thermogravimetry (DSC‐TG), and the results showed that the designed catalysts possessed much higher heat release and catalytic activity on AP thermal decomposition than that of widely used catalyst of catocene in the solid propellant, and EMFcs‐2 with three ferrocene units showed the best catalytic performance due to the highest Fe content in one molecule of EMFcs‐2. The composite of AP containing 5 wt% of EMFcs‐2 can reduce the HTD temperature of AP from 394°C to 285°C and low the activation energy from 185.81 to 103.18 kJ·mol−1 with heat release increasing from 630.60 to 1841.50 J·g−1. Furthermore, the thermal decomposition gaseous products of AP under the catalysis of EMFcs were confirmed by TG‐FTIR to explore the catalytic decomposition mechanism.

Influence of water on thermo-oxidative behavior and kinetic triplets of shale oil during combustion

The oxidation reactions between oxygen and shale oil directly affect the feasibility and performance of air injection. In this work, the influence of water on thermo-oxidative behavior of shale oil was studied using high-pressure differential scanning calorimetry (HP-DSC). Subsequently, the kinetic triplets for shale oil oxidation in the absence and presence of water were determined using Friedman and Ozawa-Flynn-Wall (OFW) models as well as one advanced integral master plots method. The HP-DSC results showed that at 5 MPa, the shale oil was vulnerable to obviously higher heat release at the low-temperature oxidation (LTO) region compared to the high-temperature oxidation (HTO) region, resulting in shortening the oxidative induction time and achieving in-situ upgrading of shale oil. Water delayed the initial heat release due to the fact that heat release yielded by LTO compensated the heat adsorption yielded by evaporation of water and light hydrocarbons. Additionally, the heat release was reduced with the elevated water saturation as a result of the reduction in exothermic rates and intensified evaporation of water and light hydrocarbons. The higher energy was needed to trigger off the LTO reactions while increasing water saturation from 10% to 20%. Therefore, it was believed that the presence of water extended the oxidative induction time, thereby hindering the smooth and rapid transition from the LTO to HTO stages. Water changed the reactivity of each oxidation stage for shale oil, resulting in higher energy required for the initial LTO reactions and lower energy required for the subsequent oxidation reactions. The water saturation range of 10% to 15% could accelerate the occurrence of high-temperature combustion most effectively, demonstrated by values of activation energy for the conversion greater than 0.6. The appropriate oxidation reaction models for shale oil alone and water saturations of 10%, 15%, and 20% were determined to be D2, F1, F3, and R3, respectively. The determination of kinetic triplets assisted in building the reaction schemes for modelling the air injection process of shale oil reservoirs.

Verification of temperature and toxic species in methane compartment fire using flamelet generated manifold with radiation effect

This paper examined the effect of combustion model on compartment fire simulation. The results of the flamelet generated manifold (FGM) combustion model were compared with conventional combustion models in compartment fire simulation. Methane fuel was selected and the detailed kinetic mechanism was chosen for the FGM model. In addition, the radiation effect was investigated on the FGM combustion model. It was observed that it was necessary to apply the radiation effect in the FGM combustion model for the high heat release rate. For example, the temperature of FGM-base (in the absence of radiation effect) over-predicted near the ceiling of the room at heat release rate of 265 kW. However, if radiation effect was applied, the mean temperature reached 1250 K and the relative error was reduced to less than 10%. The important point is that the computational cost of the FGM was equal to other conventional combustion models in fire simulation. In addition, the conventional combustion models could model only one or two toxic species. However, the FGM was able to model all toxic species involved in the fire.

Enhanced Separation Performance of Radioactive Cesium and Cobalt in Graphene Oxide Membrane via Cationic Control.

The great applications of nuclear power for the most promising clean energy sources have been challenged by a large amount of radioactive wastewater generated, specifically the Cs+/Co2+ separation for nuclear waste storage, retreatment or recycling of radioactive wastewater, because of their wide difference in half-life and high heat release. In this work, graphene oxide membranes (GOMs) with interlayer spacing controlled by cations were used to separate mixed Cs+/Co2+ ions. The separation factors of Cs+/Co2+ for K+-controlled graphene oxide membranes (K-GOMs) was 2∼3 times higher than that of GOMs without treatment. In addition, the separation factors of Cs+/Co2+ for K-GOMs can be further enhanced with the increase of membranes thickness and change the initial ratios of the two ions. Typically, the separation factors of K-GOMs with a thickness of ∼300 nm reached up to 73.7 ± 3.9. Moreover, the K-GOM showed outstanding stability of the separation performance under long-term operation within 7 days. First-principles calculation revealed that the enhanced ionic selectivity of controlled GOM is induced by the difference of adsorption energies between the hydrated cations and aromatic rings, resulting in a significant increase in the mobility differences between Cs+ and Co2+ through a fixed narrow interlayer spacing. This study demonstrated excellent separation performances of GO-based membranes based on their size-exclusion effect rather than electrostatic repulsion effect, and we believe this work can enable potential efficient treatment technologies for radioactive wastewater needed urgently.

The flow field behaviours of under-expansion jet flame in premixed hydrogen/air explosion venting

The short chemical reaction time and high heat release of hydrogen fuel make a fine propulsion performance. Hydrogen is recognized as an excellent new resource. However, the inherent hazard of combustion and explosion should not be ignored. In this paper, the formation of the under-expansion jet flame (UEJF) of premixed hydrogen/air in explosion venting was simulated by ANSYS Fluent, and the wave system structures of the UEJF were systematically analyzed. The changes of pressure, Mach number, and main gas mass fraction distribution in the formation of the UEJF structures were described. The results indicated that the pressure difference at the outlet of explosion venting tube induced the intersection of expansion wave and reflected wave, and the formation of an obvious negative pressure area in the flow field. Meanwhile, alternating changes of the pressure in the jet center area propagated forward with the flame, resulting in the generation of UEJF. The fluxion of airflow at the outlet of explosion venting tube can be regarded as Prandtl-Meyer flow. The expansion angle was a positive correlation to the Mach number and the pressure ratio of the internal and external of the explosion venting tube. The distribution of H2O, O2, and –OH on the Mach disk revealed that the residual hydrogen reacted with O2 to produce secondary or multiple explosions. Therefore, the attention and research on the hazard of the under-expansion jet field should be strengthened.

Performance of Waste Insulating Mineral Oil-Based Biodiesel in a Direct-Injection CI Engine

Mineral oil has been used as an insulating fluid in the power industry. However, surplus waste oil poses serious environmental threats because of disposal concerns. Waste to biofuel is an excellent way to deal with waste material from various sources. In this study, the trans-esterification method was utilised to convert the waste-insulating mineral oil into a quality bio-fuel. Waste-insulating transformer oil was converted to biodiesel, and it was tested according to ASTM standards. Four different blends of waste-insulating biodiesel with diesel in 25 per cent (WIOBD25), 50 per cent (WIOBD50), 75 per cent (WIOBD75), and 100 per cent fractions (WIOBD100), were used for performance testing in a direct injection compression ignition (DICI) engine. The combustion parameters such as BSFC, EGT, and BTE were evaluated with varying crank angles and constant engine speed. The waste-insulating biodiesel performance results are then compared with diesel fuel. BSFC increased as the biofuel mixture in diesel was raised, and the brake thermal efficiency (BTE) was significantly reduced compared to diesel for all WIOBD diesel mixtures. Due to the combustion process, a high pressure and heat release rate (HRR) were noticed inside the cylinder with the waste-insulating oil-derived biodiesel samples. WIOBD biodiesel blends produced lower levels of hydrocarbon, carbon monoxide, and smoke emissions than diesel fuel, but greater levels of nitrogen oxides (NOx) were produced than diesel fuel. In addition to lower emissions combined with improved engine performance, the WIOBD25 fuel blend has been found to be experimentally optimal for practical application. As a result, the test findings indicated that WIOBD biodiesel might be used as a substitute for conventional diesel fuel.

Influence of injection pressure and injection timing on pollution levels of insulated diesel engine fuelled with CNG and cotton seed biodiesel

In the context of fast depletion of fossil fuels, increase of pollution levels with fossils and increase of economic burden due to increase of import cost of crude petroleum, the search for alternative fuels has become pertinent. The most common alternative fuels for CI engine are vegetable oils, biodiesel and alcohols. Gaseous fuels have many advantages than liquid fuels, as the pollutants emitted by gaseous fuels are low, calorific value of the gases is very high and running and maintenance cost is low. The drawbacks associated with vegetable oils such as high viscosity and low volatility can be rectified to some extend by converting them into biodiesel. How they (biodiesel) cause combustion problems in diesel engine and hence call for low heat rejection (LHR) engine, which can burn low calorific value fuel, give high heat release rate and faster rate of combustion. Investigations were carried out with CNG as primary fuel inducted by port injection and cottonseed biodiesel blended with 15% of diethyl ether (DEE) was injected into the engine in conventional manner with LHR engine consisted of ceramic coated cylinder head. The purpose of DEE was to improve cetane (a measure of combustion quality in diesel engine) and to reduce viscosity of the cotton seed biodiesel. Particulate matter (PM), oxides of nitrogen (NOx), carbon mono oxide (CO) levels and un-burnt hydro carbons (UBHC) are the exhaust emissions from a diesel engine. They cause health hazards, once they are inhaled in. They also cause environmental effects like Green-house effect, acid raining, Global Warming etc,. Hence control of these emissions is an immediate effect and an urgent step. The pollutants of PM, NOx, CO and UBHC were determined at full load operation of the engine and compared with diesel operation on conventional engine. The maximum induction of CNG was 35% of total mass of biodiesel, with CE, while it was 45% with LHR engine at full load operation. Particulate emissions were determined by AVL Smoke meter, while other emissions were measured by Netel Chromatograph multi-gas analyzer at full load operation. The optimum injection timing with cottonseed biodiesel was 31obTDC (before top dead centre), with CE, while it was 28obTDC with LHR engine. These pollutants were drastically reduced with induction of CNG and further reduced with the provision of LHR engine. They were further reduced with advanced injection timing and increase of injection pressure.

Planar Laser-Induced Fluorescence and Chemiluminescence Analyses of CO2-Argon-Steam Oxyfuel (CARSOXY) Combustion

Strict regulations and acts have been imposed to limit NOx and carbon emissions. The power generation industry has resorted to innovative techniques to overcome such a low level of tolerance. Amongst those in the literature, CO2-argon-steam oxyfuel (CARSOXY) gas turbines have theoretically been proven to offer an economically sustainable solution while retaining high efficiency. Although theoretical studies have characterized CARSOXY, no experimental evidence has been provided in the literature. Therefore, this paper attempts to experimentally assess CARSOXY in comparison to a CH4/air flame. OH* chemiluminescence integrated with OH Planar Laser-Induced Fluorescence (PLIF) imaging has been utilized to study flame stability and flame geometry (i.e., the area of highest heat intensity (AOH¯Max center of highest heat intensity (COH¯Max)) over a range of working fluid Reynolds’ numbers and oxidizing equivalence ratios. In addition, the standard deviation of heat release fluctuations (σOH*/OH¯) has been utilized as the base-criteria to compare the stability performance of CARSOXY to CH4/air combustion. Moreover, turbulence-chemistry interactions have been described using Damköhler numbers and by plotting Borghi regime diagrams. This paper suggests a modified numerical approach to estimate Damköhler numbers and plot regime diagrams for non-premixed combustion by utilizing the Buckingham π theorem based on experimental observations and results. CARSOXY flames showed lower flame intensity than that of the CH4/air flame throughout the entire Re interval by approximately 16%, indicating higher heat release. The Damköhler numbers of the CARSOXY flame were also greater than those of the CH4/air flame in all conditions, indicating more uniform CARSOXY flames. It was found that the tendency of the CARSOXY flame of approaching the concentrated reaction zone is greater than that of the CH4/air flame.

INVESTIGATION OF THE NEUTRALIZATION PROCESS OF SULFATION PRODUCTS IN THE SURFACTANTS PRODUCTION

The process of sulfation products neutralization in the production of surfactants is not basic, but at this stage the positive effects obtained at the stage of sulfation of organic matter with sulfur trioxide gas are fixed. To preserve the degree of sulfation obtained, it is necessary to carry out the neutralization process under conditions precluding the occurrence of hydrolysis in an acidic medium. The neutralization reaction takes place with a high heat release of about 40 kJ / mol. Analysis of the literature data showed that the neutralization process is not well covered. Little data and hardware and technological design of the process. The process of neutralization in industrial conditions is carried out in apparatus with mechanical turbine mixers, to remove the heat of the exothermic reaction, the paste from the neutralizer is fed into a water-borne heat exchanger and returns to the neutralizer again. The purpose of this study is to determine the optimal technological parameters of the process of neutralization of sulfate products and the development of a mathematical model of this process. The results of experimental studies of the process of sulfation products neutralization with an aqueous solution of sodium hydroxide are presented. During the research, the influence of technological parameters on the quality indicators of neutralization products was determined, the main of which is the degree of sulfation. The optimal technological parameters for carrying out this process in a reactor with a stirrer under laboratory conditions were found. Based on the data obtained in the basis of this process, the use of a continuous-action reactor with a turbine mixer and with a combined heat exchanger. For the transition to an industrial reactor-neutralizer, a mathematical model has been developed, which makes it possible, by means of mathematical modeling, to correct technological parameters in industrial conditions.

Optical diagnostics and chemical kinetic analysis on the dual-fuel combustion of methanol and high reactivity fuels

Dual-fuel combustion is an effective method to utilize methanol because of its high octane number and latent heat of evaporation. Two ways to use methanol are discussed. One is port-injected high reactivity fuel and directed-injected methanol, named as active-thermal atmosphere combustion (ATAC). The other is port-injected methanol and direct-injected high reactivity fuel, which is reactivity-controlled compression ignition (RCCI). In the current work, both methanol combustion modes were investigated in an optical engine. Several optically diagnostic methods were utilized to characterize flame features, including flame natural luminosity imaging, OH* natural luminosity imaging and two-color method by wavelength integration. Meantime, the chemical kinetics simulation was also combined to investigate the effects of active atmosphere and thermal atmosphere on methanol combustion. Results show that as for methanol ATAC, when the methanol is direct-injected during the low temperature heat release (LTHR) stage of n-heptane, it causes significant effects on the combustion phasing of the following high temperature heat release (HTHR). When the methanol is direct-injected during the HTHR stage of n-heptane, the single-peak HTHR turns to the double-peak HTHR. Besides, the yellow diffusion flame of methanol can also be observed. Affected by the in-cylinder vortex, the area and intensity of the OH* signal in the vortex squeeze zone are greater than those in the vortex stretch zone. The flame temperature of methanol maintains in 1800–2500 K at CA50 (the crank angle of 50% mixtures is burned completely), while the maximum KL factor maintains in 0.04–0.05. The thermal atmosphere created by the n-heptane combustion has the dominant effects on shortening the ignition delay of methanol. The effects of active atmosphere are limited. As for methanol/high reactivity fuel RCCI, because of the existence of homogeneous low reactivity methanol, the misfire condition occurs when the direct injection (DI) timing is late. With the DI timing of high reactivity fuel advancing, the combustion stability improves. But the flame development progress is mainly low-speed flame propagation, which results in long combustion duration. The combustion characteristics can be further improved by utilizing higher reactivity fuel, such as n-dodecane, specifically, the combustion phasing advances and the number of auto-ignition spots increases.

Computational optimization of a hydrogen direct-injection compression-ignition engine for jet mixing dominated nonpremixed combustion

Hydrogen (H2) nonpremixed combustion has been showcased as a potentially viable and preferable strategy for direct-injection compression-ignition (DICI) engines for its ability to deliver high heat release rates and low heat transfer losses, in addition to potentially zero CO2 emissions. However, this concept requires a different optimization strategy compared to conventional diesel engines, prioritizing a combustion mode dominated by free turbulent jet mixing. In the present work, this optimization strategy is realized and studied computationally using the CONVERGE CFD solver. It involves adopting wide piston bowl designs with shapes adapted to the H2 jets, altered injector umbrella angle, and an increased number of nozzle orifices with either smaller orifice diameter or reduced injection pressure to maintain constant injector flow rate capacity. This work shows that these modifications are effective at maximizing free-jet mixing, thus enabling more favorable heat release profiles, reducing wall heat transfer by 35%, and improving indicated efficiency by 2.2 percentage points. However, they also caused elevated incomplete combustion losses at low excess air ratios, which may be eliminated by implementing a moderate swirl, small post-injections, and further optimized jet momentum and piston design. Noise emissions with the optimized DICI H2 combustion are shown to be comparable to those from conventional diesel engines. Finally, it is demonstrated that modern engine concepts, such as the double compression-expansion engine, may achieve around 56% brake thermal efficiency with the DICI H2 combustion, which is 1.1 percentage point higher than with diesel fuel. Thus, this work contributes to the knowledge base required for future improvements in H2 engine efficiency.

Cascade phase change based on hydrate salt/carbon hybrid aerogel for intelligent battery thermal management

Working performance of Li-ion battery in electric vehicle will degrade under cold environment. Excess heat of battery can be stored via melting of calcium chloride hexahydrate (CCH) and then released to warm battery when environment temperature drops. Formation of composite can improve thermal conductivity and stability of pristine CCH but reduce loading content. Meanwhile, energy stored in phase change material (PCM) is utilized in low efficiency as homogeneously filled PCM releasing heat uncontrollably. Therefore, there is an urgent need to achieve efficient heat storage and controllable heat release by designing an intelligent phase change system. In this research, MOF-derived carbon (MOF-C)/graphene oxide (GO) hybrid aerogel was proposed to load CCH. PCM loading content could be enhanced by the synergistic effect between MOF-C and GO, while thermal conductivity of PCM composite could be improved due to the formation of hybrid aerogel three-dimensional network. Furthermore, CCH@MOF-C/GO structures with gradient freezing point (FP) were designed to build a cascade phase change system to release heat efficiently, in which CCH with high FP triggering heat release of adjacent PCM with low FP. Comparing with the homogeneously filled PCM, warming time was prolonged and discharge capacity of battery was enhanced successfully under cold environment by utilizing the cascade PCM.

Facile N≡N Bond Cleavage by Anionic Trimetallic Clusters V3-x Tax C4- (x=0-3): A DFT Study.

Activation of N2 on anionic trimetallic V3-x Tax C4- (x=0-3) clusters was theoretically studied employing density functional theory. For all studied clusters, initial adsorption of N2 (end-on) on one of the metal atoms (denoted as Site 1) is transferred to an of end-on: side-on: side-on coordination on three metal atoms, prior to N2 dissociation. The whole reaction is exothermic and has no global energy barriers, indicating that the dissociation of N2 is facile under mild conditions. The reaction process can be divided into two processes: N2 transfer (TRF) and N-N dissociation (DIS). For V-series clusters, which has a V atom on Site 1, the rate-determining step is DIS, while for Ta-series clusters with a Ta on Site 1, TRF may be the rate-determining step or has energy barriers similar to those of DIS. The overall energy barriers for heteronuclear V2 TaC4- and VTa2 C4- clusters are lower than those for homonuclear V3 C4- and Ta3 C4- , showing that the doping effect is beneficial for the activation and dissociation of N2 . In particular, V-Ta2 C4- has low energy barriers in both TRF and DIS, and it has the highest N2 adsorption energy and a high reaction heat release. Therefore, a trimetallic heteronuclear V-series cluster, V-Ta2 C4- , is suggested to have high reactivity to N2 activation, and may serve as a prototype for designing related catalysts at a molecular level.

Laser ignition of iso-octane and n-heptane jets under compression-ignition conditions

This work aims to investigate the effect of laser-induced plasma ignition (LI) on combustion behaviours of iso-octane (a gasoline surrogate) at compression-ignition (CI) conditions. A high-energy laser was used to force the fuel ignition at a quiescent-steady environment inside an optically accessible constant-volume combustion chamber with 900K ambient gas temperature, 22.8kg/m3 ambient gas density and 21 vol.% O2 concentration. A diesel surrogate (n-heptane) was tested at a lower charge temperature of 735K to offset its higher fuel reactivity than the iso-octane, such that the flames of both fuels can have a similar lift-off length. Forced laser ignition was introduced either before or after the natural autoignition timing of the fuels. The laser was focused at the jet axis 15mm and 30mm from the nozzle. High-speed schlieren imaging, heat release analysis and flame luminosity measurement were applied to the flames. The high-speed schlieren imaging was used to monitor the flame structure evolution of the natural ignition and LI cases. Due to laser ignition, the flame lift-off lengths decrease, with which the uncertainties in the lift-off distances reduce by more than 80%. The laser-affected flame bases return back to the natural flame base locations. The uncertainties in the lift-off lengths also increase, as the flame stabilisation locations approach the natural lift-off distances. Under the test conditions of this work, the rates at which the iso-octane flames shift downstream are slower than the n-heptane cases. The heat release rate profiles show high heat release from the flames following the LI events, before transitioning to lower steady values. The flame luminosity measurements indicate a strong correlation between the LI affected lift-off length and increased soot formation. The luminosity levels decrease as the flame base shifts downstream over time.

Large-eddy simulation of the injection timing effects on the dual-fuel spray flame

Large-eddy simulations (LES) coupled with a partially-stirred reactor model and a finite-rate chemistry are carried out to investigate the effects of n-heptane injection timing on the methanol fueled dual-fuel (DF) combustion. Methanol is premixed with air in a constant volume chamber (T=1000 K, ρ=14.8 kg/m3) to form a homogeneous mixture (equivalence ratio ϕm of 0.3). Liquid fuel n-heptane is provided from a high pressure injector to mimic the pilot fuel injection in DF engines. First, mesh sensitivity analysis and LES model validation are conducted. The experimental data of Spray-H (n-heptane fueled) from the Engine Combustion Network is used for model validation. It is shown that the present mesh and LES model are capable of replicating the liquid and vapor penetration length, mixture fraction, temperature distribution, pressure rise profile and ignition delay time (IDT). Second, the effects of n-heptane injection timing are investigated, by varying the start of injection (SOI) time. The LES results reveal that there are three stage heat releases in the DF combustion. With the delay of SOI, the mass fraction of hydrogen peroxide in the ambient mixture increases, leading to an early formation of hydroxyl. Therefore, the two-stage IDTs of n-heptane decrease, while the ambient methanol IDT increases. Results also show the cool flame and high-temperature flame evolution after methanol auto-ignition. The cool flame disappears while the high-temperature flame is found near the injector nozzle, which leads to a relatively high heat release rate.

Design of fire scenarios for Australian underground hard rock mines – Applying data from full-scale fire experiments

One of the most significant tools when designing fire safety in an underground mine is the design fire methodology. This paper presents a number of design fire scenarios which were developed from risk assessments and risk analysis where a deterministic approach was implemented and where the results from earlier full-scale fire experiments in underground mines and analysis were included in the process. The developed scenarios showed that for scenarios, in which ventilation flow was in the same direction as the fuel continuity, continued fire spread to all major components were provided and longer and intermittent periods which resulted in high heat release rates resulted, would present a considerable risk to underground personnel. It was also found that the inclination of the decline has little influence on the resulting heat release rate – despite the flame tilt – and that the design of the mining vehicles was found to effectively delay or even prevent the ignition of adjacent fuel items in a number of cases. The design fire scenarios developed will provide a key tool when evaluating fire protection measures in an underground mine.

Discrete One-Stage Mechanochemical Synthesis of Titanium-Nitride in a High-Energy Mill

Discrete (discontinuous) mechanochemical synthesis of titanium nitride was experimentally investigated. The experimental results show that mechanical activation intensifies the chemical conversion in the Ti-N system, and the discrete synthesis of the final product is conducted under “soft” controlled conditions without high heat release. The new theory of mechanochemical synthesis and the mathematical model based on it were used for theoretical evaluation of the dynamics of titanium activation in the nitrogen medium. It was found that the discrete mode of synthesis includes two factors accelerating mechanochemical reactions in the Ti-N synthesis: structural (grinding of metallic reagent and formation of interfacial areas) and kinetic (accumulation of excess energy stored in the formed structural defects in metallic reagent). The kinetic constants of the process were found using experimental data and the inverse problem method. The diagrams defining the controlled modes of obtaining titanium nitride particles with the given characteristics were constructed. A mathematical model for theoretical estimation of the dynamics of activation of titanium powder in the nitrogen medium was developed using a new macrokinetic theory of mechanochemical synthesis.

THEORICAL STUDY ON PROPULSIVE PERFORMANCE OF OBLIQUE DETONATION ENGINE

Detonation combustion is characterized by the high thermodynamic efficiency and fast heat release. Benefitting from these potential advantages, an oblique detonation wave (ODW) is introduced into the combustion chamber and oblique detonation engine (ODE) plays an important role in hypersonic air-breathing propulsion systems. Previous studies mainly focused on the initiation structures, standing features and wave systems of oblique detonation, but the global analysis of ODE propulsive performance is still absent at the macro-level. In this paper, the flow and combustion processes of an ODE are decomposed into four basic modules, named as inlet model, mixing model, combustion mode and nozzle model, respectively. We solve these four basic flow processes using theoretical methods and propose a systematically theoretical approach that can be used to predict the ODE propulsion performance. On the basis of previous ODW initiation structures and waves systems, four different combustion modes, i.e., over-driven ODW, Chapman-Jouguet ODW, over-driven normal detonation wave and oblique shock-induced constant-volume combustion, are chosen to describe the heat release processes of combustible mixture in the ODE combustor. The effects of different combustion modes on fuel specific impulse of the ODE are also analyzed. In addition, the influence mechanisms of inflow parameters, combustor parameters and intake-exhaust parameters on the thrust performance of ODE are also obtained, and the results show that the major factor of fuel specific impulse of an ODE consists mainly of the inflow Mach number and the expansion ratio of engine nozzle. Finally, combined with precious detonation research results, such as the standing features and initiation structures of oblique detonation in a confined space, the preliminary design direction of oblique detonation engine are proposed, which mainly involve some constrained conditions, such as geometrical constraints, inflow velocity limitations and stability ranges of a detonation wave in ODE combustor.

Design of three dimensional flower-like MXene/manganese-cobalt spinel nanocomposites for efficient catalytic thermal decomposition of ammonium perchlorate

A series of MXene/MnCo2O4.5 nanocomposites was successfully prepared by hydrothermal, ice crystal template and physical blend methods, respectively. Various characterizations indicated that hydrothermal method could successfully loaded MnCo2O4.5 nanoparticles on the surface of MXene nanosheets to obtain MMC-W nanocomposites with 3D flower-like structure, which could give MMC-W large specific surface area. The HTD temperature and decomposition heat of AP with adding 2.0 wt% MMC-W could significantly decrease to 304.7 °C and increase to 1310.9 J g-1, respectively. The lowest decomposition temperature (286.1 °C) and the highest heat release (1427.6 J g-1) of AP could be obtained by adding 8.0 wt% and 4.0 wt% of MMC-W, respectively. Moreover, MMC-W (2.0 wt%) could also significantly reduce the Ea of pure AP by 118.3 kJ mol-1 and increase the k value for AP by 11.2 times. The excellent catalytic performance of MMC-W was owing to the synergistic effect of nano-sized MnCo2O4.5 and MXene nanosheets. Owing to its high catalytic activity, MMC-W would be used as an excellent catalyst for ameliorating AP decomposition and supply an idea for the preparation of novel metal oxide nanoparticles.