Oxygen Mass Flux Research Articles

Catalytic effects of transition metal oxides on HTPB-based fuel polymer matrices

Low regression rate due to difficult pyrolysis is a major challenge in the practical application of terminated hydroxyl‑terminated polybutadiene (HTPB)-based fuels in hybrid rocket propulsion. Accelerating the decomposition of the polymer matrix is an effective method to improve the regression rate of HTPB fuels. To determine the difference in combustion performance between different transition metal oxides loaded HTPB-based fuels, nickel oxide (NiO), ferric oxide (Fe2O3), copper oxide (CuO) and manganese dioxide (MnO2) were introduced into the HTPB matrix at 5% mass fraction. The experimental results showed that the metal oxides could significantly catalyze the pyrolysis of HTPB-based fuels and enhance the fuel regression rate, and the catalytic effect was mainly concentrated in the middle and late stages of the thermal decomposition process of polybutadiene components. Among the four transition metal oxides, CuO and MnO2 showed better catalytic effects on the combustion performance of HTPB-based fuels in the high oxygen mass flux region, while NiO showed better catalytic effects in the low oxygen mass flux region. The present study compares the regression rate of fuel grains modified with different transition metal oxides, which provides a basis for the selection of future catalysts, verifies the catalytic effect of the transition metal oxides on the combustion of HTPB-based fuels and further analyzes the combustion reaction mechanism of the fuels.

Regression Rate and Combustion Efficiency of Composite Hybrid Rocket Grains Based on Modular Fuel Units

This study investigated combustion characteristics of composite fuel grains designed based on a modular fuel unit strategy. The modular fuel unit comprised a periodical helical structure with nine acrylonitrile–butadiene–styrene helical blades. A paraffin-based fuel was embedded between adjacent blades. Two modifications of the helical structure framework were researched. One mirrored the helical blades, and the other periodically extended the helical blades by perforation. A laboratory-scale hybrid rocket engine was used to investigate combustion characteristics of the fuel grains at an oxygen mass flux of 2.1–6.0 g/(s·cm2). Compared with the composite fuel grain with periodically extended helical blades, the modified composite fuel grains exhibited higher regression rates and a faster rise of regression rates as the oxygen mass flux increased. At an oxygen mass flux of 6.0 g/(s·cm2), the regression rate of the composite fuel grains with perforation and mirrored helical blades increased by 8.0% and 14.1%, respectively. The oxygen-to-fuel distribution of the composite fuel grain with mirrored helical blades was more concentrated, and its combustion efficiency was stable. Flame structure characteristics in the combustion chamber were visualized using a radiation imaging technique. A rapid increase in flame thickness of the composite fuel grains based on the modular unit was observed, which was consistent with their high regression rates. A simplified numerical simulation was carried out to elucidate the mechanism of the modified modular units on performance enhancement of the composite hybrid rocket grains.

Synergistic mass transfer and performance stability of a proton exchange membrane fuel cell with traveling wave flow channels

As one of the critical components of the proton exchange membrane fuel cell (PEMFC), the flow channel design in the bipolar plate is crucial to improve the mass transfer performance and stability. In this study, the effect of the structural characteristics and location arrangement of traveling wave flow channels, with a concave surface as the mass transfer surface, on the fuel cell performance is investigated, and the evaluation indexes, such as oxygen mass flux, net power density, synergistic coefficient, and unevenness coefficient, are established to evaluate the flow law of fluid, distribution law of pressure, synergistic mass transfer, and performance stability of the fuel cell. Results show that the synergistic mass transfer performance is better in the traveling wave channels with identical structural characteristics and uniform arrangement. Furthermore, a 21.20 % increase in the average fluid flow velocity can enhance oxygen and liquid water flux at the bipolar plate (BP)/gas diffusion layer (GDL) interfaces by about 198.48 % and 207.94 %, respectively, resulting in an 87.13 % increase in net power density and 70.95 % improvement in the performance stability of the fuel cell.

Combustion Characteristics of HTPB-Based Hybrid Rocket Fuels: Using Nickel Oxide as the Polymer Matrix Pyrolysis Catalyst

The slow regression rate induced by the high pyrolysis difficulty has limited the application and development of hydroxyl-terminated polybutadiene (HTPB)-based fuels in hybrid rocket propulsion. Nickel oxide (NiO) shows the possibility of increasing the regression rate of HTPB-based fuels by catalyzing the pyrolysis process of the polymer matrix in our previous investigation; hence, this paper studies the NiO particles in the thermal decomposition and combustion of HTPB fuel grains. The DSC/TG test shows that NiO can intensely decrease the thermal stability of HTPB, and the catalytic effect of NiO is mainly reflected in the final decomposition stages of polybutadiene components. 5 wt% NiO enhances the regression rate by 19.4% and 13.7% under an oxygen mass flux of 50 kg/m2s and 150 kg/m2s, respectively. Further investigation shows that NiO particles will also cause the reduction of combustion heat and the agglomeration at the regressing surface while catalyzing the pyrolysis process, improving the thermal conductivity, and promoting the radiative heat transfer of the HTPB-based fuels; thus, more NiO additive (5 wt% < [NiO] ≤ 10 wt%) does not lead to a faster regression rate in HTPB-based fuels. This study demonstrates the catalytic effect of NiO on the polymer matrix for HTPB-based fuels, showing the attractive application prospects of this additive in HTPB-containing fuel grains.

Investigation of applied smouldering in different conditions: The effect of oxygen mass flux

Self-sustained smouldering combustion can be a fire hazard, but also a valuable waste-to-energy tool and an effective means for the destruction of organic contaminants. In all contexts, smouldering is an oxygen-limited phenomenon and therefore oxygen mass flux plays a major role. In this study, a multidimensional, thermodynamic-based smouldering model was developed and validated against experiments to quantify the complex interplay between chemical reactions and heat and mass transfer processes. Oxygen supply was independently varied by diluting oxygen mass fraction feeding the smouldering reactions. Smouldering robustness was quantified by local and global energy analyses establishing when a negative net energy balance indicated the onset of quenching. It was confirmed that a diluted oxygen mass fraction resulted in increased heat transfer efficiency driving the smouldering front towards quasi-super-adiabatic conditions. The centreline peak temperature remained almost constant despite a decreasing smouldering front velocity and the weakening local energy balance. Under these unique conditions, key multidimensional heat and mass transfer effects could be explored systematically, showing the displacement of air towards the periphery of the reactor leading to lower peak temperatures and eventually localized quenching. The visual manifestation of localized quenching was an unburnt crust near the reactor wall.

Surface morphology evolution mechanisms of laser polishing in ambient gas

Laser polishing, as an effective surface finishing process, is significantly affected by ambient gas. Previous studies on the contribution of ambient gas to laser polishing mostly focused on experiments, but rarely on numerical simulations. Given this, this paper proposes an improved model capable of analyzing the effects of ambient gas on the laser-polished surface's morphology evolution mechanisms, by expanding an existing laser polishing model with the influences of mass transfer, solutocapillary forces, and chemical reactions. Argon and air were used as ambient gasses for comparison. Through this model, the surface morphology evolution of laser polishing in air was compared with that in argon in terms of the velocity field, temperature field, concentration field, melt surface velocity, molten pool surface profile, and surface forces. The respective contributions of chemical reaction heat, oxygen mass flux, mass transfer, and surface forces were also presented. Furthermore, the numerical model was verified on 304 stainless steel from the perspectives of polished surface roughness, molten pool depth, and oxygen element distribution.

The Mechanism Research of Low-Frequency Pressure Oscillation in the Feeding Pipe of Cryogenic Rocket Propulsion System

In the propulsion system of cryogenic liquid rockets, low-frequency pressure oscillation is a long-standing issue occurring in its feeding pipe, and is not conducive to the normal operation of the rocket. Its mechanism and excitation process are not very clear due to the limitation of the existing numerical method and the difficulty of the real dynamic experiment. Inspired by the periodic suck-back flow phenomenon of steam condensation, the fluctuation of the two-phase interface might be the crucial factor to initiate the low-frequency pressure oscillation. To simulate this interfacial characteristic of cryogenic propellant, a novel numerical model is proposed to predict the mass transfer rate weighted by the interfacial curvature. Aiming at the oxygen jet condensation simulation, the low-frequency pressure oscillation phenomenon is obtained successfully with the excitation frequency of 10.6 Hz, consistent with the natural frequency of the engine test run. It is conducted so the low-frequency pressure oscillation is caused by the periodic condensation of the continuous oxygen vapour plume, along with an oxygen suck-back flow phenomenon. In addition, the results indicate that both the oxygen and liquid oxygen mass flux promote the rise in the frequency of pressure oscillation. These conclusions provide theoretical instructions for the design and operation of the propulsion system of a cryogenic liquid rocket.

Experimental and numerical investigation on flow condensation process of oxygen jet in crossflow of liquid oxygen

The mixing and condensation process of gaseous oxygen jet in liquid oxygen flow in the outlet pipeline of oxidizer booster pump in liquid rocket engine are studied. In the present study, experiments are performed to investigate oxygen jet condensation in crossflow of liquid oxygen in a vertical pipe. The image of the test section is obtained by visualization device and processed by digital image technology. A computational fluid dynamics (CFD) model is developed to simulate the mixing and condensation process based on multiphase VOF model and Lee phase change model. The experimental results show that, under the current operating conditions, gaseous oxygen forms a crooked jet plume at the outlet of orifices, and then the gas phase gradually condenses, forming discontinuous bubbles downstream. The effects of Reynolds number of liquid oxygen, oxygen mass flux, ambient pressure and liquid oxygen temperature on the gas distribution and axial condensation length are investigated accordingly. The mass transfer coefficient r=10000s−1 which has been verified by the experiment of oxygen jet in liquid oxygen crossflow is obtained and the predicted gas distribution by CFD simulation is in good agreement with the experimental data. The experimental dimensionless axial condensation length is in the rage of 7.3 to 18.2, and a correlation of dimensionless axial condensation length has been modified. Besides, the dimensionless axial condensation length predicted by simulation is less than 13% comparing with experiment. The averaged heat transfer coefficients obtained in experiment and simulation are around 13.89–26.04 kW/(m2K) and 12-67kW/(m2K), which is much lower than the average heat transfer coefficient in the DCC of water. The results of the present investigation will be helpful in designing the pipeline between pumps in liquid rocket engine.

Regression of solid polymer fuel strands in opposed-flow combustion with gaseous oxidizer

The combustion of solid fuels is a complex feedback loop, coupling the decomposition of the solid fuel into volatile gases with the gas-phase combustion which is responsible for the heat flux that drives decomposition. This study aims to explore the combustion of a solid fuel, hydroxyl-terminated polybutadiene (HTPB), with different mixtures of oxygen and nitrogen in an opposed-flow burner (OFB) configuration to better understand these coupled processes. An experimental OFB setup is described, which utilizes a nichrome wire and linear variable differential transformer (LVDT) to capture regression rate and shadowgraph imaging to measure flame thickness. Experimental measurements are compared with results from a complimentary one-dimensional opposed-flow combustion model with a pyrolyzing solid fuel boundary condition that conserves mass, species, and energy at the solid-gas interface. The oxidizer mass flux, ratio of oxygen to nitrogen, and separation distance of the fuel and oxidizer are varied to understand their influence on the combustion process and subsequently their effect on the regression rate. In numerical results, fuel regression rate increases when oxygen mole fraction or mass flux increase, or when separation distance decreases. Experimental regression rates and flame thicknesses are compared to simulated results. Though the actual values do not agree exactly, numerical and experimental results are reasonably close and present similar trends. These results demonstrate the utility of simple optical diagnostics in measuring OFB flames and provide a starting point for future opposed-flow combustion model improvements.

Effects of swirl injection on the combustion of a novel composite hybrid rocket fuel grain

The combustion characteristics obtained from the coupling effect between swirl injection and a novel composite hybrid rocket fuel grain were investigated. The novel composite fuel grain was composed of a three-dimensional printed acrylonitrile-butadiene-styrene (ABS) helical substrate with an embedded paraffin-based fuel. Two swirl flow injectors with opposite injection directions were designed: one with the same injection direction as the swirling direction induced by the ABS helical substrate and the other having the opposite direction. Axial injection trials were also performed as a baseline for comparison. Firing tests were carried out using a lab-scale hybrid rocket engine with oxygen as the oxidizer at average mass flux values in the range of 2.1–4.5 g/(s·cm2). When combined with either swirl flow injector, the novel composite fuel grain exhibited excellent combustion properties. Compared with the axial flow injector, both swirl injectors greatly improved the regression rate of the novel composite fuel grain, by 82.4% and 50.6% respectively, at an oxygen mass flux of approximately 4.25 g/(s·cm2). Three-dimensional imaging of the inner surface of the novel composite fuel grain and cold flow numerical simulations were employed to assess the mechanism by which the regression rate was increased. The results of these analyses elucidated the effects of different injection methods on the oxidizer-to-fuel ratio distribution during combustion of the novel composite fuel grain.

Nickel acetylacetonate as decomposition catalyst for HTPB-based fuels: Regression rate enhancement effects

The slow regression rate induced by the difficulty of pyrolysis has limited the practical application of hydroxyl-terminated polybutadiene (HTPB)-based fuels for hybrid rocket propulsion. A possible strategy is the use of suitable transition metal elements promoting polymer matrix thermal decomposition of fuels. This paper investigates the effects of nickel acetylacetonate, Ni(acac)2, on the thermal stability and combustion of HTPB-based fuel formulations. The presented experimental results show that the addition of Ni(acac)2 can intensely decrease the thermal stability of HTPB thus enhancing the solid fuel regression rate even at a small additive mass fraction: under an oxygen mass flux of 50 kg/m2s, HTPB + 5 wt% Ni(acac)2 shows a 25.5% increase over the non-loaded baseline. Kinetics analyses reveal that the catalytic effect is mainly induced by the Ni2+ in Ni(acac)2 at the early stage of decomposition, and by the NiO produced from the oxidative decomposition of Ni(acac)2 in the fuel final degradation stage. On the other hand, the addition of Ni(acac)2 decreases the combustion heat of HTPB-based fuels significantly and implies the accumulation of its decomposition products (much metal Ni, moderate elemental C, and a little NiO.) at the fuel regressing surface. Eventually, when the content of Ni(acac)2 exceeds 5 wt%, the growth of regression rate slows down rapidly, and a performance detriment occurs at 40 wt%. This study verifies the catalytic effect of Ni(acac)2 on polymer matrix for HTPB based fuels showing the attractive regression rate performance of this additive.

Variational-principle-optimized porosity distribution in gas diffusion layer of high-temperature PEM fuel cells

Porosity distribution in gas diffusion layer has a significant impact on cell performance by affecting the oxygen transport and the electrical conductivity. This contribution presents a theoretical optimization model for porosity distribution in the cathode gas diffusion layer based on the variational principle. First, the optimization equations for maximizing the total oxygen mass flux diffused through the cathode gas diffusion layer are derived with the constraints of the momentum conservation, the species conservation and the specified average porosity. Then, the application of a typical high-temperature proton exchange membrane fuel cell with twelve parallel flow channels gives the optimized three-dimensional non-uniform porosity distribution that could increase the current density at 0.2 V by 13.7% and the maximum power density by 10.0%. Besides, the optimized porosity distribution also improves the uniformity of oxygen mass fraction field and the current density distribution. Finally, seven design schemes with in-plane non-uniform porosity distribution or thickness-direction linear gradient porosity are proposed and evaluated. The results indicate that the optimized porosity distribution has the best performance, followed by the in-plane non-uniform porosity, and the linear gradient porosity along the thickness direction shows the weakest improvement. This finding further demonstrates the rationality and necessity of the proposed optimization model.

Numerical and Experimental Study of the Effects of Surface Temperature and Oxygen Mass Flux on the Ablation of Carbon–Carbon Composites

The ablation performance of carbon–carbon composites depends on the environment in which the ablation occurs. At temperatures below 3000 $$K$$ , the ablation performance of carbon–carbon composites is determined by oxidation, and so it is not sufficient to describe the environment only in terms of surface heat flux, which is the criteria that has typically been adopted for test conditions in ground tests. In this study, the effects of surface temperature and oxygen mass flux on the ablation of carbon–carbon composites were investigated, since they are key factors in the oxidation of carbon–carbon composites. Oxy-kerosene torch experiments were conducted under two surface temperature conditions, of about 1700 $$K$$ and 2600 $$K$$ , and with three equivalence ratio conditions. The experimental results were then numerically reconstructed through a coupled analysis of oxy-kerosene torch flow-field modelling, surface thermochemistry, and gas-surface interaction. The effects of surface temperature and oxygen mass flux on the ablation of carbon–carbon composites were analyzed in terms of the mass ablation rate, surface heat flux, and morphology. It was determined that the mass ablation rate is proportional to the increase in oxygen mass flux, even when the surface heat flux and surface temperature were similar. The proportion of heat flux reduction by ablation heat flux was proportional to the increase in oxygen mass flux, and the contribution of oxygen mass flux to the ablation heat flux was enhanced under high surface temperature conditions. Depending on surface temperature and oxygen mass flux, a flat-shape fiber was observed in the morphology analyses, unlike the typical needle-shaped fiber.

Self-consistent surface-temperature boundary condition for liquefying-fuel-based hybrid rockets internal-ballistics simulation

A novel methodology for the calculation of the surface temperature of liquefying fuels typically burned in hybrid rockets is proposed. This procedure stems from the formulation of a fuel in-depth pyrolysis model coupled with the resolution of the thermo-fluid-dynamic field in the rocket combustion chamber, which allows for the characterization of the unstable liquid layer formed on top of the fuel surface. The aim is the simulation of the internal ballistics of hybrid rocket engines fed by paraffin-based fuels without the need for parametrically assigning the surface temperature to match the experimental data as, indeed, required in the authors’ previous work. With the presented technique, surface temperature and fuel vaporization rate are calculated locally along the wall, and, with the integration of a liquid fuel entrainment model, which requires the tuning of just one parameter (i.e. the so-called entrainment factor), the fuel regression rate is determined. The overall numerical approach, upon the assumption that the liquid fuel is in the supercritical pressure regime, is based on the solution of the Reynolds-averaged Navier–Stokes equations for single-phase multicomponent turbulent reacting flow. A series of numerical simulations are carried out to unveil the effect of the oxygen mass flux, which allowed deriving an approximate analytical equation for the regression rate prediction. A set of hot fires of a laboratory-scale hybrid rocket are reproduced through single numerical simulations carried out on the fuel port average geometry in the burn to validate the computational model, showing deviations between the measured and predicted average regression rate less than 4.5%. In order to fairly match also the fuel consumption axial profile, transient numerical simulations over the entire engine firing are conducted with which the post-burn port shape is captured with maximum error of 8%.

Comparative study of embedded functionalised MWCNTs and GO in Ultrafiltration (UF) PVC membrane: interaction mechanisms and performance

ABSTRACT This work presents the development of polyvinyl chloride/functionalised multi-carbon nanotube (PVC/F-MWCNT) membranes and PVC/graphene oxide (PVC/GO) membranes for the improved removal of chemical oxygen demand (COD) from actual petroleum wastewater. Also, this work for the first time presents the proposed interaction mechanism between the contents of PVC/GO and PVC/F-MWCNT membranes as well as the interaction mechanism of each composite membrane with water molecules. The effect of both F-MWCNT and GO content on the characteristics and performance of the PVC/F-MWCNT membrane and PVC/GO membrane were studied. Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscopy (AFM), contact angle (CA), differential scanning calorimetry (DSC), porosity and tensile strength were used to examine the properties of F-MWCNT, GO, PVC/F-MWCNT and PVC/GO membranes. The composite membranes’ performance was studied by measuring the rejection of chemical oxygen demand (COD) and mass flux. It was found that F-MWCNTs and GO played significant roles in the membranes’ structural morphology. A significant improvement was obtained in the CA, porosity and tensile strength of the membranes by embedding the PVC casting solution with 0.12 wt% of each F-MWCNTand GO. The PVC/F-MWCNTs membrane showed higher performance in term of mass flux and COD rejection that reached 88.9%, which makes using a PVC/F-MWCNTs membrane preferable to remove COD from petroleum wastewater.

Performance Evaluation of Boron/Hydroxyl-Terminated Polybutadiene-Based Solid Fuels Containing Activated Charcoal

Numerous researches have been conducted on boron-based fuels and propellants due to the attractive theoretical energy potential of boron. However, sustained energy production during combustion of a boron-based fuel/propellant is still uncertain because efficient burning of boron is challenging. The present paper deals with various boron-loaded polymeric fuels, where activated charcoal (AC) is introduced as a burning enhancer for application in hybrid fuel ducted rocket. The solid fuel samples are tested with the help of a classical screening tool, which is known as opposed flow burner (OFB) or stagnation flow burner. Opposed flow burner is run with oxygen mass flux between 20 and . The fuel is evaluated on the basis of major performance parameters, such as regression rate, species formation during combustion using a spectrometer, residual active ingredients in postcombustion product using standard material characterization techniques, etc. The major outcome is evaluated from thermogravimetric analysis (TGA), where active residual boron is found to be around 6% only in postcombustion product for the fuel sample containing B and AC in equal proportion. Opposed flow burner helps in reducing the time and cost of research involving expensive fine fuel ingredients, and also facilitates to identify optimum fuel formulations for hybrid gas generator in ducted rocket applications.

Nano-Sized and Mechanically Activated Composites: Perspectives for Enhanced Mass Burning Rate in Aluminized Solid Fuels for Hybrid Rocket Propulsion

This work provides a lab-scale investigation of the ballistics of solid fuel formulations based on hydroxyl-terminated polybutadiene and loaded with Al-based energetic additives. Tested metal-based fillers span from micron- to nano-sized powders and include oxidizer-containing fuel-rich composites. The latter are obtained by chemical and mechanical processes providing reduced diffusion distance between Al and the oxidizing species source. A thorough pre-burning characterization of the additives is performed. The combustion behaviors of the tested formulations are analyzed considering the solid fuel regression rate and the mass burning rate as the main parameters of interest. A non-metallized formulation is taken as baseline for the relative grading of the tested fuels. Instantaneous and time-average regression rate data are determined by an optical time-resolved technique. The ballistic responses of the fuels are analyzed together with high-speed visualizations of the regressing surface. The fuel formulation loaded with 10 wt.% nano-sized aluminum (ALEX-100) shows a mass burning rate enhancement over the baseline of 55% ± 11% for an oxygen mass flux of 325 ± 20 kg/(m2∙s), but this performance increase nearly disappears as combustion proceeds. Captured high-speed images of the regressing surface show the critical issue of aggregation affecting the ALEX-100-loaded formulation and hindering the metal combustion. The oxidizer-containing composite additives promote metal ignition and (partial) burning in the oxidizer-lean region of the reacting boundary layer. Fuels loaded with 10 wt.% fluoropolymer-coated nano-Al show mass burning rate enhancement over the baseline >40% for oxygen mass flux in the range 325 to 155 kg/(m2∙s). The regression rate data of the fuel composition loaded with nano-sized Al-ammonium perchlorate composite show similar results. In these formulations, the oxidizer content in the fuel grain is <2 wt.%, but it plays a key role in performance enhancement thanks to the reduced metal–oxidizer diffusion distance. Formulations loaded with mechanically activated ALEX-100–polytetrafluoroethylene composites show mass burning rate increases up to 140% ± 20% with metal mass fractions of 30%. This performance is achieved with the fluoropolymer mass fraction in the additive of 45%.

Intrinsic hydrogen yield from gasification of biomass with oxy-steam mixtures

In this paper, experimental investigations on oxy-steam gasification of biomass in downdraft packed bed reactor are presented; propagation regimes and the associated hydrogen yield will be the focus of the current work. Steady flame propagation is shown to be established for a range of oxygen mass flux (16–120 g/m2s) covering ‘gasification’ and ‘combustion’ regimes with O2 fractions of 23, 30 and 40% by mass (rest steam). By restricting the upstream bed temperatures between 120 °C (to avoid steam condensation) and 150 °C (to prevent bulk devolatilization of bed), the intrinsic H2 yield from biomass is determined over an equivalence ratio (Φ) range of 3.5 to 1.2. This is shown to correspond to a ‘volatiles’ based equivalence ratio (ϕv) of 2.2 to 1. Interestingly, the H2 yield over this entire range is within 30–40 g/kg of biomass. Using equilibrium calculations, it is shown that the ‘unburnt volatiles’ is the major H2 source when ϕv > 2 and as ϕv → 1, ‘volatiles’ H2 drops close to zero and the major contribution is through the reaction, C + H2O → CO + H2. Increase in char conversion from about 20% at ϕv ∼2.1 to almost 100% as ϕv → 1, the corresponding increase in peak bed temperature and decrease in ‘higher hydrocarbons’ are consistent with the observed H2 yield. The important insight is, operating close to ϕv = 1, under slightly rich condition, leads to tar free exit gas with little or no compromise on H2 yield. This hitherto unknown result is perhaps the reason why all earlier works focused only on highly fuel rich conditions and/or very high steam temperatures (∼800 °C), tolerating higher tar content.

Model simplification of coal combustion kinetics: a case study of Weihuliang coal in Urumchi, China

The present study reports the determining the evolution stage of coal combustion bases on its corresponding characteristic behaviours and the oxidation kinetics during different evolution stages including the newly ignited stage (NIS), accelerating stage (AS), consistently burning stage (CBS), slowly burning-out stage (SBS), and extinct stage (ES). The main characteristic behaviours during coal combustion, namely, temperature gradients, oxygen consumption, gaseous products, and heat release, were investigated using an experimental apparatus. Preliminary criteria for distinguishing the evolution stage of a coal fire were developed based on these characteristic behaviours. The results showed that for the Weihuliang coal, the CO/CO2 ratio could be regarded as an indicator of an extinct coal fire, and SO2 could be used to distinguish newly ignited, accelerating, or consistently burning coal fires. The heat release during the CBS, SBS, and ES was classified into three heat levels, with the first-level heat occurring during the CBS, second-level heat during the SBS, and third-level heat during the ES. A minimum value of oxygen mass flux required for ideal coal combustion was proposed to ensure the applicability of the first-order Arrhenius equation during the ES. Lastly with the oxygen supply considered, unifying the first-order Arrhenius equations (the chemical equations) during different evolution stages was put forward as an approach of model simplification. This work will be helpful in the understanding the evolution process of coal fires, and also useful for the effective control and sustainable recovery utilisation of coal fires.

Experimental Observation and Characterization of B−HTPB‐based Solid Fuel with Addition of Iron Particles for Hybrid Gas Generator in Ducted Rocket Applications

AbstractAn extensive diversity in the formulation of HTPB‐based solid fuels with metal additives has now been accepted in rocket and missile applications. Boron, which is a metalloid and often occurs in compound form has maintained its dominance mainly due to its significant theoretical energy potential. Therefore, it is preferred as the primary choice for rockets and solid fuel ramjet (SFRJ) or ducted rocket (SFDR). In this paper, performance enhancement of B−HTPB‐based solid fuel is assessed through a rapid screening tool which is called an opposed flow burner (OFB). Screened fuel combinations may be further evaluated in the gas generator of a ducted rocket (DR) to fulfill the intention of the present investigation. The baseline fuel (B−HTPB) is included with a metal fuel/catalyst (iron) with the expectation that it would enhance the combustion performance of boron. Boron−iron loading has been taken 10 % of the total sample weight (wt.) giving a wt. ratio of 90 : 10. Pure oxygen has been used as an oxidizer which impinges on the fuel surface where oxygen mass flux (Gox) varies between 20–57 kg/m2‐s. In this study, the research focuses mainly on regression rate and amount of residual active boron in the condensed combustion product (CCP) of the samples. Addition of iron to B−HTPB increases the regression rate by around 12 % and active boron content in CCP reduces significantly to 2.5 % compared to 16 % of the baseline fuel. In addition to that, the heating value of the fuel samples and identification of gas phase intermediate species (OH, CH, C2, BO, BO2) are the other vital investigations undertaken in the present study.