Researches on fragmentation of a single coal particle during gasification contribute to the establishment of a complete evolutionary system of coal particles in gasifiers. In this study, the behavior ...of char fragmentation and ash coalescence as well as the number and size of sub-particles are microscopically recorded to investigate the fragmentation mechanism. The proportion of small-sized sub-particles with particle sizes of 4∼10 μm are all above 50 % under different atmospheres, nevertheless the average particle size of the sub-particles decreased with the increase of the proportion of oxygen and the total number of sub-particles differed approximately by a factor of 2.5 at most. Additionally, the instantaneous production of sub-particles increases with the particle surface temperature, while the average sub-particle size follows a different pattern with the particle surface temperature under different atmospheric conditions. When the oxygen concentration is over 60 %, the sub-particle size decreases as the particle surface temperature increases, while an opposite pattern is observed when the oxygen concentration is below 60 %. It is attributed to the fact that although the increase in surface temperature enhances the char fragmentation behavior, the agglomeration of ash and production large-size ash pellets would be promoted once the particle surface temperature higher than the ash flow temperature for char particles at low reaction rate. Besides, coalesced ash would attract the small-size char fragments, which may ultimately lead to an elevated ratio of large-size char fragments.
•Gasification of coal particle in rapid heating process is microscopically recorded.•Sub-particles are mainly composed by particles with diameters of 4∼10 μm.•Mean diameter of sub-particles rises with temperature increases at O2-poor condition.•Fragments are reduced due to the adsorption of small-size char by molten minerals.
Combustion characteristics of a rapid mixed swirl torch igniter of CH4/O2 for hybrid rocket motors has been experimentally investigated. The igniter torch consists of four tangential slits ...circumferentially equispaced on the internal micro-combustion chamber allows tangential injection of O2 gas, meanwhile the CH4 flows into the main channel and interacts with four tangential O2 injections flow to generate a swirl mixing of CH4 and O2. The ignitability of this swirl torch igniter was verified by large number of experiments in variation of equivalence ratio and total flowrate of CH4/O2. The flame structure of the igniter and effect of main oxidizer injection acting as a cross flow on the flame has been investigated by using OH* and CH* chemiluminescences techniques. It is found that the torch igniter can reliably ignite instantaneously in the range of equivalence ratio 0.2∼1.4 and the effect of main oxidizer injection on the flame is tiny and can be neglected. In addition, the performance of this rapid mixed swirl flame has been investigated by using a lab scaled hybrid rocket motor and compared with the same hybrid rocket motor ignited by catalytic bed. The performance of this igniter and its comparison with catalytic bed ignition will be discussed and analyzed in detail.
Microwave Discharge Igniter (MDI) is an ignition device that operates based on the microwave resonance phenomenon. Receiving the microwave pulses from a semiconductor generator, the MDI generates ...non-thermal plasma to enhance the combustion. A new igniter plug consists of multiple MDIs in its structure is developed to achieve leaner operation limit as well as higher dilution limit, which are essential strategies to meet current and future emission regulations. The prototype multi-point MDI plug contains 3 separate MDI port which are all connected and controlled by the semiconductor MW generator. The prototype 3-point MDI is tested in both a single cylinder performance engine and a production multi-cylinder engine. At target conditions of part load and low load, low engine speed, the multi-point MDI performs much better than single MDI and the traditional spark plug in both engines. In the performance engine, the 3-point MDI results in the shortest burn duration especially during the early stages. However, the 3-point MDI exceeds the lean running capability of the production engine when operate as a plug with two active MDI ports and hence the full potential of 3-point MDI currently exceed the current generation of production engines.
Compared with the conventional igniters, a liquid hydrogen/liquid oxygen (LH2/LOX) torch igniter has significant advantages of ignition energy, reliability, and reusability for LH2/LOX rocket motors. ...However, the mechanisms that underpin the LH2/LOX torch igniter are not fully understood yet. In this study, the effects of the injection distance and droplet size on the igniter, typically on the torch power (i.e., ignition energy) and thermal protection, were numerically investigated. Meanwhile, two fire tests with different conditions were conducted to validate the numerical model prior to the simulation. The simulation results show that increasing the injection distance is beneficial to improve the torch power but not conducive to thermal protection under our conditions. Moreover, LOX droplet size marginally affects the torch power and thermal protection because of the fuel-rich combustion in our study. Nevertheless, the increase of LH2 droplet size results in a higher inner wall temperature, which contradicts the purpose of thermal protection.
Display omitted
A low-power-driven and carrier-gas free arc igniter microplasma optical emission spectrometry (AIM-OES) was coupled with hydride generation (HG) to detect arsenic in soils, only ...utilizing by-product H2 produced therein as a working gas.
•A low-power-driven arc igniter microplasma optical emission spectrometry (AIM-OES) was fabricated for determining arsenic in soils.•The by-product, H2, formed by hydride generation (HG) process acted as the sole working gas for the construction of a miniaturized, carrier-gas free device.•The discharges in air and Ar, with and without hydrogen content (from the HG step) were systematically studied.
Rapid on-site assessment of arsenic contamination in soils is crucial for environmental protection and human health. In order to build an effective and affordable device for the determination of arsenic, the use of carrier gas supplies and high power energy consumption largely limit the miniaturization of microplasma-based optical emission spectrometry (OES). An arc igniter microplasma (AIM) can be powered by a low DC power supply and operated in the atmosphere of air without gas infusion, which is beneficial to construct a carrier-gas free and low power supply setup. Hydride generation (HG) can improve sample transport efficiency and reduce matrix effects, but the generated by-product hydrogen has not been explored as a sole working gas for plasma excitation. In this work, a hydride generation arc igniter microplasma optical emission spectrometer (HG-AIM-OES) was fabricated for detecting arsenic in soils. H2 derived from HG was served as a working gas to transport AsH3 to excite, eliminating the use of a carrier gas unit. Under the optimized operating conditions, the limit of detection (LOD) for arsenic was 164 μg/L (the analytical line at 234.98 nm), and good linearity of the method was achieved in the range of 0.5–20 mg/L with a precision of 3.14 % (the concentration of arsenic at 1 mg/L). In addition, the influence of H2 on AIM physical properties was carefully studied in the air and Ar discharge atmospheres. The accuracy of the proposed device was validated by the analysis of certified reference materials (CRMs) and a real soil sample, resulting in good agreement with the obtained results by air and Ar as working gas. This HG-AIM-OES system provides a miniaturized, carrier gas-free and low power consuming tool for monitoring and assessment of arsenic-contaminated soils.
The paper is part of the research aimed at determining if the vortex flow pancake (VFP) hybrid rocket engine is feasible as green in-space chemical propulsion. The objective of this study is to test ...an N2O/HDPE VFP hybrid ignited with N2O/C3H8 torch igniter. The N2O is used in self-pressurizing mode, which results in two-phase flow and varying inlet conditions, thus better simulating real in-space behavior. The study begins with characterizing the torch igniter, followed by hot-fire ignition tests of the VFP. The results allow for the improved design of the torch igniter and VFP hybrid. The axial regression rate ballistic coefficients are reported for the N2O/HDPE propellants in the VFP configuration.
Nitrocellulose is a flammable compound produced by cellulose nitration. The nitrocellulose production and handling are associated with a risk of fire and explosion. Nitrocellulose is used as either ...collodion cotton (<12.5% N) or as an explosive (>12.5% N). Nitrocellulose is a fibrous or powdered substance and may detonate or burn upon certain conditions. The article compares the combustion parameters of dry nitrocellulose in the KV-150M2-UIBE explosion chamber at the concentrations of 250, 500 and 750 g m−3. To ignite a nitrocellulose sample, six different types of igniters were used. A commercially available 5 kJ pyrotechnic igniter was used as the standard. Also used were a nitrocellulose igniter, a pyrotechnic igniter with magnesium powder and KNO3/KClO3, and an exploding wire (Kanthal and tungsten wire). The examined igniters were found to affect the explosion parameters of dispersed nitrocellulose. The deviation of the explosion constant Kst reached 50% of the standard value. The highest pressure of 12.73 bar g was reached at a concentration of 750 g m−3 and an igniter exploding wire with Kanthal wire. The highest Kst value of 287.9 bar.m.s−1 was achieved at a concentration of 750 g m−3, when using the pyrotechnic igniter with KClO3 and magnesium powder.
Display omitted
•Ignition of a nitrocellulose sample dust cloud was investigated.•Explosion parameters of nitrocellulose ignited by six types of igniters were compared.•Explosion parameters were compared to standard Sobbe igniter.•Explosion dynamics and explosion parameters were found to strongly depend on the type of igniter.
This study evaluates the ignition performance of a new miniaturised igniter that operates based on microwave resonance phenomenon. This igniter, named Flat Panel Igniter (FPI), consists of a flat ...ceramic panel with a metal strip inlay on the top surface acting as a resonance cavity. The FPI and a standard spark plug is used to ignite air–propane mixtures at various equivalence ratio inside a constant volume chamber. The results show that FPI requires much less ignition energy than spark plug at any given equivalence ratio. Furthermore, at the same energy, ignition with FPI results in a faster ignition delay and a shorter burnt duration. FPI ignition also allows for better lean limit as the ignition energy increases. Observation at non-reactive condition shows that the plasma from FPI is a lot larger than that of the spark plug, most likely due to the enhancement by MW energy. Via optical spectroscopy, FPI spectrum is also shown to be much more intense than the spark plug, with a higher level of OH* radicals and slightly higher temperature. Schlieren images of the combustion shows a more spherical appearance of the resulting flame, suggesting that the design of the FPI will induce less heat loss to the early flame kernel and hence facilitate faster flame growth. The igniters were also tested under the influence of cross flow by injecting an air stream across the plasma location. Due to its geometry the FPI plasma has a longer stretch distance compared to the spark discharge from spark plug and interestingly, the FPI does not suffer from blow-off even at high flow speed where spark plug suffers from very early blow-off and restrikes. Overall, the FPI has been shown to be a promising igniter that outperforms the traditional spark plug to enable further advancement in engine design.
Solid propellants are employed in a range of applications from the inflation of airbags to propulsion systems for rockets. The ignition of solid propellants must be carefully controlled and modified ...on a per-use basis due the specific ignition requirements of each application. Using tailored photoreactive materials as a source of ignition for solid propellants, or other energetic materials, could reduce the added weight and risk of traditional initiators and result in safer, more effective solid rocket motor ignition systems. This study demonstrates the tunability of the ignition delay and propagation properties of optically-sensitive, nearly full density reactive aluminum/polyvinylidene fluoride (Al/PVDF) films and additively manufactured igniters. A single printed layer of pure nano-aluminum (nAl) at ideal stoichiometry in PVDF was found to flash ignite, but frequently yielded delayed transitions in steady propagation from the igniter to the propellant. To improve the continuity and steadiness of the transition, fuel particle size, igniter thickness, and a combination of layers of nAl and micron-sized aluminum (μAl) were investigated. In printed igniters with layers of μAl, only a single layer of nAl was needed to flash ignite the material and propagate to the layers of μAl without delay. For igniters cast onto strands of ammonium perchlorate composite propellant, continuous ignition was achieved with a single layer of nAl printed atop a triple layer of μAl for the flash-activated igniters and a single layer of nAl printed atop a single and triple layer of μAl for laser-driven igniters. The nAl/PVDF layer enabled good flash or laser ignition sensitivity, while the μAl/PVDF produced more sustained heat transfer to produce a reliable ignition process.
Over the past few years, there has been a growing recognition of the importance of multi-spacecraft missions for a variety of purposes, including Earth observation, navigation, guidance, climate ...monitoring, and environmental monitoring. The trend amongst agencies is to favour constellations of smaller satellites, which can aggregate data from various sources, rather than relying on larger satellites. The numerous benefits of multi-spacecraft formation flying missions have led to an increasingly growing interest to explore its propulsion technologies, i.e., micro propulsion. Thoroughly characterising and studying the behaviour of the energetic materials is essential to ensure the safe and effective use of these micro-thrusters. Through the optimisation of micro-thruster design, the current research aims to generate outcomes that can be utilised to enhance the design and optimisation processes. Consequently, this will facilitate the widespread utilisation of micro-thrusters in multi-spacecraft missions. To optimise the performance of pyrotechnic micro-electromechanical systems, an efficient heater design, appropriate base material, channel dimensions, and electrical resistance must be considered based on available power and heat transfer requirements. A unique firing and monitoring test setup has been developed to produce a current-time plot for the device. Additionally, different micro-heater configurations, including spiral, loop, and meander types, were designed for the igniter. Experimental observations indicate that the spiral micro-heater design resulted in the lowest ignition delay and produced highly reliable combustion. The proposed microthruster design demonstrated efficient combustion and yielded promising results when tested with energetic materials such as Zirconium Potassium Perchlorate (ZPP) and Boron Potassium Perchlorate (BPN).
Display omitted
