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The design of efficient plasma reformers requires both efficient fuel conversion of fuel and chemical energy extraction. In this regard, liquid fuels provide the advantages of high gravimetric and volumetric energy densities, therefore yielding high energy; in particular, diesel is promising for use in plasma reformers. In this study, we investigated the ignition process in a diesel reformer driven by a rotating gliding arc using a high-speed camera. The locations of the flame kernel generated by the arc were clearly identified under different power conditions. At high power, the flame kernel was generated at the nozzle tip, which grew into a fully developed flame. This indicates that the period for fuel vaporization and mixing with air (which is a necessary step prior to chemical reactions and is typically longer than the characteristic chemical reaction time) is extremely short. Moreover, with low oxygen concentrations, we observed a rotating flame kernel. At low power, the flame kernel was generated at a distance from the nozzle tip and the arc. This result indicates that the generation mechanism of the flame kernel in the plasma reformer is not straightforward; flow and arc dynamics also influence the interactions between the arc and fuel droplets.

Controllability of the kinetic path of methane conversion in plasma driven oxidation reaction is investigated. Different geometries in a rotating gliding arc reactor are adopted to control reaction paths in methane oxidation reaction. Diverging and converging type reactor product different reaction environments in view point of both the reaction time and the degree of thermal activation. In the diverging reactor, the partial oxidation process is dominant with high methane conversion because the diverging section facilitates to elongate the arc length and decrease the flow velocity. Thus, the convective and radiative heat transfer from the arc column to the reactants could be enhanced. The role of plasma in the diverging reactor is mainly igniting and sustaining the partial oxidation, which is rather different from that in the converging reactor where the plasma plays as a heat source for thermal pyrolysis of methane with the help of focusing thermal energy of the arc.

Green hypergolic propellants have been extensively studied. In the present study, we attempted to improve the measurement technique for the ignition delay in hypergolic reactions by using a drop-test apparatus. The evaluation method for the hypergolicity is important because an increase in the diversification of green hypergolic combinations is inevitable. Hydrogen peroxide (90 wt%) was used as an oxidizer, and six different reactive fuels were prepared. Sodium borohydride was utilized as an ignition source for the fuels. Optical and acoustic sensors were employed to reliably measure the ignition delay. The proposed measurement technique used in this study accurately reflected the physical phenomena of the hypergolic interactions. The technical limitations in the conventional measurement technique using a high-speed camera were experimentally investigated. Liquid-phase reactions were dominant in the hypergolic reactions of the glyme-based reactive fuels. Gas-phase reactions significantly influenced the hypergolic reactions of most of the amine-based reactive fuels. The pyridine-based reactive fuel had a longer delay time for the gas-phase reaction process than the liquid-phase reaction process. Recognizing the rate-determining step of the hypergolic ignition is necessary for not only designing a rocket injector but also reducing combustion instability, e.g., reactive stream separation.

Feasibility of using the pintle injector as a sole-throttling device was tested with a focus on the acquisition of sufficient injector orifice areas for uniform liquid injection considering the maximum throttling ratio of 4 to 1. Cold flow tests using 95 wt% hydrogen peroxide were performed with a relatively long and a short variable-area continuous-radial orifice of an average surface roughness condition of 1.6 μm to explore hydraulic and liquid injection characteristics of the sole-throttling concept device. The required orifice gap size in the long orifice case was always larger than that in the short orifice case based on the same throttling ratio owing to lowered discharge coefficients. The transition from the uniform annular sheet injection to injection of jets with the sheet was observed as the decreased orifice gap size reached approximately 0.2 mm in both cases. The liquid injection in the short orifice case was more uniform compared to the long orifice case in the jet-sheet injection region. The feasibility of attaining the uniform annular sheet injection for the shallow throttling level was discussed from the test results.

An effort is presented to seek a promising candidate for a green energetic monopropellant based on hydrogen peroxide. The novel premixed monopropellant is composed of 90 wt.% H2O2 as the oxidizer and tetraglyme (C10H22O5) as the fuel. Different mixture ratios were prepared by varying the weight percentage of the fuel in the mixture, and the mixtures were named HPM-08 (8 wt.% of fuel), HPM-12 (12 wt.% of fuel), and HPM-20 (20 wt.% of fuel). The theoretical performance of the mixtures was estimated, and their thermostability in air was evaluated via thermogravimetric analysis. A small-scale packed-bed catalytic reactor was utilized to assess the feasibility of the catalytic ignition of HPM-08 with a lanthanum-doped manganese oxide catalyst. Ground hot-firing tests were implemented with an engineering model monopropellant thruster on the scale of 10 N. The demonstrations of the thruster operation using HPM-08 and HPM-12 were successful, but an explosion was caused in the case of HPM-20. A technical speculation suggested that the explosion could be closely related to the phenomenon of detonation. In this study, the configuration of the catalyst bed was regarded as the principal factor in the triggering of detonation in the thruster module. The packed-bed-type catalyst bed containing millimeter-scale pellets may accelerate the phenomenon of deflagration-to-detonation transition, resulting from the rapid compressive heating process based on the superposition of the pressure waves. These results should be taken into account during the design of the catalyst bed in order to utilize particular types of this premixed monopropellant. In addition, a new ignition technique may be applied to prevent the explosion.

Plasma catalysis has been extensively investigated on both plasma and catalyst sides to explore the possible synergies, with most studies focusing on reactivity enhancement and the search for pathways other than those of simple plasma or catalytic reactions. However, there is currently much room for plasma applications beyond reactivity control in catalyst preparation and regeneration phases. This review introduces the use of plasma for accelerated catalyst regeneration and proposes a corresponding mechanistic explanation, showing that the effectiveness of this regeneration can be ascribed to the chemical and/or thermal effects of plasma such as the formation of reactive reductants/oxidants and cost-effective catalyst heat-up. Moreover, plasma-assisted catalyst regeneration is shown to involve low-temperature activation and gas-phase radical–based reactions, be a viable method of avoiding catalyst sintering during conventional high-temperature regeneration, and exhibit the advantage of cost effectiveness.

This study aimed to conceptually introduce a novel method of dual-mode operation of nontoxic hypergolic thruster using decomposition gas of hydrogen peroxide (H2O2) and to experimentally assess the...

A liquid injection thrust vector control (LITVC) system was designed for a hybrid rocket that uses 95 wt % hydrogen peroxide, and the system was demonstrated by using the hydrogen peroxide as the i...

The on-board reforming technique for de-NOx is attracting increasing interest because of the fast start-up and size of the device. However, due to the limited amount of energy available from the battery, a full understanding of the characteristics of the plasma reforming reaction is important to optimise this technology to achieve hydrogen production with minimal power consumption. This paper reports the relative role of the thermal effect of plasma in octane oxidation induced by rotating arc plasma. The thermal effect or gas temperature increased with increased electric power; the conversion of the electric energy to heat was estimated to be higher than 40%. The increased thermal effect was the main consequence of further increasing the plasma power, which controlled the syngas yield and was the main determinant of the energy efficiency of the reaction. In comparison, although the O-2/C ratio was the main parameter determining the thermal environment in the reactor, it had only a small influence on the energy efficiency of the reaction. The optimal O-2/C ratio for maximum energy efficiency depends on the electric power (e.g. the optimal O-2/C was 0.8 at 80 W and 0.5 at 280 W). The results provide guidance for determining the optimal conditions for plasma-driven reforming processes.

A high length-to-diameter ratio of a rocket leads to unstable flight performance, affects structural loads, and makes a high dry mass of the rocket with a diameter constraint. To improve the volume...

Green liquid monopropellant thrusters provide an alternative to toxic hydrazine. A premixed liquid monopropellant based on hydrogen peroxide with ethanol blending was suggested to replace hydrazine...

This Paper suggests two speculations on the nontoxic hypergolic propulsion using hydrogen peroxide as an oxidizer based on the experimental data. Drop tests were repeatedly performed with the nonto...

The conceptual design of high-speed underwater jet engine was conducted and demonstrated using high concentration of hydrogen peroxide as a green propellant. On the basis of the principles of steam jet ejector, the central water jet configuration was applied for the engine where a central water jet was surrounded by an annular steam flow. The annular steam flow as the primary fluid was the decomposition gas of hydrogen peroxide and cold water was the secondary fluid. The catalyst pack was composed of the alumina pellets doped with manganese oxides. The performance evaluation of the engine was performed without the flow field of the secondary fluid. The demonstrator successfully generated a practical propulsive force, which could be applied for the systems of unmanned underwater vehicles. For design of experiments, the nozzle exit areas were dealt with. It should be ensured that the exit area of nozzle was sufficiently large to prevent thrust instabilities due to the disturbance in the high-speed flows. In contrast, the excessively large area of the nozzle exit might decrease the efficiency of the engine performance in that the geometry of the engine failed to encourage the heat energy transfer between the primary and the secondary fluids.

A novel concurrent process for CO2 reduction and plastic upcycling was successfully developed based on a rotating gliding arc plasma process, where CO2 gas and Low-density polyethylene (LDPE) powder were used as reactants for the process. Herein, the LDPE powder was regarded as an alternative of plastic waste, and the high temperature of the plasma jet thermochemically decomposed the plastic powder. Based on gas chromatography analyses, the yields of the C1 and C2 chemicals were confirmed, which demonstrated the possibility for the chemical upcycling of the plastic powder with CO2 plasma jet. At the same time, the conversion of CO2 at the exhaust gas increased with increasing electric power of the plasma jet. In addition, as the electric power further enhanced, the reverse reactions were efficiently suppressed by the chemical quenching process due to complete depletion of the oxygen by the light hydrocarbon gases generated from the pyrolysis of the plastic powder. Based on the molecular balance of C and O, the calculated syngas to CO2 ratio was achieved up to 32 % in a batch-type plasma reactor with a power supply of 1170 W. It is rational inference that the efficiency will be significantly improved if a plug-in type plasma reactor with higher power supply is implemented. In conclusion, this novel concurrent process would be a promising approach for an efficient and scalable technology of CO2 utilization.

The present study focused on experimental studies on the hydrogen peroxide film-cooling method for a 500 N scale nontoxic hypergolic thruster. The nontoxic hypergolic fuel used was Stock 3 and the main oxidizer was 95% high-test peroxide (HTP). Two different liquid film coolants, water and 95% HTP, were tested to qualitatively analyze the effects of the thermal decomposition of hydrogen peroxide on film-cooling performance. The results of the film-cooling performance tests were examined from three different perspectives: propulsive performance analysis, film-cooling performance analysis, and gaseous film-cooling analysis. The thermal decomposition process of the hydrogen peroxide film coolant contributed to alleviating the loss in propulsive performance, but degraded the film-cooling performance. Two simple analytical approaches, the inverse problem method and gaseous film-cooling method, were utilized to predict the interior surface temperatures of the chamber. The Stineman interpolation method was also useful in estimating the temperature profiles of the chamber even without temperature data from the area downstream of the nozzle throat.

The present paper describes the phenomenon of hard start observed from a demonstrator of 500 N scale nontoxic hypergolic thruster using high-test peroxide as an oxidizer. When 90% concentration of hydrogen peroxide was used, the hard start was observed even under the fuel lead operation. To effectively suppress the occurrence of hard start phenomena in the startup phase of the thruster, oxidizer-to-fuel mass ratio and concentration of hydrogen peroxide have been individually considered. In drop tests, the ignition delays of hypergolic reactions became longer in the oxidizer-rich condition than those measured in the fuel-rich condition. By regulating oxidizer-to-fuel mass ratio with deliberate control of the oxidizer mass flow rate, the thruster operated smoothly even using 90% high-test peroxide in the fuel-rich environment. Furthermore, without the utilization of the flow control device, the thruster successfully operated when higher concentrations of high-test peroxide (95 and 98%) were used under the f...

The present research dealt with the concept of green hypergolic combination to replace the toxic hypergolic combinations. Hydrogen peroxide was selected as a green oxidizer. A novel recipe for the non-toxic hypergolic fuel (Stock 3) was suggested. Sodium borohydride was blended into the mixture of energetic hydrocarbon solvents as an ignition source for hypergolic ignition. The main ingredient of the mixture was diethylenetriamine. By mixing some amount of tetrahydrofuran with diethylenetriamine, the mixture became more flammable and volatile. The mixture of Stock 3 fuel remained stable for four months in the lab scale storability test. Through a simple drop test, the hypergolicity of the green hypergolic combination was verified. Comparing to the toxic hypergolic combination MMH/NTO as the reference, the theoretical performance of the green hypergolic combination would be achieved about 96.7% of the equilibrium specific impulse and about 105.7% of the density specific impulse. The applicability of the green hypergolic combination was successfully confirmed through the static hot-fire tests using 500 N scale hypergolic thruster.

Non-toxic hypergolic propellants have considerably generated recent research interest in the field of green propulsion technology because they can replace highly toxic hypergolic combinations currently used. In this experimental research, sodium borohydride-based non-toxic hypergolic fuel was prepared by blending sodium borohydride in the mixture of energetic hydrocarbon solvents. In a drop test, sodium borohydride as an ignition source enabled the hydrocarbon mixture to initiate hypergolic interactions with H 2 O 2 oxidizer. Two different heating methods were utilized to analyze the characteristics of autoignition and combustion of the hypergolic fuel. As a reference fuel, a non-hypergolic fuel which has the identical chemical compositions to the hypergolic fuel except for sodium borohydride was tested and compared. As a one of the heating methods, thermogravimetric analysis was not suitable for evaluating the inherent thermophysical properties of the hypergolic fuel. In a droplet combustion chamber test, the autoignition and combustion of the hypergolic fuel droplets occurred exposed to elevated temperatures (in a range of 400–800 °C) at atmospheric pressure (1 bar), whereas the non-hypergolic fuel droplet was automatically ignited only at 800 °C. The ignition delay and total combustion time of the hypergolic fuel droplet were lower than those of the non-hypergolic fuel droplet. According to the temporal histories of the droplet size, sodium borohydride-based hypergolic fuel droplets did not obey the d 2 -law of diffusion-controlled combustion, which indicates the droplet evaporation rate was not a controlling factor in the combustion process. Consequently, the addition of sodium borohydride into the hydrocarbon mixture expedited the autoignition and combustion process of the fuel at elevated temperatures.

A novel experimental method to evaluate the ignition characteristics of hypergolic propellants was investigated. Three hypergolic liquid fuels with different ignition characteristics were prepared, and their reaction rates with hydrogen peroxide were measured in a microreactor fabricated using a microelectromechanical systems lithography process. To prevent evaporation and boiling by the reaction heat, a low-concentration of hydrogen peroxide of 34.5 wt % was used as a reference oxidizer. The reaction rates of the hypergolic fuels were obtained from temperature measurements in the microreactor and correlated with the ignition delays that were separately measured by drop tests with high-test peroxide. The reaction rate measurements were fully compatible with the drop test results and proved to be useful as an alternative method for the selection of hypergolic propellants by ignition characteristics.

The decomposition process of hydrogen peroxide can be applied to a bipropellant thruster, as well as to monopropellant thruster. To provide a framework for the optimal design of the injector and catalyst bed depending on a type of thruster, this research scrutinizes the effect of injection patterns of the propellant on the performance of the catalyst bed. A showerhead injector and impinging jet injector were tested with a 50 N monopropellant thruster. Manganese oxide/γ-alumina catalyst and manganese oxide/lanthanum-doped alumina catalyst were prepared and tested. The showerhead injector provided a fast response time, suitable for pulse mode operation. The impinging jet injector mitigated the performance instability and catalyst attrition that is favorable for large scale bipropellant thrusters. The design of a dual catalyst bed was conceptually proposed based on the data obtained from firing tests.

While shedding light on green space propulsion, the development of non-toxic hypergolic bipropellants has provided alternatives to the conventional, highly toxic propellants. Non-toxic energetic hydrocarbon fuels promoted by sodium borohydride were produced, and their hypergolicity with rocket grade hydrogen peroxide was confirmed. Ignition delays ranged from 4 ms to 17 ms, depending on the oxidizer concentration. A 500 N scale thruster utilizing a non-toxic hypergolic bipropellant combination was also developed. With an oxidizer-to-fuel ratio of 5.48, the injector was designed with pentad unlike-impinging jets, one fuel jet orifice and four oxidizer jet orifices for enhancing the mix and atomization of the hypergolic propellants. The operation test was performed, and burning time was established to be 3.5 s. For the demonstrator, the rising time was approximately 158 ms, and the pressure oscillation inside the combustion chamber was approximately ±7.69%. These results indicate the feasibility of this novel concept engine for future space missions.

The proliferation of natural gas production had led to increased utilization of methane as a raw material for chemicals. The most significant bottleneck in this process is the high activation energy of methane. This paper reports the direct conversion of methane to acetylene in a novel rotating arc driven by AC electrical power. By feeding a sufficiently high concentration of CH4 (greater than 43%) diluted in H2 (the discharge gas) through the arc column, a low specific energy requirement (SER) of 10.2 kW h kg−1 C2H2 was achieved. The use of hydrogen as the discharge gas strongly suppressed soot formation during the methane conversion process under high methane concentration conditions, resulting in a carbon balance of greater than 95% and a C2H2 selectivity of greater than 90% while maintaining a methane conversion rate of greater than 70%, depending on the conditions. The novel rotating arc enabled the elongation of the arc column itself, which controlled heat loss and improved the energy use for reaction. The ability to control the arc length based on low-current type arc generation has additional benefits for reaction enhancement. These results demonstrate that arc control, optimization of the reaction conditions, and a full understanding of reaction pathway are viable means for the energy-efficient direct conversion of methane to acetylene.

Plasma-assisted nitrogen fixation is a promising sustainable and clean alternative to the classical Haber–Bosch process. However, the high energy consumption and low production rate of plasma-assisted nitrogen fixation limit its application. This study shows that the non-thermal (non-equilibrium) enhancement of the arc plasma significantly reduces the energy consumption of nitrogen fixation. The highest energy efficiency with high NO selectivity is observed with a low specific energy input (SEI). However, the highest production rate is reached at a high SEI. The studied process offers high NO selectivity (up to 95%) with low energy consumption (∼48 GJ per tN) at 0.1 kJ L−1 SEI, which is much lower than the previously reported value of plasma-assisted atmospheric nitrogen fixation and is close to that of the Haber–Bosch process.