This work was supported by the National Natural Science Foundation of China (Grant Nos. 11802315, 11872368 and 11927803) and Equipment Pre-Research Foundation of National Defense Key Laboratory (Grant No. 6142701190402).

1. Experimental setup and procedures
<ol>
	<li>Preparation of fuel grain 
	NOTE: The fuel grain with novel structure consisted of two parts, which are shown in Figure 4. As the main part of the novel grain, the paraffin-based fuel accounts for more than 80% of the total mass. The ABS substrate is used as an additional fuel. The preparation of this fuel grain was realized by combining 3D printing and centrifugal casting.
	<ol>
		<li>Substrate preparation
		<ol>
			<li>Open 3D software for ABS substrate drawing. 
			NOTE: The ABS substrate, which intended to provide the helical framework and support for the paraffin-based fuel, is comprised of twelve integrated blades that rotate 360&#176; clockwise in the axial direction and the wall.</li>
			<li>Save the 3D structure of the ABS substrate as a STL file.</li>
			<li>Open the 3D slicing software and import the structure of ABS substrate.</li>
			<li>Click Start Slicing, and select Speed print mode from Main Template. 
			NOTE: For the Primary Extruder choose ABS 1.75 mm.</li>
			<li>Double-click Speed, change the infill density to 100% and select Raft with Skirt for the Platform Addition. 
			NOTE: In order to improve the print quality and prevent warping, it is necessary to use a structure of print base (Raft with Skirt) to increase the contact area between the print body and the bottom plate.</li>
			<li>Click Save and Close, and then click Slice.</li>
			<li>Turn on the 3D printer and import the ABS substrate slice file.</li>
			<li>Set the temperature of the heated bed and nozzle to 100 and 240 &#176;C, respectively.</li>
			<li>Click Start to print after stabilization.</li>
		</ol>
		</li>
		<li>Paraffin-based fuel preparation
		<ol>
			<li>Prepare raw materials of paraffin, polyethylene (PE) wax, stearic acid, ethylene-vinyl acetate (EVA), and carbon powder. Configure the paraffin-based fuel according to the ratio of these components as 0.58:0.2:0.1:0.1:0.02. 
			NOTE: The specific information of each raw material is shown in the material table. The distribution ratio of paraffin-based fuel is not fixed and can be adjusted appropriately according to the purpose of the experiment. The purpose of adding carbon powder is to block radiant heat transfer and prevent the fuel grain from softening and collapsing during combustion.</li>
			<li>Place the configured raw materials into the melt mixer, and fully melt and stir until completely mixed. 
			NOTE: The paraffin-based fuel is heated to 120 &#176;C to ensure complete melting while preventing deformation of the ABS blades.</li>
		</ol>
		</li>
		<li>Fuel grain manufacturing 
		NOTE: To better demonstrate the effect of improving the combustion performance, paraffin-based fuel grains with the same composition were set as the control.
		<ol>
			<li>Place the ABS substrate into the centrifuge, and secure it with an end cap.</li>
			<li>Plug in the power and turn on the water-cooling pump switch.</li>
			<li>Turn on the centrifuge relay and increase the speed to 1400 rpm.</li>
			<li>Open the valve on the melt mixer and start casting. 
			NOTE: The molten paraffin-based fuel flows into the initial section of mold through the pipe and the end cover with a central opening. Under the effect of gravity, the liquid fuel spreads along the axial direction of the mold. Combined with effective cooling, a multiple-casting method, which is to divide the original one-time filling process into multiple times, is required to reduce the thermal stress.</li>
			<li>Remove the fuel grain and trim the shape.</li>
		</ol>
		</li>
		<li>Fuel grain measurement and recording
		<ol>
			<li>Measure and record the weight, length, and inner diameter of the fuel grain.</li>
			<li>Photograph the complete fuel grain.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Preparation of hybrid rocket engine system 
	NOTE: As shown in Figure 5, the hybrid rocket engine system consisted of four parts: the supply system, the ignition system, the engine, and the measurement and control system. The engine part included five parts: the torch igniter, the head, the combustion chamber, the post-combustion chamber, and the nozzle. The total length of the hybrid rocket engine is about 300 mm, and the inner diameter of the combustion chamber is 70 mm.
	<ol>
		<li>Hybrid rocket engine assembly 
		NOTE: The exhaustive details of the laboratory-scale hybrid rocket and the composition of the experimental system can be found in the previous paper32.
		<ol>
			<li>Fix the combustion chamber section of hybrid rocket engine on the slide rail.</li>
			<li>Load the fuel grain and install the post-combustion chamber section.</li>
			<li>Install the head and nozzle.</li>
			<li>Install the torch igniter on the head of the hybrid rocket engine.</li>
			<li>Install the spark plug and connect the power supply.</li>
		</ol>
		</li>
		<li>Connect the nitrogen, oxidizer, ignition methane, and ignition oxygen gas supply lines between the test bench and the gas cylinder.</li>
		<li>Connect the industrial computer, the multi-function data acquisition card, the mass flow controller, and the control box of the test bench.</li>
		<li>Power on the test bench, the mass flow controller, and the igniter.</li>
	</ol>
	</li>
	<li>Check the test system and set the experimental conditions.
	<ol>
		<li>Open the FlowDDE software and click Communications settings from the Communication.</li>
		<li>Click the corresponding connection interface and click OK.</li>
		<li>Click Open communication to establish communication with the flow controller and open the measurement and control program (MCP).</li>
		<li>Set the I/O channel of the multi-function data acquisition card and click Run to establish communication with the entire system.</li>
		<li>Check MCP running status and set to manual control mode. 
		NOTE: The MCP includes two modes: manual control is used for debugging and automatic control is used during experiments. The MCP written by LabVIEW is shown in Figure 6.</li>
		<li>Check the working condition of the spark plug and perform a valve test.</li>
		<li>Test data recording function.</li>
		<li>Open the setting interface and set test time, including valve opening and closing time, ignition time, and data recording duration. 
		NOTE: It takes some time for the mass flow controller to regulate the oxidizer flow to the set value, so the ignition time was set to 2 s after the supply of oxidizer.</li>
		<li>Set safety requirements and clear personnel from the experimental area.</li>
		<li>Open the cylinder valve and adjust the output pressure of the regulating valve according to the different mass flow rate conditions. 
		NOTE: With the supply pressure of 6MPa, the range of mass flow rate of the oxidizer is between 7 g/s and 29 g/s.</li>
		<li>Open the setting interface and set the oxidizer mass flow rate.</li>
	</ol>
	</li>
	<li>Hybrid rocket engine ignition
	<ol>
		<li>Turn on the camera.</li>
		<li>Set the MCP to automatic control mode and wait for trigger.</li>
		<li>Click Start on the MCP to start the experiment.</li>
		<li>After about one minute, click Stop on the MCP and turn off the camera.</li>
		<li>Close the gas cylinder and open the valve in the pipeline to relieve the pressure.</li>
		<li>Power off the test bench and remove the fuel grain.</li>
		<li>Repeat Step 1.1.4.</li>
	</ol>
	</li>
</ol>
2. Analysis of combustion performance
<ol>
	<li>Analysis of pressure oscillation 
	NOTE: The saved combustion chamber pressure data is represented as Pc(t).
	<ol>
		<li>Open Pc(t) with the data processing software.</li>
		<li>Choose the time period during the combustion process of the hybrid rocket engine.</li>
		<li>Select Analysis &#62; Signal Processing &#62; FFT to analyze the pressure oscillation.</li>
		<li>Use the default settings and click OK.</li>
	</ol>
	</li>
	<li>Analysis of regression rate
	<ol>
		<li>Calculate the regression rate of the fuel grain according to the following function: 
		<img alt="Equation 1" src="/files/ftp_upload/61555/61555equ01v2.jpg" /> 
		where &#916;D represent the change of average inner diameters of the solid fuel grain after the firing test; <img alt="Equation 5" src="/files/ftp_upload/61555/61555equ05.jpg" /> represent the change of quality of the fuel grain; L is the length of the fuel grain; &#961; is the average density of the solid fuel; t is the working time. 
		NOTE: The average density &#961; of the novel grain was expressed as: 
		<img alt="Equation 2" src="/files/ftp_upload/61555/61555equ02v2.jpg" /> 
		where <img alt="Equation 6" src="/files/ftp_upload/61555/61555equ06.jpg" /> and <img alt="Equation 7" src="/files/ftp_upload/61555/61555equ07.jpg" /> represent the density of the nested paraffin-based fuel and ABS material, respectively; <img alt="Equation 8" src="/files/ftp_upload/61555/61555equ08.jpg" /> and <img alt="Equation 9" src="/files/ftp_upload/61555/61555equ09.jpg" /> represent the mass fraction of the nested paraffin-based fuel and ABS material, respectively.</li>
		<li>Fit the regression rate as a function of oxidizer flux. 
		NOTE: The fitting function was selected as Allometric1 <img alt="Equation 10" src="/files/ftp_upload/61555/61555equ10.jpg" />, and the iterative algorithm was selected as Levenberg&#8211;Marquardt optimization algorithm.</li>
	</ol>
	</li>
	<li>Analysis of combustion efficiency
	<ol>
		<li>Calculate average combustion chamber pressure Pc by the following function: 
		<img alt="Equation 3" src="/files/ftp_upload/61555/61555equ03v2.jpg" /> 
		where Pc(t) represents the combustion chamber pressure at different times; t1 and tn represent the initial and final times at which the combustion chamber pressure was greater than 50% of the average pressure, respectively; n represents the number of pressure data points between and t1 and tn.</li>
		<li>Calculate the combustion characteristic velocity C&#8432; according to the following function: 
		<img alt="Equation 4" src="/files/ftp_upload/61555/61555equ04v2.jpg" /> 
		where Pc is the average combustion chamber pressure; At is the throat area; &#7743; is the total mass flow rate.</li>
		<li>Calculate the theoretical characteristic velocity of paraffin fuel C&#8432;P by NASA CEA code33.</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

The technique presented in this paper is a novel approach using a fuel grain with a nested helical structure. There are no difficulties in setting up the necessary equipment and facilities. The helical structure can be easily produced by 3D printing, and nesting of paraffin-based fuels can be easily carried out by centrifugal casting. Fused deposition molding (FDM) 3D printers are not expensive and the cost of centrifuges is low.
When the inner surface of the shaped fuel grain was found to hav...

A technique to improve the combustion performance of a hybrid rocket engine is urgently required. To date, practical applications of hybrid rocket engines are still far less than those of solid and liquid rocket engines1,2. The low regression rate of traditional fuels limits the improvement of thrust performance for the hybrid rocket engine3,4. In addition, its combustion efficiency is slightly lower than that of other chemical energy rockets due to internal diffusion combustion5, as shown in Figure 1. Although various techniques have been studied and developed, such as the use of multi-ports6, enhancing additives7,8,9, liquefying fuel10,11,12, swirl injection13, protrusions14, and bluff body15, these approaches are associated with problems in volume utilization, combustion efficiency, mechanical performance, and redundancy quality. Thus far, structural improvement of the fuel grain, which does not have these shortcomings, has attracted more attention as an effective means of improving combustion performance16,17. The advent of three-dimensional (3D) printing has brough an effective way to increase the performance of hybrid rocket engines through the ability to rapid and inexpensively produce either complex conventional grain designs or nonconventional fuel grains18,19,20,21,22,23,24,25,26,27,28,29,30. However, during the combustion process, these improvements in combustion performance diminishes with the characteristic structure burning, resulting in a decrease in combustion performance23. We have demonstrated that a novel design is useful in improving performance of hybrid rocket engines31. The detail for this technique and representative results is presented in this paper.
The fuel grain consists of a helical substrate made by acrylonitrile-butadiene-styrene (ABS) and a nested paraffin-based fuel. Based on centrifugal and 3D printing, the advantages of the two fuels with different regression rates were combined. The special helical structure of the fuel grain after combustion is shown in Figure 2. When gas passes through the fuel grain, numerous recirculation zones are simultaneously created at grooves between blades, which is shown in Figure 3. This characteristic structure on the inner surface increases the turbulence kinetic energy and swirl number in the combustion chamber, which increase the exchanges of both matter and energy in the combustion chamber. Ultimately, the regression rate of the novel fuel grain is effectively improved. The effect of improving the regression rate has been well proven: in particular, the regression rate of the novel fuel grain was demonstrated to be 20% higher than that of the paraffin-based fuel at the mass flux of 4 g/s&#183;cm2,32.
One advantage of the fuel grain with a nested helical structure is that it is simple to manufacture. The molding process mainly requires a melt mixer, a centrifuge, and a 3D printer. The ABS substrate formed by 3D printing greatly reduces the manufacturing cost. Another significant and unique advantage is that the enhancement effect does not disappear during the combustion process.
This paper presents the experimental system and procedure for improving the combustion performance of a hybrid rocket engine using the novel fuel grain structure. Additionally, this paper presents three representative comparisons of combustion performance parameters to prove the feasibility of the technique, including oscillation frequency of combustion chamber pressure, regression rate, and combustion efficiency characterized by characteristic velocity.

<table><tbody><tr><td>3D printer</td><td>Raise3D</td><td>N2 Plus</td><td>305 &amp;times; 305 &amp;times; 605 mm</td></tr><tr><td>3D drawing software</td><td>Autodesk</td><td>Inventor</td><td></td></tr><tr><td>ABS</td><td>Raise3D</td><td>ABS black</td><td>1.75 mm</td></tr><tr><td>Camera</td><td>Sony</td><td>A6000</td><td></td></tr><tr><td>Carbon</td><td>Aibeisi</td><td>ATP-88AT</td><td></td></tr><tr><td>Centrifugal machine</td><td>Luqiao Langbo Motor Co.Ltd</td><td>Custom</td><td>&amp;le;1450 rpm</td></tr><tr><td>Data processing software</td><td>OriginLab</td><td>Origin 2020</td><td></td></tr><tr><td>EVA</td><td>DuPont Company</td><td>360</td><td>binder</td></tr><tr><td>Mass flow controller</td><td>Bronkhost</td><td>F-203AV</td><td>0-1500 ln/min</td></tr><tr><td>Melt mixer</td><td>Winzhou Chengyi Jixie Co.Ltd</td><td>Custom</td><td></td></tr><tr><td>Multi-function data acquisition card</td><td>NI</td><td>USB-6211</td><td></td></tr><tr><td>Paraffin</td><td>Sinopec Group Company</td><td>58#</td><td>Fully refined paraffin, Melting point&amp;#8776;58&amp;deg;C</td></tr><tr><td>PE wax</td><td>Qatar petroleum chemical industry Company</td><td>Custom</td><td></td></tr><tr><td>Slicing software</td><td>Raise3D</td><td>ideaMaker</td><td></td></tr><tr><td>Spark plug</td><td>NGK</td><td>PFR7S8EG</td><td></td></tr><tr><td>Stearic acid</td><td>ical Reagent Company</td><td>Custom</td><td>hardener</td></tr></tbody></table>

improving the combustion performance of a hybrid rocket engine using a novel fuel grain with a nested helical structure

A technique to improve the combustion performance of a hybrid rocket engine using a novel fuel grain structure is presented. This technique utilizes the different regression rates of acrylonitrile butadiene styrene and paraffin-based fuels, which increase the exchanges of both matter and energy by swirl flow and recirculation zones formed at the grooves between the adjacent vanes. The centrifugal casting technique is used to cast the paraffin-based fuel into an acrylonitrile butadiene styrene substrate made by three-dimensional printing. Using oxygen as the oxidizer, a series of tests were conducted to investigate the combustion performance of the novel fuel grain. In comparison to paraffin-based fuel grains, the fuel grain with a nested helical structure, which can be maintained throughout the combustion process, showed significant improvement in the regression rate and great potential in improvement of combustion efficiency.

Figure 7 shows the changes in combustion chamber pressure and oxidizer mass flow rate. To provide the necessary time for flow regulation, the oxidizer enters the combustion chamber in advance. When the engine builds pressure in the combustion chamber, the oxygen mass flow rate drops rapidly and then maintains a relatively steady change. During the combustion process, the pressure in the combustion chamber remains relatively stable.
Images showing a comparison of c...

Watch this Scientific Journal Video about Improving the Combustion Performance of a Hybrid Rocket Engine using a Novel Fuel Grain with a Nested Helical Structure at JoVE.com

Improving the Combustion Performance of a Hybrid Rocket Engine using a Novel Fuel Grain with a Nested Helical Structure

A technique utilizing a solid fuel grain with a novel nested helical structure to improve the combustion performance of a hybrid rocket engine is presented.

A technique to improve the combustion performance of a hybrid rocket engine using a novel fuel grain structure is presented. This technique utilizes the ...

improving-combustion-performance-hybrid-rocket-engine-using-novel

Research

JoVE Journal

Engineering

5.6K Views.  Chinese Academy of Sciences. Deze methode kan helpen bij het beantwoorden van de vraag hoe de verbrandingsprestaties van granen te verbeteren. De belangrijkste voordelen van dit protocol is dat de spiraalvormige structuur brandstofkorrels niet zal verdwijnen met het verbrandingsproces. Deze methode kan ook worden toegepast op graanformule met verschillende materiaalcompilasaties zoals EBS en PUX.Begin met het bereiden van de acrylonitril butadieen styreen, of ABS substraat, met behulp van 3D-software. Sla de 3D-su...

Video: Improving the Combustion Performance of a Hybrid Rocket Engine using a Novel Fuel Grain with a Nested Helical Structure

Biomass Conversion to Produce Hydrocarbon Liquid Fuel Via Hot-vapor Filtered Fast Pyrolysis and Catalytic Hydrotreating

Lignocellulosic biomass conversion to produce biofuels has received significant attention because of the quest for a replacement for fossil fuels. Among the various thermochemical and biochemical routes, fast pyrolysis followed by catalytic hydrotreating is considered to be a promising near-term opportunity. This paper reports on experimental methods used 1) at the National Renewable Energy Laboratory (NREL) for fast pyrolysis of lignocellulosic biomass to produce bio-oils in a fluidized-bed reactor and 2) at Pacific Northwest National Laboratory (PNNL) for catalytic hydrotreating of bio-oils in a two-stage, fixed-bed, continuous-flow catalytic reactor. The configurations of the reactor systems, the operating procedures, and the processing and analysis of feedstocks, bio-oils, and biofuels are described in detail in this paper. We also demonstrate hot-vapor filtration during fast pyrolysis to remove fine char particles and inorganic contaminants from bio-oil. Representative results showed successful conversion of biomass feedstocks to fuel-range hydrocarbon biofuels and, specifically, the effect of hot-vapor filtration on bio-oil production and upgrading. The protocols provided in this report could help to generate rigorous and reliable data for biomass pyrolysis and bio-oil hydrotreating research.

Experimental methods for fast pyrolysis of lignocellulosic biomass to produce bio-oils and for the catalytic hydrotreating of bio-oils to produce fuel range hydrocarbons are presented. Hot-vapor filtration during fast pyrolysis to remove fine char particles and inorganic contaminants from bio-oil was also assessed.

Lignocellulosic biomass conversion to produce biofuels has received significant attention because of the quest for a replacement for fossil fuels. Among ...

Biochemistry

Flame Experiments at the Advanced Light Source: New Insights into Soot Formation Processes

The following experimental protocols and the accompanying video are concerned with the flame experiments that are performed at the Chemical Dynamics Beamline of the Advanced Light Source (ALS) of the Lawrence Berkeley National Laboratory1-4. This video demonstrates how the complex chemical structures of laboratory-based model flames are analyzed using flame-sampling mass spectrometry with tunable synchrotron-generated vacuum-ultraviolet (VUV) radiation. This experimental approach combines isomer-resolving capabilities with high sensitivity and a large dynamic range5,6. The first part of the video describes experiments involving burner-stabilized, reduced-pressure (20-80 mbar) laminar premixed flames. A small hydrocarbon fuel was used for the selected flame to demonstrate the general experimental approach. It is shown how species&#8217; profiles are acquired as a function of distance from the burner surface and how the tunability of the VUV photon energy is used advantageously to identify many combustion intermediates based on their ionization energies. For example, this technique has been used to study gas-phase aspects of the soot-formation processes, and the video shows how the resonance-stabilized radicals, such as C3H3, C3H5, and i-C4H5, are identified as important intermediates7. The work has been focused on soot formation processes, and, from the chemical point of view, this process is very intriguing because chemical structures containing millions of carbon atoms are assembled from a fuel molecule possessing only a few carbon atoms in just milliseconds. The second part of the video highlights a new experiment, in which an opposed-flow diffusion flame and synchrotron-based aerosol mass spectrometry are used to study the chemical composition of the combustion-generated soot particles4. The experimental results indicate that the widely accepted H-abstraction-C2H2-addition (HACA) mechanism is not the sole molecular growth process responsible for the formation of the observed large polycyclic aromatic hydrocarbons (PAHs).

Gas sampling from laboratory-scale flames with online analysis of all species by mass spectrometry is a powerful method to investigate the complex mixture of chemical compounds occurring during combustion processes. Coupled with tunable soft ionization via synchrotron-generated vacuum-ultraviolet radiation, this technique provides isomer-resolved information and potentially fragment-free mass spectra.

The following experimental protocols and the accompanying video are concerned with the flame experiments that are performed at the Chemical Dynamics ...

Preparation and Reactivity of Gasless Nanostructured Energetic Materials

High-Energy Ball Milling (HEBM) is a ball milling process where a powder mixture placed in the ball mill is subjected to high-energy collisions from the balls. Among other applications, it is a versatile technique that allows for effective preparation of gasless reactive nanostructured materials with high energy density per volume (Ni+Al, Ta+C, Ti+C). The structural transformations of reactive media, which take place during HEBM, define the reaction mechanism in the produced energetic&#160;composites. Varying the processing conditions permits fine tuning of the milling-induced microstructures of the fabricated composite particles. In turn, the reactivity, i.e., self-ignition temperature, ignition delay time, as well as reaction kinetics, of high energy density materials depends on its microstructure. Analysis of the milling-induced microstructures suggests that the formation of fresh oxygen-free intimate high surface area contacts between the reagents is responsible for the enhancement of their reactivity. This manifests itself in a reduction of ignition temperature and delay time, an increased rate of chemical reaction, and an overall decrease of the effective activation energy of the reaction. The protocol provides a detailed description for the preparation of reactive nanocomposites with tailored microstructure using short-term HEBM method. It also describes a high-speed thermal imaging technique to determine the ignition/combustion characteristics of the energetic materials. The protocol can be adapted to preparation and characterization of a variety of nanostructured energetic composites.

This protocol describes the preparation of gasless nanostructured energetic materials (Ni+Al, Ta+C, Ti+C) using the short-term high-energy ball milling (HEBM) technique. It also describes a high-speed thermal imaging method to study the reactivity of mechanically fabricated nanocomposites. These protocols can be extended to other reactive nanostructured energetic materials.

High-Energy Ball Milling (HEBM) is a ball milling process where a powder mixture placed in the ball mill is subjected to high-energy collisions from the ...

Preparation and Evaluation of Hybrid Composites of Chemical Fuel and Multi-walled Carbon Nanotubes in the Study of Thermopower Waves

When a chemical fuel at a certain position in a hybrid composite of the fuel and a micro/nanostructured material is ignited, chemical combustion occurs along the interface between the fuel and core materials. Simultaneously, dynamic changes in thermal and chemical potentials across the micro/nanostructured materials result in concomitant electrical energy generation induced by charge transfer in the form of a high-output voltage pulse. We demonstrate the entire procedure of a thermopower wave experiment, from synthesis to evaluation. Thermal chemical vapor deposition and the wet impregnation process are respectively employed for the synthesis of a multi-walled carbon nanotube array and a hybrid composite of picric acid/sodium azide/multi-walled carbon nanotubes. The prepared hybrid composites are used to fabricate a thermopower wave generator with connecting electrodes. The combustion of the hybrid composite is initiated by laser heating or Joule-heating, and the corresponding combustion propagation, direct electrical energy generation, and real-time temperature changes are measured using a high-speed microscopy system, an oscilloscope, and an optical pyrometer, respectively. Furthermore, the crucial strategies to be adopted in the synthesis of hybrid composite and initiation of their combustion that enhance the overall thermopower wave energy transfer are proposed.

A protocol for conducting thermopower wave experiments is presented. The synthesis of hybrid composites of a chemical fuel and micro/nanostructured material, manufacturing of a thermopower wave generator, and methods for measuring the corresponding physical phenomena are described.

When a chemical fuel at a certain position in a hybrid composite of the fuel and a micro/nanostructured material is ignited, chemical combustion occurs ...

Experimental Methodology for Estimation of Local Heat Fluxes and Burning Rates in Steady Laminar Boundary Layer Diffusion Flames

Modeling the realistic burning behavior of condensed-phase fuels has remained out of reach, in part because of an inability to resolve the complex interactions occurring at the interface between gas-phase flames and condensed-phase fuels. The current research provides a technique to explore the dynamic relationship between a combustible condensed fuel surface and gas-phase flames in laminar boundary layers. Experiments have previously been conducted in both forced and free convective environments over both solid and liquid fuels. A unique methodology, based on the Reynolds Analogy, was used to estimate local mass burning rates and flame heat fluxes for these laminar boundary layer diffusion flames utilizing local temperature gradients at the fuel surface. Local mass burning rates and convective and radiative heat feedback from the flames were measured in both the pyrolysis and plume regions by using temperature gradients mapped near the wall by a two-axis traverse system. These experiments are time-consuming and can be challenging to design as the condensed fuel surface burns steadily for only a limited period of time following ignition. The temperature profiles near the fuel surface need to be mapped during steady burning of a condensed fuel surface at a very high spatial resolution in order to capture reasonable estimates of local temperature gradients. Careful corrections for radiative heat losses from the thermocouples are also essential for accurate measurements. For these reasons, the whole experimental setup needs to be automated with a computer-controlled traverse mechanism, eliminating most errors due to positioning of a micro-thermocouple. An outline of steps to reproducibly capture near-wall temperature gradients and use them to assess local burning rates and heat fluxes is provided.

We describe the use of micro-thermocouples to estimate local temperature gradients in steady laminar boundary layer diffusion flames. By extension of the Reynolds Analogy, local temperature gradients can be further used to estimate the local mass burning rates and heat fluxes in such flames with high accuracy.

Modeling the realistic burning behavior of condensed-phase fuels has remained out of reach, in part because of an inability to resolve the complex ...

Combustion Characterization and Model Fuel Development for Micro-tubular Flame-assisted Fuel Cells

Combustion based power generation has been accomplished for many years through a number of heat engine systems. Recently, a move towards small scale power generation and micro combustion as well as development in fuel cell research has created new means of power generation that combine solid oxide fuel cells with open flames and combustion exhaust. Instead of relying upon the heat of combustion, these solid oxide fuel cell systems rely on reforming of the fuel via combustion to generate syngas for electrochemical power generation. Procedures were developed to assess the combustion by-products under a wide range of conditions. While theoretical and computational procedures have been developed for assessing fuel-rich combustion exhaust in these applications, experimental techniques have also emerged. The experimental procedures often rely upon a gas chromatograph or mass spectrometer analysis of the flame and exhaust to assess the combustion process as a fuel reformer and means of heat generation. The experimental techniques developed in these areas have been applied anew for the development of the micro-tubular flame-assisted fuel cell. The protocol discussed in this work builds on past techniques to specify a procedure for characterizing fuel-rich combustion exhaust and developing a model fuel-rich combustion exhaust for use in flame-assisted fuel cell testing. The development of the procedure and its applications and limitations are discussed.

A protocol for creating a model fuel-rich combustion exhaust is developed through combustion characterization and is applied for micro-tubular flame-assisted fuel cell testing and research.

Combustion based power generation has been accomplished for many years through a number of heat engine systems. Recently, a move towards small scale power ...

Combustion Chemistry of Fuels: Quantitative Speciation Data Obtained from an Atmospheric High-temperature Flow Reactor with Coupled Molecular-beam Mass Spectrometer

This manuscript describes a high-temperature flow reactor experiment coupled to the powerful molecular beam mass spectrometry (MBMS) technique. This flexible tool offers a detailed observation of chemical gas-phase kinetics in reacting flows under well-controlled conditions. The vast range of operating conditions available in a laminar flow reactor enables access to extraordinary combustion applications that are typically not achievable by flame experiments. These include rich conditions at high temperatures relevant for gasification processes, the peroxy chemistry governing the low temperature oxidation regime or investigations of complex technical fuels. The presented setup allows measurements of quantitative speciation data for reaction model validation of combustion, gasification and pyrolysis processes, while enabling a systematic general understanding of the reaction chemistry. Validation of kinetic reaction models is generally performed by investigating combustion processes of pure compounds. The flow reactor has been enhanced to be suitable for technical fuels (e.g. multi-component mixtures like Jet A-1) to allow for phenomenological analysis of occurring combustion intermediates like soot precursors or pollutants. The controlled and comparable boundary conditions provided by the experimental design allow for predictions of pollutant formation tendencies. Cold reactants are fed premixed into the reactor that are highly diluted (in around 99 vol% in Ar) in order to suppress self-sustaining combustion reactions. The laminar flowing reactant mixture passes through a known temperature field, while the gas composition is determined at the reactors exhaust as a function of the oven temperature. The flow reactor is operated at atmospheric pressures with temperatures up to 1,800 K. The measurements themselves are performed by decreasing the temperature monotonically at a rate of -200 K/h. With the sensitive MBMS technique, detailed speciation data is acquired and quantified for almost all chemical species in the reactive process, including radical species.

An investigation of the oxidative combustion chemistry of novel biofuels, fuel components, or jet fuels by comparison of quantitative speciation data is presented. The data can be used for kinetic model validation and enables fuel assessment strategies.This manuscript describes the atmospheric high-temperature flow reactor and demonstrates its capabilities.

This manuscript describes a high-temperature flow reactor experiment coupled to the powerful molecular beam mass spectrometry (MBMS) technique. This ...

Chemistry

Optimization, Test and Diagnostics of Miniaturized Hall Thrusters

Miniaturized spacecraft and satellites require smart, highly efficient and durable low-thrust thrusters, capable of extended, reliable operation without attendance and adjustment. Thermochemical thrusters which utilize thermodynamic properties of gases as a means of acceleration have physical limitations on their exhaust gas velocity, resulting in low efficiency. Moreover, these engines demonstrate extremely low efficiency at small thrusts and may be unsuitable for continuously operating systems which provide real-time adaptive control of the spacecraft orientation, velocity and position. In contrast, electric propulsion systems which use electromagnetic fields to accelerate ionized gases (i.e., plasmas) do not have any physical limitation in terms of exhaust velocity, allowing virtually any mass efficiency and specific impulse. Low-thrust Hall thrusters have a lifetime of several thousand hours. Their discharge voltage ranges between 100 and 300 V, operating at a nominal power of &lt;1 kW. They vary from 20 to 100 mm in size. Large Hall thrusters can provide fractions of millinewton of thrust. Over the past few decades, there has been an increasing interest in small mass, low power, and high efficiency propulsion systems to drive satellites of 50-200 kg. In this work, we will demonstrate how to build, test, and optimize a small (30 mm) Hall thruster capable of propelling a small satellite weighing about 50 kg. We will show the thruster operating in a large space environment simulator, and describe how thrust is measured and electric parameters, including plasma characteristics, are collected and processed to assess key thruster parameters. We will also demonstrate how the thruster is optimized to make it one of the most efficient small thrusters ever built. We will also address challenges and opportunities presented by new thruster materials.

Here, we present a protocol to test and optimize space propulsion systems based on miniaturized Hall-type thrusters.

Miniaturized spacecraft and satellites require smart, highly efficient and durable low-thrust thrusters, capable of extended, reliable operation without ...

Reducing Willow Wood Fuel Emission by Low Temperature Microwave Assisted Hydrothermal Carbonization

Biomass is a sustainable fuel, as its CO2 emissions are reintegrated in biomass growth. However, the inorganic precursors in the biomass cause a negative environmental impact and slag formation. The selected short rotation coppice (SRC) willow wood has a high ash content (<img alt="Equation 1" src="/files/ftp_upload/58970/58970eq1.jpg" /> = 1.96%) and, therefore, a high content of emission and slag precursors. Therefore, the reduction of minerals from SRC willow wood by low temperature microwave assisted hydrothermal carbonization (MAHC) at 150 &#176;C, 170 &#176;C, and 185 &#176;C is investigated. An advantage of MAHC over conventional reactors is an even temperature conductance in the reaction medium, as microwaves penetrate the whole reactor volume. This allows a better temperature control and a faster cooldown. Therefore, a succession of depolymerization, transformation and repolymerization reactions can be analyzed effectively. In this study, the analysis of the mass loss, ash content and composition, heating values and molar O/C and H/C ratios of the treated and untreated SCR willow wood showed that the mineral content of the MAHC coal was reduced and the heating value increased. The process water showed a decreasing pH and contained furfural and 5-methylfurfural. A process temperature of 170 &#176;C showed the best combination of energy input and ash component reduction. The MAHC allows a better understanding of the hydrothermal carbonization process, while a large-scale industrial application is unlikely because of the high investment costs.

A protocol for the emission precursor depletion from low quality biomass by low temperature microwave assisted hydrothermal carbonization treatment is presented. This protocol includes the microwave parameters and the analysis of the biocoal product and process water.

Biomass is a sustainable fuel, as its CO2 emissions are reintegrated in biomass growth. However, the inorganic precursors in the biomass cause a negative ...

Laboratory Scale Slow Cook-Off Testing of Rocket Propellants: The Combustion Rate Analysis of a Slowly Heated Propellant (CRASH-P) Test

Solid rocket propellants are widely used for propulsion applications by military and space agencies. Although highly effective, they can be dangerous to personnel and equipment under certain conditions, with slow heating in confined conditions being a particular danger. This paper describes a more affordable laboratory test that is easier to set up and was developed for screening rocket propellant ingredients. Rocket propellants are cast into sample holders that have been designed to have the same confinement as standard rocket motors (propellant volume to total volume in the container) and ensure that the propellant is not easily vented. Reaction violence is quantified by the time it takes to reach 90% of the maximum pressure after autoignition, which is analogous to blast overpressure gauges used to measure violence in a full-scale test. A positive correlation was observed between the speed and pressure produced from the reaction and the power produced by the rocket propellant during the reaction.

Laboratory Scale Slow Cook-Off Testing of Rocket Propellants: The Combustion Rate Analysis of a Slowly Heated Propellant CRASH-P Test

We present a protocol for a laboratory-scale slow cook-off test for solid rocket propellants called the Combustion Rate Analysis of a Slowly Heated Propellant (CRASH-P) test. Confined rocket propellants are slowly heated until autoignition, and both the cook-off temperature and the violence of reaction are measured with dynamic pressure sensors.

Solid rocket propellants are widely used for propulsion applications by military and space agencies. Although highly effective, they can be dangerous to ...

Improving the Combustion Performance of a Hybrid Rocket Engine using a Novel Fuel Grain with a Nested Helical Structure

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