The authors would like to thank the Joint Enhanced Munitions Technology Program. Mr. Anthony DiStasio and Jeffrey Brock were instrumental in making sure this work was completed.

1. Propellant sample preparation
<ol>
	<li>Carefully mix propellant ingredients (polymeric resin, plasticizers, and solid fuel and oxidizer particles) together in a rotating planetary mixer for a set duration. 
	NOTE: The duration of mixing depends on the specific formulation, but most mixes take at least 2 h.</li>
	<li>Cast uncured rocket propellant into a specially made CRASH-P sample holder. Place a polytetrafluoroethylene mandrel in the center of the sample holder while casting to create a center perforation when the propellant cures. Use a mandrel holder (Figure 1) to ensure the center perforation in the propellant is straight and consistent. 
	NOTE: CRASH-P sample holders should scale to have the same propellant volume to internal chamber volume as an actual rocket motor to mimic the propellant confinement of a full-scale rocket motor. CRASH-P sample holders are made of polyether ether ketone (PEEK) or aluminum. Although rocket formulations without a metal fuel can use PEEK, metallized formulations should use aluminum holders so that they do not melt prematurely during autoignition.</li>
	<li>Place CRASH-P samples in an oven to accelerate any polyurethane reactions or other chemistry required to cure the propellant. Keep the oven temperature at 60 &#176;C for urethane cures, and increase or decrease the temperature depending on the rocket propellant ingredients.</li>
	<li>After the propellants have cured, trim them so that excess propellant does not protrude from the sample holder surface and interfere with the O-ring face seal. Safely remove the mandrel from each formulation by gently pulling it out. 
	NOTE: The propellant should be trimmed with a razor blade or other sharp object to minimize frictional abrasion against the propellant surface.</li>
	<li>Place a silicone O-ring inside the CRASH-P sample holder face for a proper pressure seal (Figure 1). 
	NOTE: The O-ring size will vary depending on the size of the CRASH-P sample holder. For example, a 025 size O-ring is used for the 25 g test and a 128 size O-ring is used for the 50 g test.</li>
	<li>Bolt the cover onto the CRASH-P sample holder, and tighten it with an Allen wrench. Tighten the bolts in a star pattern to distribute the sealing force more evenly.</li>
</ol>
2. CRASH-P chamber preparation
<ol>
	<li>Ensure that the CRASH-P chamber is not pressurized by opening the exhaust valve attached to the CRASH-P chamber. Remove the chamber cover, cap, and thrust washer from the CRASH-P body. Attach a plank to the CRASH-P cap for holding the CRASH-P samples.</li>
	<li>Clean the CRASH-P chamber to remove traces of the last test. Scrub all combustion residue with a wire brush, and clean the chamber with an organic solvent such as ethanol, isopropanol, acetone, or methyl ethyl ketone. Dispose of any single-use cleaning materials as hazardous waste according to local and national regulations. 
	NOTE: Personal protective equipment should be used when cleaning with the listed solvents, such as eye protection, an appropriate laboratory coat, or chemically resistant gloves.</li>
	<li>Inspect the CRASH-P dynamic pressure sensors for any unusual wear and tear. 
	NOTE: The sensors use a recessed mounting with the CRASH-P chamber because they can only handle a maximum temperature of 204 &#176;C to prevent damage to their internal electronics. These high-temperature, charge-amplified sensors use a downstream convertor (see the Table of Materials) to change the signal to an integrated circuit piezoelectric (ICP) signal.</li>
	<li>Remove the 1/8 inch American National Pipe Thread (NPT) fittings that attach the pressure sensors to the CRASH-P main body. Clean out any combustion residue with a spatula or organic solvent. Unthread the pressure sensor from the NPT coupling.</li>
	<li>Fill the NPT coupling with room temperature vulcanizing silicone sealant. Thread the pressure sensor back inside, making sure some of the sealant is extruded. Wipe the sealant off so it is flush with the 1/8 inch NPT fitting.</li>
	<li>Let the sealant cure for at least 12 h. Reinstall the NPT-coupled pressure sensors to protect the sensors from blast-induced temperature errors in the dynamic pressure readings.</li>
	<li>Prepare electrical feedthroughs for the temperature diagnostics. Strip the thermocouple wires of their insulation, and run the bare wires through the feedthrough insulating sleeve. 
	NOTE: The model and type of the electrical feedthroughs will vary depending on the wire gauge and amounts of feedthroughs needed. See the Table of Materials for the electrical feedthroughs used in the CRASH-P chamber.</li>
	<li>Use standard K-type thermocouples for the CRASH-P test as the temperature and sampling rates of the test are fairly standard. Install a mating connection on the other end of the feedthrough. 
	NOTE: For productivity reasons, it is encouraged to make multiple electrical feedthroughs.</li>
	<li>Thread the two electrical feedthroughs through the chamber cap. Leave at least 0.3 m of thermocouple for each feedthrough inside the chamber. Ensure that the beaded side of the thermocouples is inside the CRASH-P chamber.</li>
</ol>
3. Propellant sample installation
<ol>
	<li>Bolt the sealed CRASH-P sample to the steel plank (Figure 2B) attached to the chamber cap of the CRASH-P test to keep the sample in the middle of the chamber. 
	NOTE: Ensuring that the sample is in the middle of the chamber without touching the vessel wall ensures that the sample is heated by convection instead of conduction.</li>
	<li>Place one of the thermocouples from the electrical feedthroughs inside the propellant sample holder to capture any exothermic reactions. Place another thermocouple on the steel plank, pointing up to sample the air temperature inside the CRASH-P chamber (Figure 2). Ensure that the thermocouple sampling the air temperature is the controlling thermocouple for the temperature controller.</li>
	<li>Place the sealing ring in the ring-like indent on the CRASH-P chamber. Make sure the sealing ring is clean of any foreign object debris.</li>
	<li>Once the sample is secured properly on the plank and the thermocouples are placed properly, slide the chamber cap into the body of the chamber. Take care not to rotate the chamber cap by marking the chamber cap.</li>
	<li>Use a cylindrical rod to insert the thrust washer and completely thread and tighten the retaining head onto the chamber.</li>
	<li>Install the 7/8&#34;-9 set screws hex bolt into the chamber head. Tighten them in a star pattern to ensure that the chamber is tightened evenly. Use a torque wrench for the final chamber tightening to ensure uniform sealing. 
	NOTE: Generally, 169.48 N&#8729;m are sufficient for uniform sealing.</li>
	<li>Install the chamber retainer clamps, and hold them in place with dowel pins. If necessary, use a rubber mallet to ensure a snug fit for the clam and prevent vertical movement from the chamber.</li>
	<li>Install the chamber end plate by bolting this to the testing table to prevent the CRASH-P test from axial movement during an ignition event.</li>
	<li>Plug the dynamic pressure sensor co-axial cables into the signal conditioner. Plug the electrical band heaters (Figure 2D) into the outlet sockets that connect to the temperature controllers so that the band heaters can be controlled by a temperature controller that supplies 220 VAC power to the heaters.</li>
</ol>
4. Setting up and checking test instrumentation
<ol>
	<li>Program the temperature controller (requiring 120 VAC power) so that it transmits a 24 V signal to a solid-state relay-a switch that determines when the heating power is turned on or off. 
	NOTE: Like any cook-off test, programming the temperature controller is crucial for running reliable tests.</li>
	<li>Tune the temperature controller before the test to get the appropriate heating characteristics. 
	NOTE: The proportional gain, integral characteristics, and rate should all be set to minimize oscillations and overshoot.</li>
	<li>Set the temperature values needed for the 16 time intervals on the temperature controller. Use the first three intervals to set up a ramp and soak period where the temperature is kept at 50 &#176;C for at least 2 h. Then, enter the intervals to supply the data points for the test to have a linear heating profile that does not change slope during the test (15 &#176;C/h is the goal), and set the final temperature to 300 &#176;C.</li>
	<li>Make sure the inlet and outlet wires are plugged into the dynamic pressure signal conditioner. Turn on the dynamic pressure signal conditioner. If there are no shorts indicated, proceed to the next step. 
	NOTE: A red light illuminates for a shorted sensor.</li>
	<li>Use three K-type thermocouples whose ends terminate inside a thermocouple amplifier, and make sure the amplifier is turned on. Turn on the monitoring camera for the test to record the CRASH-P test by video so operators can see if anything happens to the chamber remotely. Turn on the electrical power to the heaters on the control console (Figure 3), and turn the temperature controller on to run the test remotely.</li>
	<li>On the&#160;CTRL&#160;page of the temperature controller, turn&#160;RSEN&#160;to on. Press the&#160;aux&#160;button on the temperature controller to change the test condition from&#160;standby&#160;to&#160;run&#160;so that the test starts heating the chamber.</li>
</ol>
5. Data acquisition and test clean-up
<ol>
	<li>Construct a workbench in the data acquisition system software to set up two distinct regions for test data collection: one for pressure to be measured by the main board and the another for temperatures to be taken for the thermocouple amplifier (Figure 3).</li>
	<li>Check the data acquisition system to see if there was a triggered event, which implies that the sample experienced an exothermic reaction and can be stopped. Set the system to run on a triggered sweep mechanism so that after a threshold voltage is reached, the pressure sampling rate goes from one sample a second to 50,000 samples/s to accurately resolve the work done by the reacting sample during autoignition. 
	NOTE: Inert tests should be run beforehand to investigate how to control the heating rate. The charge amplified sensors can sample at a rate up to 500,000 samples/s, but that speed is usually not necessary for this test.</li>
	<li>If an exothermic triggered reaction is observed, press the stop button on the data acquisition software. As the data acquisition does not end on its own, periodically check on the test to check for either a temperature exotherm or a triggered pressure response. If either of these are observed, manually stop the recording, and turn off the heater power, video, and temperature controller.</li>
	<li>Manually export the temperature and pressure data into text files that are tab delimited, making sure that pressure and temperature data are exported separately because of the different sampling rates. Transfer the text files to another computer to perform data analysis on the results.</li>
	<li>Wait for at least 12 h for the test to cool down before disassembling the test chamber. Vent the chamber to release any product gases from the exothermic reaction. Carefully disassemble the test chamber. 
	NOTE: Wear personal protective equipment-chemical/flame resistant lab coat, appropriate gloves, and a respirator-as rocket propellant products can be hazardous.</li>
	<li>Clean the chamber and all components, and capture sample container fragments of the sample holder.</li>
</ol>
6. CRASH-P data analysis
NOTE: Data analysis consists of the actual temperature traces and the triggered dynamic pressure data. The data acquisition system marks the location of the trigger, and the user can see the time when this occurred. The trigger corresponds to a dynamic pressure value that is 5% higher than the baseline.
<ol>
	<li>Stop the recording in the software, and export the temperature and pressure data to tab delimited text files.</li>
	<li>Open the text files with graphing software. Check the data for temperature exotherms from which the ignition temperature can be determined, and check how quickly the chamber pressurizes.</li>
	<li>Compare the CRASH-P results to full-scale SCO test data for the formulation being tested, if these are available. Compare autoignition temperature and reaction violence.</li>
</ol>

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<li>Bircumshaw, L. L., Phillips, T. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+kinetics+of+thermal+decomposition+of+ammonium+perchlorate%5BTitle%5D)+AND+%22Journal+of+the+Chemical+Society+%28Resumed%29%22%5BJournal%5D)">The kinetics of thermal decomposition of ammonium perchlorate.</a> Journal of the Chemical Society (Resumed). 12, 4741-4747 (1957).</li>
<li>Boldyrev, V. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Thermal+decomposition+of+ammonium+perchlorate%5BTitle%5D)+AND+%22Thermochimica+Acta%22%5BJournal%5D)">Thermal decomposition of ammonium perchlorate.</a> Thermochimica Acta. 443 (1), 1-36 (2006).</li>
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<li>Melita, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((US+IM+Position%5BTitle%5D)+AND+%22Proceedings+of+the+2006+Insensitive+Munitions+and+Energetic+Materials+Technology+Symposium%22%5BJournal%5D)">US IM Position.</a> Proceedings of the 2006 Insensitive Munitions and Energetic Materials Technology Symposium. , Bristol, U.K. (2007).</li>
<li>Hayden, H. F., Lustig, E. A., Lawrence, B. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Development+of+small-scale+slow+cook-off+%28SCO%29+testing+protocol+for+granular+propellants%5BTitle%5D)+AND+%22NDIA+Insensitive+Munitions+and+Energetic+Materials+Conference%22%5BJournal%5D)">Development of small-scale slow cook-off (SCO) testing protocol for granular propellants.</a> NDIA Insensitive Munitions and Energetic Materials Conference. , Rome, Italy. (2015).</li>
<li>Victor, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((C+Simple+calculation+methods+for+munitions+cookoff+times+and+temperatures%5BTitle%5D)+AND+%22Propellants%2C+Explosives%2C+Pyrotechnics%22%5BJournal%5D)">C Simple calculation methods for munitions cookoff times and temperatures.</a> Propellants, Explosives, Pyrotechnics. 20 (5), 252-259 (1995).</li>
<li>Sandusky, H. W., Chambers, G. P., Erikson, W. W., Schmitt, R. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Validation+experiments+for+modelling+slow+cook+off%5BTitle%5D)+AND+%22Proceedings+of+the+12th+International+Detonation+Symposium%22%5BJournal%5D)">Validation experiments for modelling slow cook off.</a> Proceedings of the 12th International Detonation Symposium. , San Diego, California. 863-872 (2002).</li>
<li>Cook, M. P., Stennet, C., Hobbs, M. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Development+of+a+small+scale+thermal+violence+test.+No.+SAND2018-7274C%5BTitle%5D)+AND+%22Sandia+National+Lab%22%5BJournal%5D)">Development of a small scale thermal violence test. No. SAND2018-7274C.</a> Sandia National Lab. , Albuquerque, NM. (2018).</li>
<li>Alexander, K., Gibson, K., Baudler, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Development+of+the+Variable+Confinement+Cook-off+Test.+Indian+Head+Technical+Report+1840%5BTitle%5D)+AND+%22NAVSEA+Indian+Head+Division%22%5BJournal%5D)">Development of the Variable Confinement Cook-off Test. Indian Head Technical Report 1840.</a> NAVSEA Indian Head Division. , (1996).</li>
<li>Ho, S. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Thermomechanical+properties+of+rocket+propellants+and+correlation+with+cookoff+behavior%5BTitle%5D)+AND+%22Propellants%2C+Explosives%2C+Pyrotechnics%22%5BJournal%5D)">Thermomechanical properties of rocket propellants and correlation with cookoff behavior.</a> Propellants, Explosives, Pyrotechnics. 20 (4), 206-214 (1995).</li>
<li>Erikson, W. W., Kaneshige, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Pressure+and+free+volume+dependence+in+the+cook-off+of+AP+Composite+Propellants.+No.+SAND2014-20085C%5BTitle%5D)+AND+%2246th+JANNAF+Combustion+Subcommittee%22%5BJournal%5D)">Pressure and free volume dependence in the cook-off of AP Composite Propellants. No. SAND2014-20085C.</a> 46th JANNAF Combustion Subcommittee. , Albuquerque, New Mexico. (2014).</li>
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The authors have nothing to disclose.

One of the most important parts of establishing the CRASH-P test was deciding what metric from the test would be best used to quantify the reaction violence of the rocket propellant formulations. The speed and amount of pressure produced from the reaction is directly proportional to the power produced by the rocket propellant when reacting. It is also directly analogous to the blast overpressure gauge used in a full-scale SCO test. Initially, pressurization rate (dP/dt) was used, but these data were misleading because different formulations contain different amounts of fuel and oxidizer and produce different amounts of gas with varying composition. To minimize this bias from the effects of changing the formulation ingredients, the time to 90% peak pressure was used instead, and it correlated well with full-scale SCO test violence.
Another testing operation that was found to be important is confinement. Early sample holders were made with thermoplastic materials designed to handle the high temperatures of the test. Unfortunately, while these samples did not melt, they softened and did not provide the same confinement as metal sample holders. The reaction violence for these samples was noticeably less than the reaction violence for metal sample holders. Another key finding about the test was that some rocket propellant formulations had critical sizes to autoignite reliably. Aluminized formulations had difficulty cooking off and autoigniting if they were under 50 g. This was attributed to the requirement of a threshold amount of ammonium perchlorate that was required for the violent reaction. In addition, another insight was that thermoplastic bolts did not work. The original CRASH-P sample holder bolts were made from PEEK, and this had to be changed to stainless steel. Confinement was not strong enough because of the PEEK material thermally expanding before propellant autoignition was achieved.
For some formulations that ignite at higher temperatures, mainly aluminized formulations, using an aluminum propellant holder case is desirable as they do not soften at higher temperatures. Finally, ICP dynamic pressure sensors were the original pressure sensors used. However, after ~10 tests, the results got increasingly noisy, probably from being exposed to too high a temperature. The dynamic pressure sensors were switched from ICP sensors to charge amplifier sensors. However, charge amplifier sensors lose charge if left on for too long. To minimize this effect, an in-line charge amp-to-ICP convertor was used downstream at a safe temperature region. As the maximum sampling rate of the pressure sensor is 500,000 samples/s, sampling rates faster than 50,000 sample/s could be recorded. However, there was no need for this as the events were not that fast.

Solid rocket propellants are used extensively in defense, space, and gas-generating applications. They are relatively reliable fuels that perform many functions extremely well. However, many rocket propellants contain dangerous ingredients such as ammonium perchlorate (AP). Rocket propellants with these oxidizers can explode violently when slowly heated1,2,3. There have been several high-profile accidents with the slow heating of rocket propellant or rocket propellant ingredients that have drawn attention to these issues such as the fire and subsequent cook-off of munitions on the USS Forrestal4 and the PEPCON explosion1. While these are thankfully rare events, they can be devastating because of the personnel and equipment losses that occur. Therefore, there is motivation to understand the violence of these reactions and drive them down whenever possible. One of the main causes of violent cook-off events with rocket propellant is that many of the ingredients partially decompose, leaving reactive product gases behind along with the oxidizer with an enhanced reactive surface area.
One specific example of this is the ionic salt, ammonium perchlorate. The low-temperature decomposition of ammonium perchlorate is drawn out and incomplete, leaving reactive intermediate products within a propellant framework with substantial porosity and surface area available for subsequent reactions5,6,7,8,9. In addition, rocket propellants that contain ammonium nitrate and explosive nitramine compounds can have very violent reactions when heated slowly10,11,12. Slow cook-off violence is an important insensitive munition metric because many rockets are required by law to pass these tests13. Currently, the best way to determine whether a rocket propellant formulation reacts too violently under slow heating conditions is to run a slow cook-off (SCO) test on a full-scale rocket motor. These tests involve taking a full-size rocket motor and heating it slowly in a disposable convection oven.
Temperature traces are provided in multiple locations up until the reaction where the violence is then assessed based on various indicators ranging from container damage and fragmentation to simple overpressure gauges and dynamic pressure sensors for measuring blast pressure. These full-scale tests are often expensive and are not practical for investigating minor changes in propellant ingredients14. A few laboratory-scale tests have been developed that involve heating propellants or explosives in a variety of configurations and assessing container damage after the autoignition event. Although current laboratory-scale tests predict time to cook-off well and sometimes the autoignition temperature15,16,17, they are less able to predict the violence.
One commonly used test is the variable confinement cook-off test18 that slowly heats a cylinder of propellant until it ignites. The violence of the reaction is determined by the fragmentation of the chamber and bolts during the exothermic autoignition reaction. The most common laboratory tests use the final condition of the chamber to rank reaction violence, and there is a degree of subjectivity to the assessment. Small differences in reaction violence are difficult to determine. This assessment of violence is qualitative in nature, and it can be difficult to assess whether a change in a formulation ingredient altered the SCO violence. Furthermore, unlike an actual rocket motor, current laboratory tests do not confine the propellant inside a case. Product gases can easily escape, and this is important because the gases can react with the propellant heterogeneously or be reactive themselves, as in the case of ammonia and perchloric acid if ammonium perchlorate is used.
One of the best efforts in instrumenting a laboratory scale test involved the use of a dynamic pressure sensor on a small-scale cook-off bomb19. This allowed for higher resolution, quantifiable differences in reaction violence to be determined for relatively minor changes in rocket propellant formulation. However, a critical problem with this test is that it did not confine the rocket propellants in the same manner as an actual rocket motor, and numerous modeling and subscale experiments have shown this to be an important factor for consideration20. In addition, the propellant usually does not have the same amount of exposed surface area or the same free volume and is not geometrically confined in the same way as a full-scale test. The Combustion Rate Analysis of a Slowly Heated Propellant (CRASH-P) test was conceived to improve upon these previous tests. Samples between 25 g and 100 g can be tested under similar propellant confinement conditions as a full-scale test21. It also provides a means of measuring the power produced from the reaction event quantitatively through dynamic pressure sensor measurements, which is something current subscale tests do not provide. The results have been found to correlate well with full-scale SCO tests.

<table><tbody><tr><td>&amp;frac12; x 24 x 12&amp;rsquo; Ceramic Insulative Blanket</td><td>Cotronics Corporation</td><td>370-3</td><td>Thermal Insulation for CRASH-P Chamber</td></tr><tr><td>20 gauge K-Type Thermocouple</td><td>Omega Engineering</td><td>EXPP-K-20-SLE-500</td><td>Thermocouple wire for temperature measurements</td></tr><tr><td>Dynamic Pressure Signal Conditioner</td><td>PCB Piezotronics</td><td>482C16</td><td>Converts ICP signal to voltage for data acquisition system</td></tr><tr><td>Electrical feedthrough of CRASH-P chamber</td><td>Conax</td><td></td><td></td></tr><tr><td>GC-35 Reaction Chamber</td><td>High Pressure Equipment Company</td><td>GC-35</td><td>Main Reaction Chamber of CRASH-P Test</td></tr><tr><td>Gen 3i and Perception software</td><td>HBM Inc.</td><td>Gen3i</td><td>Main Data Acquisition System for CRASH-P Data</td></tr><tr><td>High-Temperature Charge-Amplified Pressure Sensor</td><td>PCB Piezotronics</td><td>113B03</td><td>Dynamic Pressure Sensors used in CRASH-P Test</td></tr><tr><td>In-Line Charge Amp-to-ICP Converter</td><td>PCB Piezotronics</td><td>422E53</td><td>Converters pressure sensor charge amp signal to ICP signal</td></tr><tr><td>Mica Band Heaters</td><td>Omega Engineering</td><td>MBH00295</td><td>Resistive Element for Heating up CRASH-P Test</td></tr><tr><td>Quantum X Thermocouple Amplifier</td><td>HBM Inc.</td><td>1-MX1609KB</td><td>Used for getting Temperature Measurements</td></tr><tr><td>Teflon Insulated K-type thermocouple (0.02 inch diameter)</td><td>Omega Engineering</td><td>5TC-TT-K-24-36</td><td>K-Type Thermocouples</td></tr><tr><td>Temperature Controller</td><td>Omega Engineering</td><td>CN3251</td><td>PID Temperature Controller</td></tr></tbody></table>

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.

To help the reader visualize how the subsystems of the CRASH-P test interact with each other, an experimental schematic is shown in Figure 4. Thermocouples inside the CRASH-P chamber control the feed data to the data acquisition system through a thermocouple amplifier. The temperature controller operates an electric relay, which turns the electric band heaters on and off. This ensures that the correct heating profile is achieved for the rocket propellant sample. When autoignition of the sample occurs, the data acquisition system triggers the collection of high-speed dynamic pressure data at 50,000 samples/s. The test then ends, the data are saved, and the temperature-controlling system is turned off. After at least 12 h, the CRASH-P chamber should be at room temperature, and any product gases can be exhausted.
Typical representative results are seen in Figure 5. Temperature traces are provided for the inside chamber air and the internal propellant temperature by the data acquisition system. Minor exothermic reactions before ignition are often measured along with the main exothermic reaction. Usually, the exothermic reaction is not violent enough to break the thermocouple bead, so the entire event can be captured. In addition, dynamic pressure readings for the reaction are recorded for the front, back, and rear dynamic pressure gauges. Like most laboratory cook-off events, the state of the sample container after reaction can be assessed for damage (Figure 5C). Finally, Figure 5D shows that there can be quite a large degree of measured variation in the reaction violence of different propellant samples, allowing the violence to be quantified and compared for the different reactions. In general, faster pressurizing reactions had more scatter or noise in the pressure data (Figure 5D), which is consistent with the greater oscillation of the chamber due to a more violent response.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/62216/62216fig01.jpg" /> 
Figure 1: Preparation and sealing of CRASH-P samples. (A) Rocket propellant ingredients are mixed in a planetary mixer. (B) Rocket propellant is cast into a sample holder with a polytetrafluoroethylene mandrel. (C) Propellant samples are trimmed, and an O-ring is placed in the container for sealing purposes. (D) Sample container is sealed and bolted. Sample confinement is the same as that of actual rocket motors. Abbreviation: CRASH-P = Combustion Rate Analysis of a Slowly Heated Propellant. <a href="https://www.jove.com/files/ftp_upload/62216/62216fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/62216/62216fig02.jpg" /> 
Figure 2: Sample loading and preparation of the CRASH-P test. Sample placement is critical. (A) Samples are placed on a plank and centrally heated by natural convection during testing. (B) Sample is bolted and held in place on the plank. (C) Thermocouples are placed on the plank and inside the propellant sample for temperature control and diagnostic purposes. (D) CRASH-P chamber is sealed, and band heaters are connected to a 220 VAC power supply controlled by the temperature controller. Abbreviation: CRASH-P = Combustion Rate Analysis of a Slowly Heated Propellant. <a href="https://www.jove.com/files/ftp_upload/62216/62216fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/62216/62216fig03.jpg" /> 
Figure 3: Instrumentation and data acquisition for the CRASH-P test. (A) Dynamic pressure signal conditioner, (B) thermocouple amplifier, (C) test heating controls, and (D) data acquisition during test. . Abbreviation: CRASH-P = Combustion Rate Analysis of a Slowly Heated Propellant. <a href="https://www.jove.com/files/ftp_upload/62216/62216fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/62216/62216fig04.jpg" /> 
Figure 4: Experimental schematic of the CRASH-P test. The temperature-monitoring system controls the heating rate. Dynamic pressure sensors quantify the reaction violence of the autoignition event, and a data acquisition system records all these test data for the experiment. CRASH-P = Combustion Rate Analysis of a Slowly Heated Propellant. <a href="https://www.jove.com/files/ftp_upload/62216/62216fig04large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/62216/62216fig05.jpg" /> 
Figure 5: Representative test data for CRASH-P test run. (A) Temperature traces during a test. (B) Rear, back, and front dynamic pressure readings. (C) CRASH-P sample container after test. (D) Comparison of front dynamic pressure readings for six different rocket propellant formulations. CRASH-P = Combustion Rate Analysis of a Slowly Heated Propellant. <a href="https://www.jove.com/files/ftp_upload/62216/62216fig05large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Laboratory Scale Slow Cook-Off Testing of Rocket Propellants: The Combustion Rate Analysis of a Slowly Heated Propellant CRASH-P Test at JoVE.com

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.

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 ...

laboratory-scale-slow-cook-off-testing-rocket-propellants-combustion

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JoVE Journal

Engineering

3.9K Views.  Naval Air Warfare Center Weapons Division. De CRASH-P-test kan worden gebruikt om het langzame cook-off reactiegeweld van raketst voortstuwingsgassen op een veel kleinere schaal te evalueren dan de huidige testmethoden. De test is een goedkopere en snellere methode om raketstoverstulgers te screenen op hun langzame cook-off geweld dan de huidige full-scale tests. Het is moeilijk om volledige langzame cook-off tests uit te voeren in de vroege stadia van raketstuwstofontwikkeling.De CRASH-P-test kan veel van deze kritieke informa...

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

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 ...

Original Experimental Approach for Assessing Transport Fuel Stability

The study of fuel oxidation stability is an important issue for the development of future fuels. Diesel and kerosene fuel systems have undergone several technological changes to fulfill environmental and economic requirements. These developments have resulted in increasingly severe operating conditions whose suitability for conventional and alternative fuels needs to be addressed. For example, fatty acid methyl esters (FAMEs) introduced as biodiesel are more prone to oxidation and may lead to deposit formation. Although several methods exist to evaluate fuel stability (induction period, peroxides, acids, and insolubles), no technique allows one to monitor the real-time oxidation mechanism and to measure the formation of oxidation intermediates that may lead to deposit formation. In this article, we developed an advanced oxidation procedure (AOP) based on two existing reactors. This procedure allows the simulation of different oxidation conditions and the monitoring of the oxidation progress by the means of macroscopic parameters, such as total acid number (TAN) and advanced analytical methods like gas chromatography coupled to mass spectrometry (GC-MS) and Fourier Transform Infrared - Attenuated Total Reflection (FTIR-ATR). We successfully applied AOP to gain an in-depth understanding of the oxidation kinetics of a model molecule (methyl oleate) and commercial diesel and biodiesel fuels. These developments represent a key strategy for fuel quality monitoring during logistics and on-board utilization.

Oxidation stability of transport fuels has become a concern for future fuel development. This work presents an original methodology developed by IFP Energies Nouvelles for assessing fuel stability using two different reactors. This methodology was successfully applied to gain an in-depth understanding of the oxidation kinetics and pathways of model molecules and commercial fuels.

The study of fuel oxidation stability is an important issue for the development of future fuels. Diesel and kerosene fuel systems have undergone several ...

Chemistry

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 ...

Reaction Kinetics and Combustion Dynamics of I4O9 and Aluminum Mixtures

Tetraiodine nonoxide (I4O9) has been synthesized using a dry approach that combines elemental oxygen and iodine without the introduction of hydrated species. The synthesis approach inhibits the topochemical effect promoting rapid hydration when exposed to the relative humidity of ambient air. This stable, amorphous, nano-particle material was analyzed using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) and showed an exothermic energy release at low temperature (i.e., 180 &#176;C) for the transformation of I4O9 into I2O5. This additional exothermic energy release contributes to an increase in overall reactivity of I4O9 when dry mixed with nano-aluminum (Al) powder, resulting in a minimum of 150% increase in flame speed compared to Al + I2O5. This study shows that as an oxidizer, I4O9 has more reactive potential than other forms of iodine(V) oxide when combined with Al, especially if I4O9 can be passivated to inhibit absorption of water from its surrounding environment.

Reaction Kinetics and Combustion Dynamics of I4O9 and Aluminum Mixtures

A protocol for measuring flame speeds of a reactive mixture composed of tetraiodine nonoxide (I4O9) and aluminum (Al) is presented. A method for resolving reaction kinetics using differential scanning calorimetry (DSC) is also presented. It was found that I4O9 is 150% more reactive than other iodine(V) oxides.

Tetraiodine nonoxide (I4O9) has been synthesized using a dry approach that combines elemental oxygen and iodine without the introduction of hydrated ...

Synthesis and Testing of Supported Pt-Cu Solid Solution Nanoparticle Catalysts for Propane Dehydrogenation

A convenient method for the synthesis of bimetallic Pt-Cu catalysts and performance tests for propane dehydrogenation and characterization are demonstrated here. The catalyst forms a substitutional solid solution structure, with a small and uniform particle size around 2 nm. This is realized by careful control over the impregnation, calcination, and reduction steps during catalyst preparation and is identified by advanced in situ synchrotron techniques. The catalyst propane dehydrogenation performance continuously improves with increasing Cu:Pt atomic ratio.

A convenient method for the synthesis of 2 nm supported bimetallic nanoparticle Pt-Cu catalysts for propane dehydrogenation is reported here. In situ synchrotron X-ray techniques allow for the determination of the catalyst structure, which is typically unobtainable using laboratory instruments.

A convenient method for the synthesis of bimetallic Pt-Cu catalysts and performance tests for propane dehydrogenation and characterization are ...

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 ...

Experimental Procedure for Laboratory Studies of In Situ Burning : Flammability and Burning Efficiency of Crude Oil

A new method for the simultaneous study of the flammability and burning efficiency of fresh and weathered crude oil through two experimental laboratory setups is presented. The experiments are easily repeatable compared to operational scale experiments (pool diameter &#8805;2 m), while still featuring quite realistic in situ burning conditions of crude oil on water. Experimental conditions include a flowing water sub-layer that cools the oil slick and an external heat flux (up to 50 kW/m2) that simulates the higher heat feedback to the fuel surface in operational scale crude oil pool fires. These conditions enable a controlled laboratory study of the burning efficiency of crude oil pool fires that are equivalent to operational scale experiments. The method also provides quantitative data on the requirements for igniting crude oils in terms of the critical heat flux, ignition delay time as a function of the incident heat flux, the surface temperature upon ignition, and the thermal inertia. This type of data can be used to determine the required strength and duration of an ignition source to ignite a certain type of fresh or weathered crude oil. The main limitation of the method is that the cooling effect of the flowing water sub-layer on the burning crude oil as a function of the external heat flux has not been fully quantified. Experimental results clearly showed that the flowing water sub-layer does improve how representative this setup is of in situ burning conditions, but to what extent this representation is accurate is currently uncertain. The method nevertheless features the most realistic in situ burning laboratory conditions currently available for simultaneously studying the flammability and burning efficiency of crude oil on water.

Experimental Procedure for Laboratory Studies of In Situ Burning : Flammability and Burning Efficiency of Crude Oil

Here, we present a protocol to simultaneously study the flammability and burning efficiency of fresh and weathered crude oil under conditions that simulate in situ burning operations on the sea.

A new method for the simultaneous study of the flammability and burning efficiency of fresh and weathered crude oil through two experimental laboratory ...

Measuring Sub-23 Nanometer Real Driving Particle Number Emissions Using the Portable DownToTen Sampling System

The current particle size threshold of the European Particle Number (PN) emission standards is 23 nm. This threshold could change because future combustion engine vehicle technology may emit large amounts of sub-23 nm particles. The Horizon 2020 funded project DownToTen (DTT) developed a sampling and measurement method to characterize particle emissions in this currently unregulated size range. A PN measurement system was developed based on an extensive review of the literature and laboratory experiments testing a variety of PN measurement and sampling approaches. The measurement system developed is characterized by high particle penetration and versatility, which enables the assessment of primary particles, delayed primary particles, and secondary aerosols, starting from a few nanometers in diameter. This paper provides instruction on how to install and operate this Portable Emission Measurement System (PEMS) for Real Drive Emissions (RDE) measurements and assess particle number emissions below the current legislative limit of 23 nm.

Presented here is the DownToTen (DTT) portable emission measurement system to assess real driving automotive emissions of sub-23 nm particles.

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

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