University of Colorado at Boulder
Phase I


Phase 1: Hybrid engine



The end goal of Phase I of this project consists of developing, building, and testing a 1000 lb thrust LOX/HTPB hybrid rocket engine. This has been an incredible technical undertaking and an enormous Project Management effort. Several engines will be made in this phase starting with a relatively small Mx1-L class engine, ending with a large M1-P class multiport engine. The following paragraphs describe the various sub-systems that are being or have been worked on.


Mx1-L Class Engine

The culmination of Phase I thus far is the completion of the test-ready engine assembly, support equipment, and the Mx1-L grains. The sections below explain the work that has been completed, and include extensive photo-documentation. A master design document for Phase I has been created and is being worked on. A design spreadsheet has also been created that covers most of the rocket design issues. The subsystems have been individually tested as much as is practical, and the engine will be hot tested at Lockheed Martin's test facilities in Littleton, Colorado in June of 2002.


Grain Cure Ovens
This is part of the support equipment for engine R&D. These ovens are used to cure the HTPB grains after mixing. The frames are made from 3/8" plywood and 2x2" timber. The exterior is insulated with 1" polystyrene. The heat comes from two 100 watt incandescent light bulbs in each oven, controlled by a household dimmer switch. The boxes are designed to maintain a constant 160 deg F. Small fans circulate air inside each box to help eliminate temperature gradients. A thermostat with a 10 deg F hysteresis keeps ovens at the correct cure temperature. Calibration data was recorded in Excel. Click the thumbnail for a directory of pictures showing the construction process.


Grain Molds
Three prototype grain molds were built and two of them were tested. The first one didn't work out very well, but we learned a lot of info from it. The second one wasn't acutally used to make a grain, but helped in making decisions on the third prototype mold, which worked out perfectly. Some slight modifications were made to the final molds. This design will be used for all 6" diameter grains. Click on the thumbnail to see the progression of mold designs.


HTPB Mixer / Vacuum Treater
The mixer will be used to mix the fuel grain ingredients thouroghly for very large batches of fuel. It is industrial in size because we anticipate that it will be used eventually for 30 gallon batches for the final engine size. It is mostly finished, but needs some small internal mixing modifications to ensure complete mixing of the fuel occurs. It also is equipped with a vacuum pump for removing bubbles from the mixed fuel.


Grain Composition Testing
Grain composition was tested with many different combinations of HTPB, IPDI, Castor Oil, and Carbon Black in order to come up with an optimal mixture that provided good mechanical qualities, a good cure schedule, good mold characteristics, and easy manufacturability. Sixteen different tests in all were conducted. Click on the thumbnail to see the results and progression of these tests.


Mx1-L Grain Manufacturing
Each engine consists of five of these grains stacked end on end, and connected together with regular rubber cement. These grains all have a single-port cast in them. They are composed of HTPB, IPDI, Castor Oil, and Carbon Black. Castor oil is a crosslinker that gives them better structure, and carbon black hinders radiative heat transfer deep into the unburned portion of the grain. All composition and mix testing for the Mx1-L series single-port engine grains has been completed, and they are in full scale production for a 6-engine series. M1-P class engine multi-port grain production will follow later in the year after static testing and analysis of these grains is completed. Click the picture to see all of the grains that have been made so far.


Combustion Chambers
These are seamless carbon steel 6" nominal schedule 40 pipes. Flanges have been welded on the ends to facilitate easy access to the injector and the nozzle, and allow relatively simple reloading of the grains. Three will be in service for use in static testing engines up into the 5,000 lb-f range. They are built with a safety factor of approximately 10 and were hydrostatic tested to 1000 psi so that safe static testing can be conducted.


Pre and Post Combustor Insulation
The volumes between the injector and the top of the fuel, and between the nozzle and the bottom of the fuel are the pre and post combustors, respectively. They serve to help make the fuel/oxygen combustion process more efficient. The insulation will see 6000 deg F for the duration of the burn, so 1/2" phenolic tubing was used to protect the chamber walls.


The igniters are used to heat up the HTPB fuel grains before injecting the liquid oxygen into the chamber. The igniters use a propane / oxygen / spark system, and are designed to be restartable and robust so that incrimental testing can be performed on single engines if desired. A series of tests was conducted on this system to make sure that it will perform its job correctly on Test Day. A second version with higher flowrates was made and tested also. Click the thumbnails to see the design pictures and the burn tests. The *.avi movie files are best viewed using Apple's Quicktime viewer.


The injector is used to regulate the liquid oxygen flow into the engine, and to distribute it in the correct pattern with the right sized streams. This is the first-cut design, and will be a simple shower-head type injector. There will be approximately 18 LOX holes, all with a 0.065 inch diameter, which was determined from some Cd Determination testing.


Liquid Oxygen Feed System
This system is used to store the LOX and deliver it to the injector. It is designed and in the process of being built and tested. It will be hydrostatically tested and flow tested with water and liquid nitrogen before being used. Helium is used to pressurize the tanks to approximately 800 psi.


Four nozzles have been built to date, and they will be tested in New Mexico in April. They are being built out of graphite as a material behavior experiment. There are two rated for 1000 lb thrust, one for 850 lb thrust, and one for 1150 lb thrust.


Control Station
This was built to give remote control over the ignition and shutdown of the engine for static testing. It controls the gox, propane and spark for the ignitors, the liquid oxygen system helium source and vent valves, and the nitrogen purge. Each circuit is fused and the control lines use 3-conductor extension cords. The laptop is used for data acquisition.


Data Acquisition
We will be using a four-channel, 240 samples/sec data acquisition system to record LOX feed pressure, chamber pressure, thrust, and LOX tank mass during the test fires. Other data will also be taken manually, including: ambient temperature, ambient pressure, post-burn grain mass, chamber wall temperature, chamber pressure, LOX feed pressure (both manually and with DataQ), and many others. Two video cameras and several still cameras will also be used.


Test Stand
The horizontal test stand is used to both hold the engine in place during hot tests and to take the thrust that the engine generates. It is instrumented with a 10,000 lb load cell for thrust measurement. It is made as two parts: the thrust stand and the engine stand.


Subsystem Testing
Each of the subsytems have been tested as much as is practical. This includes destructive and non-destructive testing, analitical testing, subjective testing, pressure testing, cryogenic testing, concept tests, "kick the tire" testing, and anything else that we can think of in order to give us a good warm fuzzy about hot firing this thing.




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site last updated:
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