NEW MEXICO STATE UNIVERSITY

Transcription

1 Fall 2011 [HYBRID ROCKET TEAM] NEW MEXICO STATE UNIVERSITY Portable hybrid rocket motors and test stands can be seen in many papers, but none have been reported on the design or instrumentation at such a small magnitude. The design of this hybrid rocket and test stand is to be small and portable (suitcase size). This basic apparatus will be used for demonstrations in rocket propulsion. The design had to include all of the needed hardware to operate the hybrid rocket unit (with the exception of the external oxygen tank). The design of this project includes making the correlation between the rocket s thrust and its size, the appropriate transducers (physical size, resolution, range, and cost), compatibility with a laptop analog card, the ease of setup, and its portability. Beginning with the Spring 2011 setup, the Fall 2011 Capstone Team modified and minimized the previous semester s system. This included refurbishing the rocket motor, nozzle, rocket test stand, Data Acquisition, and plumbing system. In conclusion there were many redesigns and notable accomplishments completed over the course of the Fall 2011 semester. These accomplishments include the completion of 13 out of the 24 original requirements set by NASA. Future research includes finishing the 24 requirements set out by NASA and presenting it in a high manner.

2 Table of Contents Introduction... 2 Methods... 3 Project and Data Analysis... 8 Conclusion Appendix A: Requirements Appendix B: Rocket Design Assembly

3 Introduction Rockets have always been a fascination of the American people and scientists. With the association of the history and growth of rocketry in New Mexico, a project that would appeal to students, that could be used academically, would be a rocket-based project. Since this is such an appealing subject it was decided that the best way to gain involvement in the sciences is through recruitment. It has been found that recruitment is the most effective way to show high school students what a specific college is about. By traveling to prospective audiences, a school can sell itself on why they should choose it as their place of higher education. By getting more students to attend that university, more funding can be given to the school, and companies will invest in the school for resources to further improve students experiences. Many students are interested in hearing talks about the educational programs and the different types of majors available to them. In addition, they want to know the details of what these majors can do for them, especially in terms of acquiring jobs and careers; they want to know what kind of classes they will take and what work they will learn how to do in the future. Presentations and demonstrations are both good ways to show this; for the NMSU College of Engineering and the Mechanical and Aerospace Department, student-created demonstrations of projects can be shown to prospective students concerning what type of classes, research, and work they can do in college. Undergraduate research and Senior Design Capstone projects are among the best possible demonstration units to show students what mechanical and aerospace engineers do. These rocket-based projects could also be used for future research and laboratory experiments as well, especially in the field of aerospace engineering. These projects could be used to experimentally check researched data in many areas related to fluid dynamics, propulsions, controls, and other aerospace-related subjects. Research conducted using these projects can further the prestige of the department. By solving new and unknown problems, students will have the opportunity to write and submit research into journals, gain firsthand experimental and research experience, and gain the understanding of how research is conducted amongst engineers. Since rockets come in all sorts of shapes, sizes, configurations, and types, the possible list of projects are endless. However, to meet the needs of demonstration and research requirements, many projects would not qualify for the stated needs. In order to meet these needs the project would need to be portable, have an easy setup, have interchangeable parts, fully-automated controls, and have the ability to accurately acquire data. After collaboration from NMSU, NASA, and speaking with Dr. Ed Conley of the NMSU MAE department, a solution was formed and the hybrid rocket project was born. The idea of this project is to create a compelling hands-on facility, which will give an Aerospace Engineering (design/build/test) experience. This is to be coupled with immersion in the instrumentation and information management systems that will prevail in the new century. Specifically, this small, portable Hybrid Rocket Test Stand instrumented will offer what s known as discovery-learning designed to 2

4 maximize the ever more limited time and resources that engineering students can devote to the real world. Along with this project idea came requirements and guidelines set by NASA in order to create a device worthy of safely having the ability to enlighten and capture the eye of prospective students. These requirements can be found listed in Appendix A. Methods Since, this is a continuing project an understanding of previous designs needed to be taken into account along with the method. What was found was that the focus of the Spring 2011 semester s work was primarily on testing with mobility being further out of scope. From the results of that testing it was concluded that the first design lacked the sensitivity needed to record accurate thrust data. The second design acquired more accurate data but was crude and far from mobile. With that in mind, the goal for the Fall 2011 semester was to create a third design, which consisted of fabricating a test stand that could be easily transportable and take meaningful data measurements. The rocket motor has undergone two minor modifications in design 3. First the inlet base was remanufactured to be lighter and slightly smaller. Thermocouple measurements from the previous semester provided the insight needed to make this decision. The new part was manufactured from aluminum and is a quarter inch thinner than the old. Previous ignition ports that are no longer used were also left out of the new component. All other geometric entities of the part remained constant. The nozzle used in previous semester s tests was fabricated based off drawings provided from NASA in the student project center at NMSU. However the student project center lacked sufficient tools to precisely produce the specifications. This semester an outside machine shop was utilized to improve nozzle performance. The geometry of the nozzle also changed after research was conducted in nozzle theory. The diverging section was tapered to 30 and the throat of the nozzle was tightened to an eighth of an inch. More advances in the nozzle design under way along with more testing. Design 3 incorporated a bending beam load cell for taking thrust measurements. Initially load cells used in measuring the thrust of the hybrid rocket were oversized. Therefore with the third design came the most sensitive load cell thus far. The bending beam load cell used at the beginning stages of design 3 had a working range of 5lbs. However mid semester that load cell became non-functional and required replacement. This gave an opportunity to decrease the operating range once again. This in return increased the sensitivity. The new load cell has a working range of 600 grams or approximately 1.3 lbs. This load cell was mounted directly 3

5 underneath the inlet end of the rocket motor. The opposite end was held in place by pinned connection. This pinned support restricted translation in the vertical and transverse direction, but allowed for translation in the axial direction. With these constraints in place the rocket was able to produce thrust in the axial direction causing a force to be placed on the load cell. Pressure data was taken in the same fashion as design 1 and 2. In these designs the calibration for the testing instruments became key in making sure the changes in voltage of the instruments actually represent what is really changing in force, pressure, or temperature. This was done through calibration tests, with the load cell being the main device that was calibrated. Figure 1 and 2: Left: Side view of rocket and test stand. Right: Isometric view of rocket and test stand assembly. In both views the pinned supports can be seen on the right side, underneath the nozzle end, and the load cell can be seen on the right side of the test stand under the inlet side of the motor. The ignition system has been notoriously difficult to work with. As a result a more reliable solution was sought out in this design. The new system utilizes fuses that ignite when electrically charged. Each fuse is Halliburton welded into a 3/8 NPT to ¼ PEX adapter in order to create an air tight seal. The fuse adapter combination could then be screwed directly into the plumbing assembly. This configuration placed the fuses right into the back of the combustion section of the rocket. The fuses could then be ignited when charged with a 12Vdc battery. This 4

6 method has proven to be very reliable and incorporated only a small set up procedure. Safety in the third design has also been revised. This would be the first design to incorporate an automatic shutdown switch. To do so, a solenoid valve was inserted into the plumbing system. When electrically charged the solenoid valve is opened and allows the oxygen to flow into the rocket motor. The switch that provides power to the solenoid valve has a latch when pressed action, therefore the automatic shutdown switch must be pressed for the entire duration of the test. Once the switch is released the solenoid valve loses charge and cuts the flow of oxygen to the rocket. Efforts were also made to integrate the ignition system with the cutoff switch. Ideally the system will fire with the initial pressing of the shutdown switch and terminate when the switch is released. The mass flow controller used in design 1 and 2 is also incorporated in the current setup. The controller function has yet to be fully integrated because of difficulties presented with programming the instrumentation. Rather the mass flow controller has been used as a gauge by providing measurements on flow rate. A second more easily programmable mass flow controller has been ordered at the beginning of the fall semester but has yet to arrive. Design 2 Drawings may be seen on the following pages in the Spring 2011 section. The overall rocket and plumbing assembly for the Fall 2011 semester can be seen in Figure 5. The DAQ and control system were proven to be the major priority of this Fall 2011 semester. The idea for this system is to control the ignition switch, pressure transducer, oxygen flow, the load cell, and any other device needed and or wanted. Although, the same idea is the same as the previous semester the setup has changed and is more compact. Instead of each device having its own module inserted into a chassis unit and having a power supply, the unit for this semester still has a power supply but has only one module that connects all of the devices and connects to a computer through a USB device. Just as before the program that allows the data to be collected and that will control the system is LabVIEW. The LabVIEW Program was designed to interpret data from one load cell, one pressure transducer, and the oxygen flow rate. The LabVIEW layout below shows the input from the strain gauge, voltage form the transducer, and the oxygen flow unit running into a sample clock. The clock tracks the time data and allows the user to set the amount of data taken per time unit as desired. The timed data is then run into a loop that activates at a button push and begins to record the data. The data is then exported to a waveform file and converted in an excel spreadsheet for data 5

7 interpretation and interpolation. In Figures 3 and 4 the Front Panel and Block Diagram of LabVIEW are shown from this semester. Figure 3: Front Panel Figure 4: Block Diagram 6

8 Since this is a continuation project and it is still in the process of improving everything is subject to change. For this semester procedures are still followed just at a more compact level. Shown below in Figure 5 is the final assembly of this Fall 2011 semester. The main objective of this design is reducing the amount of oxygen based hoses in order to make the plumbing more compact. In this set up the safety factor played a major role as mentioned above. Figure 5: Rocket and Plumbing Assembly 7

9 Project and Data Analysis Throughout the current semester many portions of this project have been completed. The redesign of the before mentioned items (Facet 4) have been accomplished. The integration of complete electronic controls is still under way due to their complicated nature and constantly changing technology. The current state of the test stand, rocket engine, and electronics are shown below. Figure 1 : Rocket Test Stand with a platform load cell on the left side of the stand. Figure 2 : Rocket motor consisting of fuel grain and attached to the ignition system and pressure transducer. Figure 3: Electrical setup with bread board which connects the power supply to the flow meter, pressure transducer, solenoid valve, and load cell. 8

10 Figure 4: Complete assembly including rocket motor, test stand, plumbing, and the electrical setup. As seen above the test stand and rocket engine have been manufactured to completion and are currently in working order. The electronics currently control the oxidizer flow to the engine along with data handling and filtering. These subsystems are continually changing to allow for increasingly better and cleaner results. The integration of an electronically controlled ignition subsystem along with more sophisticated data handling hardware and software is currently underway. Approximately four tests have been completed and logged with the current system with acceptable results. A picture of the system while under test situation is shown below. For every test during this Fall 2011 semester, a test log was kept and an analysis of the data was ran using Excel. Shown below are the test logs for each test and the data collected. 9

11 Data Analysis Test 1 10

12 For this first test analysis of the results were not essential. This test consisted mostly of testing the nozzle and making sure the pressure transducer s wires were connected to the breadboard correctly. From the graph above it is seen that no satisfactory data was gathered, meaning the wire connection was not correctly assembled. 11

13 Test 2 12

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15 Test 3 14

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17 For both the second and third tests the results proved to be satisfactory. Both tests measured the amount of pressure entering the combustion chamber, the oxygen leaving the flow meter, and the amount of thrust the rocket motor produces. Described below are the results for each test. Test Two: The second test was set at a low pressure which read at an average of 5.5 psi. This produced a thrust of 0.6N. The graph for the oxygen flow showed that the oxygen remained constant from the beginning of the test until the oxygen was shut off. Test Three: For the third test the oxygen flow was set at a higher rate than test two causing the average pressure to read at about 8.2 psi. The average thrust measured followed the same trend as the pressure and read at about 0.8N. The graph for the oxygen flow followed the same inclination as test two. From these results it is concluded that all devices are properly functioning and synchronized with each other. 16

18 Conclusion There were many redesigns and notable accomplishments completed over the course of the Fall 2011 semester. First, 13 of the 24 original requirements set by NASA were completed. This included the addition of the emergency shut-off subsystem along with the redesigning of the data acquisition and analysis package. The semester also allowed for the addition of a specialized electronics group to join the team, greatly enhancing the electronics package still in the foundation stage. Next, hardware such as the oxidizer supply system, test stand, and the engine top plate have been redesigned and remanufactured to completion. This permitted the achievement of six test burns and the collection of four complete data sets for further analysis. Redesigns of other hardware components such as the graphite nozzle and data instrumentation have been engaged and will continue throughout the fall break. The most distinguished accomplishment of the Fall 2011 semester was the conference, in which a test burn along with a requirements review was completed with the NASA (Stennis) representatives. Finally, there has been thought placed to the future plans of this project. The completion of all NASA requirements along with the delivery of the finished product (the classroom propulsion demonstrator) to NASA, is the ultimate goal for the Spring 2012 semester. The Final product shall include a functioning portable hybrid rocket engine and test stand along with a fully automated system control and data analysis package that is safe to operate within its designed constraints. 17

19 Appendix A: Requirements Requirements for Classroom Propulsion Demonstrator (CPD) (new pocket rocket) 1. CPD shall be easily portable. Able to move from a car/truck to a classroom via one person. Envision a suitcase size device. 2. CPD Combustion products shall not be toxic, nasally overbearing, or visually disturbing (i.e. not much smoke, don t want to set alarms off) 3. CPD shall be able to be set up in no more than 15 minutes. 4. CPD shall have the following instrumentation: Thrust Measurement, Oxidizer flow, Chamber Pressure, Gas Oxygen Temperature, Nozzle Exit Temperature, Battery voltage. 5. CPD shall be able to perform a preset thrust profile (i.e. Oxidizer flow automatically adjustable). 6. All CPD components shall be able to be repaired or replaced in the field. 7. All CPD instrumentation shall be able to be replaced with spare in the field. 8. All CPD instrumentation data will be displayed on a flat LCD screen. 9. CPD data from firings shall be saved and easily retrieved. 10. Activation and Control of CPD shall be automatically with provision for manual control. 11. The CPD shall have a reusable in place ignition system. 12. CPD shall be able to fire continuously for duration greater than 20 seconds. 13. CPD shall be able to do at minimum 4 test firings in one hour. 14. The CPD controls shall assess readiness for operation (eg. Electrical power; Igniter continuity; oxidizer pressure; article temp for restart). 15. CPD demonstrator shall be able to present a pre-recorded video data of actual rocket testing on its LCD screen. 16. CPD shall operate via graphic user interface. 17. CPD shall display propulsion graphically. Showing discharge changing in respect to fuel and oxidizer changes. 18. CPD shall graphically show the relationship between all propulsion variables. 19. Both recorded data and video shall be time-stamped. 20. The post-test data shall be time-aligned to a start event. 21. CPD shall have an Emergency Shut-Off capability which will remove the oxygen supply from the device. 22. Data Display shall not interfere with data acquisition and recording operations. 23. CPD shall be capable of firing horizontally. 24. CPD design team shall provide end-to-end system uncertainty calculations in terms of percentage of full scale ranges. 18

20 Appendix B: Rocket Design Assembly 19