ROCKET TEAM: DESIGN PACKAGE

Transcription

1 Reusable Ignition Tests Chemical Ignition Test- Gas and Igniter System Objective: Our team is trying to find a reusable ignition system by means of a chemical lighting Apparatus: Using a butane lighter, the internal components were removed and modified to be able to make a reusable ignition system. The chemical ignition is shown below FIGURE 1: Chemical Ignition Test 1: A test was scheduled for the testing of this chemical ignition system, but upon doing extensive research the ignition proved to be volatile. The test was cancelled due to unsafe conditions of the ignition system. Results The maximum adiabatic flame temperature a butane torch can achieve with air is 2243 kelvin (3578 F / 1970 C). Given the increased oxygen flow, more pressurized butane is needed to prevent backflow. Conclusions: This ignition system is still a design that may be used in the future with the right amount of pressures. More testing is needed as well as more precautions to be able to test this ignition system. The first thing that needs to be done is to increase the pressure from the butane to a level higher than the pressure from the oxygen to prevent the oxygen to retract to the butane container and cause an explosion. New Mexico State University Spring 2012 Page 1

2 Reusable Ignition Tests- Continued Resistance Wire Ignition Test Objective: Our team is trying to find a reusable ignition system by means of electrical resistance Apparatus: using a transformer, we took 120 volts and 10 amps and transformed to 6 volts and 140 amps. This source was then run through 3 different specimens. The specimen was placed in line with the plane of fuel as shown below A thermocouple was placed 1.25 in (1/8 in) from the test specimen in attempt to measure the radiant heat from the resistor Test 1: 20 gauge Tinned Copper Wire The copper wire melted immediately giving us no results Test 2: Ni chrome wire ohm/ft, cut to 6 in. Reached a temperature of C (284 0 F) This does not suffice for an ignition Conclusions: Test 3: This time we wrapped two 6 in long specimens together in order to increase the resistance. 0.2 ohms was measured with a volt meter. After 6 seconds the acrylic ignited with a reading of C (446 0 F) from the thermocoupler We still believe this may be a possible ignition system with the right materials, however further testing is needed. First we will redesign the apparatus so that the wire does not move at all during the test. On test three, the wire moved slightly which may have altered the results. For the next test, we need to redesign the apparatus to get solid results New Mexico State University Spring 2012 Page 2

3 Find: The conditions at which TF >= F 1310 R Assume: Tw = F =2060 R, Epsilon =.8 Heat flow from the wire is given by A 1 = A 1 = 1.1 x 10-4 ft 2 qr= X qr= 2.7 To find the temperature of the fuel cell: qr= AF 1-2 ) T F = ) 1/4 Assuming F 1-2 = 1 (slope factor depends on emittances and relative geometrics) T F = [ 1/4 ======= T F = R = 925 This is assuming that all the radiation transmitted is absorbed by the fuel cell New Mexico State University Spring 2012 Page 3

4 What is our shape factor? We assumed 2 parallel disks of unequal diameter, distance L apart with centers on same normal to their planes, smaller disk A, of radius a, larger disk of radius b From pg. 575 Heat transfer book [*1] F 1-2 = F 1-2 = F 1-2 =.8 So assuming F 1-2 =.8, T F = [ 1/4 T F = 573 R = 113 [*1] Kreith, F. Manglik, R.M., and Bohn, M.S., 2011 Principles of Heat Transfer, 7 th edition, Cengage learning, Stanford, CT What if we bring up the temperature of the wire to 2000 Tw = 2460 R A= 1.1 x 10-4 ft 2 qr = === qr= ) qr= 5.5 TF = 1650R ==== 1190 Thus, if the wire temperature is 2000 which is about the limits of the wire, the temperature of the fuel cell could be anywhere between If the ignition temperature of the fuel is 850, we do not believe this will work as a possible ignition system. New Mexico State University Spring 2012 Page 4

5 Reusable Ignition Tests- Continued Mechanical Ignition System The main idea for this project is to design a portable hybrid rocket that will be used by NASA for recruitment and gaining interest in the science and engineering fields. In designing this system there was a list of requirements to be fulfilled. One such requirement is to create a reusable ignition system. This requirement is significant in the fact that to the knowledge of this team, no such device has ever been commercially produced. Due to the use of a solid fuel grain, burning particles or sparks were thought to be needed to ignite the acrylic. Immediately, one design that came to the surface included the use of parts from hand-held butane lighters. These lighters utilize a combination of materials to produce sparks that ignite the impinging butane flow. This idea soon grew into a system similar to the sketch shown below. The above sketch presented the use of a remanufactured top plate designed to encase a solid rod rigidly attached to a barrel taken from a standard lighter. The plate also included a hollow tube that would enclose a spring loaded cylinder of ferrocerium, a man made substance that when struck against a hard surface, produces the sparks in a majority of hand held butane lighters. The design proposed that when the rod was spun, the contact between the ferrocerium cylinder and the barrel would produce burning particles similar to the reaction seen when flicking a hand-held lighter. After some deliberation the design was determined and manufacturing began. Once completed the ignition system looked similar to the photograph below. New Mexico State University Spring 2012 Page 5

6 Initial testing demonstrated that by rotating the aluminum rod sparks were produced. In order to create a large amount of sparks an electric motor was placed on the top of the plate and paired with a pinion and gear set to rotate the rod. This completed the design for the mechanical ignition system. The next step included a full test firing of the rocket using the new ignition system. A photograph is shown below of one such test. The test was thought to be a success, as the ignition system was capable of igniting the fuel within 1.5 seconds of commencement. This success was short lived however when the rocket engine was taken apart after testing and the ignition system was found to have destroyed itself. Photograph of the damage can be seen below. New Mexico State University Spring 2012 Page 6

7 This meant that the ignition system was no longer reusable. The initial rationale for this included the negative effects of heat on the ferrocerium. It was thought that the heat produced by the rocket exceeded the tolerance of the substance, triggering it to become volatile and combust, destroying everything around it. Oxidation was also thought to be a possible negative effect, but it is not entirely understood what happened. Attempts to lower the temperature in the top plate included the design and manufacturing of a thicker diffuser plate as well as decreasing the ignition and total test burn timing, but again the ignition system was damaged after testing. The thicker diffuser plate can be seen in the photograph below. New Mexico State University Spring 2012 Page 7

8 With resuability out of the question, the current ignition system fell back to the original case which utilized pyrotechnic hobby rocket fuses to light the acrylic. Unfortunately this means that the NASA requirement is not fulfilled. Although in its current iteration the mechanical ignition system is not a viable solution, further testing and development is under way. The use of alternate materials to produce sparks is a promising possibility. One such material under scrutiny is titanium. This metal produces bright white sparks when placed in contact with fast moving abrasive surfaces. Currently the mechanical ignition system prototype top plate has been remanufactured to accept titanium in place ferrocerium and some small scale testing has been conducted. The use of a larger motor and a modified gearing ratio is required to achieve the higher barrel speeds needed to produce sparks from titanium. This will be left to the next team for further research and development. New Mexico State University Spring 2012 Page 8