Research Status Update

Difficulties with the instrumentation used to collect the cooling curve data seriously limited the number of possible trials and the credibility of the data itself. Hence, only the data collected using the MEL-Temp device was used to determine the melting points of the n-paraffin fuels. However, some useful information was collected from the cooling curves. The curves established for paraffin-D support the conjecture that there exists a bimodal distribution of carbon chain lengths present within the sample, suggesting two melting points on the range of 55-57 deg C and 72-76 deg C. This conjecture is also supported by observations through the MEL-Temp device, yet these data suggest that the first melting point is much higher. Paraffin-D exhibited primary melting starting around 67 deg C and ending around 70 deg C. Secondary melting was observed on the interval of 72-75 deg C. The melting points of the four n-Paraffins are as follows:

paraffin-A: 54.8 deg C

paraffin-B: 56.8 deg C

paraffin-C: 64.5 deg C

paraffin-D: 71.0 deg C

I have acquired two 0-2000 psi Taber pressure transducers along with a RATTworks X-form k-250 nitrous oxide injector and the proper nitrous oxide fittings for the injector assembly. Designs for the injector face and forward rocket motor closure have been made and will be posted soon. A 12" length of 1.5" dia aluminum rod stock has been acquired and will be used for the machining of these components. An injector port, graphite pre-combustion chamber, and pressure tap will be integral components of the forward closure. Photos of the machining progress will be posted.

I will need to construct an instrumentation amplifier in order to convert the millivolt strain-gauge readings from the transducers into detectable output for the provided Vernier data acquisition equipment. An amplifier can be purchased for $60 or simply made from three operational amplifiers, a couple of resistors and a gain adjusting potentiometer for much less money. 

Basic Instrumentation Amplifier

Overall Voltage Gain Equation

The transducers must be calibrated against a range of known pressures prior to use. Such an operation will generate a calibration curve which gives the pressure as a function of amplified output voltage. In order to calibrate the transducers I will construct a pressure vessel out of high pressure rated tubing and fittings. The vessel will be equipped with a visual pressure gauge. The vessel will be connected to a high pressure supply of an inert gas like nitrogen or argon from a cylinder. The voltage output from the transducer will be plotted against the pressure displayed on the gauge.

Further design work and parts acquisition must be done on the testing assembly as a whole.

1. Construction of Instrumentation amplifiers.
2. Location of a high pressure inert gas supply.
3. Construction of pressure vessel.
4. Acquisition of standoff wiring.
5. Calibration of transducers with the standoff.
6. Acquisition of a tap set in order to thread ports in the injector face.
7. Machining of the injector face and forward closure.
8. Machining of the pre-combustion chamber.
9. Obtaining a supplier for nitrous oxide bottles. 
10. Acquisition of fill, vent, arming. and relief valves.
11. Acquiring a high-flow nitrous oxide solenoid valve and required fittings.
12. Acquisition of proper fittings and tubing.
13. Acquisition of a pressure-rated cylinder.
14. Construction of nitrous oxide tank for trials out of a tapped, pressure-rated cylinder.
15. Construction of a test stand.

More Cooling Curves

Here are the data for the last two trials. The sensors appear to have malfunctioned during the trial with paraffin A and B. However, the level portion of the curve indicating melting point is preserved. Again, Paraffin D has exhibited two distinct melting points, lending credibility to the results.

Cooling Curve for n-Paraffins A and B

Cooling Curve for n-Paraffins C and D