2010 Year Month 10 Day 10
HYDROGEN PEROXIDE THRUSTER EXPERIMENT
Aerospace Engineering Laboratory II
Name
: Martin Suhartono
Student ID : 20106182
1. Objective To familiarize ourselves with the experimental process of monopropellant thruster as well as to evaluate the performance by analyzing the experimental result 2. Introduction and Background A thruster is generally a propulsive device used in spacecraft which plays an important role in installing a satellite, or any outer space device in that sense, to the desired orbit. Thrusters are generally classified into two categories; chemical and electrical/electronic depending on the source of its energy. The electrical thrusters have high specific impulse but are rarely used due to its low thrust level generated as well as weight constraint. In contrast, the chemical thrusters, like the monopropellant or bipropellant thrusters, are able to provide high level of thrust and are significantly lighter. Hence, the chemical thrusters are more commonly used for launch vehicle control system. Specifically, monopropellant thrusters can generate high level of specific impulse with rarely any failure and thus they are highly recyclable. Compared to bi-propellant thrusters, the monopropellant thrusters are more advantageous due to its lighter mass and smaller volume and hence it's reduced complexity. Monopropellant thrusters are then extensively used for launch vehicle attitude control. A common example of the propellant (chemical) used in a chemical thruster is hydrogen peroxide, H2O2. Hydrogen peroxide in high concentration of around 90% readily decomposes into steam and oxygen. Hence, unlike other hydrazine compounds, it is not toxic. For thruster application, hydrogen peroxide is pumped into a reaction chamber where a catalyst such as silver or platinum is used to cover the chamber wall. The high temperature steam generated through the decomposition is then expelled through a nozzle where it consequently generates thrust. In this experiment, we will try to evaluate the performance of such hydrogen peroxide thruster. The evaluation of thruster performance is correlated with the degradation rate of the propellant. The following formula indicates the decomposition rate based on characteristic velocity.
The characteristic velocity is then used to evaluate the reactor performance (or characteristic velocity efficiency when nozzle effect is excluded) based on
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Lastly, the degradation efficiency can be represented by the temperature efficiency as the degradation is proportional to the temperature and the formula involved is
3. Material and Equipment a. b. c. d. e. f. g. h. Thruster Measurement stand Thermocouple and pressure stand Load cell Data processing computer Nitrogen tank for pressurization Hydrogen peroxide Catalyst
4. Method a. Check the installation of the apparatus after putting the catalyst into the reaction chamber and fixing the injector, nozzle and other equipment. b. Set the device on the measurement stand and ensure that it is firmly in contact with the load cell. c. Install the thermocouple and pressure sensor. d. Check the data processing computer to make sure that everything has been installed correctly. e. Fill the propellant tank with one liter of hydrogen peroxide. Check whether there has been any leakage. f. Use the nitrogen tank to pressurize the device up to the appropriate pressure for experiment. g. Remove and hazardous material around the testing site. h. Conduct the testing and record the result. i. Evaluate the performance using the aforementioned formulas.
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5. Results Example of the values of pressure and temperature recorded in the course of the experiment for feeding pressure of 20 bars:
Graph of Pressure (in V) against Time
3 2.5 2 1.5 1 0.5 0
0 100 200 300 400 Time 500 (10-2 s) 600 700 800 900 Voltage (V)
Graph of Temperature against Time
600 500 400 300 200 100 0 0 100 200 300 400 Time 500 (10-2 s) 600 700 800 900 Temperature (C)
On the other hand, the graphs for feeding pressure of 15 bars are:
Graph of Pressure (in V) against Time
2.5 Voltage (V) 2 1.5 1 0.5 0 0 100 200 300 400 500 600 700 Time (10-2 s)
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Graph of Temperature against Time
600 Temperature (C) 500 400 300 200 100 0
0
100
200
300
Time
400
(10-2) s
500
600
700
The above graphs show that the recorded values are fluctuating because of the inconsistencies existing the in real life experiment. The injection of the hydrogen peroxide into the chamber as well as the following decomposition needs a certain period of time to stabilize. After stabilizing, the recorded values become approximately constant. Moreover, as the amount of injected hydrogen peroxide depletes and the decomposition finishes, the recorded values fluctuate further. Considering that the whole injection lasts for approximately five seconds, we will take the average between the values in second, third and fourth seconds of the experiment to evaluate the thruster performance. This time frame is taken because I perceive that one second after the injection starts, the decomposition should have stabilized. The temperature graph for 15 bar is specifically inconsistent and this may be due to an experimental error which will be discussed further in the Discussion section. Additionally, the mass flow rate in this experiment is for 15 bar, for 20 bar, Moreover, pressure is measured in terms of voltage. Hence we need to convert the measurement to bar. To do this, we need two independent points and they are Pressure (bar) 1 35 Voltage (V) 1.111693 5
With these points, we can establish the relationship as
And by substituting the first set of values, we get
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In calculating the chamber pressure and temperature we have to deduct the initial atmospheric pressure of 1 bar as well as the initial temperature of 17 K from the recorded values. We can then tabulate the following results: Items Nozzle Type Nozzle Throat Diameter Nozzle Area Ratio Nozzle Throat Area Concentration of H2O2 Adiabatic Temperature Theoretical Characteristic Velocity Feeding Pressure (bar) 15 20 Mass Flow Rate (g/s) 42.48 60.14 Values Conical C-D nozzle 6.8 mm 2.78 36.317 mm2 90% 750 0C 960.6 m/s Temperature (o C) 221.68 513.52 Pressure (bar) 9.239 12.714
For feeding pressure of 15 bars:
( )( )
For feeding pressure of 20 bars:
( )( )
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6. Discussion As shown above, the experimental values are generally lower than the theoretical values. This is so because the decomposition as well as ejection of the propellant is not completely an adiabatic phenomenon and thus there is bound to be energy lost to the surroundings. This yields lower chamber temperature and pressure compared to the theoretical values and hence a hundred percent efficiency is impossible to achieve. Nevertheless, the characteristic velocity efficiency is generally in the order of 80% and thus the hydrogen peroxide thruster seems to be relatively effective in producing the desired momentum. In contrast, the specific temperature efficiency is in the order of 50 and 70% only. This means that the working temperature of the thruster is not optimal. Hence, if we rise the chamber temperature before the propellant is injected, we might improve the efficiency of this hydrogen peroxide thruster. Moreover, as the feeding pressure is increased from 15 bars to 20 bars, the specific velocity efficiency decreases but the specific temperature efficiency increases. We expect that both efficiency to show the same trend and so this phenomenon may hint at a major error in the experiment, specifically in measuring the temperature efficiency for the feeding pressure of 15 bars. This error is also indicated at the temperature graph that has been mentioned before in the Results section. The temperature actually jumps several times in the course of the experiment and fluctuates greatly. This may be due to the lag in time for the chamber pressure to be equal with the propellant temperature as well as the sudden increase of decomposition rate that may suddenly yield enormous amount of heat. These reasons render the temperature graph obtained from the experiment deviates more than the theoretical expectation, yielding less accurate reading of temperature. To counter this problem we should have let the thruster to operate for more than five seconds so as to ensure that the reaction and chamber environment have stabilized. Nonetheless, the remaining results have clearly indicated the efficiency and potential of a monopropellant thruster for a control launch device. 7. References a. High Test Peroxide Wikipedia the Free Encyclopedia http://en.wikipedia.org/wiki/High_test_peroxide Accessed: 10 October 2010 b. Chisholm, Hugh, et al (1911). Encyclopaedia Britannica : Propellant (Eleventh Ed.). Cambridge University Press.
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