We're going to build a small hybrid rocket motor.
Adam, James, Jack, Mikolaj, David, Chris, Einar, Sam
Quaser had it's first successful test.
Summary of discussion
Need to find location nearer to Cambridge to test ignition. - contact EARS landowner?
Need to get larger valve - 8mm orifice solenoid valve rated to 60bar now possibly sourced at cost of £350 - need to check if PEEK as a seal material is Nitrous safe.
Bore out combustion chamber to ?mm ID and then get CP to remake nozzle ( or bush nozzle? ) and get igniter remade.
Re cast fuel grain. / make casting equipment and jigs
Summary of discussion
Discussed various possible different methods of ignition and potential fuels that would allow for easier ignition. Also discussed changes that could be made to improve instrumentation. Overall it was felt that the current version has quite a lot of scope remaining and we'd generally rather we got that working rather than completely redesigning the hybrid. The usefulness of having a servo valve that could be used to control the oxidiser flow was also raised.
Things to do
- Design/source an appropriate servo valve.
- Locate a possible test site so we could do small tests at Cambridge
- Investigate other fuels - namely paraffin/cardboard - but also investigate castable fuels e.g. sugar
- Think about potential designs for a 2" diameter hybrid.
- Write up the test firing and produce a 'Things we Learnt' document.
- o rings (http://www.hse.gov.uk/mvr/priorities/fluoroelastomers.htm what I was saying about burnt O rings appears to be a myth)
- high pressure pipe
- valves (electronic, manual)
- pressure gauge
- regulator (electronic?)
- nitrous-safe grease
- nozzle retainer
- safety stop valve
- check valve
- video camera(s)
- strain gauges
- datalogging electronics
- Get Solidworks discs
- datalogging kit
- test stand
Task List (1/Nov/12)
Ask BOC about nitrous awaiting response we're golden, ask H&S about testing rocket motors, buy some fuel fuel has arrived
Ask about using the student workshop, see what Cambridge Precision will be willing to do The guy in the student workshop wanted drawings or CAD files before he agreed to anything. Cambridge precision seemed willing to machine anything we wanted.
btain SolidWorks licenses applied online, investigate valves/fittings/gas piping. BOC sell valves, and pipes, so may be the best source. Valves: http://www.leengatevalves.co.uk/. Need to know the pressures of the gas cylinder before going much further.
Find some suitable steel pipe for the case steel pipe ordered
Mikolaj: <del>Get in contact with the guy who can make graphite nozzles, estimate lead time/price </del> E-mail is away. No reply yet.
Look for some computer controlled valves http://aeroconsystems.com/cart/solenoid-valves/lake-axial-solenoid-valve/ David: Are these any good? http://www.finecontrols.co.uk/burkert/high-pressure-solenoid-valves http://www.solenoidvalvesuk.com/resultcatalog.asp
Sam: Obtain/test some ignition systems ignition
Team: MacKay shopping trip
Other things to obtain: nitrous safe grease, O rings
The technical pages on http://www.aspirespace.org.uk/ have a lot of relevant information.
Fuel Grain Research
The fuel can be made from a number of substances:
- High Energy Density
- Easy to machine, or mould
- Available (cheap too would be good!)
- Not too sooty, or melt too easily. We need to ensure the nozzle is not clogged during usage.
- Most have a single hole in the middle, although some designs have grooves for additional surface areas, other make use of several holes through the material.
(http://science.nasa.gov/science-news/science-at-nasa/2003/28jan_envirorocket/): Pros: Cheap, readily available, easy to form
Disadvanages: Melts easily so could be problematic to ignite. Can melt and be spewed out the nozzle unburnt:http://myweb.tiscali.co.uk/aspirespace/wax%20hybrids.htm
Pros: Can buy set yourself urethane rubber.
Cons: Could be difficult to handle, potentially toxic when burnt.
Cheap, easy to cast into desired shape.
May melt or clog nozzle
Should be stored in freezer bags to avoid absorbing moisture.
Sorbitol and dextrose are preferred.
- Pros: Available and easy to shape to the required size. Easy to light, as burns on its own
Cons: Could fall apart when burnt
High density polyethylene:
Pros: Easy to machine (likely to be best to buy a rod, and machine to size( Fairly cheap and available. Clean burning, and popular in the hybrid rocket community.
Increase the specific impulse and burn rate. Generally powdered metals such as iron or aluminium. Carbon black could be used. I've been looking into ignition methods. All the sites I've looked at which describe how to ignite a hybrid rocket seem to talk about a quite controlled method of ignition, so I doubt lighter fluid or black powder will be that suitable. The most commonly described method involves using something called a pyrograin, or pyrovalve. These appear to be some solid that burns steadilyin the case of the pyrovalve this releases the oxidiser when it has burnt through, but no site I have looked at yet actually says what they are. Other methods mentioned include using a very high voltage, but that only seems to work if the oxidiser is pure oxygen. This site seems to have the best info:
Looking into pyrograins, as far as I can discover they are just any piece of non inert fuel. I haven't found any exact compositions yet though. Injector
Assuming that the Nitrous has a pressure of ~ 55 Bar and that we have a pressure of 35 Bar in the combustion chamber (figures taken from here) then we can get a rough estimate of the flow rate using a simple injector (i.e. with sharp orifices created using drill bits in a 'shower head' configuration).
Using Q = A*Cd*sqrt((2*DeltaP)/Rho) we can show that for a configuration of n 2mm diameter holes (where Cd is roughly 0.61) then Q = n*3*10^-4 m^3s^-1 and the mass flow rate is .048n kg s^-1.
In order to reduce pressure instabilities it is recommended to have a recirculation zone near the injector by providing a sufficiently large gap between the injector and the top of the fuel grain (will try and upload a diagram of this later).
Nozzle Design for Project Quasar
Nozzle Preformance Calculator 1
I successfully (at least I believe it works) made simple MatLab script which calculates key conical nozzle parameters with input of:
- Combustion chamber temperature and pressure
- Gas properties (Molecular mass and cp/cv coefficient)
- Ambient pressure
- Half angle of nozzle
- Combustion products flow rate.
All these values are calculated under following assumptions:
- Working gas is homogeneous
- All combustion products are gaseous
- Working gas is a perfect gas
- Flow is adiabatic
- Friction and boundary layer effects are neglected
- There are no shock waves or discontinuities in the nozzle flow
- Flow is steady.
- All gases at the exhaust have axially directed velocity
- Gas pressure, velocity, temperature and density are uniform across any section normal to the nozzle axis.
- Flow is frozen i.e. there is no change in gas composition during nozzle expansion
(All theory is taken from a lovely book "Rocket Propulsion Elements" by G.P. Sutton and O. Biblarz)
Here is a code:
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %% Nozzle and gas properties definitions (You need to fill this section, User!)%% T1 = 2000; % Combustion chamber temperature [K] p1 = 2 * 10^6; % Combustion chamber pressure [Pa] k = 1.3; % cp/cv of the gas miu = 16; % Molar mass of gas [kg/kmol] p2 = 10^5; % Ambient pressure [Pa] mdot = 0.1028; % Mass flow rate [kg/s] alpha = 15 * pi/180; % half angle of the conical nozzle %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %% Key preformance parameters equations (Just lots of equations) %% R = 8314.3 / miu; disp ('Supersonic throat condition') condition = p1/p2 - ((k+1)/2)^(k/(k-1)) disp ('All calculations are valid only if above number is positive') disp ('Throat area') At = mdot * (p1 * k * sqrt( (2/(k+1)) ^ ((k+1)/(k-1)) / (k * R * T1)))^(-1) disp (' Throat temperature [K]') Tt = 2* T1 /(k+1) disp('Ratio of exit to throat area') epsilon = (((k+1)/2)^(1/(k-1)) * (p2/p1)^(1/k) * sqrt( (k+1)/(k-1) * (1-(p2/p1)^((k-1)/k))) )^(-1) disp ('Exit area [m^2]') A2= epsilon * At % Exit area [m^2] disp ('Nozzle lenght [m]') L = cot(alpha) * sqrt(At/pi) * (sqrt(epsilon)-1) % Nozzle lenght [m] disp ('Exit velocity [m/s]') v2 = sqrt ( 2*k /(k-1) * R * T1 * (1 - (p2/p1)^((k-1)/k) ) ) disp ('Total Theoretical Thrust [N]') F = mdot * v2 disp ('Theoretical Specific Impulse') Is = v2/9.81 %% End of the script %% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Nitrous Oxide (N2O) - Nitrous Oxide, also known as Dinitrogen Monoxide, NOx, or laughing gas, has a boiling point of -89.5 degrees Celsius at 1 atm, and is normally maintained as a liquid at a pressure of 54 bar (783 psi). Nitrous Oxide has a molecular weight of 44.0 and a density of 1222 kg / m3 at 20 degrees. The critical pressure and temperature of Nitrous Oxide is 7.27 MPa and 36.6 degrees Celsius.
The nitrous oxide bulbs for kitchen seem to be 8 or 16 grams of N2O but I can't find anywhere that gives the pressure. They are very cheap.
Bigger bottles can be bought from car performance shops, but not sure if any in Cambridge.
N20 Thermophysical properties Data sheet
Found on the internet. Might be quite helpful later. http://edge.rit.edu/content/P07106/public/Nox.pdf
Static Test Rig
Nearly complete, but needs some more holes drilling and parts attaching for mechanical completeness. We have the required datalogging kit but no software has been written (in LabView) to complete a log. This would probably be more useful for a full size test. We might need to take it elsewhere to do the test -- some sites may be available.
Small scale testing
Securing the motor to a set of digital scales would probably suffice. Something that could be sampled quicker would be better -- maybe something with a digital output. SparkFun sell a simple cheap load cell here, or we could use the existing high quality load cells we already have (but they might not be sensitive enough).
Things to Measure
The main one will be thrust delivered on-axis. Off-axial thrust is a nice second. Pressure in the combustion chamber could be hard to measure for small models but digital sensors are readily available. Temperature of the outsides is easily measured.
Probably not really an issue until we actually have a rocket.