Transcript Reaction Selection - Florida Institute of Technology

Autonomous Vehicle Design
Florida Tech AIChE
1999
P. Engel, T. McKenney, M. Mensch
Reaction Selection
The optimum propellant to use for the autonomous
vehicle would be one that has a high thrust and a low
production cost. The simplest and most obvious choice
would be to use a solid rocket propellant. The rocket
propellant chosen has a high burn rate and relatively clean
exhaust. A high burn rate propellant will yield a very high
initial thrust, this will overcome the coefficient of static
friction quickly and effectively.
The Reaction
NH4ClO4 (s) + Mg(s)
CuO
MgO(s) + MgCl2 (s) + NO(g)
+ H2O + energy
•NH4ClO4 (ammonium perchlorate) oxidizes the metallic fuel
(magnesium) in the presence of a burn-rate catalyst (copper
oxide).
•The majority of the product formed is water vapor and
magnesium chloride.
Laboratory Requirements
• Vacuum Chamber
– Needed to remove unwanted gases formed during mixing.
– Makes the composition more uniform.
• Mixer
– Needed to obtain the desired propellant composition.
– Reduces the presence of temperature gradients during heating.
• Heating Pad
– Needed to reduce the viscosity of the propellant.
– Reduces the amount of work on the mixer
• Process Controller
– Needed to regulate the temperature within a specific range.
– Keeps the heater from overheating the propellant.
Experimental Procedure
1 First HTPB, the binder, is added to the bowl and heated to
55° C while mixing.
2 Next magnesium, the metallic fuel, and copper oxide, the
catalyst, are added appropriately and mixed until uniform.
3 Finally ammonium perchlorate, the oxidizer, is added, the
power is turned off, and the mixture is placed into the
vacuum chamber.
4 The vacuum pump is engaged, when pressure stabilizes
then the power to the mixer and heater is turned on.
Experimental Procedure
5 After the mixture has been in the vacuum chamber for 30
minutes, the pressure is removed slowly and
diphenylmethane diisocyanate, the curing agent, is added.
6 The mixing is continued until the mixture is homogenous,
then the heating source and mixer are turned off.
7 The propellant is then removed, placed into molds, and left
to cure.
Environmental Considerations
The most widely used fuel in solid propellants is
aluminum because it offers a better burn. The downside
of using aluminum is that after combustion it yields
aluminum chloride, this then hydrolysis and produces
hydrochloric acid (HCl). Hydrochloric acid will corrode
metals and lower the pH of the environment in which it
comes in contact with. Therefore we chose to use a
magnesium fuel, which yields magnesium chloride.
Magnesium chloride is found in large quantities in the
ocean and does not cause any environmental problems, nor
does it form an acid.
Exhaust Evaluation
The propellant chosen had a very clean burn, resulting
in a very low smoke content. The exhaust consists mostly
of water vapor and small quantities of nitric oxide. Nitric
oxide is a lung irritant, but since the reaction only produces
a very small quantity of this, the hazards related to it can
be neglected. Other products that may be produced are:
oxygen (O2), nitrogen (N2), and hydrogen (H2). The
Earth’s atmosphere consists of nitrogen and oxygen, these
two elements are stable in the diatomic form. Hydrogen is
highly flammable and therefore will only add to the
propulsion flame.
Explosion Safety
• To prevent the rocket engine from becoming a pipe bomb,
an aluminum nozzle was used. Aluminum is a relatively
soft metal and therefore will yield if enough pressure is
applied.
• This became the downfall of the design. After a number of
tests, the threading on the nozzle became weak and gave
out. The nozzle was projected out of the back end of the
engine, and rendered useless for further tests.
Nozzle Design
• Aluminum Metal Material
– Easier to machine than steel.
– Resists melting and corrosion well.
– Safer to use as a nozzle than steel.
• Necessity of Nozzle
– Controls the pressure drop through the end of the engine.
– Focuses exhaust and increase exhaust escape velocity.
• Size of Nozzle
– Nozzle throat should be 1/3 surface area of pipe
– 3/8” engine requires nozzle diameter of 0.217 in, since this
diameter could not be machined a 1/8” diameter was used.
Chassis Design
• Carbon Fiber Chassis
– Heat and explosion resistant
– High mechanical strength
– Low body weight
• High Grip Wheels
– Increases traction
• Flat Bed Body
– Practical for carrying load
Rocket Engine Design
• Carbon Steel Material
– High mechanical strength.
– Heat and explosion resistant.
• Variable Length Piston
– Able to use one engine for any amount of propellant.
• Heat Resistant Rubber Coating
– Adds friction between rocket engine and chassis
Ignition Design
• Electrical Ignition
– Ran a current through a highly conductive metal to ignite the fuel.
– Safer than using a fuse.
– More professional.
• Mounted Ignition
– Allows ignition source to be placed directly in the engine.
– Increases ignition success.
Vehicle Budget
$62.85
$70.53
$89.95
Body
Fuel
Ignition