RATIONALE
FOR THE STUDY
A hybrid rocket is a rocket with a rocket motor which uses propellants in two different states of matter -
one solid and the other either gas or liquid.
Hybrid rockets exhibit
advantages over both liquid rockets and solid rockets especially in terms of simplicity,
safety, and cost. Because it is nearly impossible for the fuel and oxidizer to
be mixed intimately (being different states of matter), hybrid rockets tend to
fail more benignly than liquids or solids. Like liquid rockets and unlike solid
rockets they can be shut down easily and are simply throttle-able. The
theoretical specific
impulse performance of hybrids is generally
higher than solids and roughly equivalent to hydrocarbon-based liquids. as high as 400s has been measured in a hybrid rocket using metalized
fuels. Hybrid systems are slightly more complex than solids, but the significant
hazards of
manufacturing, shipping and handling solids offset the system simplicity
advantages.
·
To study hybrid rocket
·
To study the components
of hybrid rocket.
·
To study the advantages
and disadvantages hybrid rocket.
·
To study the problems
associated of hybrid rocket.
METHODOLOGY
OF STUDY
ROCKET
PRINCIPLES:
A rocket in its simplest form is a chamber enclosing a
gas under pressure. A small opening at one end of the chamber allows the gas to
escape, and in doing so provide a thrust that propel the rocket in the opposite
direction. A good example of this is a balloon is compressed by the balloons
rubber walls. The air pushes back so that the forces on each side are balanced.
When the nozzle, with space rockets, the gas is produced by burning propellants
that can be solid or liquid in form or a combination of the two
Newton’s first law’s for
rockets
Newton’s first law can be stated as:
“An object at rest tends to stay at rest and an object
in motion tends to stay in motion unless acted upon by an unbalanced forces.”
Newton’s second law can be stated as:
This law is essentially a statement of mathematical
equation. The three parts of equation are mass(m), acceleration(a), and
force(F). Using letters to symbolize each part, the equation can be written as
follow:
F=ma
Newton’s third law can be stated as:
Every action has equal and opposite reaction.
HYBRID ROCKET:
The sketch below depicts a hybrid rocket. The hybrid normally uses a liquid
oxidizer that burns with a solid fuel although reverse hybrids liquid hydrogen
burning with solid oxygen.
FUELS
The fuel for a small hybrid rocket motor is
generally a tube of combustible material (most frequently Polyethylene or
Acrylic, although even cardboard is used in some cases!). The tube is known as
the fuel grain. The hole down the centre of the tube is called the fuel port.
For a larger hybrid rocket motor, multi-port grain geometries are common, where
there will be several separate ports in the fuel grain, with oxidiser injected
down each port.
REGRESSION RATE
·
In a hybrid rocket motor,
liquid oxidiser is fed into the combustion chamber from the oxidiser tank,
where it is ignited by an ignition source such as a pyrotechnic igniter. The
fuel is then ignited and burned in the presence of the oxidiser, where it
vapourises, and burns along the length of the fuel grain. The rate at which the
fuel burns, is called the regression rate, and is measured in metres per second
(m/s).
·
The combination of fuel
burn rate and oxidiser flow rate is called the mass flux, and is measured in
kilograms per metre squared seconds (kg / m2 s). The oxidiser flow
rate affects the rate of regression of the solid fuel, and enables the
following equation for solid fuel regression rate to be derived:
·
r = aGnxm
·
where;
r = fuel regression rate (m/s)
G = propellant mass flux (kg / m2 s)
x = length along the fuel grain port (m)
a,n,m = regression rate constants
·
The regression rate then,
is dependent on the mass flux and the length along the fuel grain port.
OXIDISER TO FUEL (O/F) RATIO
·
A hybrid motor differs
fundamentally in terms of combustion behaviour compared with solid and liquid
rockets, in that the Oxidiser to Fuel ratio (O/F), varies along the length of
the hybrid fuel grain, i.e., it has an axial dependency.
·
In a liquid rocket, the
injectors generally inject both the fuel and the oxidiser at one end of the
combustion chamber thus there is no axial dependency.
·
In a solid rocket motor,
there is no injector head, and every particle is bound of fuel and oxidiser,
thus ensuring the O/F remains pretty much constant.
COMBUSTION CHAMBER
The combustion chamber in a hybrid rocket motor not
only provides the location for propellant combustion, but also contains the
whole fuel grain. The length of the combustion chamber is determined by the
fuel grain configuration (e.g. a single port or multi-port fuel grain
configuration). Also, the longer the combustion chamber, the more stable
the combustion, since the propellant has more opportunity for even mixing.
FUEL GRAIN CONFIGURATION
From
checking sources such as Spacecraft Propulsion Analysis and Design (Humble and
Larson) and Rocket Propulsion Elements (Sutton), as well as following through
with the calculations, a single cylindrical port geometry for a hybrid fuel
grain, provides more volumetric efficiency for any high power or amateur
rocket, than does a multi-port geometry.
The disadvantage of the single port configuration however, is that it
generally requires long length to diameter ratios compared to a multi-port
configuration. The multi-port configuration can be made quite short and
compact, with length to diameter ratios of between 3-7.
In
general however, for high power or amateur rocketry, the single cylindrical
port geometry configuration is probably the best choice for most hybrid
propulsion applications.
INJECTION SYSTEM
There
are two methods of injection that can be used for injecting oxidiser into the
combustion chamber of a hybrid rocket motor:
- Direct injection into the fuel
grain port.
- Injection into a pre-combustion
chamber.
For
hybrid rocket motors on the high power and amateur rocketry level, where a
single circular port geometry is most frequently used, direct injection of the
oxidiser is the best approach, since there is no need to inject multiple
oxidiser streams down multiple ports, and hence less requirement for a
homogenised oxidiser stream from multiple injector nozzles.
Ingestion
system:
PRE COMBUSTION CHAMBER
Injection
into a pre-combustion chamber in a hybrid rocket motor is more useful for
larger hybrid motors, or hybrid motors where a multi-port geometry is used for
the fuel grain, since multiple injectors are more common, and even mixing of
the oxidiser stream needs to be achieved before it is passed over the fuel
grain.
POST COMBUSTION CHAMBER
Post combustion chambers are used in hybrid rocket
motors to enable more complete burning of the combustion products before the
combustion products are expelled through the nozzle throat on into the nozzle
and the exhaust. Post combustion chambers are less widely used than pre
combustion chambers since they can cause quite severe erosion of the combustion
chamber in the region of the post combustion chamber,and the benefit of using
the post combustion chamber can often be outweighed by the increased mass of
the insulation required to prevent burn through of the post combustion chamber.
IGNITION
There are a variety of methods of igniting Hybrid motors. On
larger hybrid rocket motors, a solid rocket motor pyro grain, or a complete
small solid rocket motor attached at the injector end of the hybrid rocket
motor combustion chamber are used to ignite the fuel and oxidiser.
On
smaller hybrid rocket motors where a plastic fill line is used to fill the
oxidiser tank, a variety of methods of ignition are used, pyrovalve/pyrograin
with the fill line running through a hole in the pyrograin, PIC wrapped around
the plastic fill line, and Gaseous Oxygen filling of the combustion chamber
combined with High Current electrical ignition. Where a metal fill line is run
into the oxidiser tank through the combustion chamber, Gaseous Oxygen high
voltage spark ignition can also be effected.
ADDITIONAL CHALLENGES NOTED
Non-Technical Challenges
•
Lack of technological maturity
•
Hard to compete against established solid and liquid technologies
•
Established propulsion industry is fine with the status quo
•
Smaller group of rocket professionals relative to solid and liquid rockets
Technical Challenges
•
Low regression rates for classical hybrid fuels
–
Results in complicated fuel grain design
•
Low frequency instabilities
–
Instabilities are common to all chemical rockets
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They need to be eliminated
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Expensive and long process
•
Lack of benign, high performance, cost effective oxidizers (common to all
chemical rockets)
EXPECTED CONTRIBUTION
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To help in
study of hybrid rocket.
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To implement
the hybrid rockets for future space mission purpose.
LIMITATIONS
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Take off
problems from normal roads.
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The width of
wings when the vehicle is on road mode.
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Types of
fuel used for thrust generation
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