30-05-2012, 12:13 PM
PISTONLESS DUAL CHAMBER ROCKET FUEL PUMP
PISTONLESS DUAL CHAMBER ROCKET FUEL PUMP.pdf (Size: 490.49 KB / Downloads: 119)
Introduction
With the advent of low cost ablative liquid
fueled rocket engines and composite tanks, the
problem of propellant pressurization becomes the
last stumbling block to affordable launchers.
Turbopumps are currently used in the majority of
launch vehicles, although piston pumps have
been designed and flown1 and pneumatic
diaphragm pumps have been proposed by
Godwin2and Sobey.3 The pump considered
herein is much simpler and less expensive than a
turbopump. The pump concept is simple: instead
of having the whole fuel tank pressurized to 2-7
MPa, the main tank is at pressurized to 100-400
kPa and it is drained into a pump chamber, and
then the pump chamber is pressurized to deliver
fuel to the engine.
Basic Pump Design
The basic pump design is shown in Figure 1. In
this design, two pumping chambers are used,
each one being alternately refilled and
pressurized. The pump is powered by pressurized
gas which acts directly on the fluid. The pump is
designed so that the time required to vent, refill
and pressurize one pumping chamber is less than
the time to dispense a given quantity of fuel from
the other.
Pump design Considerations
Although the pump design is simple, the
optimization process is not. Making the pump
cycle as fast as possible would make it
lightweight, but higher flow velocities cause
problems. A pump with a small chamber must be
filled and vented quickly, with minimal head loss
through the gas and liquid valves and plumbing.
The maximum inflow rate is limited by the main
tank pressure (usually about 300 kPa) and the
area of the inlet valves. Also, if the inflow
velocity is too high, the propellant will be
aerated, which may cause problems with the
engine. The ullage volume in the pump chamber
should be small to minimize gas usage, but if it
is too small, there will be a loss of propellant
through the vent. Furthermore, the pump cycle
frequency must not excite any combustion
instabilities in the rocket motor.
Pump Weight
One of the most important benefits of this pump
is the low weight for a given propulsion system.
The weight may be calculated by determining the
weight of the pump chambers and the valves. For
valves or chambers, the weight is found to be
proportional to the flow rate and the pressure.
The weight of the chambers can be easily figured
as spherical or cylindrical pressure vessels. The
weight of the fluid and pneumatic valves may be
estimated based on the weight of commercially
available check valves and actuated butterfly
valves.
Pressure Fed Weight Savings
Pressure fed systems include the weight of a high
pressure tank, whereas the pump fed system
includes the weight of a low pressure tank and
the pump. Assume both systems use a similar
high pressure gas supply.