April 13th, 2009 13:24 EST
Rocket Fuel Piston Pump Hot Ticket To Space
Liquid fuel rockets are simple in concept. You light the propellants, which blast out one end and provide the thrust you need. In practice, however, liquid fuel engines are quite a bit more complex, and one of the keys to successful and safe space flight is how you get liquid oxygen and fuel into the engine. XCOR solves the problem with proprietary and highly unique piston pumps.
Most of the complications arise from getting the fuel to the rocket engine, " says XCOR`s chief engineer Dan DeLong. How you solve that problem determines how well your rocket propulsion system will work. "
The simplest systems use pressurized tanks to force the propellants into the engine, but these tanks have to be heavy and strong enough to withstand hundreds of pounds of pressure per square inch.
This weight can be prohibitive in a vehicle intended to fly to space, because even lightweight tanks account for 85-90 percent of the weight of a typical rocket-powered launcher. To enable engineers to use lightweight tanks, rocket propulsion systems use pumps instead of pressurization.
Knowing this, the XCOR team began developing proprietary pumps early in its program. Using internal funds, we started development of a super-cold cryogenic piston pump and filed IP claims on our work. Later we won a DARPA contract to further this initial development. We then extended the original design by developing a piston pump for fuels at room temperatures and demonstrated it successfully, further extending our IP portfolio. The developed fuel piston pump was later incorporated into the second generation rocket-powered test bed aircraft and successfully run hundreds of times and flown 40 times in flight without any noticeable wear or tear.
The test bed vehicle was powered by a 1,500 lbf thrust kerosene-liquid oxygen engine that had pump-fed kerosene and pressure-fed LOX. The use of a piston pump was a departure from usual rocket engineering. If not using pressure fed systems, most designs use turbine pumps (much different from piston pumps), but XCOR selected a piston pump because they are more flexible and can be scaled up or re-engineered to pump either cryogenic materials or typical fuels, such as kerosene, alcohol or methane.
XCOR will now use pumps to supply liquid oxygen as well as the kerosene to the Lynx`s four engines. As a result, the team has been working hard on an updated cryogenic piston pump based on our previous works. Mike Valant is the lead engineer on this project.
We are currently testing the cryogenic pump using liquid nitrogen instead of liquid oxygen, " he explains. The liquid nitrogen is actually a little colder than the liquid oxygen and has roughly the same fluid properties. Because liquid nitrogen is inert (you can use it as a fire extinguishing agent), we can do our tests much more conveniently. Using liquid nitrogen also allows us to build and to test pumps without having to make every single wetted pump component oxygen-compatible, so the tests and test articles are much more cost-effective. "
Liquid oxygen is not poisonous, but you have to be careful with it, because it makes it awfully easy to start a fire, " says XCOR`s safety officer Randall Clague. For example, if you spill LOX on asphalt, it can cause the asphalt to become highly reactive and potentially burst into flame. "
Valant has been supervising a series of tests of the new cryogenic piston pump to check its reliability, pumping capacity and speed. He says the results give him confidence that the pumps will have more than enough capacity and reliability to supply the Lynx rocket engines with all of the propellants they need to carry the two-seat craft to the edge of space.
These tests are providing us a lot of information, and teaching us what adjustments we need to make to improve pump performance, " Valant says. These pump tests may not be as exciting to watch as the engine hot fires, but they are just as important. "