Jeff Bezos Explains How Blue Origin Will Prevent Its Rocket Engine From Melting

Look BE-4 you leap

BE-4 test fire
A test fire of the BE-4, Blue Origin's next generation rocket engine.Blue Origin

For all that rocket science gets a reputation for being complicated, it all boils down to some simple concepts. You burn stuff, and spew the resulting gases out a nozzle. Those gases coming out at high speeds push the rocket in the opposite direction.

Of course, it does get more complicated than that. The BE-4, a rocket engine that Blue Origin is developing, uses a preburner to set up that big combustion reaction that generates all those flames and propulsive gases. Basically what the preburner does is it burns a small amount of fuel, and uses the steam from that to drive some pumps that move the fuel—methane and oxygen—into the combustion chamber.

The problem is, that preburner reaction can get hot. Very hot. Like 3,000 degrees Fahrenheit, which is hot enough to melt a lot of rocket parts. In an email to a mailing list, Blue Origin and Amazon.com founder Jeff Bezos explained how Blue Origins works around that. It involves a lot of computer modeling.

Basically, the company has to cool down the steam coming from the pre-burner to about 700 degrees Fahrenheit, otherwise it might melt the turbines that power the pumps that dump fuel into the combustion chamber. To cool it, they mix unburned oxygen gas into the steam. And to make sure the oxygen mixes in thoroughly and there aren't any hotspots, they use a fancy computer modeling system.

Model of the BE-4 turbine

Model of the BE-4 turbine

From Bezos' email: Modeling of the BE-4 preburner shows temperature distribution of hot gaseous oxygen entering the turbine.Jeff Bezos/Blue Origin

From Bezos' email:

To design the preburner to provide uniform temperature, we use 3-D Computational Fluid Dynamics (CFD) to model the LNG and liquid oxygen combustion process. CFD predicts fluid behavior by solving the Navier-Stokes equations to describe how the velocity, pressure, temperature, and density of a moving fluid relate. CFD of reacting flows, especially those that also involve a phase change, is much, much harder because it must also solve chemistry along with state equations. Combusting CFD has only become practical with recent advances in chemical physics models and computing power.

And so far, so good, says Bezos. The computer modeling will hopefully cut down on physical testing, saving money and time as the company develops the next-generation rocket engine, which will be used to power the future rockets of both Blue Origin and the industry giant United Launch Alliance.

To date, we’ve completed several million core hours of CFD modeling of BE-4 combustion processes. Modeling of the preburner shows good mixing and temperature uniformity upstream of the turbine. The combustion and temperature data we’ve gathered in our subscale testing correlate with our CFD predictions and show that our preburner sizing and injector element design meet design requirements. The ability to do combusting CFD simulations doesn’t eliminate the need for rigorous testing, but it will significantly shorten the test-fail-fix loop on the test stand. We’ll keep you updated.

The company is hoping to fire up the rocket in stationary tests later this year.