Tom Mueller interview 02 May 2017

[LouScheffer]

In the interview, Tom Mueller said:

by going face-shutoff, we got rid of the main valves

Makes sense, but then why does the launch sequence still talk about pre-chilling the engines?  If there are no main values, then I'd think that as soon as they loaded the tank, the fuel/LOX would flow down through the engine until it encountered the shutoff at the injector face.  So the engine would already be chilled, just sitting there.

I bet they don't want any of their LOX boiling into gas as it "just sits there" in the lines.

I agree they don't want this.  But how do they prevent it?  If there are no main valves, won't LOX just flow into the engine, whether they want it or not?

There have to be valves on the inlets to the turbine or they'd never be able to shut off or throttle the engine. LOX sitting in the engine doesn't necessarily cool the turbine and the turbopumps.

I'd think that in the absence of valves, the turbopumps would be full of LOX and cold kerosene.  And I don't think you would want to pre-cool the turbine, which is hot in operation.

[IainMcClatchie]

So it sounds like there are two LOX valves, in parallel.  One is at the injector face -- so now the injector has actuators in the back, as well as both LOX and kerosene manifolds.  The other is the throttle/shutoff valve in front of the gas generator's burner.

That means the turbopump is full of LOX.  One end of this shaft is at 70K for at least 30 minutes and maybe much longer while the vehicle fills with propellant and does it's countdown.  Is there any chance the GG turbine isn't also going to be near LOX temperatures?  If you don't want that, you'd have to have heaters on it.

This LOX is going to be boiling during prelaunch.  All those bubbles are going up.  If the LOX plumbing has any high spots, there's going to be a big gas bubble in those spots.  As anyone who's turned on a faucet after partially draining and then repressurizing their house plumbing knows, when that gas bubble gets to the injector face the mass flow rate is going to rapidly vary by way over an order of manitude.  Sounds like a hard start to me.

This line of thinking brings to mind the Raptor design, which IIRC has a LOX path which is essentially a straight vertical shot, through the engine gimbal, through pump, preburner, turbine, and then into the main combustion chamber, all stacked in a vertical line.  I can imagine that LOX bubbles forming at, say, the injector face, would travel straight up through each of those parts and into the propellant tank.  Seems like it would leads to less bubble volume and less mass flow variation during starts.  Nice.

[Gliderflyer]

This LOX is going to be boiling during prelaunch.  All those bubbles are going up.  If the LOX plumbing has any high spots, there's going to be a big gas bubble in those spots.  As anyone who's turned on a faucet after partially draining and then repressurizing their house plumbing knows, when that gas bubble gets to the injector face the mass flow rate is going to rapidly vary by way over an order of manitude.  Sounds like a hard start to me.

Usually there is a "chill valve" near the main valves (or pintle in this case) that dumps a small amount of LOX overboard. This causes a steady flow of LOX through the plumbing that chills everything down to the proper temperature and eliminates large gas pockets. You can sometimes see the LOX venting from the chill valves in the webcasts (example image attached).

[Chris_Pi]

If I recall correctly there's sometimes a surprisingly largish fireball blown out of the flame trench at start-up that's probably caused by a large pool of cold GOX accumulating from the chill venting. Don't remember which launches/hotfires it was, But somebody did notice it a couple of times.

[Zed_Noir]

If I recall correctly there's sometimes a surprisingly largish fireball blown out of the flame trench at start-up that's probably caused by a large pool of cold GOX accumulating from the chill venting. Don't remember which launches/hotfires it was, But somebody did notice it a couple of times.

Maybe you could reduce the startup fireball effect by spraying liquid nitrogen into the flame trench just before Falcon 9 ignition.

[HVM]

If I recall correctly there's sometimes a surprisingly largish fireball blown out of the flame trench at start-up that's probably caused by a large pool of cold GOX accumulating from the chill venting. Don't remember which launches/hotfires it was, But somebody did notice it a couple of times.

Maybe you could reduce the startup fireball effect by spraying liquid nitrogen into the flame trench just before Falcon 9 ignition.

Or maybe you can spray burnt hydrogen there (you can think it as liquid ash), it can also suppress the sound waves!!! Two flies in one swat! How nobody have think that before.

(sorry Zed I had to...)

[QuantumG]

Someone transcribed it https://zlsadesign.com/post/tom-mueller-interview-2017-05-02-transcription/