So why haven't pintle injector rockets taken over the world?

[rbroome]

@Stranger_On_A_Train

This engine is actually renown for its unparalleled combustion stability, the recent catastrophic failure of a -62 in ATP at Stennis (alleged to be an aging issue) notwithstanding.

A large amount of empirical testing is required for any rocket engine. The combustion conditions and environments that an engine is exposed to are just beyond our capability to effectively simulate without physical test data to tune and validate any model.

Stranger

I work out at Stennis, though not for NASA. One of my favorite stories from the early days of engine testing was the case of the disappearing engine. An O2 line ruptured in the middle of an engine test, I don’t know what engine but this happened during Apollo, spewing large amounts of pure O2 onto the red hot engine. Everything instantly oxidized and blasted out of the test cell as a fine powder. When the engineers looked in the cell, there was literally nothing left of the engine. It had completely disappeared leaving minor damage to the rest of the cell. Just poof. gone.

[Dr.Strangelove]

Ouch. An Antares rocket just failed on the Orb-3 mission:

Rocket Lab will try to catch falling booster with helicopter today: Watch live

This rocket uses two AJ26-62 on the first stage, which are somewhat modified versions of the NK-33 engines that SoaT mentioned previously.

Not clear yet precisely what went wrong, but it seems clear from the video that it’s some variant of “engine rich exhaust.” Even if the problem can’t be directly traced back to the Russians, it certainly can’t be good for the general attitude that we shouldn’t be depending on them for engines.

[augustinejose48]

Pintle injector with its face shut off feature can avoid the sequencing computer and the upstream valves for controlling the propellant flow rates. I have worked on few pintle injectors as a part of my Masters project.You can view more information about pintle injectors here: www.pintleinjector.blogspot.com

[Dr.Strangelove]

Neat! Just a suggestion–you may want to clean up your site a bit, as it appears a bit “spammy” at the moment. I don’t believe it is, but on first glance it is hard to tell the difference. I would move away from a blog-based platform as it doesn’t seem appropriate for this material.

I’m glad you brought up the “face shutoff” feature as it’s something that came up recently in an interview with Tom Mueller (lead designer of the SpaceX Merlin engines).

@Tom Mueller

And, uh, I’ve seen that hurt us before, I’ve seen that fail, but I’ve also seen— where nobody thought it would work— it was the right decision. It was the harder way to do it, but in the end, it was the right thing. One of the things that we did with the Merlin 1D was; he kept complaining— I talked earlier about how expensive the engine was. <inaudible> [I said,] “[the] only way is to get rid of all these valves. Because that’s what’s really driving the complexity and cost.” And how can you do that? And I said, “Well, on smaller engines, we’d go face-shutoff, but nobody’s done it on a really large engine. It’ll be really different.” And he said, “We need to do face-shutoff. Explain how that works?” So I drew it up, did some, you know, sketches, and said “here’s what we’d do,” and he said “That’s what we need to do.” And I advised him against it; I said it’s going to be too hard to do, and it’s not going to save that much. But he made the decision that we were going to do face-shutoff.

So we went and developed that engine; and it was hard. We blew up a lot of hardware. And we tried probably tried a hundred different combinations to make it work; but we made it work. I still have the original sketch I did; I think it was— what was it, Christmas 2011, when I did that sketch? And it’s changed quite a bit from that original sketch, but it was pretty scary for me, knowing how that hardware worked, but by going face-shutoff, we got rid of the main valves, we got rid of the sequencing computer; basically, you spin the pumps and pressure comes up, the pressure opens the main injector, lets the oxygen go first, and then the fuel comes in. So all you gotta time is the ignitor fluid. So if you have the ignitor fluid going, it’ll light, and it’s not going to hard start. That got rid of the problem we had where you have two valves; the oxygen valve and the fuel valve. The oxygen valve is very cold and very stiff; it doesn’t want to move. And it’s the one you want open first. If you relieve the fuel, it’s what’s called a hard start. In fact, we have an old saying that says, “<inaudible>[When you start a rocket engine, a thousand things could happen, and only one of those is good]”, and by having sequencing correctly, you can get rid of about 900 of those bad things, we made these engine very reliable, got rid of a lot of mass, and got rid of a lot of costs. And it was the right thing to do.

Interesting stuff that I hadn’t heard before. Basically, you control the flow in the pintle and eliminate a bunch of valves upstream of that point. Has a bunch of advantages, one of them being that if the valves are upstream, then some spare propellant is sitting in the pipes below that point. This unregulated propellant can cause control issues, hard starts (=boom), etc.