Turbopumps pumping liquids?

[dharak1]

So I was thinking recently, a car turbo works by using exhaust gasses to drive an air intake helping the engine run faster. Would it be possible to use a regular car turbo for pumping liquids? My source of gas would probably be some regular compressed air running through where the exhaust would go and the liquid running through the area the air would come in. I remember hearing somewhere that turbos had very low torque so they couldn't pump liquids very well when they ran off of gasses. I know rockets use turbopumps to pump liquids but I'm not sure if those work like a car turbo. So I'm asking here if its viable to pump liquids through a car turbo using compressed air as the force to spin the turbo. The liquid wouldn't be very thick, just water.

[SomeGuy123]

You can build a machine that would have the same basic set of spinning blades connected by a common shaft that pumped liquids while using gas to drive the other set of blades.  This is probably what you mean.  The governing design constraints would be radically different - it depends on the gas temperature and pressure, the liquids properties, etc.  

So the engineer who designed it would totally change how the impeller was shaped on one side and how the gas turbine was designed on the other.  It would vaguely resemble a car turbo in the same way a jet engine vaguely resembles a car tubo - some comparable parts but basically a totally different machine.  

[mikegarrison]

Are you asking whether a turbine can pump liquid? Certainly. Many boats use the marine gas turbines, which are just aviation jet engine cores with big power turbines attached to them. Sometimes they power a generator that then drives an electric motor for the ship, but sometimes they mechanically drive the propeller shaft(s) through a gearbox.

[kunok]

The compressor of the car probably can pump liquids but the efficiency will be very bad

And you can't pump a liquid with is "heavy" fluid with the exhaust of an "light" fluid when both the compressor and the turbine are designed for similar caudal.

[Hannu2]

You can not use stock turbo to pump liquid. Liquid's density is hundreds of times larger and viscosity too. Pump would be very inefficient and would not work practically.

Water would give extra problems because corrosion. Materials of turbos can not stand water. It would go to bearings and whole turbo would fail.

[Kerbart]

On 2/14/2016 at 10:59 PM, dharak1 said:

So I was thinking recently, a car turbo works by using exhaust gasses to drive an air intake helping the engine run faster. Would it be possible to use a regular car turbo for pumping liquids? 

Can I use part x, designed for a specific task, to perform a different task that shares some words in the name of the task?

Let's take a look:

“I live in an apartment building. There's an elevator in the building. I know that there are elevators that can lift ships. Therefore, it should be possible to use the elevator in the building to bring a yacht to the top floor, no?”

I’ll leave it to the student to work out the problem here.

[K^2]

@Kerbart That's not entirely fair. The actual turbine stage on a car turbo is exactly what you want for a cheap turbo pump. Author might not have been aware of it, and then your comparison stands, but at least through dumb luck he wasn't that far off.

Compressor from a turbo charger, however, is completely the wrong type. It will not pump fluids. Still, the pump is the easy part. So if you want to build a small-ish rocket engine at home, starting with car turbo is a pretty good idea. What you want to do is take the car's turbo apart, separating the turbine from compressor. You can throw compressor away, but keep the common shaft. Then grab two centrifugal pumps, the kind that are typically used with electric motor to pump water out of wells. You want high RPM, low torque pumps, which electric driven ones typically are. Then connect both of these pumps to the common axle from the charger. Now you can feed gas from your pre-combustion stage into the turbine, and it will power the pumps. The output from the turbine goes into your main combustion chamber, and output from pumps should be split between pre-combustion chamber, main combustion chamber, and regenerative cooling piping as appropriate.

This wouldn't be exactly commercial grade rocket pump, and it'll be far more likely to fail under the real launch conditions. but on the flip side, it should be sufficiently powerful for either a heck of a hoby rocket or even a second stage of a small orbital rocket.

P.S. I should warn, though, that this is getting into seriously dangerous stuff territory. I don't expect OP to be able to build a complete rocket engine, but if you just get pre-combustion chamber going, or even simply feed the system from external pressure source for testing, this thing can pump ludicrous quantities of fuel and ox. I would strongly advise not trying a live test without a full engine built. What you can do reasonably safely is to test the concept by feeding water through both pumps and using something like a leaf blower to power the turbine.

P.P.S Ok, on closer inspection, I might have jumped the gun on that "second stage" thing. I'm not seeing a lot of commercial, easy to find centrifugal pumps that go above 0.5 MPa, and you need at least ten times that to have an efficient RP-1 engine. In fact, charts I've found don't even start until about 1MPa. But 0.5MPa isn't terribly bad for a hobby engine. Of course, at mixture ratios that involves, you're kind of building a giant turbo charged flamethrower...

Edited February 15, 2016 by K^2

[Hannu2]

Commercial water pumps use typically 3000 rpm electric motors (or 3600 rpm in countries with 60 Hz electrics). Typical car turbo works at about 100000 rpm. You should have a high speed gear. It does certainly not fit in hobby budget.

However, it is possible to use a turbo charger to make a simple gas turbine. You need burning chamber in which you feed air from compressor side of turbo and suitable fuel, for example gasoline or gaseous propane. Burned gases is used to run turbo. It is useless but gives fun, smoke and noise. Larger truck turbo is even better (as always when you play with fire, the larger the better). Google gives many hobby turbine projects.

[K^2]

6 minutes ago, Hannu2 said:

Typical car turbo works at about 100000 rpm.

Alrighty. That's about an order of magnitude higher than I thought it was. And apparently, they go even higher. So I stand corrected. Bad idea. Thank you.