[AR] Re: Amateur biprop - pressure fed vs automotive pump fed

Ben Brockert <wikkit@xxxxxxxxx> · Thu, 27 Feb 2014 17:40:32 -0700

The address says this came from the old ARocket list, which is weird.
You'll want to resub to arocket@xxxxxxxxxxxxx.

That pump does not appear large enough for your flowrate. "At that
same 80 PSI the equivalent HP (high pressure) fuel pump will flow over
210 liters (50 gallons) per hour."

That's 0.058 l/s. If your chamber is 150psi then your feed is
something like 190 psi, which is 95 psi per pump. At 95 psi the flow
rate will probably be lower than the 0.047 l/s you need to hit your
massflow.

In-tank pumps are cooled by being submerged in fuel. Outside a tank
they might run long enough for an engine test, or you might burn them
out. They also burn out really quickly if you run them dry, since the
bearings are usually cooled by the fluid they are pumping. You would
have to be very careful to never run the tank empty.

It would be an interesting experiment. I don't expect that it will be
cheaper than blowdown. Electric pumps have been used in rockets, but
it's still a new area.

You're going to be using a hell of a lot more gox bottles than
nitrogen, the cost of nitrogen bottles is not a significant part of
the cost of this project.

Regarding your three concerns, find out what happens when you deadhead
a fuel pump and be careful not to do it if it's bad.

Ben

On Fri, Feb 14, 2014 at 9:51 PM, Edward John Mercieca
<ejmer1@xxxxxxxxxxxxxxxxxx> wrote:
> Hi all,
>
> Long time arocket lurker, posting for the first time, so I hope I'm doing
> this right. Friend and I are building a methanol / gox engine (first bi
> prop). We're both strapped for cash so we're constantly looking for ways to
> decrease the expenses.
>
> We've got this idea to use two automotive methanol pumps in series instead
> of using nitrogen pressurant gas, as it comes out cheaper since we'd be
> refilling the N2 bottle quite a few times, and we wouldn't need a regulator
> between the N2 and methanol. These are the pumps we're considering:
>
> http://www.ebay.com.au/itm/Genuine-Walbro-GSS342-255LPH-In-Tank-High-Pressure-Fuel-Pump-Installation-Kit-/281042853650?pt=AU_Car_Parts_Accessories&hash=item416f759f12
>
> For oxygen, we're using the typical blow down method. We've got relatively
> low pressures in the lines, and that's why we've been able to find pumps
> that fit properly at a low cost.
>
> So our questions are:
> 1. Does anybody know if this is a good idea / Has anyone ever built amateur
> rocket engines with automotive pumps?
> 2. Will the pumps cause any issues which we do not foresee?
>
> Personally, I don't believe this could work due to two reasons:
>
> 1. The pump only cares about pumping fluid at a certain flowrate and a
> certain exit pressure, so if fuel line pressure fluctuates due to the
> varying chamber pressure, it may cause sporadic flow, which could turn the
> engine off, or have other consequences. I'm not 100% sure if using a
> regulator would reduce the amount of pressure fluctuations in the fuel line,
> but I believe this is the case.
>
> 2. Starting the engine may cause issues, since the pump and the mass flow
> valve will need to be switched on at exactly the same time, or there would
> be massive pressure differences in the fuel line compared to the design
> condition. Or we could just leave the fuel valve constantly open and just
> switch on the pump?
>
> 3. Likewise, shutting off the fuel line could be an issue. If the pump is
> shut down first, a large amount of fuel still exists in the fuel line. If
> the valve is shut off first the fluid pressure between the pump exit and the
> valve will probably cause a rupture in the line.
>
> That said, I'd like to hear any opinions as all of you are way more
> experienced than us. For reference, our fuel flow rate is 0.0374 kg/s and
> our chamber pressure should be around 150 psi or slightly under.
>
>
>
> _______________________________________________
> aRocket@xxxxxxxxxxxxxx
> http://exrocketry.net/mailman/listinfo/arocket
>

[AR] Re: Amateur biprop - pressure fed vs automotive pump fed

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