M500 build log

[metiz]

The frame is done, I'll take some pictures later. Next up are the pumps. I'll be using a Karcher cip (12 bar at 5.5L/min) and a Karcher 695 (130 bar at 7.5L/min) The pump on the left is the 695. On the left pump there are 2 knobs. they were both pretty seized up so I couldn't rotate either of them when I tested the pumps. Now that they're clear of their housing, the knobs are loose and rotate freely. One knob has 0-5 on it and the other on at the top (markings are on the housing)has "- +". Doesn anyone know what these controll? I can't find a manual anywhere of course.




The engine will consume an estimate of 10 liters of fuel a minute so neither one of these pumps alone will do. Prefably I'd like to hook them up together so I can controll fuel flow with a fuel return valve. Both of these pumps pruduce way more pressure than I need: does anyone have a suggestion on how I might manage this? If I use bernoulli's equations to increase fuel speed, that would get rid of the excess pressure. If I get both pumps to 8 bars of pressure, could I hook them up like that (paralel for greater debit)?

Any suggestions are welcome!

[racket]

If these pumps are like most pumps, the pressure generated is influenced by a "restriction" downstream , without that restriction they'll simply pump fluid without any pressure.

I'd imagine the pumps will have some sort of inbuilt over pressure relief/bypass valve set to the level required by the downstream restriction to produce the required "discharge" pressure ..........your 12 or 130 bar

Your fuel injection flow area will determine the pressure generated ................a simply "dump" valve sending fuel back to the fuel tank, will regulate the flow............exactly the same as we have when using automotive EFI pumps , they run at rated rpm with max flow , the "pressure" is varied by how much flow is dumped back to the fuel tank , with less being dumped the pressure increases so as to pass more fuel through the fuel injector into the engine .............simple :-)

Cheers
John

[metiz]

Hey John,

So that means I can just hook 'em up together to get the right debit and controll the pressure with a simple bypass without blowing the smaller one up? that's awesome. Makes things a lot easier

[racket]

Yeh , I'd imagine thats how it'd work , as long as your peak fuel injection pressure was below the smaller pumps 12 bar , things will/should be OK .

Those "knobs" might be for "degreaser" addition to the water flow , if they have smallish diameter clear plastic tubing , its for a "cleaning agent" .

Cheers
John

[racket]

I just had another thought , ...........try the high pressure 695 pump on its own first , you might find it will supply your required fuel flow when delivering at a pressure lower than 130 bar, most pumps have considerably more flow at lower pressures .

Cheers
John

[metiz]

Definitely worth a shot. Both pumps combined will draw 3.5kW, not easy to manage on site. That said, I still want the possibility to swith on the 2nd pump if the first one doesn't suffice. Thanks for your imput, John!

[racket]

Hi Metiz

You probably only need a maximum of ~500 psi - 30 bar to get more than acceptable atomisation of the fuel , if you checkout this graph .............. www.engineeringtoolbox.com/hydraulic-pumps-horsepower-d_1464.html
You'll notice that it'd require less than 1 hp - 750W to pump 10 litres/min to 500 psi ............you'd be able to drive a small hydraulic type fuel pump with a reasonable sized DC motor to have a "mobile" unit .

My turboprop PJ used an automotive EFI pump to feed the petrol to the spray nozzle, an 18 gph semisolid spray patterned nozzle with an 80 degree spray angle, with 80-90 psi fuel pressure.

Cheers
John

[metiz]

Hey John,

My injectors require 0.8mPa to get up to 3.3l/min each. When testing with water, that gave me a fine mist. The oil I'll be usig has a higher viscosity so I might need a bit more pressure, but not 30 bar.
If I knew how hard it would be to find injectors and pumps I would've chosen a lot less pressure so I could use those EFI pumps...Oh well.

The big pump will pull 2.3kW at full capacity. It would be very usefull if that was closer to 0.75

[metiz]

Build a fueltank. 12 liter capacity.




Both pumps have 22 and 26mm outside diamater thread. Can I asume that those are 1/2" and 3/4" NPT?

[metiz]

I just finished the fueling system, minus a few details. All that's left now is an air supply and a realy beefy ignitor with a nice hot spark. I'm open to suggestions on both accounts!
(the threads are BSP btw, if anyone was curious )

[metiz]

Just bought an Echo pb-2100 leafblower to supply air for staring the engine. It'll come in the mail by friday

[racket]

You must be getting close to firing her up in that case :-)

[metiz]

Mar 5, 2014 16:22:23 GMT -5 racket said:

You must be getting close to firing her up in that case :-)

Indeed!

Do you have a suggestion for a beefy ignitor, prefably running of off 12V?

[racket]

I use to fire my turboprop PJ up using a small electric 12 V motor (2,500 rpm) which had a homemade cam mounted on its shaft , the cam opened up a set of points and I used a standard auto coil/condenser to produce the spark .................I use the same setup for all my turbine engines that are mounted on the test stand .

Sparkfun produce an interesting unit www.sparkfun.com/products/11218 , these do work and they're cheap to buy .

Cheers
John

[wolfdragon]

on the super cheap:

Any bottle style ignition coil (preferably with a ballast resistor), a condenser (read: capacitor to calm the spark down on the contactor/points end), and an old fashioned 2 prong turn signal indicator aka flasher module as the points.

+12 on one side of the flasher, the other flasher lead goes to the the low voltage side of the coil
the ballast resistor and condenser go from ground to the low voltage side of the coil

Basically, you are using the natural on/off/on frequency of the flasher as the set of points, makes slow but sufficient spark.

added bonus!!! along with the normal dink..dink..dink.. form the flasher, you get a loud crack from the spark in the combustor section



Edit: the resistor is in series with the +12V to the coil not parallel, it is a current limiter