120 FS Fuel Feed w/ Crankcase pressure  
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All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> RC Fuels >> 120 FS Fuel Feed w/ Crankcase pressure
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120 FS Fuel Feed w/ Crankcase pressure - 1/1/2003 9:51:51 AM   
N2AV8N


 

Posts: 6
Joined: 10/6/2002
From: Beijing, CHINA
Status: offline 		This post is about using the crankcase presure to presurize the fuel tank, with a different approach.

The engine will be run inverteted on a short coupled Bi-plane, hence I would prefer for the fuel tank to be close to the CG, (before the YS zelots jump on this and say "just get a YS and for get it", I want to say I enjoy experimenting and wanted to try this idea). I have several YS engines, including a new YS 110, but I would like to know if there is an option to putting 400 dollar engins on 300 dollar models, that only get flown 10 times per year?

The test engine is a new ASP 120 FS, which has a presure (breather) line that runs from the crankcase to the intake manifold. The purpose of this line is to allow the discharge of the crankcase oil, which is forced by crankcase pressure to lubricate the front bearings, to be induced into the intake system instead of just dumping it on the side of your airplane.

As the piston goes up and down, the crankcase pressure responds by being both positive and negative.

My experiment, (bench tests only at this point)

Step 1 was to put a "T" in the breather line with a "YS spring-loaded check-valve" allowing only the "peak" of the positive pulses to go to the fuel tank, and to be closed on the negative pulses.
So now we have "un-regulated" pressure in the tank.

Step 2 was to put anouther YS spring loaded check valve on the vent line of the tank, allowing the excess pressure (that pressure which is greater than what is necessary to overcome the spring tension in the check valve) to escape in to the muffler tap.
So now we have constant tank pressure regulated by 2 forces.

The result... At low rpm settings, the tank pressure is maintained equal to the pressure required to overcome the spring tension of the check valve. At high rpm, the pressure is balanced / regulated by the pressure of the exhst tap.

On the bench, I have this set up with 24 inchs of fuel line so I can test the effects of raising and lowering the tank. Tank position seems to have no effect on engine running at any throttle setting.

Of course the needle settings had to be adjusted to the new fuel pressure settings, The low speed needle became very sensitive, but i managed to find a seting which works pretty good. The High speed dialed right in, and I picked up about 200 rpm on the top end. An additional benifit was a very steady rpm at any throttle setting.

The next step is to set this up on the bench with the engine inverted and see how it performs.
I am already a little concerend how the fuel system will work when the plane goes inverted, at that point the tank pressure will be pushing fuel toward the muffler instead of air, but it will depend on the spring tension vs the muffler pressure as to which way the line will be flowing.

A side comment about this engine. In general it seems to be a very reasonable engine. A YS it is not, but at 1/3 the price it is a viable consideration. It started on the second flip, achieved a steady peak rpm setting in about 45 minutes of break in time.

An interesting note on prop perfomance, I did the break-in with a 16x6 wood prop (national brand). Towards the end of break-in period, I was only getting 8200 rpm, at that point I was disapointed with the power of this engine. I then switched to the prop I intend to fly with, a APC 16x7, and the rpm went up to 8400, and a big increase in thrust. With the fuel presurization I an getting 8600 to 8700 rpm with the APC 16x7, on 15% Cool power, OS F plug, OST 40 deg.

If anybody has any comments or suggestions about this set-up I would be glad to hear them.

It would be interesting to know how much pressure is required to over come the spring in the YS check valve. Has any body already tested this?
       Post #: 1

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All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> RC Fuels >> 120 FS Fuel Feed w/ Crankcase pressure
Page: [1]





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