FUEL INJECTION NOZZLE Question Ram Tubes

rv969wf · #1 12-19-2006, 05:58 PM

I've seen a few Experimental airplanes with ram tubes tied to the fuel injector nozzle bodys to help with atomization of the fuel at the nozzles that extend towards the cowl inlets and I'm curious what testing has been done with this.

(Atomization is common practice to inject the fuel into the combustor (or premixer) through a nozzle, which atomizes the fuel. That is, the continuous stream of fuel is broken up into a mist of tiny droplets. There are many types of nozzles, some of which rely on very high feed pressures to atomize the fuel, and some of which rely on assistance from steam and air to effect good atomization. Generally, the finer the spray produced by the nozzle the better the combustion process.

What I've seen is maybe only one or two injectors with these tubes that extend to the front of the cowl inlets and some of the other injectors are not done this way. I understand that at high altitude the injectors act quite differently and do not atomize the fuel as well at low altitude. Turbo charged engines have different injector nozzles for this reason so that they can receive pressurized air at the nozzle body to help with this.

Question: how many EXP have used turbo charged style injectors on normally aspirated engines with another source to pressure the body of injector to help with atomization at high altitude? I have some ideas on this but I'd like a little feedback. I'm thinking about fuel economy and a small horsepower increase at high altitude if the nozzles were pressurized on a normally aspirated engine. Thanks

Allen Barrett · #2 12-20-2006, 07:10 AM

Alan, Ron Bryce has turbo nozzles on his normally aspirated IO-550 N in his Lancair with the upper deck lines installed. He has them running to his throttle body. This is to do exactly as you say, to help atomize the fuel charge. I don't know what the volume of air is, but I'll try to find out how it helps and let you know

Allen

f1rocket · #3 12-20-2006, 12:18 PM

I, and several other F1 Rocket fliers, have them installed on the AFP system. However, they are not to improve performance, but rather they are an attempt to solve a problem with the engine running rough LOP. Fuel stains seem to indicate that at low fuel flows, fuel is backflowing down the injector line and out the vent at the injector fitting. The turbo nozzle rails are an attempt to increase the pressure above what's in the plenum to prevent this.

rv969wf · #4 12-20-2006, 12:40 PM

Quote:

Originally Posted by f1rocket

I, and several other F1 Rocket fliers, have them installed on the AFP system. However, they are not to improve performance, but rather they are an attempt to solve a problem with the engine running rough LOP. Fuel stains seem to indicate that at low fuel flows, fuel is backflowing down the injector line and out the vent at the injector fitting. The turbo nozzle rails are an attempt to increase the pressure above what's in the plenum to prevent this.

Hey thanks Randy for the info. Makes since to me. Something I saw on a few planes at Oshkosh kinda made be scratch my head because what I saw was maybe 3 out of 6 injectors done like this on the same engine/aircraft, is there a reason why someone would only run the nozzle rails on only a few injectors instead of all of them?

Another question: I guess what your saying is the pressure at the forward portion of the cowl inlet is higher than inside the plenum say towards the back cylinders? Just asking because I have not tested the pressures in various areas of the plenum, just at a couple of locations. Has anyone tested the nozzled rail pressure with a monometer to see what the pressure gain is if any? I've got some ideas on this for high alltitude flying and the LOP issue that you stated. Thanks for the help. AJ

Quote:

Alan, Ron Bryce has turbo nozzles on his normally aspirated IO-550 N in his Lancair with the upper deck lines installed. He has them running to his throttle body. This is to do exactly as you say, to help atomize the fuel charge. I don't know what the volume of air is, but I'll try to find out how it helps and let you know

Allen

Allen, Can you tell me where Ron Bryce is picking up his source from on the throttle body? AJ

Allen Barrett · #5 12-20-2006, 02:13 PM

Correction, Ron has alternate air, unfiltered that he uses. It's a y, that he has tapped a -6 'T' into and has hooked the upper deck lines into the 'T' on the unfiltered side. A cable actuated flapper is used on the alternate side and a magnetic flapper on the filtered side. So, he's only using filtered air while on the ground, thinking that the air is 'clean' upstairs. Well, it may very well be but that's another argument. It's not installed at the throttle plate as I mistakenly said earlier. My apologies. I havent been able to get ahold of Ron as he is one of those guys who always seems to be on vacation

but I'll keep trying. I'll also try and get some pictures to post... If I can figure out how to post them. #*@&#% computors!

Allen

f1rocket · #6 12-21-2006, 07:54 AM

Yep, we had one guy perform extensive testing including same day comparisons with the rails and without the rails. Someone did do some pressure checks but they are inconclusive for your purposes because we were trying to solve another problem.

I don't know if the pressure is higher where my nozzles are at or in the back of the plenum. Mark Fredericks runs his from the back of his plenum. I took the easy way out. I couldn't figure out a way to run the rails from the air intake without creating a situation where it took a 5-armed monkey to install the bottom cowl.

Overall, in the side-by-side comparison on the same airplane on the same day, the rails allowed for a leaner mixture at every altitude and resulted in the engine reaching peak EGT at a lower fuel flow. If I recall, at 7,000 MSL, the difference was 1.5 GPH, which is quite a bit. At the other altitudes, the differences were smaller.

aadamson · #7 12-21-2006, 08:07 PM

If you check the Bob Axiom post about "air filter" removal. I posted the links to the Lancair Ram air setup and the discussion about the turbo rails that *may* be needed.

On a Continental, there is no difference between the injectors of a NA or a Turbo engine (at least on the 550). However the injector takes ambient air from a little skirt on each. This air keeps the fuel from leaking while under injection. In a "forced induction" setup like ram air (the Legacy runs about 1-1.5" of additional ram air with the little "snorkle"). You *may* need the turbo rails. The rails take their air in the later case from a tap on the pressure side of the ram air. The do not connect to the TB.

But this is all explained in the links that I posted in the other thread.

In the Legacy, anything around or over 2" of MP from ram air will cause fuel to leak onto the heads without the turbo rail for the injectors. BTW, that little bugger is *expensive* and you need 2, hence the thread about building one from tubing, etc. (in the links I posted in the other message referenced above)

Hope this helps.

rv969wf · #8 12-22-2006, 07:37 AM

Quote:

The rails take their air in the later case from a tap on the pressure side of the ram air. The do not connect to the TB.

But this is all explained in the links that I posted in the other thread.

In the Legacy, anything around or over 2" of MP from ram air will cause fuel to leak onto the heads without the turbo rail for the injectors.
Hope this helps. Alan

[/quote]

Hi Alan, thanks for the info. One question about tapping into the pressure side of the ram air. Is this pressurized air filtered or unfiltered feeding to the fuel injector rails and if I read correctly your picking up the ram air on the inlet side of the air box on the side forward of the Servo / Throttle body?? The most MP increase I've seen on my -6 is around 1.2"-1.3"" depending on the day. I have noticed a small amount of fuel staining around the injectors but it's very small. I'll look at the post on the Bob Axsom thread and see if I can find your article. Any pictures???? Thanks a Million, AJ

aadamson · #9 12-22-2006, 09:46 AM

Alan,

It's unfiltered on the Ram side. See picture below

You have to be careful as the injectors will leak if they have less air than the ram air.

This is the rail that Cont sells, it's really expensive

So some of the guys have made thier own.

Repost of the thread that starts this all on the Legacy.

http://mail.lancaironline.net:81/lis...age/27403.html

Hope this helps.

rv969wf · #10 12-22-2006, 11:05 AM

[quote]

Quote:

Originally Posted by aadamson

Alan,
It's unfiltered on the Ram side.
You have to be careful as the injectors will leak if they have less air than the ram air.
So some of the guys have made thier own.
Hope this helps

Thanks for the Pictures A. Adamson, Really appreciate the info. I think I'm on the right track now. Cool looking intake / air cleaner system you have BTW. The reason I asked if the pressurized air feeding the fuel rails was filtered or not was concern about trash / dirt entering the O.D. of the injector nozzles. I'm not familiar with Continetal Injectors or if they have a screened filter, but the Lycoming Injectors can get plugged with dirty external air. The Lycoming normally aspirated injectors do have an external fine mesh screen on the O.D. of the injector to keep debris out but they aren't the greatest design. Thanks again for the info.