Planing for next years speed weekend, (1/2 scale Argus)

Moderator: Mike Everman

Post Reply
Rocket Man
Posts: 144
Joined: Sat Sep 26, 2009 9:59 pm
Antipspambot question: 125

Re: Planing for next years speed weekend, (1/2 scale Argus)

Post by Rocket Man » Fri Apr 22, 2011 11:58 pm

You are right about the German V1 using acetylene to get it started but they had a short tail pipe and that made it very hard to start.

A removable extension exhaust pipe could be made for the engine to get it started then once the engine starts the extension can be pulled off.

The German V1 had 3 air injectors for starting the engine. I will have to go back and read the German research data again I seem to recall they used about 120 psi but I do not recall the information saying anything about air volume, CFM.

With an engine that large you need a lot of air volume to get started.

I have noticed with my larger engines not enough air is just as bad as too much air. Once you get it right it starts easy. The longer exhaust pipe allows me to start my engines at 20% throttle they start extremely easy at low throttle.

I know what your saying about cold fuel not wanting to burn. When I fly my model airplane in the winter I keep the fuel in the house so it is 74 degrees F. I put the fuel container in a styrofoam ice chest to keep it warm in 20 degree F weather at the flying field. The engines start easy with warm fuel but they won't even try to start on cold fuel.

Just to prove a point about the combustion chamber needing to be a certain size build yourself several jar jar jets. Only difference is each one is about 1" longer than the other. Build about 6 jam jars jets and test each one. You will see the short jam jar jet tries to pulse very fast if it is too short it will not run. The long jam jar jet tries to pulse slow if it is too long it will not run. Find some larger diameter jars double the diameter of the first experement. Do the same test make 6 jar jar jets each one longer than the other. When you find the one that runs best compair it to the one that ran best is the first test. You will find the combustion chamber diameter to length ratio is the same in both tests if you are using the same fuel.

racketmotorman
Posts: 503
Joined: Sat Jul 23, 2005 11:11 pm
Antipspambot question: 0
Location: Australia

Re: Planing for next years speed weekend, (1/2 scale Argus)

Post by racketmotorman » Sat Apr 23, 2011 3:56 am

Hi

One of the things I suggest earlier to Linus was to install the start air "inside" the engine as the Argus had , rather than using the current external setup , the internal airjets would have helped with vapourisation of the fuel spray as well as sending it further into the combustion chamber for a "bigger bang" to get things cycling .

Yeh , gotta have lotsa air for starting , even with my relatively small turbine engines I've found my starter leafblower is running out of breath before the engine reaches idling speed http://www.youtube.com/watch?v=8Y8jpaDTkEY , I've had to invest in an "industrial sized" blower with a 4hp motor on it .

Getting a new engine fired up for the first time is always frustrating , thankfully a PJ doesn't get expensive if you stuff up those first few start attempts unlike a turbine engine which can be wrecked within seconds .

Cheers
John

PyroJoe
Posts: 1743
Joined: Wed Aug 29, 2007 5:44 pm
Antipspambot question: 125
Location: Texas

Re: Planing for next years speed weekend, (1/2 scale Argus)

Post by PyroJoe » Fri Apr 29, 2011 3:13 pm

One thing that may help is to apply a extension sleeve to the tail to bring the total tailpipe length to 2566mm. This should allow the engine to self pump and prime until the starting parameters can be better adjusted, and allow the main duct to heat.

After started and warm the tailpipe extension could be removed with caution. This somewhat echos Rocket Mans suggestion of a tailpipe 2860mm in length. IMO some compromises in the Argus were made in the duct length to create a shorter engine.
(Try to avoid high throttle with the extension applied, as it may crush a portion of the tailpipe)

Resonant volumes tend to not do so well if the low pressure swing is backfilled inside the resonator volume. This is a little tough to explain. IMO I would keep the starting air supply some where outside the resonator volume(CC).

From what I can tell it looks like Rocket Man is building around volumetric expansion. This works great for starting an engine, Reynst used a piston in the bottom of his combustor to allow that type of expansion to easily start resonating combustion. After the combustor was running he would run the piston up to decrease the volume. Why I ask would he do that?

When a fuel air mixture burns it increases the temperaure of the gas. This leaves basically two paths for the gas to react, one path is to expand in volume, the other to create pressure.

I think it is good to have a little of both paths in the engines, some volumetric expansion to allow them to start, but after they start and the CC fill ratio increases, there is a need to disallow the volume increase and build pressure. This is part of the basis for the Midway engine, but I may have slightly overshot into the pressure side.

LinusN
Posts: 13
Joined: Wed Mar 16, 2011 8:28 pm
Antipspambot question: 125

Re: Planing for next years speed weekend, (1/2 scale Argus)

Post by LinusN » Mon Aug 22, 2011 8:21 am

Que?
Green Durant wrote:accost accompany alluring plan. I just do not accept how you put the injector
use alone 1 injector?
I about did not address me actuality because the accent is complicated and not consistently construe some humans accept me

Viv
Posts: 2158
Joined: Sat Oct 04, 2003 2:35 pm
Antipspambot question: 125
Location: Normandy, France, Wales, Europe
Contact:

Re: Planing for next years speed weekend, (1/2 scale Argus)

Post by Viv » Mon Aug 22, 2011 3:54 pm

Its just a link spambot Linus, ignore it Mike will delete it when he gets time

Viv
"Sometimes the lies you tell are less frightening than the loneliness you might feel if you stopped telling them" Brock Clarke

Viv's blog

Monsieur le commentaire

MANOLO
Posts: 149
Joined: Mon Jan 24, 2005 3:19 am
Antipspambot question: 125
Location: CARLET (VALENCIA )SPAIN
Contact:

Re: Planing for next years speed weekend, (1/2 scale Argus)

Post by MANOLO » Mon Nov 21, 2011 2:52 am

erik for starting???????? video 1/2 argus????
Image

PyroJoe
Posts: 1743
Joined: Wed Aug 29, 2007 5:44 pm
Antipspambot question: 125
Location: Texas

Re: Planing for next years speed weekend, (1/2 scale Argus)

Post by PyroJoe » Tue Feb 14, 2012 2:27 pm

Looks like its getting closer:
http://svarthaletracing.se/

Under extreme cold the fuel appears to not be reaching a vapor point acceptable to allow mixing with air. Even if the (petrol I assume?) fuel were heated to warm temperature, the air would probably re- condense the vapor back to liquid droplets. A reported temperature was -32 degrees.

One of the few fuels that has a boiling point lower than -32 degrees is liquid propane (-42 degrees). The one problem is that at those very low temperatures the propane vapor rate may be so low that it will not generate enough pressure (6 to 7 psi - 0.5 bar) to promote a high quantity of flow to the injectors. If the liquid propane were maintained at reasonable warm temperature it may provide enough pressure to feed the injectors. Another solution may be to use the existing pumps to pump the liquid propane to the injectors. Although I haven't found any information on pumping liquid propane using mechanical pumps.

If one petrol tank could be exchanged for propane a dual fuel system could be utilized. Maybe with enough propane vapor the petrol droplets could be heated to the point that they are turned to vapor. The diffusor (after the valve grid) could also be removed to allow the heat of the CC to reach the petrol droplets sooner in the cycle.

Its amazing these engines will even run in the extreme cold with petrol, I should have caught that earlier.

Propane vapor pressure chart from
http://www.engineeringtoolbox.com/propa ... _1020.html
Attachments
propvapor.JPG
CLICK TO ENLARGE

LinusN
Posts: 13
Joined: Wed Mar 16, 2011 8:28 pm
Antipspambot question: 125

Re: Planing for next years speed weekend, (1/2 scale Argus)

Post by LinusN » Tue Feb 14, 2012 3:50 pm

Hi Pyro,

Actually, the temperature was a lot higher at the time of the test run. We had -32 Celcius (actually down to -35) the weekend before that, when we did a test run of the generator and the starting fan, but only -3 when we ran the motor.

It's a pity the automatic translations by Google are quite bad.
To summarize the last test run a bit:
What we had done was to decrease the "bend angle" of the valves, so they actually are a bit open rather than completely closed (with some tension). We also had modified the fuel system so we can run 4 injectors (the center row) and 8 injectors (the outer rows) separately. We can also adjust the flow of the center/outer row/rows independently.
We also now have a big fan to start the engine, instead of compressed air.

To major changes/improvements were noticed:
1. Last year the engine started in maybe 1 try out of 30. Now it starts every time.
2. It runs much better. Not good, but better.

The fan really is great! The compressed air tank was emptied in a couple of seconds, and then we had to wait for minutes for the compressor to refill it. Also, it was very hard to control the flow with enough accuracy. The fan makes this a lot easier. We also have the benefit of being able to ventilate and cool the engine between test runs.

As you can see, the motor still runs bad, but if we compare to last year it's a great improvement. We actually tried to open the valves even more, but this did of course made them harder to close. We really believe thinner valves will work a lot better, and have already ordered a new set of 0.1" valves. The plan is to do a new test run with the new valves the upcoming weekend.

PyroJoe
Posts: 1743
Joined: Wed Aug 29, 2007 5:44 pm
Antipspambot question: 125
Location: Texas

Re: Planing for next years speed weekend, (1/2 scale Argus)

Post by PyroJoe » Tue Feb 14, 2012 8:48 pm

Its good to hear the improvements are working. Good work and effort from the team.
My apologies this translates badly through Google.

I think vapor pressure is important, I offer this example:

-Place 1 liter of petrol in open bucket and measure time it takes for the bucket to vapor until empty.

-Place 1 liter of liquid propane in a bucket and measure the time it takes for the bucket to vapor until empty.

Even with various cold temperatures the propane will vapor and mix with the air much more quickly.

Now think of a bucket filled with 1/2 liter petrol, and 1/2 liter liquid propane. Its a mix of the energy density of petrol, with the low temperature vapor pressure of propane.

kevin lee
Posts: 100
Joined: Mon Dec 05, 2011 3:54 pm
Antipspambot question: 125

Re: Planing for next years speed weekend, (1/2 scale Argus)

Post by kevin lee » Tue Feb 14, 2012 10:04 pm

joe i think he was referring to the swedish not translating very well for us english lanquage folks :)

its awesome to hear some stuff about this engine 8)

LinusN
Posts: 13
Joined: Wed Mar 16, 2011 8:28 pm
Antipspambot question: 125

Re: Planing for next years speed weekend, (1/2 scale Argus)

Post by LinusN » Tue Feb 14, 2012 10:23 pm

kevin lee wrote:joe i think he was referring to the swedish not translating very well for us english lanquage folks :)
Correct! I have checked the Swedish to English translations made by Google myself, and they are pretty hilarious. Not that my English is perfect, but I really believe I'd make a better job myself. Maybe we'll summarize the entire project in English later on. I believe we have gathered some experience that would be of interest/use for others.

JimN
Posts: 15
Joined: Sun Feb 13, 2011 9:00 pm
Antipspambot question: 125
Location: Sweden
Contact:

Re: Planing for next years speed weekend, (1/2 scale Argus)

Post by JimN » Fri Feb 24, 2012 11:14 pm

:evil: :evil: :evil: :evil: :evil: :evil: :evil: :evil:
Take a look at this clip on Youtube: http://www.youtube.com/watch?feature=pl ... Ml4go72Y_8
For now the subtitles are in Swedish but i think you will enjoy this one anyway . We will post an english version later on.

PyroJoe
Posts: 1743
Joined: Wed Aug 29, 2007 5:44 pm
Antipspambot question: 125
Location: Texas

Re: Planing for next years speed weekend, (1/2 scale Argus)

Post by PyroJoe » Mon Feb 27, 2012 4:20 pm

Wow, much better! Is that meter reading 125.4 indicating frequency? How is the tail holding up, any signs it is trying to collapse yet?

metiz
Posts: 1523
Joined: Fri Apr 21, 2006 6:34 pm
Antipspambot question: 125
Location: Netherlands

Re: Planing for next years speed weekend, (1/2 scale Argus)

Post by metiz » Mon Feb 27, 2012 4:51 pm

PyroJoe wrote: any signs it is trying to collapse yet?
Good point. At the 2 minute mark you can realy see the tailpipe flexing up and down. It might be a good idea to weld a ring or two around it to prevent collapse or metal fatigue, causing the pipe to tear.
Quantify the world.

LinusN
Posts: 13
Joined: Wed Mar 16, 2011 8:28 pm
Antipspambot question: 125

Re: Planing for next years speed weekend, (1/2 scale Argus)

Post by LinusN » Mon Feb 27, 2012 7:37 pm

PyroJoe wrote:Wow, much better! Is that meter reading 125.4 indicating frequency? How is the tail holding up, any signs it is trying to collapse yet?
Yes, it runs really well now. And feels incredibly powerful.
No, the meter reads 125.4 dbA at about 2-3 meters from the front of the engine. Not sure how accurate that is though. A cheap Ebay model.

Post Reply