RE: DIESEL FUELS, OILS, COMBUSTIBLES AND ADDITIVES  
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RE: DIESEL FUELS, OILS, COMBUSTIBLES AND ADDI... - 9/19/2007 6:46:02 PM   
slope-soarer


 

Posts: 226
Joined: 10/12/2004
From: Barrow in Furness, UNITED KINGDOM
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quote:

ORIGINAL: gkamysz

If you go as far as a cowl, you could probably add a throttle controlled louver to reduce air flow at lower settings. The engine quiting is temperature related. I saw the same thing in my engines without ether. For whatever reason the four stroke never quit though. Prolonged periods of idling would result in missing until temperature came back up. I did send it up a bit over compressed because it would otherwise miss as RPM climbed with airspeed.


Like you I also reckon it was due to the temperature. I kept the plane on the ground after the first two engine cutouts and ran the engine for a couple of minutes or more before launching.

Unfortunately, the engine was mainly running at full throttle during these periods. I was ensuring that the compression and needle were indeed optimum and couldn't be improved. I throttled down to idle and back up again without any problems. It was only when the engine had been idling, while flying, that it would cut out. There was no brrrppping as a warning, it just stopped. A cold and windy moor is not conducive to thinking things through, so I just increased the ether and flew until my hands were getting too cold !

I could only assume that the engine was cooling off sufficiently to cause the low ether fuel to not be able to work. I will look at keeping the engine from getting too cold when I get chance to try it. It's much better to work these things out when sat in a chair at home

Reg




(in reply to gkamysz)
       Post #: 176

RE: DIESEL FUELS, OILS, COMBUSTIBLES AND ADDI... - 9/19/2007 7:58:10 PM   
gkamysz


 

Posts: 1768
Joined: 6/24/2003
From: Crystal Lake, IL, USA
Status: offline 		One thing I noticed with my latest project the FS-91 is that the engine is very sensitive to temperature on the bench. I had it running on a low or no ether mix and it would tuned to run well for full throttle. By throttling like you did I was able to get full range with full response. After a short while of idling the engine would not pick up to full like it should. There was no change in idling while it cooled. I think this has to do with RPM and timing advance needed for combustion at higher RPM. The high speed was pretty lean so it wouldn't run unless up to peak operating temperature. It would run at about 80-90% throttle until things warmed up though. I haven't been able to measure head temperatures yet so I don't have any figures to compare. You may also try running a little on the rich side to see if anything improves. I noticed the carb I have on it now was very rich in mid-range.

_____________________________

Greg

(in reply to slope-soarer)
       Post #: 177

RE: DIESEL FUELS, OILS, COMBUSTIBLES AND ADDI... - 9/20/2007 6:51:03 PM   
slope-soarer


 

Posts: 226
Joined: 10/12/2004
From: Barrow in Furness, UNITED KINGDOM
Status: offline 		Thanks for the comments Greg,

This engine has run the same 10% ether mix on a cold day last autumn. It would idle very slowly for 4 minutes or more at a time and then respond perfectly as the throttle was shoved open by hand.

It was however in a test stand during 2 hours of testing on that day. Yes, 2 hours with only slight pauses for refuelling.... I had gone to a deserted spot away from people ! This was just one of a number of test sessions with fuel mixes using different lubricants with 15%, 10% and no ether at all.

I reckon the problem now stems from the far better cooling effect as the plane scoots about with the engine on a power pod above the fuselage..... no cowling or screening around the engine at all, it just hangs out there in the cold airstream. I have also just changed the prop from 4" to 6" pitch and the plane is scooting around quicker at lower revs...... more cold airflow !

This mix has run well both in a test stand and also flying during warmer weather. I guess I am going to have to look at a way of shielding the engine from a good deal of that cold airflow.

It looks like I will need to modify my power pods to include some cowling and, while at it, I might as well box in and streamline the servo and fuel tank . Just like the seaplanes that have the engine on a pod above the wing.

Reg


(in reply to gkamysz)
       Post #: 178

RE: DIESEL FUELS, OILS, COMBUSTIBLES AND ADDI... - 9/20/2007 7:23:58 PM   
pe reivers



Posts: 2991
Joined: 1/23/2002
From: Arcen, , NETHERLANDS
Status: offline 		That might indeed be a good idea. Still, it supports our first disagreement, on the use of so little ether. It has all the makings of a more critical setup. I found this too in my recent experiments, and almost a straight line (correlationwise) can be drawn from full ether setups, to the low ether contents that you experiment with.
Below a certain point, which I believe to be 25% ether, Ignition improvers are needed to get a decently throttling engine.
I am designing a double venturi setup this moment, alas without throttling capabilities, to find out the virtues of better fuel draw and better atomisations. My hopes are high, so let's hope my hope matches experience.

< Message edited by pe reivers -- 9/20/2007 7:24:55 PM >

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Pe, Dealer for MVVS, MTW and Mejzlik; www.mvvs.nl
There is sanctuary in analisys.

(in reply to slope-soarer)
       Post #: 179

RE: DIESEL FUELS, OILS, COMBUSTIBLES AND ADDI... - 9/20/2007 8:16:44 PM   
AndyW


 

Posts: 1919
Joined: 1/17/2003
From: Timmins, ON, CANADA
Status: offline 		The issue of throttling on no or low ether fuels was covered to a degree in the substitute for ether thread. Kerosene has a certain cetane rating and it's a bit too low for easy starts and smooth running due to the high compression needed. The solution is to raise the cetane rating by adding ether and ignition improver. It was found the adding more ignition improver wasn't a substitute for ether in this way.

Adding more IP did give you a reduced compression setting once the engine came up to temperature. In fact, the same as with using lots of ether. HOWEVER, raising the cetane rating by using a LOT of ether, as in 40%, allowed you to start the cold engine at the hot, running compression setting. Using just ignition improver meant that you had to increase the compression to get a start and then, as the engine warmed up, you could back off the compression. In both cases, the compression setting, at running temps, was the same.

How this applies to throttling is that with lots of ether, the compression setting is nearly the same for a hot AND cold engine. That's why the compression requirement doesn't change when you idle for prolonged periods in cold weather and the engine cools off well below the temperature of the engine at full throttle.

_____________________________

Andy Woitowicz

(in reply to pe reivers)
       Post #: 180

RE: DIESEL FUELS, OILS, COMBUSTIBLES AND ADDI... - 9/20/2007 8:20:18 PM   
AndyW


 

Posts: 1919
Joined: 1/17/2003
From: Timmins, ON, CANADA
Status: offline 		Question. What would happen if you took your well running, diesel engine and installed one of those heli type, heat sink heads? Would it run better, worse, idle better, worse, how would that alter the running compression, starting characteristics, etc.

What if the answer really isn't less cooling, but MORE cooling?

< Message edited by 1705493-AndyW -- 9/21/2007 5:23:54 PM >

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Andy Woitowicz

(in reply to AndyW)
       Post #: 181

RE: DIESEL FUELS, OILS, COMBUSTIBLES AND ADDI... - 9/21/2007 5:09:52 PM   
gkamysz


 

Posts: 1768
Joined: 6/24/2003
From: Crystal Lake, IL, USA
Status: offline 		Running the engine cold is the opposite of what we need to vaporize fuel. I know that in the four strokes on etherless fuel the temperature must be up to run well and lean. A cool engine must be rich in order to run and compression must be increased. Running rich with a lot of oil also increases compression ratio. When the engine is hot I have a virtually dry exhaust.

_____________________________

Greg

(in reply to AndyW)
       Post #: 182

RE: DIESEL FUELS, OILS, COMBUSTIBLES AND ADDI... - 9/21/2007 8:58:08 PM   
slope-soarer


 

Posts: 226
Joined: 10/12/2004
From: Barrow in Furness, UNITED KINGDOM
Status: offline
quote:

ORIGINAL: pe reivers

That might indeed be a good idea. Still, it supports our first disagreement, on the use of so little ether. It has all the makings of a more critical setup. I found this too in my recent experiments, and almost a straight line (correlationwise) can be drawn from full ether setups, to the low ether contents that you experiment with.
Below a certain point, which I believe to be 25% ether, Ignition improvers are needed to get a decently throttling engine.
I am designing a double venturi setup this moment, alas without throttling capabilities, to find out the virtues of better fuel draw and better atomisations. My hopes are high, so let's hope my hope matches experience.


Thanks for the comments Pe,
I agree there should be a straight line correlation between high to low ether content.
I do use ignition improver 2-ethylhexyl at 2% in the fuel mix.
I think what caught me out was the fact that I have run this mix on a very cold day, but in a test stand. The prop wash in the test stand is obviously not cooling the engine off anywhere near as much as when the engine is operating on the plane.
The engine started much as usual and throttles perfectly before launching, the engine was given time to heat up - a good minute or so as settings were finalised. Only after the initial full throttle run to gain altitude and then a minute or two after throttling back did the engine cut out.
It was evidently getting too cold for efficient vapourisation of the fuel , or the compression was altering due to the engine cooling.

It will be interesting to see how that double venturi works out.

Greg,
Your comments are spot on. The kerosene is supposed to be a difficult fuel to vapourise effectively. One of the benefits (to my way of thinking) about reducing the ether is increased engine temperature. That increased temperature should be beneficial to the fuel mix.
I find with low ether content that the needle must indeed be set a 1/4 to 1/2 turn rich until the engine starts and generates some heat. The compression usually needs backing off quite quickly after starting and later the needle can be leaned out to normal running position.

I think (and I may well be wrong) that the crankcase temperature is important with 2 strokes. If the crankcase cools because of the cold air flowing past it then the paraffin is not going to vapourise as well as if the crankcase is hotter.

I will enclose the engine and fuel tank and see if restricting the airflow during cold weather restores the good running of the 10% ether mix. If I still get problems then I can revert to the 15% ether mix which has always run well, starts easily and I had no problems with it when I had to use it the other day.

Andy,
Your comments are also spot on. I don't want to revert to high ether content if at all possible. I reckon that I can use 15% without much problem. I reckon that if I prevent too much cold air flowing past the engine then I should be able to use the 10% ether mix. Possibly I need a cowl for cold weather and just remove it for summer flying. As I mentioned in the other post the whole engine, fuel tank and servo are completely unshrouded and hanging out in the full airflow....
Brrrrrrrr !

Reg

(in reply to pe reivers)
       Post #: 183

RE: DIESEL FUELS, OILS, COMBUSTIBLES AND ADDI... - 9/21/2007 9:16:42 PM   
Motorboy



Posts: 1717
Joined: 2/7/2004
From: Bergen, NORWAY
Status: offline 		slope-soarer...

Here in the cold norway i live, are the diesel engine not difficult to run in winter. Too little ether are not enough to run the engine. Ether works as thinner for kerosene and will be easier to atomize in cold winter. I will keep between 33 and 36% ether in fuel for winter use. Smaller diesel engine under 1-1.5 cc are more difficult to run in winter.

Tried to increase than 10% ether???

_____________________________

Jens Eirik
All landings are just controlled crashes!

(in reply to slope-soarer)
       Post #: 184

RE: DIESEL FUELS, OILS, COMBUSTIBLES AND ADDI... - 9/22/2007 7:34:38 PM   
slope-soarer


 

Posts: 226
Joined: 10/12/2004
From: Barrow in Furness, UNITED KINGDOM
Status: offline 		Hi Jens,
I hope we don't get as cold as you do during the winter.... brrrrrrr.
I will try reducing some of the airflow past the engine as a trial and see if it makes a difference.

The engine, a PAW 2.49, was starting easily but stopping after a few minutes flying.

I used some 15% ether mix that I had with me and the engine ran well when I swapped to that.

It may be that I will have to settle for 15% ether content in colder weather. If we get as cold as Norway then I reckon I will have to use 30% + ether.... or move further south

Reg

(in reply to Motorboy)
       Post #: 185

RE: DIESEL FUELS, OILS, COMBUSTIBLES AND ADD... - 10/1/2007 6:09:05 PM   
slope-soarer


 

Posts: 226
Joined: 10/12/2004
From: Barrow in Furness, UNITED KINGDOM
Status: offline 		That's more like it !

Nice day for flying today. Never one to miss an opportunity off I went.

Since last using my 10% ether mix, and having trouble with it, I had exchanged emails with my "Guru" ! I had a couple of flights with 15% ether and they went well. Then it was time for lunch sprawled out in the heather and enjoying the fantastic views. Two RAF fighters passed some way away and about 400 feet below me. They were practising low flying.

Lunch over I filled the tank with 10% ether mix and started the PAW 2.49 up. Mindfull of my "Gurus" advice I set the engine up for peak performance with both compression and needle, this is exactly what I was doing when I had problems. I then richened the carb and backed off a bit more on the compression, this cost a few revs but what the heck if it works !

It certainly worked, 3 flights later I hadn't had any problems at all. Seems like I just needed to be less greedy with obtaining the most power possible and this has solved the problem. My 10% ether mix is back on course again

I had the chance to see a Focker DR1 with petrol engine and something like an Acro Watt with glow engine flying on Sunday. My diesels are far quieter than either of those a much softer sound that is difficult to hear at any distance.

Never saw a soul all day. There were a few buzzards about, I reckon I was the oldest one though !

Reg

(in reply to slope-soarer)
       Post #: 186

RE: DIESEL FUELS, OILS, COMBUSTIBLES AND ADD... - 11/11/2008 12:00:59 PM   
bogbeagle


 

Posts: 61
Joined: 4/21/2003
From: York, UNITED KINGDOM
Status: offline 		I wonder whether any of you guys have tried to run your diesel engines on glow fuel? I understand that it has a much higher auto-ignition temperature and will require more compression, but is it possible?

As has been said, in this thread, diesel fuel is hard to come by in the UK and costs about £36/gallon.

I'm tempted to experiment, but I thought that I'd seek others' experiences, rather than try to re-invent the wheel.

David Turner

(in reply to slope-soarer)
       Post #: 187

RE: DIESEL FUELS, OILS, COMBUSTIBLES AND ADD... - 11/11/2008 8:12:54 PM   
merugo


 

Posts: 289
Joined: 12/13/2006
From: rome, ITALY
Status: offline 		David, I tried running model diesel by substituting kero in ordinary diesel fuel with increasing percentage of alchool, indifferently methyl or ethyl. The test did not seem to be succesful since alcohol was spit out unburned and the engine required higher compression and ran erraticaly.
This does not put the last word on the topic, since the possibility remains for experimenting with strong ignition enhancers in high percentages, i.e.significantly more than 5%. Accompanying this with 10-20% of ether should be fruitful.
ugo

(in reply to bogbeagle)
       Post #: 188