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Why is it so?

Old 08-14-2011, 09:26 PM
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Recycled Flyer
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Default Why is it so?

I have read and believed in the power of model diesels but what bothers me is that both methanol and kerosene has an energy rating of 48 foot/pound per inch and further the fuel/air ratio of diesel is 15:1 whereas glow fuel is 7:1.
The leaner and drier mix in diesel means that you will need to factor in more oil to get the same percentage of lubrication for the engine for any given period of time - kero only has about the equivalence of a 2% castor oil/methanol mix for lubricity so will not make up that much of the difference.
And any added ether, it could be up to 33% of the total fuels volume, further reduces the total power available due to its even lower calorific value.

So for any given rpm a glow engine is using burning twice the amount of fuel so should be a heck of a lot more powerful ............. and yet it is not always the case.

What am Imissing here since any engines power is given as how much fuel it can burn in a set period of time and a glow wins that race hands down.

I have taken the rose coloured glasses off for this one!
Old 08-14-2011, 10:01 PM
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steve111
 
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Default RE: Why is it so?

Combustion efficiency?

I was just out flying a diesel MP Jet 061BB, and that thing absolutely howled on a 7x3. Subjectively, it's more than a match for a Norvel BigMig 061 glow.
Old 08-14-2011, 10:06 PM
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Default RE: Why is it so?

The diesel fuel is more "fatty" than glow plug engine fuel due the kerosene is not "dry" as methanol. Some time we can replace kerosene with autodiesel in case the kerosene is not available there we live.., alternative fuel: Lamp oil, white spirit, autodiesel.

The castor oil can replace with motoroil, better high viscosity to example 15w-50. The oil will not burn away in the oil since the engine is running colder than glow plug engine.

The diesel fuel has more energy than glow plug engine and the model diesel engine will run longer than glow plug engine in same size and tank volume.
Old 08-14-2011, 10:45 PM
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Default RE: Why is it so?

ORIGINAL: Recycled Flyer

I have read and believed in the power of model diesels but what bothers me is that both methanol and kerosene has an energy rating of 48 foot/pound per inch ...

Chris where on earth did you come up with this "energy rating"?

Ray

Edited to correct spelling of "where".
Old 08-14-2011, 11:51 PM
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Default RE: Why is it so?

foot pounds per inch? This is meaningless drivel in terms of fuel energy! The energy rating of fuel components is expressed as a calorific value-and determined in a calorimeter. The units may vary-calories, joules, kilocalories, BTU (British Thermal Units) [and there are relationships between all these units-allowing interconversion] but will be expressed as 'x' energy units per unit mass of the fuel. There are some conventions which vary from fuel to fuel-gas fr example is often given as BTU/gram or kjoules/100gm

Quoting directly from Ron Moulton's 'Model Aero Engine Encyclopaedia' p119, gives paraffin as 11,000 calories-more than twice that of methanol at 5,330 calories (and FWIW nitromethane at 5,370 - nitro is about as good a fuel as methanol....but that's another story!)

In fact it ISN'T about how much fuel it can burn in a set time-but how much energy is liberated from the fuel per unit time.

ChrisM
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Old 08-15-2011, 03:36 AM
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Default RE: Why is it so?

Kerosene is actually a pretty good lubricant in its own right. It is also an excellent penetrating oil too, which you might have noticed when you try to wash it off your hands. Thus you do not need to add extra oil to the fuel when you are mixing it up for your engine.
So besides the oil added to the fuel the kerosene also lubricates the engine, especially the lower end.

Old 08-15-2011, 04:14 AM
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Default RE: Why is it so?


ORIGINAL: earlwb

Kerosene is actually a pretty good lubricant in its own right. It is also an excellent penetrating oil too, which you might have noticed when you try to wash it off your hands. Thus you do not need to add extra oil to the fuel when you are mixing it up for your engine.
So besides the oil added to the fuel the kerosene also lubricates the engine, especially the lower end.


On what basis do you suggest that kero is a lubricant suitable for replacing some of the oil in the mixture?

This goes against every fuel mixing doctrine I've heard or read of or used in fifty five years of owning and running diesels.

Ray
Old 08-15-2011, 04:19 AM
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Default RE: Why is it so?

EARL, One factor is being overlooked here even after BTUs per unit of fuel etc, burn rate Oil %, combustion, or what ever factor
you want to call it and easily seen if you run the engine at night no muffler on glow you will see flame comming
out the exhaust thus is an incomplete burn fuel wasted in the power stroke, lost energy that is wasted, in a diesel there is
none. all the fuel combustion has pushed down the piston its over when at piston at bottom of stroke, thus better
effiency for the volume of fuel used hence less needed and increased power as the result martin
Also/ sure we have all done it contact with a muffler on a glow engine a burn quite likely not so on diesel, that heat
is energy loss was not converted to useful work
Old 08-15-2011, 05:18 AM
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Default RE: Why is it so?

ORIGINAL: locktite401
ORIGINAL: earlwb
Kerosene is actually a pretty good lubricant in its own right. It is also an excellent penetrating oil too, which you might have noticed when you try to wash it off your hands. Thus you do not need to add extra oil to the fuel when you are mixing it up for your engine.
So besides the oil added to the fuel the kerosene also lubricates the engine, especially the lower end.

On what basis do you suggest that kero is a lubricant suitable for replacing some of the oil in the mixture?

This goes against every fuel mixing doctrine I've heard or read of or used in fifty five years of owning and running diesels.

Ray
A reference here is one reason http://en.wikipedia.org/wiki/Kerosene
It can be used in conjunction with cutting oil as a thread cutting and reaming lubricant. When machining aluminium and its alloys, kerosene on its own is an excellent cutting lubricant.
It used to be a old practice for lubricating clocks many years ago: http://mb.nawcc.org/showthread.php?t=21235
It is used to clean and lube a bicycle chain too: http://www.nordicgroup.us/chain/
Another mention of it here http://www.ehow.com/list_8077455_lub...-kerosene.html
Some one wrote a book about it, but I haven't bought or read the book though http://www.ebay.com.au/itm/Lubricant...-/140558070554
Some discussion of it here too http://flashoffroad.com/Diesel/Diese...iesel_fuel.htm

Obviously it doesn't work well to lubricate the top end as it burns, but for the bottom end it works.


Old 08-15-2011, 05:56 AM
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Default RE: Why is it so?

Earl and Locktite Is you look at fuel formulas (castor) the old paw is the 30/30/30 bit- MVVVS ranges from 10% parrafin oil 10% castor mix for racing this could lower engine life?? do not think so still 20% oil they show
but they upped the kero to 47%, on this one for racing I would say 20% castor is safe 15%?? you must have some coming out the pipe this assures

plenty of lube htey show 3% IGN improver Amyl nitrate in all except break in formula ether 49-Kero 32 castor 26

MVVS also shows a 25 castor 25 ether 47 castor ans 3% ignition improver for racing too in all this was in the MVVS 09D instructions
Using the Davis stuff 1/2A and ABC mixes have had no issues

I am not sure what the syn/castor % would be martin

a point this is a classic MVVS iron piston the newer ones ABC AAC would most likely be fine on 15% oil














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Old 08-15-2011, 07:25 AM
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Default RE: Why is it so?

Recycled, I know where your data came from. You must be specific about the figures you quote because nobody else seems to understand what you're getting at. http://modelenginenews.org/cornell/p7.html The data in the fuels chart is normalized to engine displacement. If we have an engine design that is equally compromised from each fuel's ideal requirements we would see similar output. Because each fuel has such different characteristics, ideals can be very different, favoring one or the other. We see plenty of examples of diesel converted glow engines making more power than stock. Chances of seeing an F2A diesel are nought. One of these days I'll track down a Q500 or F3D engine and put a diesel head on it. That's an expensive experiment for now though. I'm not going any deeper than this so as not to stray from the intent of this forum. If you look at the chart at the bottom of the page, and dig deep in the data you'll find glow engines that consume less fuel per unit power than some diesels!

As far as kerosene lubricating anything, forget it. It only works as a lubricant for extremely lightly loaded parts, or where the bearings are flooded of pressure fed with relatively small loads. The link about the chain talks about kerosene for cleaning and oil for lubrication. The clock link talks about kerosene being a bad practice. In fact, not one of those links has anything positive to say about kerosene as a lubricant. I'll say that kerosene or a close relative is excellent for cutting aluminum, but I'm sure there are water based lubes that are just as good at the job and better for the environment.

There was a time when engines where very expensive. Extra oil while messy, kept the engine alive for a long time. Today engines are cheap. The typical argument is that if you can save enough money on oil costs, you can replace the engine and still be ahead.
Old 08-15-2011, 10:19 AM
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Default RE: Why is it so?

I ran a K&B 4011 on Sig Champion 10% nitro, 20% oil, half synthetic, half castor. Tuned like I would for a control line stunt airplane, it turned an APC 11 x 5 at 9,700 RPM. Switched to Eric Clutton Old English diesel fuel. Kept the glow plug lit for maybe 20 seconds until it didn't run undercompressed when I took the battery off. Turned the ST NVA in 1 1/2 turns. Sounds nice, and turns the APC 11 x 5 at 9,700 RPM.

Our two cycle engines are air pumps and how much horsepower they generate depends on how much air (and proper fuel mixture )they pump.

I think it is true that diesels turn big props more happily than a similar glow engine, but have not done that experiment as such.
Old 08-15-2011, 12:54 PM
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Default RE: Why is it so?

On the week end I ran in a NIB (well, it was ) OS 40 FP. Prop used was a taipan composite 10x6.

I ran it on 10% Klotz syn, 10% castor, 80% methanol. Top RPM 11,500 steady. 2 1/2 turns out on main needle

I then put on a Mecoa/RJL diesel conversion head. 25% castor, 33% ether, balance kerosene with 1% EHN. Top RPM 12,000 steady. 2 1/8 turns out on main needle.

This engine runs stronger on a sports PB diesel mix, and I am sure, much more economically on fuel consumption.

I did this to prove to myself and a club sceptic that on plain fuels (ie no nitro methane in the glow mix) the engine would perform better on diesel.

Starting was so easy either way, just a few flicks.

I don't know why this is the result. Maybe someone can come up with a definitive answer.
Old 08-15-2011, 02:14 PM
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Default RE: Why is it so?


ORIGINAL: locktite401

ORIGINAL: Recycled Flyer

I have read and believed in the power of model diesels but what bothers me is that both methanol and kerosene has an energy rating of 48 foot/pound per inch ...

Chris where on earth did you come up with this "energy rating"?

Ray

Edited to correct spelling of "where".
Here Ray -

http://modelenginenews.org/

Under Model engine development. towards the back of that article in part 7.
And a direct quote "In model engine size although the base fuel energy of Methanol and Paraffin when mixed at the correct air to fuel ratio is similar (48 ft lb per cubic inch)."

The rapid burn bit by Steve I understand well enough and accept.

Thanks.
Old 08-15-2011, 02:55 PM
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Default RE: Why is it so?


ORIGINAL: gkamysz

Recycled, I know where your data came from. You must be specific about the figures you quote because nobody else seems to understand what you're getting at. http://modelenginenews.org/cornell/p7.html The data in the fuels chart is normalized to engine displacement. If we have an engine design that is equally compromised from each fuel's ideal requirements we would see similar output. Because each fuel has such different characteristics, ideals can be very different, favoring one or the other. We see plenty of examples of diesel converted glow engines making more power than stock. Chances of seeing an F2A diesel are nought. One of these days I'll track down a Q500 or F3D engine and put a diesel head on it. That's an expensive experiment for now though. I'm not going any deeper than this so as not to stray from the intent of this forum. If you look at the chart at the bottom of the page, and dig deep in the data you'll find glow engines that consume less fuel per unit power than some diesels!

As far as kerosene lubricating anything, forget it. It only works as a lubricant for extremely lightly loaded parts, or where the bearings are flooded of pressure fed with relatively small loads. The link about the chain talks about kerosene for cleaning and oil for lubrication. The clock link talks about kerosene being a bad practice. In fact, not one of those links has anything positive to say about kerosene as a lubricant. I'll say that kerosene or a close relative is excellent for cutting aluminum, but I'm sure there are water based lubes that are just as good at the job and better for the environment.

There was a time when engines where very expensive. Extra oil while messy, kept the engine alive for a long time. Today engines are cheap. The typical argument is that if you can save enough money on oil costs, you can replace the engine and still be ahead.
Ok, Greg.
Specific to a given engine displacement - I will go back and reread that data with that in mind mate.

Thanks for the explanation.

Old 08-15-2011, 05:13 PM
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Default RE: Why is it so?

..."when mixed at the correct air to fuel ratio is similar (48 ft lb per cubic inch)."


Sounds reasonable to me (torque per unit of swept volume)..and the critical thing is they say "when mixed at the correct air to fuel ratio"...which means that the diesel mix will be leaner, using less liquid fuel from the tank. No worries!
Old 08-21-2011, 12:57 AM
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Default RE: Why is it so?


ORIGINAL: Jim Thomerson

I ran a K&B 4011 on Sig Champion 10% nitro, 20% oil, half synthetic, half castor. Tuned like I would for a control line stunt airplane, it turned an APC 11 x 5 at 9,700 RPM. Switched to Eric Clutton Old English diesel fuel. Kept the glow plug lit for maybe 20 seconds until it didn't run undercompressed when I took the battery off. Turned the ST NVA in 1 1/2 turns. Sounds nice, and turns the APC 11 x 5 at 9,700 RPM.

Our two cycle engines are air pumps and how much horsepower they generate depends on how much air (and proper fuel mixture )they pump.

I think it is true that diesels turn big props more happily than a similar glow engine, but have not done that experiment as such.
I'd heard this is mainly because you can vary the compression on a diesel. This allows you to use a wide range of props within reason - if the prop's too big for the compression ratio, it will lead to pre-ignition, but with a diesel you can back off the compression as needed. Only true for a contrapiston-equipped model diesel, of course. You could also run larger props on a glow by adding head shims, I suppose. Power may not be optimal, though.

Iskandar

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