Enlightenment

I've been taken to task several times here for my reference to our compression ignition engines as diesels. I had read in the past a definition that backed my assertion but had forgotten where it was. In a bit of research at work today I came across it in the SAE Handbook. If that's not a trustworhty enough source, you'l have to find a better one to refute this.

1992 SAE Handbook; 3:25.32 (volume 3, section 25, page 32)
paragraph 2.2 Definitions:
line 2.2.1 Diesel Engine-Any compression ignition engine.

I know you purists out there will still argue timed fuel injection to facilitate the Diesel cycle, but the definition encompasses simple compression ignition as also recognised as a Diesel engine.


Nyaaa Nyaa!!!!


Randy Ryan <><
AMA 8500
SAM 36
BO all my own M'

I still like Col. Taplins's term, "detonation engines", which is not quite correct.

Hey Randy,
What do a bunch of Automotive Engineers know about engines anyway!!!????
I'm with Jim....I like the term "detonation engine"

Randy C

Hi Randy. I will back you 1000%. I am a retired Diesel Tech and taught the subject for over 6 years. I was also a Master Truck Technician.

The Diesel principal is iginiton via compression of the air/fuel mixture. Fuel injection has absolutely nothing to do with it. In fact the early Diesels used no injection, but a crude intake system, not unlike our toy airplane engines and in the early experiments used coal dust. They are engines by the by, not motors, as they create the engergy needed to run, not "import" it as do electric, compresssed gas (CO2) or hydraulic motors.

They are also at times, but rarely, refered to as semi Diesels. What evfer that means. FWI [photo not recovered: sipcof.gif]

Thanks, Randy - both'a'ya...

But then, does that make glow engines diesels as well? Platinum catalyzed methanol heating, plus compression heating to ignition temperature?

Only timed-spark engines might be said to have the ignition point determined externally, and not by compression conditions...

I thought those glow engines smelled funny...

>Thanks, Randy - both'a'ya...

>Only timed-spark engines might be said to have the ignition
>point determined externally, and not by compression
>conditions...
>


Hmmmmm......
Unless of course they're pre-igniting due to too much compression...or heat as some do after the ignition is shut off.
"Dieseling".....

Randy C

There's not much point in arguing whether a model "diesel" really is what we say it is. Glo engines are also semi-compression ignition, but with the help of a hot glo plug.

My diesel tractor has glo plugs, which I almost always use for easier starting. So is my Allis-Chalmers a "glo tractor"?

Floyd

Floyd,

Of course this is a silly-season opportunity...

Shall we also discuss engines vs motors? A classic definition of 'engine' is that it develops the energy it converts to work, while a 'motor' requires energy, developed somewhere else, to convert into work.

Examples: an electric motor needs a source of electric power; a steam locomotive has steam motors (the wheel cylinders), which use steam generated in the boiler. ...but, then, the boiler is usually part of the locomotive... ???

General usage can be vague and sometimes "inaccurate," depending on the standard of accuracy we apply. If we have clear understanding of the essential intent of the discussion, we can let the pedants go off into their corners and argue among themselves.

>Thanks, Randy - both'a'ya...
>
>But then, does that make glow engines diesels as well?
>Platinum catalyzed methanol heating, plus compression heating
>to ignition temperature?
>
>Only timed-spark engines might be said to have the ignition
>point determined externally, and not by compression
>conditions...
>
>I thought those glow engines smelled funny...

Glow ignition engines do fall under the compression ignition catagory, but rather then ether as an ignition improver, the glow element first supplies heat for starting, then stores heat for running ignition.

Randy Ryan <><
AMA 8500
SAM 36
BO all my own M's

According to my dictonary a motor is (1)anything that produces or imparts motion, (2) an engine; esp., an internal-combustion engine for propelling a vehicle.

An engine is any machine that uses energy to develop mechanical power; exp., a machine for starting motion in some other machine. (Such as an electric engine in a stunt airplane, for example?)

Motorboat, motorcycles, motorhome, motorbike, motorscooter, motorcar, stunt motor, etc.

Hmmm! My detractors are silent.


Randy Ryan <><
AMA 8500
SAM 36
BO all my own M's

Glow engines fall into a kind of grey area because they require compression but also a heat source (like a spark ignition engine). Unlike a diesel engine which relies on compression to give adiabatic heating to drive the temperature up to the ignition point of the fuel, a glow engine requires compression to pack methanol molecules more closely around the heat source (glow plug) to begin the catalytic reaction so long as the coil has enough heat from an earlier reaction or from a battery. The ignition timing is controlled by an inverse relationship between the compression and the heat. Raise one and lower the other to keep the ideal ignition point. Theoretically you could raise the compression to the point of autoignition but it'd probably be around 50:1 . Conversely, with too low a compression to get a catalytic reaction a spark could be used to supply enough heat.

With a model diesel where all the air/fuel mixture undergoes adiabatic heating (as in a full sized diesel) it's theoretically possible for the entire mixture to reach the autoignition point all at once and then it could be said to detonate (a detonation engine) but, in practise, contact between the mixture and surrounding walls (piston crown, liner, combustion chamber) will give localised cooling so only one smaller volume will reach its autoignition point first. It's likely this small volume moves around a little depending on turbulence so there'd be no fixed point as in a spark or glow ignition but still quite localised.

This isn't a detraction, it's an addtraction (have I just invented a new word? ).

The Webster's dictionary definition of Diesel Engine is :-

diesel engine

Main Entry:
diesel engine
Function:
noun
Date:
1894

: an internal combustion engine in which air is compressed to a temperature sufficiently high to ignite fuel injected into the cylinder where the combustion and expansion actuate a piston

In comparison, the Oxford English Dictionary has this to say :-

The Oxford Pocket Dictionary of Current English | Date: 2008

die·sel / ˈdēzəl; -səl/ • n. (also diesel engine) an internal combustion engine in which heat produced by the compression of air in the cylinder is used to ignite the fuel: (example) a diesel locomotive.
• a heavy petroleum fraction used as fuel in diesel engines: (example) eleven liters of diesel.

By these definitions, I'd say our model diesels are indeed based on the on the defining principle of a diesel engine, being "pure" compression ignition by adiabatic heating. In comparison, glows run at compression ratios where adiabatic heating is insufficient to auto-ignite the fuel/air mixture and thus require an ignition source (catalytic reaction with hot glow-plug element).

In any case, I'm going to continue calling my PAWs and MARZes diesels regardless of what anyone else tells me, because its much more convenient than talking about my PAW Compression Ignition Engine. PAW seems to agree, as the D in DS stood for DIESEL. (DS = Diesel Squish).

cheers,
Colin

It should also be added that no diesel even now, actually operates in the Diesel cycle, now refered to as the "ideal" diesel cycle. The ideal cycle required that the fuel be injected at a rate that holds the cylinder pressure constant throughout the power stroke and that has never been accomnplished.


Randy Ryan <><
AMA 8500
SAM 36
BO all my own M's

I think Downunder is correct that the burn in one of our diesels is not universal and uniform. However I think it is much more so than in a glow engine where the burn starts at the glowplug and proceeds out the exhaust. The burn in a diesel must be long over by the time the exhaust port opens, because diesel exhaust is expanding and cooling gas. I routinely stick my finger in diesel exhaust long enough to accumulate oil and see what color the exhaust is. Doing the same with a glow engine would give a badly burned finger.

So the power pulse in a diesel must be much sharper than in a glow engine. I think this is why there can be problems with broken cranks, thrown prop blades, etc. with a diesel more than with a similar glow. I don't think it is necessarily due to the higher compression of the diesel because I have run a glow plug engine (K&B 4011) on model diesel fuel and it run just fine. It is a matter of keeping the glow plug lit for maybe 20 seconds as they warm up. Glow engines with lower compression ratios will run undercompressed, ie, intermittent missing. Relight the glow plug and they quit missing.

>I think Downunder is correct that the burn in one of our
>diesels is not universal and uniform. However I think it is
>much more so than in a glow engine where the burn starts at
>the glowplug and proceeds out the exhaust. The burn in a
>diesel must be long over by the time the exhaust port opens,
>because diesel exhaust is expanding and cooling gas. I
>routinely stick my finger in diesel exhaust long enough to
>accumulate oil and see what color the exhaust is. Doing the
>same with a glow engine would give a badly burned finger.
>
>So the power pulse in a diesel must be much sharper than in a
>glow engine. I think this is why there can be problems with
>broken cranks, thrown prop blades, etc. with a diesel more
>than with a similar glow. I don't think it is necessarily due
>to the higher compression of the diesel because I have run a
>glow plug engine (K&B 4011) on model diesel fuel and it
>run just fine. It is a matter of keeping the glow plug lit
>for maybe 20 seconds as they warm up. Glow engines with lower
>compression ratios will run undercompressed, ie, intermittent
>missing. Relight the glow plug and they quit missing.


Ron B.
F4Fguy

Thank you! You've just explained why the model "diesel" is not a Diesel but an Otto cycle!

Ron B.

Just a thought...

One of the key items in Colin's quote from the dictionary is the injection of fuel into adiabatically heated air in the cylinder...

Randy R's and Ty's simpler definition is no less valid because industrial and vehicle diesel engines went to timed fuel injection somewhere back in the 19-teens or -twenties.

A series of SAE combustion tests, many years ago, studied the speed of flame-front travel in an ideal combustion chamber. I had a copy of part of those tests, once. Oddly, they were able to 'time' the speed of flame travel for gasolines and kerosenes in ideal combustion conditions, but declared the flame travel speed of methanol (and possibly ethanol) too fast to estimate.

No relevance, since those were idealized tests.

We don't burn our fuel in isolated (e.g., methanol/air only) conditions, nor at the most perfect fuel/air ratios. We use a fuzzy, confused blend of vaporized fuel, partially vaporized (still in droplet form) fuel, a bunch of oil ( - I hope in droplet, not vapor, form -) and other things like nitro, or an ignition improver for ""diesels"".

And NOT at the most perfect fuel/air conditions...

Glow fuels usually have near twice as much methanol as there is ether in diesel fuels. Methanol and ether both absorb heat changing to vapor, so the glow engine enjoys greater cooling from that than the diesel. Kerosene probably doesn't vaporize much, if at all, yet absorbs some heat from its surroundings. So does the oil. All that heat absorption reduces the efficiency of compression heating.

Methanol will also burn well in a wider range of fuel/air proportions than either gasoline or kerosene, so we can run glows far richer, and get more cooling that way. Methanol can yield about half the heat as kerosene or gasoline, per unit, but we can use quite a bit more than twice as much methanol and get loads of power that way. Kerosene and gasoline are fussier, so we can't run comparably rich - and they don't cool the engine as well. This may answer why sparkers and diesels are much more economical than glows.

Jim, I DO think the higher pumping loads are involved in converted engine breakages. I know you've run K&B 4011s on diesel fuel. I've run a glow 25 on 3:1 gasoline/oil. Needed a compression tweak, like one of your 4011s, and needed the plug continuously heated. With higher compression, it might have got the plug hot enough to sustain running without the battery. Didn't mess with it. The engine got wa-ay hotter than when running on glow fuel...

I'm also of the opinion that diesels run generally cooler than even glows, but since the ether is the only chilling-on-vaporization fuel component, the whole engine soaks a bit warmer than glows. The chilling below the choke on a running glow engine helps cool more... Diesels can mislead about net final temperature, since the kerosene does 'fume' - steam-like vapors - slightly at end temperatures.

The 'damped' combustion (oil, kerosene, whatever; partial vaporization, etc.) burn rate is an interesting problem.

-- Slower burning gasoline, still going gangbusters when the exhaust opens, may explain why they are so much louder than glows.
-- The excess (rich) settings we use with glows may mean there's still methanol burning, making the noise as exhaust opens.
-- Kerosene, also, supposedly slower burning (SAE), but burned at a fuel/air ratio closer to ideal, may provide more of a sustained push over most of the power stroke before the exhast opens - diesels are quieter than sparkers or glows.

That fits with the ability of diesels to produce greater torque at the same RPM than glows - but note: that RPM is right around the engine's maximum volumetric efficiency point. (Most capable of processing intake air efficiently, also known as torque peak RPM range? Since the kerosene is somewhat limited in the ratio to air in which it burns well, it makes sense that it does best where the engine can draw the most air the most effectively.)

With (?)ethanol's greater tolerance to fuel/air ratio, we can wind glows a long way past torque peak. As HP is a product of torque x RPM, HP continues to rise until torque has fallen so far that the multiplication product actually declines.

Specialty engines of all types can be developed that prove or contradict anything most of us say or believe about our ordinary engines.

All the above is IMHO... [photo not recovered: devil.gif]

On the torque question of diesel vs glow, I'm not so sure. When I ran the K&B, I first ran it glow, APC 11 x 5, Sig Champion 10% nitro, 20% 50/50 oil. It turned the prop 9,700. With diesel fuel, the ST needle in a turn and a half, RPM 9,700. So that engine, under the settings and prop I ran, produced the same torgue diesel or glow. I was somewhat surprised, but did not follow up. I suspect if I had tried, say, a 12 x 6, the diesel would have produced higher RPM. In my experience with converted Tower and Magnum 40's, RPM with a 12 x 6 is around 9,000 RPM.

Another caviat, with the K&B, we are talking an engine expertly designed to run glow. Perhaps the timing, port area, etc, was not optimum for diesel operation. However, I've looked at a lot of Aeromodeller tests of both glow and diesel engines. I see great variance among diesels on the shape and magnitude of the torque curve, and do not see, on average, much difference from glow engines.

Jim,

I value your comments, and am not picking a fight...

Another way to check the relative "performance" of the better running 4011 on diesel might be to see how far it could wind up on a smaller prop. IIR, the 4011 torque peak range is right about where you ran the good one on the same prop/different fuels.

As you pointed out, the K&B 4011 was designed and developed to a definite, clearly defined purpose. That it turned out flexible enough to serve very well in other circumstances is a fortunate thing.

Re: torque curves: I believe you've pointed out somewhere in the past few years that tested diesels seemed to have a flatter curve. The RPM range and the Y-Scale on the P.G.F. Chinn tests seemed variable, perhaps so that the rounded-off curve-point values looked more familiar from test to test. ...and the gamut of the torque and power numbers fitted well with the engine's displacement. Later, Billinton's tests had very 'uneven' looking curves, if you recall those.

Fortunately/unfortunately - diesels can provide very good torque around max volumetric efficiency RPM, which for most of our engines seems to be in the RPM range we use for moderate pitch props and stunt laptimes.

Problems:

--- On the Barton site, I asked a flier in the UK how they controlled the diesels' tank fill to get done and back down within the 7 minutes FAI F2B allows. "We don't. It's always a gamble." ...or some such wording...

--- There remains that local bigotry against us olfactorily-enhanced greasy rag types.

BTW, glad someone else sees it that the kerosene burn might approach more closely the "constant pressure" type of combustion cycle. Do you concur that the cooler exhaust might in part be from a longer, slower -hence somewhat cooler- burn?

In contrast, the potentially "instantaneous" burn (which I think was how that SAE report termed our alcohols) can be demonstrated. When squish and bowl combustion chambers first came into general use, many engines had a large, flat squish area and a small bowl. The high swirl velocity and rapid final compression as the squish 'closed' provided excellent combustion conditions. One engine I ran long about then was harsh, and tricky to needle unless turning muchos RPM-os. I looked at the combustion chamber, and found oil charring ONLY inside the bowl. The flat squish lands had no charring. I carved that head to a broad cone from stock depth at the cylinder wall to the end of the glow plug threads. Much smoother, and more economical - plus more dependable and progressive to tune.

After a few hundred more flights, I pulled the head and noted an even, light colored hot oil surface over the entire chamber face: no charring, no bare metal areas.

Nowadays, our ordinary engines DO NOT use large, flat squish bands.

>I've been taken to task several times here for my reference
>to our compression ignition engines as diesels. I had read in
>the past a definition that backed my assertion but had
>forgotten where it was. In a bit of research at work today I
>came across it in the SAE Handbook. If that's not a
>trustworhty enough source, you'l have to find a better one to
>refute this.
>
>1992 SAE Handbook; 3:25.32 (volume 3, section 25, page 32)
>paragraph 2.2 Definitions:
>line 2.2.1 Diesel Engine-Any compression ignition engine.
>
>I know you purists out there will still argue timed fuel
>injection to facilitate the Diesel cycle, but the definition
>encompasses simple compression ignition as also recognised as
>a Diesel engine.
>
>
>Nyaaa Nyaa!!!!
>
>
>Randy Ryan <><
>AMA 8500
>SAM 36
>BO all my own M's:sp:


Ron B.
F4Fguy

Randy,

Nyaaa Nyaa!!! Right back atcha!

Your logic is flawed. You can call it anything you want to, Fred or Cecelia for instance, but it won't change the facts. A Diesel engine, is defined by it's operating principle. True, all diesels are compression ignition engines, but all compression ignition engine engines are not Diesels. Even a cursory glance at the cycle diagrams will reveal the difference between the Diesel and Otto cycles.

[photo not recovered: 29486.jpg]

[photo not recovered: 29487.jpg]

From: Combustion Engine Processes, Lichty, McGraw Hill

The Diesel¹ cycle is, theoretically, a constant pressure cycle. The Otto² cycle is constant volume. Not only are the PV/TS curves different, but the way in which the fuel/air is consumed is totally different.

1) Named after Rudolf Diesel, 1858-1913

2) Named after Nikolaus August Otto, 1832-1891

Diesels always operate with excess air. They are fuel throttled. They burn fuel by vaporizing individual droplets as injection proceeds.

Otto cycles always operate with excess fuel. They are air throttled. They burn a prepared mixture of fuel and air.

All model piston engines are Otto cycle engines, whether compression ignition, spark ignition, glow plug, or a match through a touch-hole. The means of ignition are not definitive.

Nit picky? Maybe, but I deplore sloppy language almost as much as sloppy engineering, and combining them is just too much.

Sorry to have risen to your bait,

Ron B.

Attachment #1, (jpg file)
Attachment #2, (jpg file)

>>I've been taken to task several times here for my
>reference
>>to our compression ignition engines as diesels. I had read
>in
>>the past a definition that backed my assertion but had
>>forgotten where it was. In a bit of research at work today
>I
>>came across it in the SAE Handbook. If that's not a
>>trustworhty enough source, you'l have to find a better one
>to
>>refute this.
>>
>>1992 SAE Handbook; 3:25.32 (volume 3, section 25, page
>32)
>>paragraph 2.2 Definitions:
>>line 2.2.1 Diesel Engine-Any compression ignition engine.
>
>>
>>I know you purists out there will still argue timed fuel
>>injection to facilitate the Diesel cycle, but the
>definition
>>encompasses simple compression ignition as also recognised
>as
>>a Diesel engine.
>>
>>
>>Nyaaa Nyaa!!!!
>>
>>
>>Randy Ryan <><
>>AMA 8500
>>SAM 36
>>BO all my own M'
>
>
>Ron B.
>F4Fguy
>
>Randy,
>
>Nyaaa Nyaa!!! Right back atcha!
>
>Your logic is flawed. You can call it anything
>you want to, Fred or Cecelia for instance, but it won't change
>the facts. A Diesel engine, is defined by it's operating
>principle. True, all diesels are compression ignition engines,
>but all compression ignition engine engines are not Diesels.
>Even a cursory glance at the cycle diagrams will reveal the
>difference between the Diesel and Otto cycles.
>
>[photo not recovered: 29486.jpg]
>
>[photo not recovered: 29487.jpg]
>
>From: Combustion Engine Processes, Lichty, McGraw Hill
>
> The Diesel¹ cycle is, theoretically, a constant pressure
>cycle. The Otto² cycle is constant volume. Not only are the
>PV/TS curves different, but the way in which the fuel/air is
>consumed is totally different.
>
>1) Named after Rudolf Diesel, 1858-1913
>
>2) Named after Nikolaus August Otto, 1832-1891
>
>Diesels always operate with excess air. They are fuel
>throttled. They burn fuel by vaporizing individual droplets as
>injection proceeds.
>
>Otto cycles always operate with excess fuel. They are air
>throttled. They burn a prepared mixture of fuel and
>air.
>
>All model piston engines are Otto cycle engines, whether
>compression ignition, spark ignition, glow plug, or a match
>through a touch-hole. The means of ignition are not
>definitive.
>
>Nit picky? Maybe, but I deplore sloppy language almost as much
>as sloppy engineering, and combining them is just too much.
>
>Sorry to have risen to your bait,
>
>Ron B.
>
>
>
>
>
Not my logic Ron, but the collective logic of the SAE. I understand the Diesel cycle, but I also understand that there are no diesels that operate precisely to that cycle. Rudolph Diesel's cycle is recognized ad "ideal" but has not been accomplished.

Randy Ryan <><
AMA 8500
SAM 36
BO all my own M's

>Not my logic Ron, but the collective logic of the SAE. I
>understand the Diesel cycle, but I also understand that there
>are no diesels that operate precisely to that cycle. Rudolph
>Diesel's cycle is recognized ad "ideal" but has not
>been accomplished.
>
>Randy Ryan <><
>AMA 8500
>SAM 36
>BO all my own M's


Ron B.
F4Fguy

The fact that SAE has bowed to the common usage gods has little to do with the facts.

Of course there's no such thing as an ideal engine that operates precisely to the theoretical cycle, regardless of what that cycle may be. Due to the difference between the real world and the theoretical, there's no Otto, Brayton, Lenoir, or any other engine that can duplicate their respective air cycles.

Ron B.

I don't see regulating run time in diesels as a problem. I tend to leave needlevalve settings alone. For Example, I have not changed the setting on the Fox 35 on my Demon for a long time. It has run to suit me on the same setting in Austin, Tucson, Seguin, Dallas, and Houston. Considerable differences in altitude, relative humdidity and temperature. I do the same with diesels and have had very little problem with run time. I think there is so little fuel going into a diesel, that precisely duplicating a previous setting is almost impossible. Being 1/100 of a turn off might be undetectable with a glow engine but could make a noticable difference with a diesel.

My most striking example of a strange run is one I got with a K&B 4011 on glow. I flew the AMA pattern with the usual ten laps left. Changed nothing, flew the pattern and went an additional 68 laps. Changed nothing, flew the pattern with ten laps left. I think it flew through a Zog Ray from Venus.

Deleted incorrect post. Never mind

AHHHHHHHHHHHHHHHH!!! That was fun!!


Randy Ryan <><
AMA 8500
SAM 36
BO all my own M's

Indeed.

I will never understand why people get so steamed up about some of this stuff.

Must be time to move on to the old 'Did the millennium begin at the start of 2000 or the start of 2001' debate...

>Must be time to move on to the old 'Did the millennium begin
>at the start of 2000 or the start of 2001' debate...

If we were on an RC forum, we could discuss downwind turns.

Jim

All of MY compression ignition engines are diesels. All of MY glow engines are not. Period!

George

My two bits as a pensioned mechanical engineer.

the key-expression here is "combustion type".

Glow and petrol engine share the same type of combustion. They operate with a homogeneous fuel/air mixture ignited at one spot, with a flame front travelling through the combustion space.

The "Diesel" or the "compression ignition" engines also share a same type of combustion , the so called inhomogeneous diffusive combustion. In these engines the fuel, long hydro-carbons, has to be mixed with oxygen( out of air) molecule by molecule. This is a process that takes place in all locations in the combustion space. And then again, only the hydrogen component really burns, because it releases itself from the carbon and reacts better than the carbon component.

So, the way fuel is put into the combustion space is not important.
The way of igniting is!
Glow fuel :high octane number, low cetane number
Diesel fuel: low octane number, high cetane number