Smokey's Adiabatic Engine 6

[SBBlue]

Somebody in another discussion thread made a mention of Smokey Yunick's adiabatic engine. I had never heard of it before, and did an internet search as well as retrieve the patent and dug up some old Popular Science magazines that discussed it.

For those of you not in the know, Smokey Yunick was a legendary race car mechanic and Popular Science correspondant. He died a couple of years ago. In March 1983 Popular Science carried a story about an engine he had developed that only had two cylinders and 78 cubic inches but developed 150 hp and got 60 mpg when installed in what looks like a Volkswagon Rabbit. He called it his "adiabatic engine." Supposedly all sorts of car companies were quite interested in the engine.

A followup story done in Popular Science in November of 2000 stated that the "engine came close to going into production with General Motors several years ago, but the deal hit a stalemate when patent owners couldn't agree on details." If you visit the patent office, you will find that the patent covering the engine (US 4862859) was allowed to expire in March 2002. (Web site for patent:

http://patft.uspto.gov/netacgi/nph-...&s1=4862859.WKU.&OS=PN/4862859&RS=PN/4862859)

In reviewing the patent it appears that Smokey's engine used an "afterheater": coolant heat was used to vaporize gasoline, and exhaust heat was used to heat the air/fuel mixture coming from a turbocharger compressor to 440 deg F. In the cylinder the air/fuel mix reached a temperature of 1600 deg F before ignition -- all without detonation.

According to the Popular Science article, the reason for no detonation was "Smokey's Secret".

After reviewing some of the numbers provided in the Popular Science article and in Smokey's patent, I've been able to deduce the following about the engine;

1. The air/fuel ratio was something on the order of 22:1 to 27:1.

2. Peak combustion temperature was above 5000 degrees F.

3. Exhaust gas temperature (before the turbocharger) was about 2200 deg F.

4. Assuming no loss of cylinder heat to the cylinder walls (i.e., an actual adiabatic engine) the best possible efficiency was about 38%. If the engine used a Miller cycle modification, an efficiency of 48% would be possible (no mention was made of the Miller cycle)

My conclusions:

1. Smokey may have been able to get the engine to work, even though there was a high intake temperature, by using a very lean air/fuel mixture to prevent detonation.

2. There was no way that this engine was developing efficiencies of 50-60%.

3. It is doubtful that the engine, as described, would last long because of extremely high temperatures. With the claimed fuel flow and intake air temperature, the peak combustion temperature would be over 5000 deg F, as compared to perhaps 3500 deg F for a normal spark ignition engine.

4. I find it very hard to imagine that General Motors was ready to put the engine into production and didn't only because of patent royalty issues -- only to have the patent abandoned several years later.

==============================

Comments, anyone? Did anyone ever actually see this engine, or hear anything about it?

 

[GregLocock]

Here's some more on it.

The air fuel mixture is heated to 90 C by the coolant, then it goes through the turbo/atomiser, which heats it to 140C, then is heated further by the exhaust to 230C

Then it is compressed in the cylinder to 820C, at which point the spark fires.

Then it goes through the exhaust valve, heats the incoming mixture, and then into the expansion side of the turbo.

here are some claimed figures

Car/engine Fuel consumption 0-100 km/t
Plymouth Horizon, 4-cyl 23.51 mil/gal 14.5 sec.
Plymouth Horizon, Hot Vapor. 54.67 mil/gal 6.5 sec.
Pontiac Fiero, 4-cyl 21.97 mil/gal 14.2 sec.
Pontiac Fiero, Hot Vapor 51.10 mil/gal 5.9 sec.

My comments

(a) I'm a non believer, but it is an interesting mix of ideas

(b) As far as efficiency goes it would be better to drive the turbo direct from the exhaust and then use the exhaust from /that/ to heat the intake manifold. However that might compromise the temperature attained in the intake manifold

(c) other threads have covered the small increase in available energy you would get by pre-vapourising the fuel

(d) someone with some time on their hands could use these temperatures could probably figure out the pressure ratios in the turbine, and the likely thermodynamic cycle of the whole thing.

(e) crudely he is running diesel-like AFRs, so you'd expect diesel-like efficiencies.

(f) in order to develop 150 hp from 1278 cc he needs high rpm and/or high boost pressures. Lean mixtures burn slowly, so high rpm alone is not the answer

(g) The mpg figures imply something like 2.5 times the efficiency, admittedly off a fairly low base




Cheers

Greg Locock

 

[Metalguy]

I remember that he allowed a car magazine driver to try one of these engines in a car. Might have been "Car & Driver" mag.-can't remember. But I do remember that the driver floored the throttle at low RPM, and it didn't detonate.

 

[GregLocock]

Oh, and another fact(oid) from the Rabbit article is that there was only 2 litres of coolant and no cooling fan.

Cheers

Greg Locock

 

[tbuelna]

SBBlue:

Ol' Smokey's engine achieved those performance numbers with the use of a special additive. Most racers are familiar with the additive. Anytime someone makes incredible claims about the performance of their engine, you can be sure they're using lots of the additive. The additive goes by the initials B.S.

There was one thing Smokey Yunick was famous for: cheating.

 

[maniacle]

it does sound interesting, but last time i checked, steel melts at about half that temp (between 2300 and 2700 degrees F) even if its only exposed to those temperatures for a moment, its still enough to damage the cylinder walls...

 

[SBBlue]

Hah!!

ROTFLOL!!

You really had me going for a moment there!!

And a note to Greg Locock: I have gone through the thermodynamic calculations, and they work out something like this. . . . .

The piston compression ratio can be determined from the differences in the temperature between the intake manifold and following compression. It's about a 10:1 compression ratio.

Assuming an adiabatic system with a 100% efficient piston compression and expansion and a frictionless drive train, the overall system efficiency is 55%.

Assuming a somewhat more realistic piston compression and expansion efficiency of 85% but still with a frictionless, adiabatic engine, the maximum efficiency drops to about 38%.

Once you factor in the losses from friction, exhaust gas piston blowby, and a non-adiabatic environment -- I don't think there's a snowball's chance in hell that the engine is achieving the advertised efficiency figures.

And, one last thing;

Tbuelna, do I have to cite you every time I use your description of the special miracle fuel additive??!!

 

[Metalguy]

Maniacle,
Alum. alloys melt at much lower temps.~1,200 deg F., and *usually* they don't melt, so peak flame temp. doesn't mean didley.

 

[SBBlue]

Here's an fun experiment you can do.

Take a paper cup.

Fill it with water.

Place it on a bunsen burner or coleman propane camp stove.

It is possible to boil water in the paper cup, and the paper cup won't burn up -- even though the flames have engulfed the cup. Since water can't get above 212 deg F at atmospheric pressure, the water products the paper cup from damage from the flame.

NOTE THAT THIS DOESN'T WORK IF YOU USE A STYROFOAM CUP!! I tried it once to impress some people, and needless to say they were quite impressed.

But the same thing happens with cylinder temperatures. Temperatures much higher than the melting point of the cylinder wall metal can be tolerated, because the coolant protects the cylinder wall and the cylinder wall doesn't get close to the temperature of the gas in the cylinder.

 

[maniacle]

Ok, im not afraid to admit it. I tried the paper cup experiement.

Guess i need to read up on my heat transfer.

 

[ivymike]

of course, if you had an "adiabatic" engine, you'd be closer to the styrofoam case than to the paper cup case...

 

[ShaunT]

Another thought: We know that the leaner it is, the slower it burns. Just how lean can it get before it pops,bangs, and just wont run.

Shaun TiedeULTRADYNE/LUNATI Arl,TX(stiede@ev1.net)

 

[ivymike]

about 17:1 to 18:1, with pump gas and modern engine controls, if Honda can be considered experts in lean-burn automotive gasoline engines (new Civic, Insight are in that neighborhood)...

 

[ShaunT]

Right. That is why I too have trouble believing the Smokey thing. This spacific forum is therefore a waste of time.

Shaun TiedeULTRADYNE/LUNATI Arl,TX(stiede@ev1.net)

 

[SBBlue]

Shaun:

This particular discussion thread is useful in discussing why certain things did not work. Smokey's engine was touted in a international publication (Popular Science) as working wonders. Time has shown that the claims were a bunch of bunk.

But it is useful to look at the claims that were made and try to figure out just what they were doing and what did and didn't work.

As far as ignition with an air/fuel mixture; I agree that you do reach a point as you lean a mixture out where it will no longer ignite. But I also suspect that if you take the same mixture that won't ignite at room temperature and heat it, you will reach a point where it will ignite.

If, for instance, a 20:1 air/fuel mixture will not ignite at room temperature, will it ignite at 500 deg F? 1000 deg F? 5000 deg F?

For the same reason, I also suspect that leaning out an air/fuel mixture will prevent detonation -- or spontaneous ignition.

Hence the value of this discussion.

 

[Metalguy]

Agree, this discussion is worth it. Obviously those who want to "change the channel" can do so, but I hope they don't.

I have very mixed feelings about this whole engine/concept. Ol' Smokey was a very sharp guy-eg., his reverse-rotation Hudson flathead 6, which he did to help prevent unloading the inside front wheel. He didn't even tell the drivers what he did. Yet I remember some real goofs in his advice column in Pop. Sci. I suspect he had someone writing that stuff.

I also have a problem with some of the stuff in the patent. Even with slightly long rods for the stroke, I find it hard to believe that 13 deg. of rotation at TDC didn't move the piston 0.001". Also, at least from a mech. POV, the last thing you want is max. cyl. pressure near TDC. Much better to have it far later, when the piston/rod get some leverage on the crank. It's easiest for the piston to turn the crank when the rod is at 90 deg. to a line between the rod and main journals, and this point is reached shortly before the piston is halfway down.

 

[ShaunT]

Long rods worked really well for him largely due to the horrible heads he had access to. By todays standards, his best is our junk. The long rod helped the head work the motor.

C'ya

Shaun TiedeULTRADYNE/LUNATI Arl,TX(stiede@ev1.net)

 

[franzh]

Working with stratified charge engines has shown some interesting results:

The mid 70’s Honda and Mitsubishi pioneered the use of dual mixture engines. One carburetor venturi provided a very lean air-fuel mixture, in the 22:1 range. The other venturi provided a richer mixture, about 13:1. The aggregate was about 17:1, since the smaller but richer venturi was about 11mm, while the leaner venturi was about 25mm.
The carburetors third venturi was approximately stoichiometric. Depending on the load, the engine-out AF ratio would range from about 20:1 down to about stoich.

The engine ingested the lean mixture first, then the rich mixture. The spark plug was located in the immediate path of the rich mixture, which then ignited the lean mixture. This allowed the Honda CVCC and the Mitsubishi Micro-jet to achieve those fantastic emission and fuel economy numbers.

More modern attempts at running variable AF mixtures have been a little more difficult, primarily for catalyst control. The cost and complexity of catalyst formulation for variable AF ratios increases drastically as opposed to one which operates at a tight AF ratio.

Franz

 

[SMOKEY44211]

I was at his shop Feb. 1988 for the big auction he had. Was fortunate enough to be invited into the Holy of Holy's area where he did most of his R+D work. The engine in question was also a test bed for a number of ceramic engine components ( pistons ,valves and rings)along with ceramic coating of the same. The ceramic parts were made by a joint venture between Norton Co. and TRW. I think the high levels of NOx was the big reson GM shied away from it.As far as cheating you got to admire the guy for some of the stuff he tried and was successfull with.-----Phil

 

[SBBlue]

Adiabatic engine == high level of nitrous oxides.

Makes sense, since heat that is not absorbed by the cool cylinder walls will cause the combustion temperature to increase, which will also cause an increase in nitrous oxides.

I certainly understand the use of ceramic coatings in an adiabatic engine -- it provides a good insulation against heat loss.

You mentioned that the ceramic coating was used on rings. I can understand the use on pistons, valves and the cylinder wall. But rings? I wouldn't think that there was enough heat flux through piston rings for a ceramic coating to make much difference at all.