SBBlue
Automotive
- Oct 6, 2003
- 118
- 0
- 0
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:
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?
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:
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?
