Efficient Motors – “Massive Yet Tiny”
Fans of highly efficient internal combustion engines will be interested in this: a modern-day variant on a Wankel rotary engine of 50 years ago. By firing 16 times per revolution, it achieves extremely high torque in a very small volume; thus the name “MYT” or “Massive Yet Tiny.”
From the linked-to article:
“Besides biofuels, the MYT engine should be able to run on alcohol, hydrogen, diesel fuel and compressed air. Because of the design, there is a long dwell time at the top dead center, meaning there is a much higher chance that all of the fuel is ignited, resulting in 100% theoretical efficiency. With a gasoline engine, the theoretical efficiency is about 30%; and for Diesel, it’s about 50%.”
The above leads me to question the entire article. Anyone who understands thermodynamics would understand that even a Carnot engine cannot achieve 100% efficiency since its efficiency is limited by the equation ( (Th – Tc) / Th) x 100%. Even I understand that, and my degree is in business administration. No heat engine can be 100% efficient!
The assertion that the compression ratio can be as high as 70:1 is also doubtful. If, as stated in the article, the engine can run on a biofuel that also provides lubrication, presumably that means that the mixture will be significantly less than stoichiometric, i.e., leaner than chemically correct. With that lean mixture and ultra-ultra-high compression ratio, there would be a serious NOX problem in spite of the fact that the author states otherwise. There is no fuel with which that extreme compression ratio would be practical.
The surprisingly high number of firings per revolution is not really an advantage. At one time, Cadillac made cars with V16 engines. The advantage of the V16 engine, which fires 8 times per revolution, can perhaps be best described by a book I have on Cadillac history:
“Sixteens and twelves power Cadillacs silently, effortlessly, if not pragmatically, through the thirties.”
Once one exceeds three firings per revolution, returns diminish rapidly as the firings are increased.
Probably that engine will soon disappear and never again be heard from.
Thanks for the info, Frank. I’d like to hear your opinion on the Cyclone engine http://www.cyclonepower.com
It’s hard to tell from the description alone, but I wouldn’t rule it out. In principal, it is very similar to the conventional steam engine, but perhaps it has some advantages which aren’t immediately apparent.
To get high efficiency, a steam engine has to use super-heated steam. And, because it is super-heated, it cannot act as a lubricant. He says nothing about super-heating. He may have those details worked out; I can’t be sure.
I’ve wondered whether the Stirling engine could be made more practical; it is highly efficient. It’s principal disadvantages are that it is somewhat bigger and heavier than a conventional IC engine and its output power cannot quickly be changed. But in a hybrid car, that might not be a big problem since the hybrid system with its battery could permit the engine to run at a relatively steady output and still permit quickly changing the power to the wheels. The engine could be less powerful since it would require only sufficient power to maintain an adequate cruising speed and when additional power is required, it could come from the battery.
http://en.wikipedia.org/wiki/Stirling_engine
Thanks Frank
Cool except the holes for valves and cylinder rings for seals usually results in a high wear factor at the trailing edge of the exhaust port which destroys the rings / seals in 5,000 miles And for all the years the Wankel has been around nothing better than cast iron has been found for cylinder ring seals.
Two stroke engines sometimes last for a very long time and they have exhaust ports over which rings slide. That system has been used for outboard boat engines, two stroke motorcycle engines, and two stroke Detroit Diesel engines used in ‘busses, trucks, and railroad locomotives.
Uniflow steam engines also have exhaust ports over which the pistons slide; they were both very successful and durable.
http://en.wikipedia.org/wiki/Uniflow_steam_engine
There is a car ferry on Lake Michigan, the S.S. Badger, which has two Skinner Uniflow steam engines, double expansion type, which have exhaust ports; I rode on it a number of years ago. In total silence and with no vibration, it glided away from the dock. Unfortunately, it burns coal and there was plenty of smoke; they should convert the boilers to oil.
http://www.practicalmachinist.com/vb/antique-machinery-history/skinner-engine-works-unaflow-presently-148777/
Here’s a comment from the above link:
“Badger uses two 4,000 hp Skinner four crank, steeple or tandem compound unaflows, quite different from a quadruple expansion engine.
“The thermodynamic underpinnings of the uniflow advantage was that a temperature gradient establishes itself along the length of the simple uniflow cylinder. This temperature gradient more or less matches the temperature of the steam (minus exterior losses of course) and hence condensation losses are minimised.
“Generally, uniflow engines were not jacketed either as this would disrupt the formation of this temperature gradient.
“Meanwhile, the thermodynamic advantage of any engine in compounding (or tripling, or quadrupling) is that the temperature differential between the incoming steam and the cylinder walls is reduced as the total temperature change (expansion) is split between multiple cylinders.
“The two concepts can work in tandem but you run into difficulties with uniflow “recompression.”
“And even a single cylinder uniflow has problems with “partial load” primarily due to this recompression issue. Hence the need on most uniflow engines for a “compression release valve” which is used at reduced loads or for backpressure operation.
“Now it may be possible for the Badger engines to be compounded. But probably that is the practical limit for this methodology. I imagine the Badger engines would have been operated at some optimal point possibly determined by some previously determined receiver pressure/temperature or maybe as simply as the point where the compression relief valve just starts to open.
“In a way the uniflow engine was a throwback to a previous engine concept. A simple engine optimised based on steam expansion diagrams. But the uniflow principle was forward looking in that is was ultimately brought to it’s final expression in the invention of the steam turbine where each turbine stage is optimised for it’s temperature/pressure differential.”
What the article does not state is that the cylinders have to be taper machined to allow for the difference in temperature between the top and bottom of the cylinders.
Actually, I shouldn’t be able to understand this sort of thing since my degree is in business administration.