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Will Split-Cycle Engine Compete With EV Powertrains?

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melllowfelllow
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Gold
Re: Interesting...
melllowfelllow   9/28/2011 11:42:34 PM
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Kevin,

I agree with most of your comments. However, the "Once the avg. temperature gets too high, lubrication breaks down and engine reliability will suffer" seems a bit unfair. Saab managed to make more than a few 2 cycle engines [similar heat issues] with lifetimes warranties over 40/50 years ago. I would think that the temp problems are about the same and that modern synthetic lubricants could handle the bottom end.


Doyle Rotary
User Rank
Iron
High average temperature in power cylinder
Doyle Rotary   9/30/2011 11:52:31 AM
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Although I have a bias opinion, because of the DRE, I do not believe cooling the power cylinder is going to be a problem.

We build race engines that have no water jackets between each cylinder to allow for very large cylinder bores. These engines are used in sprint cars that run nearly wide open throttle for the entire race and produce more than 700 hp. The average amount of heat that is developed in each cylinder to produce this much HP has to be far higher than that of a power cylinder on a split cycle engine even when you consider the cool intake air bringing the average temperature down. Yet we can do this lap after lap with no cooling issues.

Today’s direct injection engines also introduce oil under the pistons to assist with cooling.

Also if the engine is in fact more efficient it will have less heat to deal with.

When running superchargers the compressor discharge temperature can exceed 200 degrees F. Since this is higher than the normal operating temperature of an engine it has a negative cooling effect. Yet they too can be run for long periods of time without adverse effects.

 

 

Kevin
User Rank
Platinum
Re: Interesting...
Kevin   9/30/2011 7:37:09 PM
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OK...I'll concede that of all my criticisms of the split-cycle concept, the temperature comments are the ones I'm least certain about.  Although I still contend overheating will be a challenge based on my knowledge - it may indeed be engineerable.  For example, the wankel engine has compression / combustion / exhaust always in the same location of the engine (except for the rotor).  I know that this was a big development challenge for Mazda (I once owned a racing rotary), but they worked it out with special coatings on the walls, carbon seals, and (check it out) a huge radiator vs. engine size.  Efficiency was (and is still) not good, unfortunately.

The main question for the split-cycle concept is "what does it bring to the table that a miller or atkinson cycle engine doesn't?".  I contend - almost nothing, and it has some disadvantages to boot.

I really like what Mazda is trying to do with their Activ engines - they are exploring limits of optimization from several angles: gasoline engines with high 14:1 compression ratios, and diesel engines with low 14:1 compression ratios.

Stuart21
User Rank
Gold
Re: Interesting...
Stuart21   12/5/2011 10:24:57 AM
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Similar (bigger) questions arise about the french aircar - look for it on google or youtube. Always 1 or 2 years away from production (invest now! ;-) 

PM even reported a possible 1,000 mile range.

But the best tested published range ~ 10 yrs ago was 7.22 km. & a huge shopping list of improvements - none of which have been shown to be achieved.

Indian Tata Co. (got sucked in) invested 28 big ones AFAIK.

Charles, how about some journalism with a capital J?

sbkenn
User Rank
Gold
Split Cycle Engines
sbkenn   4/4/2014 1:02:46 PM
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This is basically a supercharged two-stroke, with stage one being a turbo-supercharger, and the 2nd, a piston pump.

I have a pair of engines which could be regarded as split cycle, albeit with just a single stage supercharger.  They are Foden FD6's, which have a Rootes blower and a 2-stroke diesel engine.  The Rootes blower is more compact that a piston pump, and far simpler.  This arangement could easilly have a turbo-supercharger added to compete with the current split cycle engines that are being developed, but more compact, and far fewer parts, moving and otherwise.

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