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Efficent use of energy
Bringier   9/26/2011 9:18:52 PM
In 1990 I 'designed' a concept car. Ideas were shared with friends, mostly Electrical Engineers. At the time I had a Mazda RX-7 GSL-SE. It was best car I ever owned. (Stolen in 1995!). Concept car was to be like a Ford Escort 2/4/5 door car - small and light. (Maybe even a VW Beatle). Rear wheel drive by a 30 kw motor (40 hp). Top speed could be about 75 mph. Lithium-Ion was just starting then, but it seemed that a 20 kwh battery would do. Onboard would be a generator set of about 25 kw & optimized for maximum effiency at a specific constant speed. Car would have regenerative braking and a 120/240 volt charger.

Problem today is the 'Safety Standards' have added so much weight. It is no fun driving one today.


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Re: Better than many / still mainly hype
Tim   9/26/2011 9:13:59 PM
Sometimes you need to go totally outside of the box to get any advancement at all.  It is totally possible that this engine is hype and will never work its way into a common mainstream vehicle like an F150, but it just might.  Due to limited range, EV's are not always the best choice, so redesigning the existing liquid fuel engines might the best bet to meet new government regulations.

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Re: split cycle .. reason for improvment
JOsborn   9/26/2011 8:34:18 PM
I don't see how this design reduces negative work.  You have the dead zone of the transfer port from one cylinder to the other absorbing your compressed air and then you don't ignite the power cylinder until after the expansion stroke has started.  How is this anything more than a complicated Miller Cycle engine?

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Re: split cycle .. reason for improvment
Kevin   9/26/2011 8:10:44 PM

Yes, Mazda's new Skyactiv G engine is a practical example of what I was talking about - they are optimizing existing technology without resorting to strange new engine mechanisms:  reducing chamber temp by better scavenging of exhaust gasses, multi-point direct injection, increasing compression ratio.  They claim a 15% efficiency boost - which seems quite credible (unlike Scuderi's claims of "20%-30% and ultimately up to 50%", which are ridiculous IMO).

RalphyBoy & JesseL,

Yeah...your comments are pointing out some of the areas where I believe Scuderi's hype extends beyond credibility.  Any company that claims that one of their TOP PRIORITIES is to "go public" before they have 100% operational prototypes should be viewed with great caution.  They have been around a long time, burned though mountains of venture capital, and yet the data on their website says "The data in the above tables is simulated".  They should complete a proof-of-concept prototype and then use the actual data to sell the product, no hype needed!

The other thing you can see on the Scuderi website (but seems strangely absent from this article, although the tank in the CAD image shows it) is that they accumulate "extra" compressed air from the first piston stage into a tank, during cruising or during deceleration (regenerative braking).  Then, during acceleration they plan to use this stored energy for a "boost".  I find this idea interesting, because it theoretically could allow hybrid-like advantages without any extra batteries or electric motor.  However, I think that in practice this is a dubious claim, as the PSI and volume required for significant energy storage is HUGE, the inefficiency of storing energy as compressed air, and there are many other practical problems, such as the varying pressure in the tank.  Also, if this concept could be made workable - I'd rather see it done in a diesel instead of a newfangled split-cycle engine.  Diesels already have "jake brakes" - why not try to recover the braking energy?




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Obvious drawbacks galore
JesseL   9/26/2011 7:10:57 PM
Like a two-stroke, this engine requires the incoming charge to displace the exhaust in the power cylinder. This can obviously be made to work, but it's hard to tune across a very wide dynamic range. If the incoming charge doesn't adequately displace the exhaust you run a higher risk of preignition due to the higher temperature and remaining partially burned hydrocarbons, and you're reducing the output potential of the engine. If too much incoming charge is used to thoroghly scavenge the exhaust, you're wasting energy by pumping fresh air out the exhaust.

The usual two-stroke tricks for optimizing scavenging, such as shaping the piston to minimize the mixing of fresh air with exhaust, also comes at the price of reducing combestion chamber swirl (and burn efficiency).

I just don't seen anything here that isn't done better with a Miller-Cyle or even an arrangement more like a blown two-stroke diesel.

Ralphy Boy
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Ralphy Boy   9/26/2011 4:36:42 PM
"However, split-cycle efficiency was never very good until Scuderi changed a key part of the combustion process."

"But if you fire after top dead center, the efficiency exceeds that of a conventional engine."

With all the backyard mechanics working of engines over the years, and with the racing industry squeezing every drop of out of engines while looking for an edge, I'll be shocked if a simple change in timing leads to something as big as they are claiming.

And I agree that balancing the airflow is a concern.

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split cycle .. reason for improvment
Thinking_J   9/26/2011 3:13:46 PM
Like many of previous commenters.. following the subject closely.

It appears the biggest reason for the split cycle engines improvement is the following:

The lowering of temperature of working cyclinder - allowing higher gross compressioin without increasing N0x

Good explaination on Mazda website.. because they are doing the same thing with a different mechanical layout.

see: http://www.mazda.com/mazdaspirit/skyactiv/engine/skyactiv-g.html

New Mazda 2 using this technology.. already on the road in Japan.. 70+ mpg!

No need to change emissions standards to get the improvment.

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Re: That's the point: they are matched!
RNDDUDE   9/26/2011 2:50:16 PM
"Now, a piston compressor is always more efficient than a dynamic (centrifugal or axial, or screw compressor types)."

THAT is the part that I question. Any emperical data to qualify that? It seems almost all industrial air compressors have adopted screw type designs over the older piston type design, why would they do that if it were less efficient?

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Re: That's the point: they are matched!
Amclaussen   9/26/2011 2:32:39 PM
That's exactly the point: The engine airflow needs need to be matched by the section feeding the air in. Let's remember so called "affinity Laws" that govern flow, pressure and power in dynamic machines.  Very different from positive displacement or piston devices. (Flow proportional to speed, Pressure proportional to speed squared, Power proportional to speed elevated to the third power...)

In a turbo you need to match a very different performance map (that's because a dynamic compressor -or expander- uses -or produces- power to the cube of it's RPM,  therefore the operation line is curved, where the line for a piston engine would be straight).  The Turbocharger in a typical engine does not produce any real power surge at lower RPM's, it needs a relatively large exhaust flow to be eable to speed-up and start producing appreciable pressure into the inate manifold, and at high RPM's, the pressure and flow will be way too much over the piston engine needs, requiring a wastegate and controls to avoid overboosting the engine, overheating piton tops and valves or blowing the engine!  By coupling the a compression cylinder to the same crankshaft, the matching of the flows and power appears to be easier to be established and kept over the RPM range of the engine... At least that's the main advantage I guess this design could have.  Now, a piston compressor is always more efficient than a dynamic (centrifugal or axial, or screw compressor types).  by placing the compression piston on the same crankshaft would be advantageous compared to having an external supercharger, not only for its intrinsic compression efficiency, but taking together the unavoidable transmission losses at the Supercharger belt and pulleys or gears.  I hope I made it clear, sorry for the lenghty explanation, English isn't my native language.

The more I look to the idea, the more advantageous it seems.. unless I'm ignoring some catch!  Someone ready to find it?


User Rank
Re: Shaking the Automotive Industry.
wlawson   9/26/2011 2:09:11 PM
I have written letters E Mails to my congressman, president, EPA etc and received absolutly no response to the idea that perhaps the US should reconsider our emission requirements  for NOx and other emissions in light of new knowledge and better understanding of global warming and effects of these various regulations. 

The politicians are not interested in dealing with the rulings of an entrenched bureaucracy and perhaps making them revaluate their regulations

FYI Based on the fleet milage obtained in Europe and in the US, if the US adopted the european emission regulations, the US fleet average mileage could be in the order of 50% better.  In other words we would use a lot less foreign oil if we changed our automotive emission requirements.  thus reducing drastically the CO2 emissions among other things

We all need to push to make sure our government revalutes things in the light of new information.

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