The future of the engine as we know it 1

[franzh]

I normally run like crazy when someone asks me questions about a "new" engine, but when one of my directors asks me to evaluate a "new design" design, my knees shake. That happened this morning.

We have seen free pistons, opposed oscillating pistons, scotch yoke pistons, toroidal blocks, ball valves, sliding sleeves, and tons of other combinations. Strangely, or not so strangely, none of these has ever reached any significant success. The old, inefficient Otto cycle engine still hangs around. With the exception of sealing refinements and air-fuel metering, almost nothing has changed in 100+ years, not including OHC engines which is a refinement, or phased cams, also a refinement, or exhaust aftertreatments, which is not a refinement, but an attempt at fixing an engine inefficiency.

I wonder how long it will take before something else pops up and takes a reasonably strong stand against the tried and true engine design?

Lets look at the true IC engine replacement, not hybrids (although I feel that is where we are heading for the next 25 years). Turbines are nice but not practical for a number of reasons.

When we look at H2 as a potential fuel, it still uses the Otto cycle engine as a base, only the fuel has changed. Are we really gaining anything on the engineering side? I recognize the significant advantage on emissions, but fuel transport, storage, and infrastructure have still to be perfected.

Any ideas, fellow engineers?
Franz


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[CCycle]

The Miller Cycle is not an independent thermodynamic cycle. It is a way of operating an Otto Cycle. I prefer to call it the Miller toggle. It requires two conditions.
1. The Otto Cycle
2. That the engine operate a significant amount of its time at reduced output
Given the above conditions the Miller cycle can be applied as a method of reducing engine power. This method of power reduction is more efficient than intake throttling because it reduces pumping loss. An engine with its power reduced by the Miller method will use less fuel than the same engine with power reduced by intake throttling.
As for the future of the Miller Cycle, we probably will see more of this as long as we continue with Otto Cycle engines. It will probably bring in variable valve timing.

 

[Grimfiend]

I think the question we're looking at now is what is going to happen to the tried and true engines that currently exist vis a vis cutting edge materials engineering.

The internal combustion engine stands to benefit greatly from cutting edge thermoelectric technology... to the best of my recollection, almost all heat produced by an IC engine is lost to the environment, except for the minor amount used to heat the chassis during the cold weather months. Since the thermoelectric hype died down greatly from what it was in the 50s, we should be wary that this technology doesn't go the way of the Stirling Engine.

This is same with the electric motor, resistance in the windings escapes as heat... superconducting motors are 99% efficient at converting electrical energy into kinetic energy. Currently it would be ridiculous to have a superconducting motor in a car... but our understanding of nanoscale engineering seems to suggest that within the next 30 years, superconductors requiring "minimal cooling" are possible.

 

[GregLocock]

Since it is entirely possible to design a 98.4% efficient electric motor that is suitable for vehicle use, I don't see why we are waiting for superconductors, unless that last 0.6% has some importance I have yet to understand.

Cheers

Greg Locock

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[franzh]

If I am not mistaken, its not especially difficult for the motor side, but the batteries and controllers are the biggest stumbling block. The simple lead acid battery works great but is heavy, lithium ion is lighter, but lower amperage and other problems, and a multitude of other battery options.
This is where the next technology hurdle lays in hiding.

Franz

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[Grimfiend]

Its true we can produce very efficient motors without superconductors (99% efficiency is actually 99.9% btw)... I am not sure the limitations of this though. Perhaps the 98.4% efficient motors are laptop hard drive motors as opposed to 200 HP car motors (these do tend to heat up a BIT more at least), I am not entirely certain.

It seems to me that the prevailing question here is not the engine design but rather the fuel source. Of course we want to use a fuel source that is efficient in terms of energy density because our cars are ridiculously heavy to begin with.

If it were a viable solution to redesign the car from the ground up what method of locomotion would you end up using? Obviously you could create the "Popular Mechanics Gas Turbine Powered 3 Ton convertible" we were supposed to all be driving this millenium. To me it seems far more sensible to make a super light car that has a small engine and as high efficiency as possible regenerative braking techniques... this way the energy density of our fuel sources would cease being the key issue.

Im now really getting into a realm where I have much less understanding now, but theoretically if you have a 99% efficient motor and a similarly efficient method of recovering the energy through breaking, battery banks would be uncessary... you could have a single backup battery and run the car off a very large capacitor!

 

[kenre]

How about the 2 stroke? I believe the Orbital engine company has some running in cars for evaluation. There fuel system seemed to be quite good.
A 2 stroke certainly has less moving parts, meaning less friction, less weight, Maybe we should look at the uniflow 2 stroke again, like the Detroit Desiel, but with some modern design and technology thrown at it to see what bounces!

Ken

 

[tbuelna]

What's wrong with a recip internal combustion engine with an overall brake thermal efficiency of 60 percent?

http://www.eere.energy.gov/vehiclesandfuels/pdfs/deer_2005/session6/2005_deer_fairbanks2.pdf

 

[j2bprometheus]

Hi-
I disagree with the assertion that Stirling engines have a very low power to weight ratio. While there are plenty of issues with Stirling engines, the power to weight ratio issue was overcome long ago by pressurizing the crankcase. GM, FORD and AMC had Stirling engine programs some years back. The FORD & AMC programs reached the point where the performance of a car powered by the Stirling engine was nearly identical to a car powered by their stock IC engines. See

http://www.stirlingengine.com/faq/one?scope=public&faq_id=1

On Two-Stroke engines: The Detroit Diesel two stroke engines had the piston rings pinned so that they could not rotate. This lead to, in their case, high oil consumption and high particulate emissions. Perhaps this difficulty could be overcome, but it would take some engineering effort.

 

[GregLocock]

"Perhaps the 98.4% efficient motors are laptop hard drive motors as opposed to 200 HP car motors (these do tend to heat up a BIT more at least), I am not entirely certain."

No, I have designed, assembled and used a 98.4% efficient electric traction motor in a vehicle that has completed in excess of 15000 km on public roads.

Electric motor efficiency is NOT the problem. Batteries and energy source are. If we could eliminate the current fleet, or segregate electric transport from the current fleet, then electric commuter cars are feasible now. Basically it is not a problem I worry about, at some point someone will bite the bullet, and make the necessary changes, and it will happen. Then everybody else will say, oh that was not too hard, and join in.

Cheers

Greg Locock

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[globi5]

An internal combustion has the inherent advantage that it doesn't really need a separate system to generate and dissipate heat to the extent a stirling engine does. (The heat generator is part of the engine and the combusted air dissipates most heat automatically.)
A stirling engine has to sepearte hot and cold side of the engine. An internal combustion engine doesn't, which means it requires less volume (less mass) and it can reach higher temperatures, since its parts are not constantly exposed to extremely high temperatures.
For the above reasons I have difficulties to believe that stirling engines will ever reach the power density of an internal combustion engine.

There are engines for passenger vehicles (not research or race engines) reaching well over 100HP/l. So far I haven't seen a stirling engine with a similar power density.
Unfortunately this link doesn't contain any specific information about power and mass of the stirling engine powered cars used in research:

http://www.stirlingengine.com/faq/one?scope=public&faq_id=1

 

[globi5]

Peltier (or Seebeck generators) cooling elements are currently hardly even used to cool PC processors. Eventhough it definitely better than having all these noisy cooling fans or water tubes (Apple G5). So as long as there not even powerful or efficient enough to cool PC processors, I doubt that they will be useful to gain energy from exhaust systems.

 

[j2bprometheus]

globi5 - I agree that the stirling engine has some significant disadvantages when compared to an IC engine. It also has some advantages, such as higher theoretical cycle efficiency.

The Ford stirling engine project used a Ford Torino (a big car, not a small car): "The Ford Torino swashplate Stirling car engine was based on a 4-65 engine pressured to 225 Atmospheres, and 50kw power at 5000 RPM. " ( see

http://www.rotarystirlingengines.com/featuredengines.htm

).

Note the high pressures used by the Stirling engine. I think that the working fluid was hydrogen.

The 50 Kw power from the Stirling engine was more useful than 50 Kw from a four stroke IC engine because the stirling engine has a power stroke on every revolution. The four stroke IC engine only has a power stroke every other revolution.

 

[GregLocock]

"The 50 Kw power from the Stirling engine was more useful than 50 Kw from a four stroke IC engine because the stirling engine has a power stroke on every revolution. The four stroke IC engine only has a power stroke every other revolution."

Please justify that remark. What do you mean by useful?



Cheers

Greg Locock

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[kenre]

On Two-Stroke engines: The Detroit Diesel two stroke engines had the piston rings pinned so that they could not rotate. This lead to, in their case, high oil consumption and high particulate emissions. Perhaps this difficulty could be overcome, but it would take some engineering effort.

I havent had a huge amount to do with the engines to know there shortcomings. But yes with some engineering of the modern kind, who knows what could be achieved.

On electric, There are some big gains being made in Lithium Polymer batteries, in a few years they just might be practical for all electric transport. Let the Sparks fly!!

Ken

 

[ivymike]

Please justify that remark. What do you mean by useful?

Aw, c'mon Greg. Obviously if the power comes out every fourth stroke, you'll have to use some sort of high-efficiency rotating mechanical energy storage device to absorb the surges and fill the troughs. Some kind of big spinning disk, perhaps...

 

[GregLocock]

Hmm, I wonder if we could invent a 100% efficent device to do that? I think I'll patent it and call it a big wheel that flies round, or, possibly, a Fly Wheel.

Any takers?

Cheers

Greg Locock

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[kenre]

Sorry Greg, Im keeping my money for that gram of anti-matter ive been promised!

Ken

 

[turbocohen]

Heard about them that hunerd percent efficient flywheels before.. Theyre made out of unobtainium right?

 

[j2bprometheus]

Greg-

Here's my justification for saying a power stroke every revolution is more effective than a power stroke every other revolution: smaller, cheaper, lighter flywheel. Simpler, cheaper, and lighter transmission.

Also, a power stroke every revolution also results in lower peak torque on the crankshaft (for the same brake torque) than a power stroke every other revolution. So the crankshaft can be smaller and lighter on a Stirling engine than a four stroke IC engine.

Don't misinterpret what I am saying: the Stirling engine has lots of issues. But it does have some niche uses.

Some company in the US recently started manufacturing five KW Stirling engine gen sets to run off poor quality natural gas (natural gas that damages IC engines). I suspect that the company will sell quite a few of these.


j2bprometheus

 

[franzh]

Hmm, a flywheel that runs in a total vacuum, suspended on superconductive electromagnetic bearings, never powering any load (no drain).

Hey! This may just work!

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