Elastic piston
Elastic piston
(OP)
I heard that Ford was working on elastic pistons at some point, but couldn't find any information online. Does anyone know more about this? What was it exactly and what were the results?
(There's supposed to be an elastic connection between the piston crown and the actual piston.)
Advantages:
* You can increase the compression ratio without increasing peak pressure. At peak pressure some of the heat energy (pV) would be transfered into spring energy which would then transfered back again at a lower pressure.
* Torque should go up, because pressure is reduced at TDC, but increased at a larger crank angle.
Disadvantages:
* The forces are tremendous so it might only work with smaller pistons (small diameter pistons).
* Material fatigue could be an issue.
* The mass and the complexity of the piston would increase.
(There's supposed to be an elastic connection between the piston crown and the actual piston.)
Advantages:
* You can increase the compression ratio without increasing peak pressure. At peak pressure some of the heat energy (pV) would be transfered into spring energy which would then transfered back again at a lower pressure.
* Torque should go up, because pressure is reduced at TDC, but increased at a larger crank angle.
Disadvantages:
* The forces are tremendous so it might only work with smaller pistons (small diameter pistons).
* Material fatigue could be an issue.
* The mass and the complexity of the piston would increase.





RE: Elastic piston
RE: Elastic piston
Assuming you have detonation at TDC. How are these pressure peaks transfered to the crank (other than damaging the bearings?)
RE: Elastic piston
RE: Elastic piston
If the spring rate is low enough to compress, you lose compression and hence power. If the spring is stff enough to resist compression during the compression stroke it will just transmit the force directly to the wrist pin bearing.
RE: Elastic piston
I realize that this is not a solution of striking simplicity. I was curious whether anybody heard about this, but maybe this was only some rumor.
RE: Elastic piston
Here you go an immage that I found.
http://img
A tidy mind not intelligent as it ignors the random opportunities of total chaos. Thats my excuse anyway
Malbeare
RE: Elastic piston
What the garage inventors say is that pressure is somehow recovered later in the expansion stroke so that it creates more torque, because the crank angle is nearer to 90 degrees. As I said, hogwash.
RE: Elastic piston
RE: Elastic piston
malbeare
A tidy mind not intelligent as it ignors the random opportunities of total chaos. Thats my excuse anyway
Malbeare
RE: Elastic piston
(As SomptingGuy correctly pointed out before, a truly elastic piston wouldn't do anything other than simply decrease the compression ratio.)
Btw, if knock occurs, is the increased pressure the main damaging part or does the vibration caused by the high frequency of the pressure peaks pose a problem as well?
RE: Elastic piston
Whether the gains outweigh the many other losses and disadvantages is up for discussion.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Elastic piston
This effect would increase with the square of the speed.
How much effect this has on preload would also be up for debate.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Elastic piston
I guess this would be another reason why it would only work with smaller pistons (less mass).
If you had an engine with sleeve valves you could place an elastic (static piston) on top (cylinder head) and then you wouldn't have to worry about the inertia and a relatively complex part moving up and down. However the elastic piston on top would need to be ring shaped to allow space for a spark plug or an injection nozzle.
RE: Elastic piston
Jeff
RE: Elastic piston
The preset tension has to be higher than the inertia, otherwise you'd deal with a stroke that increases with rpm.
RE: Elastic piston
RE: Elastic piston
http://www.evanguy.com/HFE/index.htm (see US pat.,5,476,072)
However, an undampened or uncontrolled spring-loaded system is not a very good idea in a high speed recip engine. It would be noisy and would have a limited life span.
RE: Elastic piston
My patent is for a VERY specific area of internal-combustion reciprocating-piston operation. Specifically, a VERY low octane fuel in a spark-ignited realm.
Let's first look at what's happening with this concept. Constant-volume combustion is MUCH favorable to constant-pressure combustion, from both a power output AND cycle efficiency standpoint!! Unless you have some REALLY strange reasons for doing what I've done, the best scenario is to CLOSELY approximate Constant-Volume combustion!! Burn the fuel and make a LOT of pressure! (In a substantially-constant volume of a reciprocating piston AT TDC)
The stuff I was doing is NOT presently viable (although it's REALLY FREAKING CLEVER if one was to look into it deeply enough!!)
A non-elastic combustion chamber WILL give better results, in terms of power output, specific power output, specific fuel consumption, hardware design/implementaion, and patent attorney FEES!!!
An elastic chamber wishes to allow constant-pressure combustion. My concept is (was) really neat and I have exemplary prototype hardware, to boot. But in the long run, doesn't make sense. More on this, if queried....Best, Billet142....
RE: Elastic piston
This way you could have constant volume combustion at low throttle settings and constant pressure combustion at high throttle settings. This should allow a very high compression ratio at low throttle settings that would otherwise not be possible without damaging the engine at full throttle or shouldn't it?
Also constant volume combustion would basically mean to build an engine that can handle constant detonation or would it not? (Are there engines that can handle this?)
Evan it would be nice if you could elaborate a little more. Thanks.
RE: Elastic piston
Agreed. But isn't this the opposite to the flexible-piston crew? They suggest that constant pressure combustion somehow reduces thermal losses. I scanned your website but couldn't find your 'big idea'. Care to disclose it here? It is patented after all.
RE: Elastic piston
htt
Brief description:
http://www.vegburner.co.uk/engines.htm
The point here is that if you can keep the piston longer at TDC, you can delay the ignition point (and therefore reduce pressure before crank reaches TDC) and complete combustion can be achieved before piston leaves TDC (which leads to increased peak pressure at the same compression ratio). In addition, since the piston spends more time at TDC it should be an advantage in expelling exhaust gases. Finally, the extra linkage reduces the side-forces on the piston.
The disadvantage is obviously more moving parts, more mass, larger engine and the maximum piston speed is also higher and if added together probably offset any merits that this concept could produce. (Note: this engine concept wouldn't have any advantage at all, if combustion was much faster (HCCI engine)).
RE: Elastic piston
The impressive 30-ish highway gas mileage of late model V-8 2WD sedans and Corvettes was earned largely with steep rear gears, and strict fuel and ignition management (controlled by a CPU applying rules developed with hard work, and many R&D bucks financed by those of us who bought a heap of the less efficient cars). Put headers, a Holley carb and premium street manifold, and a magneto ignition on one of them, and I suspect the highway mileage and throttle response and maybe even power would plummet.