The kinematics of a crank mechanism is generally arbitrary relative to the thermodynamics and heat transfer considerations of an air engine.
Instead of hoping for the right linkage, wouldn't it be better to position, as well as receive power from the pistons, with cams?
If you had one cam for the displacer and another for the power piston, you would have the option of varying the phase angle, changing the speed of expansion, addition of heat etc., however and whenever you wanted at any part of the cycle.
For high torque / low rpm, external ring cams would rotate about stationary cylinders or, in the alternative, stationary cams would rotate the radial cylinder arrangement. The external ring cam engine would probably be self starting, rare for a Stirling.
For higher rpm, the cams could be at the center of the radial engine, spinning a drive shaft.
The rpm in many low delta T engines is low so balancing issues would not be much of a problem.
Consider that a camshaft is about at the limits of its design capability...
The camshaft runs at 1/2 engine rpm. And still "float" is a problem.
The valves are lifted an inch or so, while the piston moves nearly 10 times as much.
The peak forces involved are roughly equal to the ratio of the areas, and the average forces are dominated by the springs (in the case of the valve), and pressurizing air, withstanding combustion, and *pulling* a vacuum (in the case of the piston).
No, I'd say that standard piston linkage could be enhanced through the use of "inflatable head gaskets" much easier.
Better still would be to go to external combustion...
This idea was mostly for Stirling and other closed cycle air engines that typically have cranks like steam, otto and diesel engines but don't have or need valves.
The crank was grandfathered in from steam but it doesn't make much sense on air engines where heat transfer is THE issue.
As you already know, the Quasiturbine has no sinusoidale crankshaft.
But in matter of heat engine, I would like to bring your attention to the Stirling page at
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and particularly the paragraph: Simple Quasiturbine Brayton Open Cycle as follows:
It is all about transforming heat into usable pressure. As an introduction to heat engine, let consider a pneumatic Quasiturbine where the engine block is kept hot by an external heat source, and into which relatively low pressure cold air is introduced through checkvalves at intake ports. Cold air will adsorbs heat from the Quasiturbine chamber walls and expand, making the rotor to turn (intake checkvalves prevent the pressure increase to flow back into the feed line). The rotor must spent part of its energy to drive a small (Quasiturbine) compressor to provide the low pressure cold air needed, but overall efficiency could be fairly good. This is an open Brayton cycle very similar to the complex one used in turboshaft jet engine, and it is usable in numerous applications, not to exclude cogeneration and conventional engine exhaust heat recovery. Stirling cycle does almost de same, but without any intake or exhaust, using rather a captured gas volume going alternatively into hot and cold areas.
You may also like to read on the same page the short steam circuit concept, making a Stirling run as a Ranking machine...
Instead of wasting heat energy in the radiator, after the fuel is burned in the conventional 4 stroke part of the cycle, water is injected in the last cycle to scavange some power from the hot engine.
The water flashes to steam for a "free" power stroke.
The heat transfer rate of liquid water on a hot cylinder wall is two (2) orders of magnitude higher than what you will get from just air in your engine.
And guess what? That two orders of magnitude higher is _still_ too low.
Heat transfer rate is not the dominent parameter here:
- First, the 6-stroke do not atempt to recover energy from combusted gas, but only the residual fraction transfered to the engine cylinder.
- Second, water required a lot of latent heat to evaporate before steam heating starts and some push become available. This kill the heat transfer benefit over air only machine (which recover the exhaust gas heat, and not only the residual cylinder heat).
- Third, the slow steam speed process is not well matched with the high speed combustion process of the 4 other strokes, while all strokes in an air machine are well matched in speed.
I encourage everyone to be "attempters" including engine design but if you want to be taken seriously you need to at least be coherent.
You need to have some pertinent numbers.
Certainly not in an IC engine adapted to transfer heat from the cylinder walls to air because the heat transfer coefficient for air is two orders of magnitude lower than nucleate boiling.
Heat transfer to air can be assumed to be zero.
Which is more than the energy from the power stroke.
Which means there is a lot of recoverable mechanical energy in the steam.
With that reasoning they should shut down steam power plants.
You need to support your statements with some numbers to be taken seriously.
Exhaust gas?
You can't even make up your mind on if this is closed cycle or open cycle?
!?!?!
With engine design you cannot just rationalize after the fact like Bush Administration officials.
It's better matched than air only by two orders or magnitude.
We agree here. If one stroke is moving at zero speed then it is certainly well matched to every other stroke moving at zero speed.
My point is that it is irrelevent to state that heat transfer rate of liquid water on a hot cylinder wall is two (2) orders of magnitude higher than what you will get from just air (? the heat transfer coefficient for air is two orders of magnitude lower than nucleate boiling ?), because once the liquid water is converted into dry steam, the most important heat transfer rate become almost the same as just air. Worst, the cylinder surface heat has then been used for latent water evaporation, and there is much less wall temperature to heat up the dry steam, while with air machine, this wall temperature is totally used to heat up the air.
Consequently, it is not fair to say the transfer rate is zero with air or dry steam, as all heat exchanger people know it does work (even for steam super-heater), and even better as the gas pressure increases, which is the case. It is not neither correct to state that a lot of latent heat means there is a lot of recoverable mechanical energy in the steam? Steam Power plant get their output from dry steam overheating, not from the latent heat.
Remember also that as the chamber pressure goes up, steam condensation increases, and it become more and more difficult to flash steam, which reduces the steam volume gain transformation.
In an internal combustion engine, all strokes have same duration, such that the slow steam speed process is not well matched with the high speed combustion process of the 4 other strokes, and it is mis leading to let people believe that dry steam matches better than air by two orders or magnitude... In air only machine, the strokes speed is not driven by an other type of engine process, and all air strokes are well matched in speed with the local heat transfert process, which is not the case in your hybrid 6-stroke concept.
I would like the heat transfer rate of air or dry steam to be higher, but apparently we have nothing to say about that. let do with what it is!
A better way to make use of a 6-stroke is explained at
- Save gas with a high efficiency Quasiturbine: A Six-Stroke, High-Efficiency Quasiturbine Concept Engine With Distinct, Thermally-Insulated Compression and Expansion Components -
Then it is irrelevant to discuss closed cycle engines because CC engines are all 100% dependent on heat transfer.
Once you have sat. steam at high pressure you can expand it for a Rankine cycle efficiency.
It's not necessary to super heat the steam for the cycle to be 25% efficient.
Nuke plants expand sat. steam for a Rankine cycle.
Which provides the steam power stroke.
Because the engine has efficiently converted the heat to mechanical energy.
It is less than 1% because of the low heat transfer rate.
Just that it's _near_ zero.
Not in an IC engine design.
Nuke plants expand sat. steam in the Rankine cycle, the closest you can get to Carnot in real life.
The space above the piston expands keeping pressure constant.
The temperature and the pressure never drop that low . . .
No numbers = no credibility.
It's better than just 4 strokes.
Then stop doing it. The issue was the heat transfer coefficient of _liquid_ water on hot steel being two oreders of magnitude greater than air.
True. The speed of all strokes is zero.
6 stroke is not my engine concept.
There are ways to increase heat transfer but adapting an IC engine ain't one of them.
You'ld be better off trying to think of _one_ advantage your engine has and then stick to hyping that.
By trying to hype everything you are like the woman in Clearwater, Florida who got her husband arrested by claiming he was a child molester.
That felt so good she decided to claim he was a drug kingpin, a nazi war criminal, a mafia don, etc.
She could have had him locked up for at least awhile but by the time she claimed he was an aid to Chinghis Khan she had blown her credibility and they let him out of jail.
You undermine any case your engine is good for anything by claiming it is good for everything.
The hybrid combustion steam cycle you support and defent is far from useful and practical. Your credibility numbers are not there neither!
If you like to flash steam into an engine, make it all steam, not an hybrid part of an internal combustion engine. Then you will be close to our water injection cycle at
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where:
III - Cold water injection engine This mode would definitively be unimaginable with conventional turbine, since they react to the speed of steam flow, which must be pre-conditioned. In fact, if a burner heats the Quasiturbine engine bloc directly, there is no need of a boiler any more (The Quasiturbine acting simultaneously as the boiler, the over heater and the evaporator), and one can then inject cold water (which will be preheated in the injector) at a pressure superior to the internal maximum working pressure. Ideal mode for thermal solar concentrator heating directly the Quasiturbine engine bloc ! (This mode is equivalent of using the Quasiturbine engine bloc as a "flash steam generator") (Notice that a remote heat source could use an un-evaporating fluid like oil or liquid sodium to transfer heat to the engine bloc)...
With internal combustion the explosion travels at near sonic speeds so the addition of heat to air is pretty instantaneous. Changing the piston wave form isn't going to help much in a high rpm IC engine so a conventional crank will do just fine.
With externally heated "air" engines, however, you can tailor the piston wave form to better match the isothermal expansion and compression strokes with a cam driven piston arrangement.
Now I see it. Yes, that's a cam driven piston engine alrighty. Very revolutionary. Must be a big problem sealing between the outer ring and the cylinders. It's surprising it even works.
Is there any thermodynamic advantage of a cam in an IC engine?
Here's another cam engine... announced with great fanfare 3 years ago and nothing since (typical)... though there do seem to be some advantages:
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-Dana
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