Toroidal Engine

[centarix]

I've been waiting impatiently for many years for a rotary engine design to replace more conventional designs. There are a handful of people who think Wenkel can still be improved. But I'm fascinated by this toroidal design:

https://www.youtube.com/watch?v=n5L0Zc6Ic8Y

This is very similar to the MYT which went exactly nowhere (warning: bad music):

https://www.youtube.com/watch?v=i0XTU7gCZV4&t=1s

The inventor of that engine swore left, right, up, and down that it was tested as a highly efficient air compressor. Yet it does not seem to be used an as air compressor either.

I've also expected a turbine hybrid to be developed by now, but no such thing was ever made on that end either. I was told that the reason turbine designs are not used in cars is because of their lack of responsiveness, which for a hybrid would be a non-issue. Yet here we are with a bunch of hybrids but no turbine in any of them. I just refuse to believe there is nothing *revolutionary* coming for engines. I'm far from this field but every few years I'm looking at another new design that should have worked but didn't. I'm disappointed! The RX-8 was great to see in production, but not that "killer app" I was hoping for.

 

[BrianPetersen]

How do you machine a toroid? (Hint: Expensively, compared to machining a cylinder.)

How do you seal the gaps between the fixed and moving parts of the toroid (necessary to transfer force between the "pistons" and whatever the mechanism is that constrains them to their path of motion)?

How do you obtain proper piston ring sealing? (Hint: Normal piston rings in a normal cylinder don't have to deal with a surface that is locally convex on one side of a piston and locally concave on the other side.)

What does this accomplish that a normal reciprocating design doesn't accomplish aside from being way more difficult to manufacture and way more difficult to seal?

Turbines don't scale down well, largely due to Reynolds number effects, and the efficiency drops off very badly when operated at part load - much, much more so than a piston engine does. At a utility power generation scale, where it almost doesn't matter what the engine weighs or how big it is, you can use a large number of stages of compression and intercooling and operate at a high pressure ratio (akin to using a high compression ratio) for decent efficiency. On an automotive scale ... that simply isn't practical. You are stuck with the single-stage, or at most two-stage, compression and expansion and the lower pressure ratio and poorer efficiency that goes along with that. "But in a hybrid it can operate at constant speed and load" ... aye, but not very well. If you size the engine to work at the power demand for cruising at 130 km/h (necessary once the batteries are dead) then it will be operating at a 1 or 2 percent duty cycle when stuck in traffic, and the starting and stopping is not so good ... AND because the power output does not even remotely match the power demand, you will be stuck with the battery charge and discharge losses.

A turbine engine on an automotive scale that matches the efficiency of a good piston engine has not been developed ... and that's at the best-efficiency point, nevermind that the efficiency drops into the toilet when operated off the best-efficiency speed and load point FAR worse than the efficiency of a piston engine drops off when operating off the best-efficiency speed and load point.

The gasoline engine in my car idles at 800 rpm, it develops functional torque from 1200 rpm up, and redlines at 6500 rpm, and it has the same pressure ratio (compression ratio) throughout that range. A gas turbine might idle at 50% of maximum RPM at which point, at least to first approximation, its pressure ratio is about a quarter of what it is at maximum RPM, and not develop any useful power below 70% of maximum RPM and not be in its efficient operating range below 90% of maximum RPM.

A central power generation plant is a great application for a gas turbine as the first stage of a combined-cycle plant. A large aircraft is another great application, because they always cruise at (pretty much) the same speed using (almost) the same power output. Automotive ... not so much.

 

[romke]

there have been lots of alternatives to conventional combustion engines - and apart from the more or less standard gasoline and diesel types all others have failed for various reasons.

there is no need for a new type of engine in terms of reliability, production costs or efficiency. reliability nowadays is no problem, production costs have been brought down over the years and efficiency, although actually quite low, is as best we can get with modern engines of the internal combustion type.

the main problem in engine design nowadays is CO2 emissions. other emissions can be more or less controlled by clever designs and aftertreatment of exhaust gases, CO2 emissions are directly related to the type and amount of fuel used.

the fossil fuelled engine thus is essentially "dead", although it will still take quite some time before it becomes "extinct" for daily use.

the future is to either generate "clean" electricity that subsequently can be used in electric motors or in alternative fuels that do not emit CO2 or other substances (eg hydrogen) that can be used in engines more or less comparable with present day piston engine designs.

 

[enginesrus]

Funny how they show machining the cylinder if that's what you call it. They are leaving out that it is not a round hole all the way through. Even single pointed boring may not accomplish what they need for proper sealing.
And then the thought of transferring the action of the combustion process through a gear set, enters more losses in the system. And then everything BrainPetersen said as well.
It is so funny how people that come up with these goofy ideas think they can replace or reinvent the wheel so to say with something so complicated and difficult to manufacture. Why do they do it? I think just so they can brag about having a patent on their supposed great idea.

 

[3DDave]

"Why do they do it?" That's an interesting question. I've thought it comes from a perceived problem within existing solutions and they develop a device/method that does not have that flaw, even if it introduces a large number of other problems.

Number one on the mechanism list seems to be alternative bicycle power transmission systems. Belt drives, the daVinci mechanism, pull-pull cable recoil drives, et al. Some provide continuous variability, others to prevent chain oil from getting on clothing, others to eliminate having to learn to use the shifter while pedaling. But mostly they are less efficient, have significantly more parts, or are significantly more expensive.

I find that the number of alternative solutions peaks where a bit more than a basic level of understanding is required. Few try to design new mousetraps; the current ones are very simple. Few try to design turbojets, the difficulty is too great. I think it explains the wide variety of clothing styles and houses. They aren't trivial, but they are difficult to go horribly wrong. And ways to convert expanding hot gas into mechanical motion.

 

[TugboatEng]

On the marine side we always used the PLAN formula (mean effective pressure x length of stroke x area of piston x number of power strokes per time) to estimate engine power. Anyways, the number results in indicated horsepower which is very close to shaft horsepower. Indicated power assumes 100% efficiency of the engine. The point is, there just isn't much to gain by changing the architecture of the engine.

 

[enginesrus]

The way I see it, why not spend all that effort attempting to improve on the Wankel engine instead of adding such complexity to an already very simple design. If it is just because !! they don't like the normal pistons and cylinders the Wankel fills the bill, and is so much simpler than all these goofy designs some folks come up with.

 

[dgallup]

Improvements of existing designs takes careful study, analysis, testing and development. While lots of companies are deeply involved in this, it's not that sexy. If you want to raise some money on Go Fund Me it's much easier and cheaper to have a flashy video and make a lot of unsupported claims.

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