For certain values of “significantly,” you need not increase the compression ratio - just the expansion ratio. That’s what the Atkinson cycle is all about.
Another option is turbo-compounding, in which a turbine extracts mechanical work from the exhaust stream of a piston engine and helps drive the crankshaft. Peak in-cylinder combustion temperatures/pressures need not be increased, but efficiency does improve.
especially if it doubles as a turbocharger like on the Detroit Diesel DD15.
I don’t have a cite at hand, but by other measurements than absolute usage of available BTUs, modern IC engines are approach 100% efficiency within their inherent limitations. That is, the design may only be capable of around 30% efficiency on an absolute usage, but within design limits there is essentially no more efficiency to be extracted.
Increasing the HP/pound and looking at engines that turn out a modest net HP rating but are much smaller than even current econo engines is the future. And that is, instead of pulling 400HP out of a midsized engine for questionable purposes, we can pull 60HP out of a tiny engine to power something Yaris-sized and look at near-100 MPG.
But anyone who claims IC engines have any significant efficiency to salvage, using pretty much any alternate engineering, is stuck in the days of the 200 MPG carburetor… which at least had 4-5% remaining efficiency to try and magically extract.
the one thing to keep in mind is that the efficiency numbers we’re talking about are for an engine running at its peak output. That is, wide-open throttle at the RPM where inherent peak torque occurs. problem is, most of us never operate our engines that way so the engine is naturally going to be operating less efficiently, plus you have to pile on the pumping losses of driving around with a throttle that is barely cracked open.
yep. Diesel gets you a bit more thermal efficiency (and the ability to run extremely lean so long as you can clean up the resulting NOx) but there’s a reason hybrids have become a thing. If you can’t eke much more efficiency out of the powerplant, then you find ways to shut the powerplant off when it’d be operating at its least efficient points.
IC engines are close to Carnot efficiency? I didn’t realize that.
That actually makes sense. I’m looking it up and indeed it’s as you guys say.
It says engines in practice do 18%-20%, but I’d imagine a lot of the difference from the ideal is simply because of the need to accelerate and decelerate.
I honestly don’t know what the problem is the OP is trying to solve The problem with the wife’s car? Lower radiator hose leaking like a sieve and had to replace a starter relay. We each had brake calipers that went bad a few months ago. I needed to change my transmission fluid/filter a while back. Had to replace a couple of water pumps. The only problem I’ve had with an actual engine was when a cylinder burned out but I found out later I was running Splitfire spark plugs and they were too hot for 4-bangers. I’d rather have a time-tested reliable IC under the hood than a more complicated one that may give me fractionally more power or efficiency.
I wouldn’t say they’re “close” (by most people’s definition of the word) to Carnot efficiency, but they’re about as close as you’re likely to get without some absolutely miraculous breakthroughs in chemistry and material science. an Otto-cycle engine running at 12:1 compression has a theoretical upper limit of about 62% efficiency, but in the real world, you’re only likely to see one max out at 30-35% efficiency (and most of the time it’s operating at part load, with far lower efficiency). If you want to get closer to the theoretical max efficiency you need to do at least two things:
make all of the combustion happen instantaneously at TDC, so that all of the combustion products can be expanded through a complete expansion stroke. In a real engine, combustion takes place over a substantial period of time; some of the combustion happens too late in the expansion stroke to get much useful mechanical work out of it, so you end up pissing useful energy out via the exhaust pipe.
eliminate heat transfer from the hot combustion products to the combustion chamber walls. A lot of useful energy gets pissed away in the radiator, a necessary evil to prevent overheating. Experiments have been done with “adiabatic” engines in which the combustion chamber surfaces were glowing red hot (I gather these were either diesel or GDI), but then the intake air gets heated to the point of being very low density, reducing peak power output to unacceptably low levels.
Gasoline spark-ignited engines also have crummy part-load efficiency in part because they use a throttle to restrict intake air flow. Try breathing through a straw for ten minutes, and you’ll know how your car’s engine feels when you’re cruising down a city street with your foot barely pressing on the accelerator pedal: it’s doing a lot of work just to get air past that barely-opened throttle plate. This is why cars with big engines get worse fuel economy than cars with small engines: they operate at a smaller percentage of full load. This is easily observed in the fuel economy ratings of a car that is offered with a 4-cylinder and a 6-cylinder engine.
I’m not trained as a mechanical engineering, but why have devices like the wave disk engine or the scuderi engine not become popular? With high gas prices (especially in europe) and fears of climate change they should be pushed.
I’ve followed energy news for almost 20 years, much of it is just stuff that works in the lab but never hits the market.
This test on the scuderi via Nissan resulted in 54% improved fuel economy. That is about 50mpg.
The wave disk generator is 3-4x as efficient as ic engines. So a family sedan could get 100mpg.
Asked and answered.
Making something work in a lab or in a carefully-built and babied test mule is a lot different from putting a turnkey version in consumer hands.
As I’ve said before, I used to live near a university famed for these kind of small-team, grad-student “breakthroughs.” Not a one lacked implementation problems ranging from the range of $100M+ engineering solutions needed to “when unobtainium is cheap, we can build this.” But there was their test vehicle, pottering around*… so it must (1) work and (2) be being suppressed or ignored, right?
I absolutely guarantee you that if you walked into any major auto maker and said, “I have an alternative hydrocarbon engine that is significantly superior to the piston IC engine,” and could prove it, and had no significant engineering issues to work out to put it on the road to production, you’d not only make the sale, be a billionaire and get your picture on every magazine in the country, but be amazed at how easy it all was.
There might have been a day - the 1950s, in GM’s backyard - when innovations were spurned. Now, with the very notion of personal cars on the block, I assure you any innovation that would extend their lifespan as a salable product would be looked at with great interest.
Until you get to the “unobtainium” part, anyway.
Like he said, things that work in a laboratory setting or as a proof-of-concept don’t always translate into something that’ll work in the real world. Even in the early days of the gasoline powered Otto cycle car engine, they worked pretty well and lasted a fair amount of time. Most of these oddball things like the wave disk, Rand Cam, and so on have serious flaws. Like, how do you keep them lubricated? With a piston engine, it’s pretty much been simple. you pump oil to where its needed, and the oil in the crankcase is kept separate from the combustion chamber by the piston’s compression and oil control rings. Piston engines have worked that way for 100 years.
With something like the wave disk, the sealing/wear surfaces are such that the engine would need total-loss oiling just to survive. This was historically a problem with the Wankel rotary engine; after a ton of work and investment Mazda was able to get the apex seals to last but still ended up with an engine that was less efficient than an equivalently powerful piston engine.
It’s even more enraging when people read an article about some guy who converted his car to an EV using a bunch of golf cart batteries and a salvage electric motor, then ask why the automakers can’t do this.
I can assure you GM was extraordinarily innovative back then. They designed and sold a mid-size car with a four cylinder engine, independent rear suspension, a rear mounted transaxle, and an optional all-aluminum V8.
in 1961. It was called the Pontiac Tempest. There was very little like it on the market. But it withered away because customers weren’t asking for these things.
and that’s the kicker. You can have the most novel and unique thing in the world, yet it’ll go nowhere if you can’t convince people to buy it.