5 ms·

Without abandoning piston engines entirely and going to turbines or something, modern auto engines are approaching maximum practical thermal efficiency for the

by beat 8y ago

Without abandoning piston engines entirely and going to turbines or something, modern auto engines are approaching maximum practical thermal efficiency for the conditions under which they must operate (being primarily horsepower-oriented rather than torque-oriented). You can get maybe 50% better if you're powering an oil tanker rather than a car, but you're not powering an oil tanker, but rather something that has to accelerate and decelerate and idle in unpredictable ways. Hybrid was the last big improvement. Barring a radical new technology (and variable valve timing ain't radical), we might squeeze, what, 10% better thermal performance out? Get 40mpg rather than 37? Big deal. And really, this is all driven by energy costs in the end. We're already hitting a point where commodity solar/wind electricity is cheaper than commodity coal, and much cheaper than commodity gasoline. This creates a tremendous market incentive for purely electric vehicles. And that tech has much more room for improvement than any gas engine - batteries will keep getting cheaper and more efficient for some time to come. When my options are a $25,000 Ford or a $90,000 Tesla, an electric car seems like a dream. But when it turns into a $25,000 Ford or a $30,000 all-electric car (maybe from Ford!)... TCO starts becoming a very attractive argument, on top of the feel-good factor.

headmelted 8y ago
"This creates a tremendous market incentive for purely electric vehicles." Can confirm. I bought a used Nissan Leaf two months ago from a dealer (being used it was a small fraction of the $25k Ford). A near-identical car (trim/mileage/colour) is now listed on their site for close to 30% more than I paid. If we were living in normal times this would make no sense - but the TCO picture is changing that rapidly (owing to oil prices going up and used EVs being so scarce).
- aphextron 8y ago
  I paid $5k for my 2011 Leaf with 10 bars and 30k miles. Best decision ever. Seems like people are catching on though since theyre getting hard to find anywhere near that now.
  - headmelted 8y ago
    Well.. these people you speak of can find their own. Something something cold dead hands, etc.
thucydidesofusa 8y ago
You seem to conflate system efficiency (e.g MPG) with thermal efficiency. You're right that the peak thermal efficiency is thermodynamically determined and we're getting pretty close to it [0], or at least some manufacturers are. However, there's a lot of work to be done in making the engines more efficient across a wider variety of operating conditions. Hybrids largely succeeded because they let manufacturers make engine torque demand more predictable / gave them new modalities to create the torque the driver requests. You're right that variable valve timing isn't new - I'm under the impression that all new cars in America with overhead cams have it. However, systems that allow the valve's lift and duration to be set independently from the crankshaft / RPM certainly are new and one first generation system is poised to increase fuel efficiency by ~14% in a steady state cruising [1]. I'm actually surprised the increase isn't higher, the amount of friction that camshafts generate is unreal and removing that source of friction is extremely compelling (the benefits of infinitely adjustable timing and lift nonwithstanding). I was in a dyno lab once upon a time, and there was a ~500 kW gas engine on the dyno, the 4 camshafts collectively generated ~200 kW of friction at ~14,000 rpm. Obviously that's a much faster speed than any road going engine outside a sporty motorcycle (and friction is proportional to engine speed), but it does illustrate the friction at play. Heck, simply reducing oil pressure to minimum-viable pressures yields 4-6% fuel efficiency increases [2]. There's no shortage to improvements in engine accessories (it's probably why so many of them have gone electric and are no longer driven off the crankshaft). And the thermodynamic cycle of the engine is something we can adjust. Mazda's next gen Skyactiv-X system is poised to deliver 30% better fuel efficiency than the current system (Skyactiv-G) [3] because it's introducing compression ignition to the car. And a lot of the benefits are delivered throughout the engine's operating range. Finally, we're guilty of treating cars as static. Better materials, more aerodynamic shapes, better packaging, etc. can contribute to massive efficiency gains. The sedans with the Prius' powertrain (the HS250h, Corolla hybrid in Japan) get much worse milage than the Prius. The reality is that the Prius is unusually light and unusually aerodynamic, it's worth at least +10% better milage on the freeway. Better materials and construction can take us a long way to better fuel efficiency. [0]: http://www.thedrive.com/tech/18919/toyota-develops-worlds-most-thermally-efficient-2-0-liter-engine http://www.thedrive.com/tech/18919/toyota-develops-worlds-mo... [1]: https://www.motortrend.com/news/is-the-era-of-the-camless-valvetrain-finally-upon-us-technologue/ https://www.motortrend.com/news/is-the-era-of-the-camless-va... [2]: https://www.asme.org/engineering-topics/articles/automotive/better-fuel-efficiency-through-a-better-oil-pump https://www.asme.org/engineering-topics/articles/automotive/... [3]: https://www.caranddriver.com/reviews/2019-mazda-3-with-skyactiv-x-compression-ignition-gas-engine-prototype-drive-review https://www.caranddriver.com/reviews/2019-mazda-3-with-skyac...
petre 8y ago
We still have to see how HPPI and turning off two cylinders out of four at low speed improves fuel consumption. There are also alternative fuel options for ICE vehicles such as LPG for petrol powered vehicles and DME for diesel vehicles. Current diesels already do 65 mpg which is a big deal compared to 36 mpg. DME can be produced locally out of syngas from industrial processes or biomass.
- beat 8y ago
  Regardless, an all-electric car is going to be pushing 90% thermal efficiency - transforming energy into acceleration. A combustion car isn't going to break 40%. Exotic tech like variable timing and taking cylinders out of service isn't going to get huge gains - they're actually a lot of work for tiny gains, because all the huge gains have already been had. Moreover, electric cars will get that efficiency with no compromise in performance, unlike combustion cars with tiny, weak, "fuel efficient" motors. A Tesla Model S is the fastest car in its class, as well as the most efficient. The only big win for combustion-based cars is the range potential, because the energy storage of liquid fuels is so much denser. I don't expect to see electric commercial aircraft in my lifetime. But biomass-based liquid fuel? Sure. It just won't be cost-competitive with solar/wind into a battery. It'll be limited to specialized applications where power/weight matters.

by beat 8y ago

headmelted 8y ago

"This creates a tremendous market incentive for purely electric vehicles." Can confirm. I bought a used Nissan Leaf two months ago from a dealer (being used it was a small fraction of the $25k Ford). A near-identical car (trim/mileage/colour) is now listed on their site for close to 30% more than I paid. If we were living in normal times this would make no sense - but the TCO picture is changing that rapidly (owing to oil prices going up and used EVs being so scarce).

aphextron 8y ago
I paid $5k for my 2011 Leaf with 10 bars and 30k miles. Best decision ever. Seems like people are catching on though since theyre getting hard to find anywhere near that now.
- headmelted 8y ago
  Well.. these people you speak of can find their own. Something something cold dead hands, etc.

thucydidesofusa 8y ago

You seem to conflate system efficiency (e.g MPG) with thermal efficiency. You're right that the peak thermal efficiency is thermodynamically determined and we're getting pretty close to it [0], or at least some manufacturers are. However, there's a lot of work to be done in making the engines more efficient across a wider variety of operating conditions. Hybrids largely succeeded because they let manufacturers make engine torque demand more predictable / gave them new modalities to create the torque the driver requests. You're right that variable valve timing isn't new - I'm under the impression that all new cars in America with overhead cams have it. However, systems that allow the valve's lift and duration to be set independently from the crankshaft / RPM certainly are new and one first generation system is poised to increase fuel efficiency by ~14% in a steady state cruising [1]. I'm actually surprised the increase isn't higher, the amount of friction that camshafts generate is unreal and removing that source of friction is extremely compelling (the benefits of infinitely adjustable timing and lift nonwithstanding). I was in a dyno lab once upon a time, and there was a ~500 kW gas engine on the dyno, the 4 camshafts collectively generated ~200 kW of friction at ~14,000 rpm. Obviously that's a much faster speed than any road going engine outside a sporty motorcycle (and friction is proportional to engine speed), but it does illustrate the friction at play. Heck, simply reducing oil pressure to minimum-viable pressures yields 4-6% fuel efficiency increases [2]. There's no shortage to improvements in engine accessories (it's probably why so many of them have gone electric and are no longer driven off the crankshaft). And the thermodynamic cycle of the engine is something we can adjust. Mazda's next gen Skyactiv-X system is poised to deliver 30% better fuel efficiency than the current system (Skyactiv-G) [3] because it's introducing compression ignition to the car. And a lot of the benefits are delivered throughout the engine's operating range. Finally, we're guilty of treating cars as static. Better materials, more aerodynamic shapes, better packaging, etc. can contribute to massive efficiency gains. The sedans with the Prius' powertrain (the HS250h, Corolla hybrid in Japan) get much worse milage than the Prius. The reality is that the Prius is unusually light and unusually aerodynamic, it's worth at least +10% better milage on the freeway. Better materials and construction can take us a long way to better fuel efficiency. [0]: http://www.thedrive.com/tech/18919/toyota-develops-worlds-most-thermally-efficient-2-0-liter-engine http://www.thedrive.com/tech/18919/toyota-develops-worlds-mo... [1]: https://www.motortrend.com/news/is-the-era-of-the-camless-valvetrain-finally-upon-us-technologue/ https://www.motortrend.com/news/is-the-era-of-the-camless-va... [2]: https://www.asme.org/engineering-topics/articles/automotive/better-fuel-efficiency-through-a-better-oil-pump https://www.asme.org/engineering-topics/articles/automotive/... [3]: https://www.caranddriver.com/reviews/2019-mazda-3-with-skyactiv-x-compression-ignition-gas-engine-prototype-drive-review https://www.caranddriver.com/reviews/2019-mazda-3-with-skyac...

petre 8y ago

We still have to see how HPPI and turning off two cylinders out of four at low speed improves fuel consumption. There are also alternative fuel options for ICE vehicles such as LPG for petrol powered vehicles and DME for diesel vehicles. Current diesels already do 65 mpg which is a big deal compared to 36 mpg. DME can be produced locally out of syngas from industrial processes or biomass.

beat 8y ago
Regardless, an all-electric car is going to be pushing 90% thermal efficiency - transforming energy into acceleration. A combustion car isn't going to break 40%. Exotic tech like variable timing and taking cylinders out of service isn't going to get huge gains - they're actually a lot of work for tiny gains, because all the huge gains have already been had. Moreover, electric cars will get that efficiency with no compromise in performance, unlike combustion cars with tiny, weak, "fuel efficient" motors. A Tesla Model S is the fastest car in its class, as well as the most efficient. The only big win for combustion-based cars is the range potential, because the energy storage of liquid fuels is so much denser. I don't expect to see electric commercial aircraft in my lifetime. But biomass-based liquid fuel? Sure. It just won't be cost-competitive with solar/wind into a battery. It'll be limited to specialized applications where power/weight matters.