4 ms·

How much more room for improvement is there in gas and diesel?

Shivetya 8y ago
consider the expansion of plug in hybrids, similar to the Volt, Clarity, Prius, and Kona, all extend the viability of the petrol engine. In many cases it moves into the roll of a range extender because its weight combined with fuel is drastically less than what battery technology can accomplish; an example is the Model 3 which has nearly 1100 lbs of batteries for 310 miles. engines directly? variable valve timing will be common place and variable compression has debuted. more forced air systems and better injection tuning all present themselves. there is even ongoing work on two strokes and some of them are delivering better performance and emissions than four strokes.
- Retric 8y ago
  That's simplified as an engine + exhaust system + gas tank + gas + transmission weighs hundreds of pounds more than an electric cars engine alone. Electric cars do weigh more, but the difference is not that massive. You can actually drive further using gasoline to turn a gas turbine > electricity > electric cars battery than using that same fuel to operate a normal IC car. But, nobody does that because wind/solar/coal/nuclear are all far cheaper than gas.
- 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...
- Brakenshire 8y ago
  Plug in hybrids are probably only viable for a particular range of battery costs. When batteries are expensive it’s worthwhile reducing that cost by spending the extra money on a duplicated drive-train. As the cost of the battery falls the savings by having the extra drivetrain complexity fall.
zeroname 8y ago
He didn't say it was due to more efficient motors. Just compare the average MPG of the cars on US roads, running on subsidized gasoline, vs. those on European roads, running on heavily taxed gasoline.
- merpnderp 8y ago
  Gasoline in the US is taxed not subsidized.
  - marpstar 8y ago
    Kind of. The ethanol that's put into the gasoline is derived from corn, which is heavily subsidized in America.
  - Gustomaximus 8y ago
    An interesting question for this is will governments start with 'electricity tax'. There will be a ~$40bn revenue hole from cars swapping to electric in USA. Even proportionally more in Europe and Australia where the fuel taxes are much higher. https://www.statista.com/statistics/249129/us-state-and-local-motor-fuel-tax-revenue/ https://www.statista.com/statistics/249129/us-state-and-loca...
scythe 8y ago
More than you think. A hybrid car gets more mileage out of its engine for two reasons: - regenerative braking reduces the efficiency penalty of city driving. While a normal car sees a 25-30% mileage drop in stop-and-go traffic, a hybrid sees about 5-8%. - the actual engine is more efficient! The gasoline engine in hybrid vehicles usually replaces the Otto cycle with the Atkinson cycle. The latter is more efficient but has lower power, which in hybrids is compensated by an electric assist that turns on when accelerating. http://en.wikipedia.org/wiki/Atkinson_cycle http://en.wikipedia.org/wiki/Atkinson_cycle By taking these two effects together a non-plug-in hybrid can reduce fuel use in a city driving condition by more than 40%. I didn't make that number up: the 2019 standard Camry has 29 city mpg, while the 2019 hybrid Camry is rated for 51. The hybrid uses 56% as much fuel as the conventional engine! With a plug-in hybrid that can drop even lower. Unfortunately the marketing around all of this was muddled and most consumers have never heard of the Atkinson cycle. The original hybrids (Prius, Insight) were molded for a Japanese market, where simple and cute is a winning proposition, but American gearheads thought it looked and drove like a toy, a perception which was compounded by the fact that early hybrids made self-maintenance nearly impossible. Just replacing the 12V battery on a Prius is a major pain (speaking from experience!). Atkinson hybrids quickly became associated with a certain type of person and, for a while, many/most car geeks thought the real efficiency breakthrough were the German companies' maintenance-friendly and appropriately-scented turbodiesels, and we all know how that turned out. Hybrids have never captured more than 3.2% of the US market, but even if no highway-viable electric cars appear, a switch to plug-in hybrids could erase more than half of car-related GHG emissions. I know all of this mostly because of one very old and very stubborn former engineer who was impervious to every kind of advertisement and cultural stereotype, and who studied the technology in the Prius and bought one new in 2009. Everyone else in the family made fun of him, but Grandpa just didn't care, and raved about the Prius to anyone who would listen. Most of us, including me at the time, believed the meme that Atkinson hybrids were a marketing gimmick and only relevant if you drove in the city often enough to take advantage of the regenerative brakes, and anyway, turbodiesels were the future. Grandpa didn't live long enough to see himself get proven right, but I still drive his car.
- stephengillie 8y ago
  As a(n obnoxiously outspoken) 2016 Camry Hybrid owner, it's true. On highway it usually gets ~40 MPG. Below 45 MPH the engine can shut off, and often it coasts along, only using the engine to accelerate or go uphill. My Costco route consistently gets 45-50 MPG, and I use about 28 gallons of gas to go 1,080 miles a month. Long term, I'm hopeful to replace the NiMH battery with lithium and a plug-in charger.

consider the expansion of plug in hybrids, similar to the Volt, Clarity, Prius, and Kona, all extend the viability of the petrol engine. In many cases it moves into the roll of a range extender because its weight combined with fuel is drastically less than what battery technology can accomplish; an example is the Model 3 which has nearly 1100 lbs of batteries for 310 miles. engines directly? variable valve timing will be common place and variable compression has debuted. more forced air systems and better injection tuning all present themselves. there is even ongoing work on two strokes and some of them are delivering better performance and emissions than four strokes.

Retric 8y ago
That's simplified as an engine + exhaust system + gas tank + gas + transmission weighs hundreds of pounds more than an electric cars engine alone. Electric cars do weigh more, but the difference is not that massive. You can actually drive further using gasoline to turn a gas turbine > electricity > electric cars battery than using that same fuel to operate a normal IC car. But, nobody does that because wind/solar/coal/nuclear are all far cheaper than gas.
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...
Brakenshire 8y ago
Plug in hybrids are probably only viable for a particular range of battery costs. When batteries are expensive it’s worthwhile reducing that cost by spending the extra money on a duplicated drive-train. As the cost of the battery falls the savings by having the extra drivetrain complexity fall.

zeroname 8y ago

He didn't say it was due to more efficient motors. Just compare the average MPG of the cars on US roads, running on subsidized gasoline, vs. those on European roads, running on heavily taxed gasoline.

merpnderp 8y ago
Gasoline in the US is taxed not subsidized.
- marpstar 8y ago
  Kind of. The ethanol that's put into the gasoline is derived from corn, which is heavily subsidized in America.
- Gustomaximus 8y ago
  An interesting question for this is will governments start with 'electricity tax'. There will be a ~$40bn revenue hole from cars swapping to electric in USA. Even proportionally more in Europe and Australia where the fuel taxes are much higher. https://www.statista.com/statistics/249129/us-state-and-local-motor-fuel-tax-revenue/ https://www.statista.com/statistics/249129/us-state-and-loca...

scythe 8y ago

More than you think. A hybrid car gets more mileage out of its engine for two reasons: - regenerative braking reduces the efficiency penalty of city driving. While a normal car sees a 25-30% mileage drop in stop-and-go traffic, a hybrid sees about 5-8%. - the actual engine is more efficient! The gasoline engine in hybrid vehicles usually replaces the Otto cycle with the Atkinson cycle. The latter is more efficient but has lower power, which in hybrids is compensated by an electric assist that turns on when accelerating. http://en.wikipedia.org/wiki/Atkinson_cycle http://en.wikipedia.org/wiki/Atkinson_cycle By taking these two effects together a non-plug-in hybrid can reduce fuel use in a city driving condition by more than 40%. I didn't make that number up: the 2019 standard Camry has 29 city mpg, while the 2019 hybrid Camry is rated for 51. The hybrid uses 56% as much fuel as the conventional engine! With a plug-in hybrid that can drop even lower. Unfortunately the marketing around all of this was muddled and most consumers have never heard of the Atkinson cycle. The original hybrids (Prius, Insight) were molded for a Japanese market, where simple and cute is a winning proposition, but American gearheads thought it looked and drove like a toy, a perception which was compounded by the fact that early hybrids made self-maintenance nearly impossible. Just replacing the 12V battery on a Prius is a major pain (speaking from experience!). Atkinson hybrids quickly became associated with a certain type of person and, for a while, many/most car geeks thought the real efficiency breakthrough were the German companies' maintenance-friendly and appropriately-scented turbodiesels, and we all know how that turned out. Hybrids have never captured more than 3.2% of the US market, but even if no highway-viable electric cars appear, a switch to plug-in hybrids could erase more than half of car-related GHG emissions. I know all of this mostly because of one very old and very stubborn former engineer who was impervious to every kind of advertisement and cultural stereotype, and who studied the technology in the Prius and bought one new in 2009. Everyone else in the family made fun of him, but Grandpa just didn't care, and raved about the Prius to anyone who would listen. Most of us, including me at the time, believed the meme that Atkinson hybrids were a marketing gimmick and only relevant if you drove in the city often enough to take advantage of the regenerative brakes, and anyway, turbodiesels were the future. Grandpa didn't live long enough to see himself get proven right, but I still drive his car.

stephengillie 8y ago
As a(n obnoxiously outspoken) 2016 Camry Hybrid owner, it's true. On highway it usually gets ~40 MPG. Below 45 MPH the engine can shut off, and often it coasts along, only using the engine to accelerate or go uphill. My Costco route consistently gets 45-50 MPG, and I use about 28 gallons of gas to go 1,080 miles a month. Long term, I'm hopeful to replace the NiMH battery with lithium and a plug-in charger.