7 ms·

One thing to keep in mind is that the energy density of gasoline is a chemistry measurement. The energy density of a gasoline power train is a different measur

One thing to keep in mind is that the energy density of gasoline is a chemistry measurement. The energy density of a gasoline power train is a different measurement taking into account chemistry and physics. Specifically car engines can only turn 33% of gasoline’s stored energy into motion. Which still puts gasoline ahead in terms of efficiency relative to hydrogen or battery powertrains but reduces the difference a lot.

agumonkey 3y ago
I remember people saying that hybrid vehicle used ICE not to generate car scale torque, thus being build differently to improve the efficiency (mostly due to better control of thermal constraints ensuring better chemical reaction, higher conversion and less pollution). Do you know how true that is ?
- schiffern 3y ago
  They might be referring to the Atkinson cycle engine, which is really just adjusting the valve timing. Lower power but higher efficiency. https://www.autoweek.com/news/green-cars/a1832081/atkinson-cycle-explained/ https://www.autoweek.com/news/green-cars/a1832081/atkinson-c...
  - etrautmann 3y ago
    No, it means that you can leverage a more efficient part of an engine’s torque curve by supplementing with electric power at the low and high end (since motors have a flatter torque curve).
    - sharpneli 3y ago
      Not just that. It does require Atkinson cycle to reach the efficiencies they have. It just means that the compression stroke is shorter than the power stroke. Basically with that cycle they can get massive compression ratios. As an example newer Toyotas are at 14:1 ratio with 41% thermal efficiency. That’s close to diesel territory on a gasoline car. Naturally when you floor it it goes to Otto cycle and efficiency drops.
    - fho 3y ago
      And, in the case of Toyotas eCVTs, keeping the ICE in the most-efficient-rpm sweet spot longer by allowing the ICE RPM to be pretty much independent of the wheel RPM. It's somewhat strange because RPM noise barely correlats with speed or acceleration anymore. Also: start-stop-automatic for free ... I am still somewhat spooked when the motor just turns off going 70 km/h because the ECU decides that the ICE is not needed anymore.
- TylerE 3y ago
  Not true at all. Torque is basically just a number you can manipulate with gearing.
- taneq 3y ago
  This is the “series hybrid” or “range extender” approach and the issue is that all of the engine’s power needs to be converted into electrical power and then back into mechanical power, even when running the traction motor directly off the generator output. This causes significant losses in efficiency which more or less cancel out the gains from being able to optimise the engine for a specific constant speed.
- Danieru 3y ago
  As of this year, and limited to three models exclusive to Japan: yes this happens. The new 2023 model year Serena from Nissan uses a generator optimized engine in a series hybrid setup. The engine runs at a fixed rpm (except in extreme situations like accelerating a bunch on the highway going from 110 to 140) then it switches to a second higher rpm mode. I bought one, it's a lot of fun to manage the engines heat and battery room. My record is 38km per liter using local driving up and down our hilly community. Pretty incredible when you consider hills are the natural enemy to none hybrid millage. The car accelerates like an EV. And with Japan's expensive electricity I'm paying only about double the millage cost of an EV. Despite the full size minivan costing us about 20k USD new. Most hybrids, and all Toyota ones, are not using a special fixed rpm engines. They use a regular motor with different timings. The Nissan fixed rpm engine is actually less powerful than the electric motor powering the wheels. Thus at max acceleration you can deplete the battery faster than it is charged.
  - galangalalgol 3y ago
    If we are just using it as a generator, a turbine engine makes more sense. Very efficient at fixed rpm. Many trains use that sort of hybrid setup. But if you put in enough battery to warm up a small proane fuel cell to warm up a larger propane fuel cell you could just fill up at the propane pump and still get battery efficiencies but with a lightening tank. And they think they have propane generation from environmental co2 over 90% efficient now too.
    - pi-e-sigma 3y ago
      Turbine in a car is completely impractical. Some tanks, like M1 Abrams use a turbine and they are painfully loud and the exhaust is so hot it can literally set on fire anything too close to it. Imagine sitting in a traffic jam and lighting up a car behind you :)
  - agumonkey 3y ago
    oh right, I remember some guy mentioning fixed RPM helping a lot.
- scns 3y ago
  The Chevrolet Volt works like that.
at_a_remove 3y ago
Power train don't pour.
TylerE 3y ago
An important point EV advocates often gloss over is that you don't get to burn battery. In aviation, especiaslly, this really matters - over half an aircraft's weight at takeout is often fuel. The later in the flight it is, the more fuel has burned off, the lighter the plane is, and the more efficient the rest of the flight will be. You have to lug that empty battery around at full weight.
- wilg 3y ago
  Technically the battery gets a teeny bit lighter because of E=mc².
  - anyoneamous 3y ago
    Over long journeys, those 3 nanograms really add up.
    - fragmede 3y ago
      https://physics.stackexchange.com/questions/34421/does-the-mass-of-a-battery-change-when-charged-discharged https://physics.stackexchange.com/questions/34421/does-the-m... It's about a microgram.
      - hermitdev 3y ago
        So, in other words, you gained more mass from bugs splating on the windshield than you lost in the battery.
        acdha 3y ago
        Don’t worry, we’ve been working on that: https://www.science.org/content/article/where-have-all-insects-gone https://www.science.org/content/article/where-have-all-insec...
        b112 3y ago
        But in the winter, as the cabin warms up, you have fewer air molecules to cart around.
tonymet 3y ago
the heat itself is useful in winter to keep the system regulated and heat the passengers
numpad0 3y ago
> can only turn 33% Energy density of gasoline is literally 12900 Wh/kg and 9500 Wh/L, Li-ion(not combusted) is ~250 Wh/kg and ~700 Wh/L. That's 50x/14x raw and 17x/13x at 33% efficiency without hybrid/ICE optimization gains. (23222915000 Wh/kg and 370000000000 Wh/L for Pu239 btw, source[1]) 1: https://en.wikipedia.org/wiki/Energy_density https://en.wikipedia.org/wiki/Energy_density
- AwaAwa 3y ago
  Had a double take on reading Li-ion (not combusted) and then immediately went looking at EV battery fires. A rabbit hole of solid fuel and it's considerations followed. I have become a trained monkey. Well done internet. And thank you for the 'x' factor. Had never seen that, outside of everyone stating ICE is only 33% efficient.
- yazaddaruvala 3y ago
  Thank you for the math. But I don’t think you really tried to understand my point. Firstly, the newest solid state batteries (relevant because that is what I was responding about) are 2x the density so that is quite good (8.5x/6.5x). Which is already pretty close. They are also going to get better through iteration likely to 3-5x or so (but let’s ignore that for now). Secondly, the power train also includes regenerative breaking, reduced weight from transmission, in hub motors (reducing axcel weight), reduced center of gravity allowing better drag profiles, no external coolant systems, no engine oil compartments, no fan belts, etc. I’m happy for you to keep doing the math, but the reality is XXX km or miles per “full tank” is the best measurement because it takes all those factors into consideration.
  - numpad0 3y ago
    Oh I'm not so against EV, I'm just being pro-nuke as I personally always has been. Honestly I don't get why some sort of EV supremacy theory has to be defended at all costs. Those are just facts that density and recyclability of Li-ion is just atrocious. Gasoline particles tho NOx bad for health yeah I get that part. Seriously, if we could just build 2-3 air-cooled Plutonium fission per each megalopolis core and use e-Fuel on existing hybrids we'd solve everything in modern society ever. The reactor could double as cityscale thermojet ventilation system as well, eliminating heat and atmosphere problems once and for all. It will of course work as a training exercise for coming real Space Age in which humanity builds bunches after bunches of cylindrical habitats fabricated and populated in space. The only two roadblocks towards that path are some NIMBYism/NPT fears and cost.
rkuodys 3y ago
I personally wonder how much more the 33% would be if we had continued the focus on ICE. I believe there is no business case anymore to invest significantly in advancing technology, if everyone wants a new shiny toy.
- iknowstuff 3y ago
  It’s been 200 years and untold amounts of R&D money thrown at this incredibly lucrative, huge industry. It’s not budging much beyond what it is.
- Tanoc 3y ago
  There's not much more you can get out of current fuel blends. Methanol is potent but very expensive to mix, the even more expensive nitromethane is so powerful it strains the science of metallurgy and thus is some of the most dangerous stuff to handle, and hydrazine is so energy dense but so unstable it's used as rocket fuel. Porsche's E-Fuel is just barely more efficient than gasoline because of the density at point six megajoules a kilogram, versus point five four for one hundred octane gasoline. The major issue is parasitic drivetrain loss from having to push the cylinder which pushes the cam which turns the flywheel which friction fits against the clutch which friction fits against the transmission flywheel which turns dozens of metal gears which rotates the driveshafts. Direct drive implementations where the engine's output shaft is mated directly to the axle are much more efficient and have been used in massive ships, but are entirely impractical for use in passenger vehicles. There's the Otto, Atkinson, Wankel, Scuderi and diesel cycles for liquid fuel combustion, and all have tradeoffs leaving them competitive with eachother instead of having a clear best solution thanks to everything else required to transfer the power from the initial combustion. In short, we've hit the mechanical engineering dead end for massive efficiency gains with ICEs. It's all chemical from here, and thus gets much more expensive to run.
- rini17 3y ago
  ICE is kind of a dead end, you convert energy from chemical to thermal to mechanical and every conversion is lossy. You want to use chemical energy directly instead, like some kind of "hydrocarbon/air cell" and we don't know how to do it. At least not with mixed hydrocarbons.

agumonkey 3y ago

I remember people saying that hybrid vehicle used ICE not to generate car scale torque, thus being build differently to improve the efficiency (mostly due to better control of thermal constraints ensuring better chemical reaction, higher conversion and less pollution). Do you know how true that is ?

schiffern 3y ago
They might be referring to the Atkinson cycle engine, which is really just adjusting the valve timing. Lower power but higher efficiency. https://www.autoweek.com/news/green-cars/a1832081/atkinson-cycle-explained/ https://www.autoweek.com/news/green-cars/a1832081/atkinson-c...
- etrautmann 3y ago
  No, it means that you can leverage a more efficient part of an engine’s torque curve by supplementing with electric power at the low and high end (since motors have a flatter torque curve).
  - sharpneli 3y ago
    Not just that. It does require Atkinson cycle to reach the efficiencies they have. It just means that the compression stroke is shorter than the power stroke. Basically with that cycle they can get massive compression ratios. As an example newer Toyotas are at 14:1 ratio with 41% thermal efficiency. That’s close to diesel territory on a gasoline car. Naturally when you floor it it goes to Otto cycle and efficiency drops.
  - fho 3y ago
    And, in the case of Toyotas eCVTs, keeping the ICE in the most-efficient-rpm sweet spot longer by allowing the ICE RPM to be pretty much independent of the wheel RPM. It's somewhat strange because RPM noise barely correlats with speed or acceleration anymore. Also: start-stop-automatic for free ... I am still somewhat spooked when the motor just turns off going 70 km/h because the ECU decides that the ICE is not needed anymore.
TylerE 3y ago
Not true at all. Torque is basically just a number you can manipulate with gearing.
taneq 3y ago
This is the “series hybrid” or “range extender” approach and the issue is that all of the engine’s power needs to be converted into electrical power and then back into mechanical power, even when running the traction motor directly off the generator output. This causes significant losses in efficiency which more or less cancel out the gains from being able to optimise the engine for a specific constant speed.
Danieru 3y ago
As of this year, and limited to three models exclusive to Japan: yes this happens. The new 2023 model year Serena from Nissan uses a generator optimized engine in a series hybrid setup. The engine runs at a fixed rpm (except in extreme situations like accelerating a bunch on the highway going from 110 to 140) then it switches to a second higher rpm mode. I bought one, it's a lot of fun to manage the engines heat and battery room. My record is 38km per liter using local driving up and down our hilly community. Pretty incredible when you consider hills are the natural enemy to none hybrid millage. The car accelerates like an EV. And with Japan's expensive electricity I'm paying only about double the millage cost of an EV. Despite the full size minivan costing us about 20k USD new. Most hybrids, and all Toyota ones, are not using a special fixed rpm engines. They use a regular motor with different timings. The Nissan fixed rpm engine is actually less powerful than the electric motor powering the wheels. Thus at max acceleration you can deplete the battery faster than it is charged.
- galangalalgol 3y ago
  If we are just using it as a generator, a turbine engine makes more sense. Very efficient at fixed rpm. Many trains use that sort of hybrid setup. But if you put in enough battery to warm up a small proane fuel cell to warm up a larger propane fuel cell you could just fill up at the propane pump and still get battery efficiencies but with a lightening tank. And they think they have propane generation from environmental co2 over 90% efficient now too.
  - pi-e-sigma 3y ago
    Turbine in a car is completely impractical. Some tanks, like M1 Abrams use a turbine and they are painfully loud and the exhaust is so hot it can literally set on fire anything too close to it. Imagine sitting in a traffic jam and lighting up a car behind you :)
- agumonkey 3y ago
  oh right, I remember some guy mentioning fixed RPM helping a lot.
scns 3y ago
The Chevrolet Volt works like that.

at_a_remove 3y ago

Power train don't pour.

TylerE 3y ago

An important point EV advocates often gloss over is that you don't get to burn battery. In aviation, especiaslly, this really matters - over half an aircraft's weight at takeout is often fuel. The later in the flight it is, the more fuel has burned off, the lighter the plane is, and the more efficient the rest of the flight will be. You have to lug that empty battery around at full weight.

wilg 3y ago
Technically the battery gets a teeny bit lighter because of E=mc².
- anyoneamous 3y ago
  Over long journeys, those 3 nanograms really add up.
  - fragmede 3y ago
    https://physics.stackexchange.com/questions/34421/does-the-mass-of-a-battery-change-when-charged-discharged https://physics.stackexchange.com/questions/34421/does-the-m... It's about a microgram.
    - hermitdev 3y ago
      So, in other words, you gained more mass from bugs splating on the windshield than you lost in the battery.
      - acdha 3y ago
        Don’t worry, we’ve been working on that: https://www.science.org/content/article/where-have-all-insects-gone https://www.science.org/content/article/where-have-all-insec...
      - b112 3y ago
        But in the winter, as the cabin warms up, you have fewer air molecules to cart around.

tonymet 3y ago

the heat itself is useful in winter to keep the system regulated and heat the passengers

numpad0 3y ago

> can only turn 33% Energy density of gasoline is literally 12900 Wh/kg and 9500 Wh/L, Li-ion(not combusted) is ~250 Wh/kg and ~700 Wh/L. That's 50x/14x raw and 17x/13x at 33% efficiency without hybrid/ICE optimization gains. (23222915000 Wh/kg and 370000000000 Wh/L for Pu239 btw, source[1]) 1: https://en.wikipedia.org/wiki/Energy_density https://en.wikipedia.org/wiki/Energy_density

AwaAwa 3y ago
Had a double take on reading Li-ion (not combusted) and then immediately went looking at EV battery fires. A rabbit hole of solid fuel and it's considerations followed. I have become a trained monkey. Well done internet. And thank you for the 'x' factor. Had never seen that, outside of everyone stating ICE is only 33% efficient.
yazaddaruvala 3y ago
Thank you for the math. But I don’t think you really tried to understand my point. Firstly, the newest solid state batteries (relevant because that is what I was responding about) are 2x the density so that is quite good (8.5x/6.5x). Which is already pretty close. They are also going to get better through iteration likely to 3-5x or so (but let’s ignore that for now). Secondly, the power train also includes regenerative breaking, reduced weight from transmission, in hub motors (reducing axcel weight), reduced center of gravity allowing better drag profiles, no external coolant systems, no engine oil compartments, no fan belts, etc. I’m happy for you to keep doing the math, but the reality is XXX km or miles per “full tank” is the best measurement because it takes all those factors into consideration.
- numpad0 3y ago
  Oh I'm not so against EV, I'm just being pro-nuke as I personally always has been. Honestly I don't get why some sort of EV supremacy theory has to be defended at all costs. Those are just facts that density and recyclability of Li-ion is just atrocious. Gasoline particles tho NOx bad for health yeah I get that part. Seriously, if we could just build 2-3 air-cooled Plutonium fission per each megalopolis core and use e-Fuel on existing hybrids we'd solve everything in modern society ever. The reactor could double as cityscale thermojet ventilation system as well, eliminating heat and atmosphere problems once and for all. It will of course work as a training exercise for coming real Space Age in which humanity builds bunches after bunches of cylindrical habitats fabricated and populated in space. The only two roadblocks towards that path are some NIMBYism/NPT fears and cost.

rkuodys 3y ago

I personally wonder how much more the 33% would be if we had continued the focus on ICE. I believe there is no business case anymore to invest significantly in advancing technology, if everyone wants a new shiny toy.

iknowstuff 3y ago
It’s been 200 years and untold amounts of R&D money thrown at this incredibly lucrative, huge industry. It’s not budging much beyond what it is.
Tanoc 3y ago
There's not much more you can get out of current fuel blends. Methanol is potent but very expensive to mix, the even more expensive nitromethane is so powerful it strains the science of metallurgy and thus is some of the most dangerous stuff to handle, and hydrazine is so energy dense but so unstable it's used as rocket fuel. Porsche's E-Fuel is just barely more efficient than gasoline because of the density at point six megajoules a kilogram, versus point five four for one hundred octane gasoline. The major issue is parasitic drivetrain loss from having to push the cylinder which pushes the cam which turns the flywheel which friction fits against the clutch which friction fits against the transmission flywheel which turns dozens of metal gears which rotates the driveshafts. Direct drive implementations where the engine's output shaft is mated directly to the axle are much more efficient and have been used in massive ships, but are entirely impractical for use in passenger vehicles. There's the Otto, Atkinson, Wankel, Scuderi and diesel cycles for liquid fuel combustion, and all have tradeoffs leaving them competitive with eachother instead of having a clear best solution thanks to everything else required to transfer the power from the initial combustion. In short, we've hit the mechanical engineering dead end for massive efficiency gains with ICEs. It's all chemical from here, and thus gets much more expensive to run.
rini17 3y ago
ICE is kind of a dead end, you convert energy from chemical to thermal to mechanical and every conversion is lossy. You want to use chemical energy directly instead, like some kind of "hydrocarbon/air cell" and we don't know how to do it. At least not with mixed hydrocarbons.