5 ms·

Although it's more complicated than that, because IC engines are only have about 15% efficiency, whereas electric motors are up at about 80%.

nradov 7y ago
Real world efficiency for modern gasoline engines is closer to 20%. In hybrid applications they can get up to 35%.
- djaychela 7y ago
  >In hybrid applications they can get up to 35%. But surely that is largely due to the electric element of the combined powertrain? The ICE part hasn't magically become more efficent?
  - tasty_freeze 7y ago
    The whole point of a hybrid is to run the ICE only in its most efficient region. At low loads the electric battery drives the car. If the battery gets too low, then the ICE runs, but rather than running at a low (and inefficient) load, it runs at its sweet spot and the excess power it generates charges the battery. When the demand is high, rather than running the ICE hard, it is kept at its sweet spot and the electric motor boosts power instead. So yes, the ICE part is more efficient in a hybrid, though it isn't magic.
  - aidenn0 7y ago
    The ICE is more efficient because the design constraints have changed. Here's a single example with the Prius: 1. The intake valve stays open for part of the compression stroke. 2. (1) means that the compression ratio for the compression stroke is lower than the compression ratio for the power stroke. 3. The efficiency of the engine is limited by the compression ratio of the power stroke 4. The compression ratio of the compression stroke is limited by engine knocking (if you compress a mixture of fuel and air too much, it will spontaneously combust) 5. So this engine can be made more efficient than an engine that closes the valve for the entire compression stroke 6. Some (non-hybrid) engines have variable valve timing and can do (1) some of the time, to a small extent. 7. Doing (1) to a larger extent makes the low-RPM torque very poor. 8. Electric motors have excellent low-RPM torque, so (7) is compensated for by having an electric motor run at low speeds.
  - rtkwe 7y ago
    Somewhat, by putting an intermediate step between the gas/diesel engine and the work the engine can be run more efficiently as well, instead of having to speed up and down at the whims of the driver it can run at a more steady and constant pace and the electric engine also allows regenerative brakes to be used which can recapture a lot of the energy lost in a normal diving situation during braking.
userbinator 7y ago
https://en.wikipedia.org/wiki/Brake-specific_fuel_consumption#Examples_of_values_of_BSFC_for_shaft_engines https://en.wikipedia.org/wiki/Brake-specific_fuel_consumptio... Over 30% efficiency for gasoline, and over 50% for diesels.

nradov 7y ago

Real world efficiency for modern gasoline engines is closer to 20%. In hybrid applications they can get up to 35%.

djaychela 7y ago
>In hybrid applications they can get up to 35%. But surely that is largely due to the electric element of the combined powertrain? The ICE part hasn't magically become more efficent?
- tasty_freeze 7y ago
  The whole point of a hybrid is to run the ICE only in its most efficient region. At low loads the electric battery drives the car. If the battery gets too low, then the ICE runs, but rather than running at a low (and inefficient) load, it runs at its sweet spot and the excess power it generates charges the battery. When the demand is high, rather than running the ICE hard, it is kept at its sweet spot and the electric motor boosts power instead. So yes, the ICE part is more efficient in a hybrid, though it isn't magic.
- aidenn0 7y ago
  The ICE is more efficient because the design constraints have changed. Here's a single example with the Prius: 1. The intake valve stays open for part of the compression stroke. 2. (1) means that the compression ratio for the compression stroke is lower than the compression ratio for the power stroke. 3. The efficiency of the engine is limited by the compression ratio of the power stroke 4. The compression ratio of the compression stroke is limited by engine knocking (if you compress a mixture of fuel and air too much, it will spontaneously combust) 5. So this engine can be made more efficient than an engine that closes the valve for the entire compression stroke 6. Some (non-hybrid) engines have variable valve timing and can do (1) some of the time, to a small extent. 7. Doing (1) to a larger extent makes the low-RPM torque very poor. 8. Electric motors have excellent low-RPM torque, so (7) is compensated for by having an electric motor run at low speeds.
- rtkwe 7y ago
  Somewhat, by putting an intermediate step between the gas/diesel engine and the work the engine can be run more efficiently as well, instead of having to speed up and down at the whims of the driver it can run at a more steady and constant pace and the electric engine also allows regenerative brakes to be used which can recapture a lot of the energy lost in a normal diving situation during braking.

userbinator 7y ago

https://en.wikipedia.org/wiki/Brake-specific_fuel_consumption#Examples_of_values_of_BSFC_for_shaft_engines https://en.wikipedia.org/wiki/Brake-specific_fuel_consumptio... Over 30% efficiency for gasoline, and over 50% for diesels.