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We're heading in a good direction with turbochargers. I suspect we're getting close to the Carnot limits for gasoline engines [1]. Next steps would be adaptin

by iaw 11y ago

We're heading in a good direction with turbochargers. I suspect we're getting close to the Carnot limits for gasoline engines [1]. Next steps would be adapting the regenerative braking technology, like that on the Porsche 918, into regular vehicles. There's a lot of kinetic energy wasted in brakes and we're soon going to be able to recapture it. [1] https://en.wikipedia.org/wiki/Carnot_cycle#Efficiency_of_real_heat_engines https://en.wikipedia.org/wiki/Carnot_cycle#Efficiency_of_rea...

maxerickson 11y ago
Is there something notable about the brakes in the Porsche? Regenerative brakes are a big win in many of the hybrids that have been brought to market.
- drcross 11y ago
  It's a significant car because it currently holds the lap record in Nürburgring for a supercar.
  - maxerickson 11y ago
    That doesn't make the brakes interesting in comparison to the system on a Prius (or whichever earlier car you want to pick).
  - Grazester 11y ago
    There is nothing notable about the regenerative brakes in the Porsche 918. Other hybrids have been using regenerative brakes for years and years now. As for a Nürburgring "record" I dont see the relevance in this conversation
- iaw 11y ago
  So there are a few components interesting in the Porsche 918's braking system that I'll speak to. 1) The brakes slow the car down through a combination of electric generation and traditional brake pads, just like the hybrids you're familiar with. Unlike the Prius, the brakes escalate in a predictable a familiar fashion. Most regenerative braking systems do not scrub speed from the car in the same linear fashion as the 918. This is a major accomplishment because it makes the transition from regular brakes to regenerative brakes seamless and allows for spirited driving. 2) The batteries are not designed to store a substantial amount of charge, instead they are designed to provide a large chunk of the acceleration power that would normally come from a gasoline engine in a hybrid. Instead of designing the car to utilize batteries for long-ranges, Porsche designed the car to utilize batteries for sprints. 3) The net result is a car that is as spirited as a traditional sports car but with greatly increased efficiency. People that wont buy a Prius or BMW Hybrid right now because of the ride quality issues would be willing to purchase a car with the 918 style system. The school of thought behind the Prius to squeeze every drop of efficiency out of the electric side, the school of thought behind the 918 is to support spirited driving with the electric side. Both lead to increases in efficiency but only the latter is something people that consider themselves 'drivers' would buy. You can see this with Turbochargers as they are just now starting to trickle onto sport vehicles such as the BMW M4 and Ferrari has acknowledged that they will be pursuing the technology in their road cars in the near future.
creshal 11y ago
> Next steps would be adapting the regenerative braking technology, like that on the Porsche 918, into regular vehicles. Virtually all hybrids already do that…
- iaw 11y ago
  Yes but you have to buy a car with a huge battery pack and crap performance (including the i8). I drive an M3, I'm not going to give up fast vehicles until self-driving cars are mandatory. Regenerative braking (with a small battery pack) could double the fuel efficiency I obtain. The existing regenerative braking systems available are horrible (in a number of ways) and not comparable to what's in existence for F1 and the 918. Regenerative braking for most cars now is where turbochargers were pre-1990s. The system I'm talking about can run only a few miles in full electric but gives a substantial boost in fuel economy because it's utilized for most acceleration below ~100 MPH.
ssmoot 11y ago
The Mazda 3 has an option for a regenerative braking system. I'm not really sure how that works in a non-hybrid TBH. Just used to charge for accessories, electric compressor, steering, etc so you can use a clutched alternator and minimize accessory loads? Just a guess.
- ollie87 11y ago
  I believe the BMW 1 Series is the same.
sliken 11y ago
As mentioned in the article. Turbos don't help MPG much. Several examples in the article who larger engines with on turbos having similar MPG to smaller turbo engines. Sure they increase peak HP, but they also increase exhaust backpressure. Seems like the main achievement of turbos is cheaper/smaller engines.
- Shivetya 11y ago
  most of the efficiency benefits we stand to gain with forced induction and other improvements is routinely lost because people cannot drive properly. the race to the next red light does nothing but wreck your mileage. some have suggested regenerative braking as if this isn't on many cars, but it has been in use but it does not necessarily have to be with large battery packs to make a difference. When combined with auto start/stop it can keep a slightly larger battery charged enough to extend engine off time.
- bluedino 11y ago
  You can only make so much power with a certain amount of gasoline - whether it's by a larger displacement engine, higher RPM, or using turbochargers to fill the cylinders with air. If you make 300hp, it's going to take around the same amount of gasoline to do so whether you do it with a 5 liter V8 or a 2 liter turbocharged 4 cylinder. Sure, the smaller engine is going to get better gas mileage when idling and such, and it's amazing how efficient the larger engines are these days. But in a heavy vehicle with the aerodynamics of a brick, the EcoBoost engines aren't seeing much better gas mileage numbers than the GM V8's.

by iaw 11y ago

maxerickson 11y ago

Is there something notable about the brakes in the Porsche? Regenerative brakes are a big win in many of the hybrids that have been brought to market.

drcross 11y ago
It's a significant car because it currently holds the lap record in Nürburgring for a supercar.
- maxerickson 11y ago
  That doesn't make the brakes interesting in comparison to the system on a Prius (or whichever earlier car you want to pick).
- Grazester 11y ago
  There is nothing notable about the regenerative brakes in the Porsche 918. Other hybrids have been using regenerative brakes for years and years now. As for a Nürburgring "record" I dont see the relevance in this conversation
iaw 11y ago
So there are a few components interesting in the Porsche 918's braking system that I'll speak to. 1) The brakes slow the car down through a combination of electric generation and traditional brake pads, just like the hybrids you're familiar with. Unlike the Prius, the brakes escalate in a predictable a familiar fashion. Most regenerative braking systems do not scrub speed from the car in the same linear fashion as the 918. This is a major accomplishment because it makes the transition from regular brakes to regenerative brakes seamless and allows for spirited driving. 2) The batteries are not designed to store a substantial amount of charge, instead they are designed to provide a large chunk of the acceleration power that would normally come from a gasoline engine in a hybrid. Instead of designing the car to utilize batteries for long-ranges, Porsche designed the car to utilize batteries for sprints. 3) The net result is a car that is as spirited as a traditional sports car but with greatly increased efficiency. People that wont buy a Prius or BMW Hybrid right now because of the ride quality issues would be willing to purchase a car with the 918 style system. The school of thought behind the Prius to squeeze every drop of efficiency out of the electric side, the school of thought behind the 918 is to support spirited driving with the electric side. Both lead to increases in efficiency but only the latter is something people that consider themselves 'drivers' would buy. You can see this with Turbochargers as they are just now starting to trickle onto sport vehicles such as the BMW M4 and Ferrari has acknowledged that they will be pursuing the technology in their road cars in the near future.

creshal 11y ago

> Next steps would be adapting the regenerative braking technology, like that on the Porsche 918, into regular vehicles. Virtually all hybrids already do that…

iaw 11y ago
Yes but you have to buy a car with a huge battery pack and crap performance (including the i8). I drive an M3, I'm not going to give up fast vehicles until self-driving cars are mandatory. Regenerative braking (with a small battery pack) could double the fuel efficiency I obtain. The existing regenerative braking systems available are horrible (in a number of ways) and not comparable to what's in existence for F1 and the 918. Regenerative braking for most cars now is where turbochargers were pre-1990s. The system I'm talking about can run only a few miles in full electric but gives a substantial boost in fuel economy because it's utilized for most acceleration below ~100 MPH.

ssmoot 11y ago

The Mazda 3 has an option for a regenerative braking system. I'm not really sure how that works in a non-hybrid TBH. Just used to charge for accessories, electric compressor, steering, etc so you can use a clutched alternator and minimize accessory loads? Just a guess.

ollie87 11y ago
I believe the BMW 1 Series is the same.

sliken 11y ago

As mentioned in the article. Turbos don't help MPG much. Several examples in the article who larger engines with on turbos having similar MPG to smaller turbo engines. Sure they increase peak HP, but they also increase exhaust backpressure. Seems like the main achievement of turbos is cheaper/smaller engines.

Shivetya 11y ago
most of the efficiency benefits we stand to gain with forced induction and other improvements is routinely lost because people cannot drive properly. the race to the next red light does nothing but wreck your mileage. some have suggested regenerative braking as if this isn't on many cars, but it has been in use but it does not necessarily have to be with large battery packs to make a difference. When combined with auto start/stop it can keep a slightly larger battery charged enough to extend engine off time.
bluedino 11y ago
You can only make so much power with a certain amount of gasoline - whether it's by a larger displacement engine, higher RPM, or using turbochargers to fill the cylinders with air. If you make 300hp, it's going to take around the same amount of gasoline to do so whether you do it with a 5 liter V8 or a 2 liter turbocharged 4 cylinder. Sure, the smaller engine is going to get better gas mileage when idling and such, and it's amazing how efficient the larger engines are these days. But in a heavy vehicle with the aerodynamics of a brick, the EcoBoost engines aren't seeing much better gas mileage numbers than the GM V8's.