Turbo compounding

Just watched a video explaining this layout. Why are we not pursuing this in normal cars? Surely those super gas sippers like Priuses would love tech like this on top of hybrid systems. AFAIK Volvo has one for its big semi trucks but it seems able to be scaled down and be mechanically simple.

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  1. 4 weeks ago
    Anonymous

    The same reasons that most engine advancements don't actually make it into cars: too much fricking money to produce at scale, too complex to fix if it breaks down, and higher chance of crippling the entire drivetrain on failure.

    Aviation repair is an immensely costly and complex process, to say nothing of aviation manufacturing. You'd be dealing with cars that are 20%+ more expensive to create and 20%+ more expensive to repair, all for the sake of slightly better fuel efficiency that doesn't meaningfully appreciate to the point of being a savings.

  2. 4 weeks ago
    Anonymous

    >Why are we not pursuing this
    Because ICEs are dead

  3. 4 weeks ago
    Anonymous

    this is bad for lower rpm situations aka traffic.

    this will drop mpgs. do some more learning op.

    • 4 weeks ago
      Anonymous

      I’ll take the extra 1-3% loss in city situations for the 10% gain at higher speeds. Maybe a system where it disconnects from the crank at lower speeds?

  4. 4 weeks ago
    Anonymous

    >watches Le hecking cool automotive science video
    >WHAT THE HECKIN HECK, WHY AREN'T WE DOING THIS?
    Reddit??

    • 4 weeks ago
      Anonymous

      >making fun of people for asking questions about things that they've just found out about
      Why?

    • 4 weeks ago
      Anonymous

      Who the frick uses Reddit, video popped up explaining a turbo system that is physically mated to a crankshaft and it seems like a decent discussion. Or should we go back to some EV truck circlejerk?

  5. 4 weeks ago
    Anonymous

    very cool tech, yes. I assume complexity reasons

  6. 4 weeks ago
    Anonymous

    F1 engines have been using it for a while, as did the lmp prototypes. The problem is that engines only need to produce about 30 horsepower to maintain highway speeds (and even less in the city), and unless you are willing to power your car with a sub 0,5 liter engine there's no point in trying to recover energy from boost if most of the time you don´t need to make any boost in the first place.

    • 4 weeks ago
      Anonymous

      So, how do you size them?

      • 4 weeks ago
        Anonymous

        What manufacturers do is size the engine for steady state highway cruise speeds naturally aspirated, and then use boost to give short term acceleration. They also use atinkson cycle valve timing (longer expansion than compression stroke) to recover extra energy from the exhaust without having to physically connect the turbo to the crankshaft.

        Electric vehicles don't need to care because their engines have next to no friction so their efficiency drops very little when they use small fractions of the total power they can produce. Turbo compound engines could make sense for range extender engines onboard electric vehicles, as those can be run at high power continuously to recharge the battery, but it's cheaper to just use an existing engine.

        • 4 weeks ago
          Anonymous

          Well, that's clear as mud.

          • 4 weeks ago
            Anonymous

            The background shows the engine´s bsfc map, in other words it measures how many grams of fuel the engine uses to produce a kw.h of energy. the lower the number, the better the efficiency. Peak efficiency is at about 80% of max torque, between 2000 and 3000 rpm.

            The curved lines indicates how much torque the engine needs to make to maintain a given speed, in either 4th or 5th gear. You can see that in 4th gear the engine is less efficient than in 5th gear because the bsfc is lower, (340 in 4th vs 290 in 5th at 100kph). You could have improved the efficiency all the way to 240 at the same speed and engine rpm by halving the engine displacement, which would halve the torque, but then you would also have a much lower top speed because the engine produces half the power.

        • 4 weeks ago
          Anonymous

          The background shows the engine´s bsfc map, in other words it measures how many grams of fuel the engine uses to produce a kw.h of energy. the lower the number, the better the efficiency. Peak efficiency is at about 80% of max torque, between 2000 and 3000 rpm.

          The curved lines indicates how much torque the engine needs to make to maintain a given speed, in either 4th or 5th gear. You can see that in 4th gear the engine is less efficient than in 5th gear because the bsfc is lower, (340 in 4th vs 290 in 5th at 100kph). You could have improved the efficiency all the way to 240 at the same speed and engine rpm by halving the engine displacement, which would halve the torque, but then you would also have a much lower top speed because the engine produces half the power.

          option 2 would be to add a 6th gear that reduces the rpm even further than 5th gear, and thus increases the torque required. Going from 350bmep x 2700rpm at 100km/h to 550 bmep x 1700 rpm would improve the bsfc to around 250, which is about as close as you can get to peak efficiency at 100km/h with that engine. So now you know why modern cars have so many gears.

  7. 4 weeks ago
    Anonymous

    why?
    expensive, hot, and more complicated, for what?

    • 4 weeks ago
      Anonymous

      It’ll run cooler due to no back pressure on the exhaust side, be marginally more complicated with a couple gears, fluid balancer, and a shaft or two to send the power back to the crank. It would just take some effort to implement well and produce.

  8. 4 weeks ago
    Anonymous

    Do they do variable geometry turbos?

  9. 4 weeks ago
    Anonymous

    Back in the day there was a guy on z31performance forum with a compound turbo 2JZ swapped 300zx, was incredibly based. Believe his username was streetfighter.

    • 4 weeks ago
      Anonymous

      That's a different type of turbo compounding than the one mentioned in the OP, instead of linking the turbo to the crankshaft that car had a big turbo boosting a smaller turbo that itself boosts the engine, which allows ridiculous levels of boost. Perhaps it's more accurate to call it staged turbocharging, just like ww2 aircraft had 2 stage supercharging.

      • 4 weeks ago
        Anonymous

        Yeah that’s common is the diesel world as well where 100+ psi is pretty achievable.

  10. 4 weeks ago
    Gears

    Pretty sure the C43 AMG actually has that.
    The reasons why it's uncommon in cars is that you won't get out shit except at seriously high loads, which cars don't see for extended timeframes.
    The Benz uses it so they can slam the wastegate shut upon acceleration and prevent overspeed with the electric motor on the turbo, giving it a better spoolup more than anything else. There's just not a whole lot of energy to be harvested there in normal driving.
    It's used in ship-diesels and really big aviation engines sometimes though, as those run in relevant conditions continuously.

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