8 ms·

But isn't the chamber full of exhaust at the beginning of the second power stroke? What will burn?

OJFord 2y ago
It says the goal is efficiency, so I assume the point is that if the first does say 80% combustion, then another cycle eeks out another 80% of 80% or whatever. (Brb, have an 8 stroke engine to patent.)
- OJFord 2y ago
  Oops, another 80% of the remaining 20%, I mean. (But also I would guess it is probably less efficient than the initial one, not another 80%.)
- _yb2s 2y ago
  When Porsche says efficiency they mean making more power, not using less fuel. Porsche has a long track record of adopting efficiency tech and using them to make fast cars that still use a ton of fuel.
  - dahart 2y ago
    What’s the difference between getting more power out of a given quantity of fuel, versus using less fuel to achieve a given power output?
    - serial_dev 2y ago
      Extremely simplified, when you drive a sports car, you want to maximize power (work per unit of time), period, you don’t care about fuel. If you want to go the farthest with a full tank, you want to maximize the total work (proportionate to traveled distance) for unit of fuel. Reality for practically all cars are between these two extremes, you want to enjoy driving, go relatively fast, and still not wasting 25 liters for traveling 100 km.
      - dahart 2y ago
        Those are correct statements that don’t answer the question I asked. You’ve explained the difference between not caring about efficiency and caring about efficiency. The article said the 6-stroke design is for “efficiency” and did not say Porsche doesn’t care about fuel and only wants to maximize power, contrary to the comment I replied to above. If an engine gives you more power with a fixed quantify of fuel, then it must also give you less fuel for a given quantity of power, right? There’s no such thing as more efficient only for power. BTW Porsche makes consumer vehicles, not just race cars. And they make engines for other types of vehicles, not just cars. It’s ridiculous to claim that Porsche doesn’t care about fuel just because they happen to make some race cars. Nothing in the article suggests this design is for a race car, nor would it; a patent is designed to be broadly applicable and if a 6-stroke design is shown to be more efficient than a 4-stroke design for fuel-efficient consumer cars, you can bet Porsche will be happy to sell you the engines or license the design.
        _yb2s 2y ago
        Porsche cares a lot about efficiency, and their cars are generally designed to be very efficient- but they use the extra efficiency to sell a more powerful car, not a more fuel efficient car. Beyond some historical agricultural tractors, Porsche has only ever made high performance cars, they don't make general purpose "commuter" or "family" cars. Even their large SUVs like the Cayenne are very high performance vehicles.
        dahart 2y ago
        The base model Cayenne takes almost 6 seconds to get to 60mph when floored. That’s not particularly fast, even by family SUV standards, it’s comparable to a Honda Passport, and slower than SUVs from Audi, BMW, and Ford, and quite a few others. The Cayenne is an SUV in the first place. What exactly is a publicly available SUV if not a general purpose family commuter car? One of my friends bought a Cayenne to shuttle his kids to school and soccer practice. Porsche absolutely does make a general purpose commuter/family car, and you named it. Porsche may well care often about high performance, I’m not disputing that at all. The problem with your repeated statement is claiming they don’t care about fuel efficiency. That’s not what “efficiency” means. They absolutely can get more power out of an engine and sacrifice fuel efficiency, and some of their models do, but if the intent of the 6-stroke design is “efficiency”, then by definition they care about fuel efficiency. Whether they use that to achieve higher power, or lower fuel consumption relative to some other car is irrelevant to what is meant by efficiency. Also you’re just assuming that their 6-stroke design is intended for high performance. You might be right, but there are other possibilities you’ve ignored or haven’t thought of.
    - Ccecil 2y ago
      My assumption is there is a context difference. Efficiency in fuel/mile. Efficiency in Power output/liter of displacement. But that is just my assumption. You can have a relatively small engine and force a ton of air/fuel into it under boost and get tons of HP but it tends to lose the ability to maintain fuel economy. Tune it for fuel economy and it tends to lose power. It is very difficult to have both in the same package for many reasons. Adding mods like discussed in the article start to allow for the overlap to be wider.
    - _yb2s 2y ago
      Porsche cares a lot about efficiency, because with higher efficiency they can make more power. They are a sports car company, and ultimately are building high performance vehicles. That is in contrast to other less performance focused car companies, which would use efficiency gains to allow them to use a smaller engine- thereby making it both more fuel efficient and cheaper/lighter, but not faster. The Porsche 918 Spyder for example is a plug in hybrid supercar, which uses the hybrid system together with a massive gasoline engine- to make it really really fast.
      - dahart 2y ago
        Porsche can get more power without higher efficiency. That they’re choosing efficiency means they’re looking for higher power with lower fuel consumption. How they choose to use that efficiency is their business, I’m just pointing out that they do, in fact, care about fuel consumption, and claiming otherwise just because they sell high performance cars, is incorrect.
  - OJFord 2y ago
    I'm not sure if that's supposed to be a correction, but if so I don't understand. The description of the two new strokes is as an addition to the normal four, one of which is the fuel intake, I was not assuming that decreases in quantity or anything. It could do, it's just orthogonal to the point - if you don't entirely combust whatever amount you inject in the first ignition , then the idea here aiui is to compress & ignite again to, yes, get some more 'power' out of it.
    - randerson 2y ago
      A recent example of what (I think) the parent is saying, is the new 911 GTS which is now a T-Hybrid [0] engine. But the electric motor doesn't give it better gas mileage than its predecessor, it is just used to eliminate turbo lag which allows them to use a bigger turbo, giving it more horsepower, and using a leaner fuel mixture at full throttle to meet the latest emissions standards. [0] https://www.caranddriver.com/news/a60914997/2025-porsche-911-gts-t-hybrid-engine-details/ https://www.caranddriver.com/news/a60914997/2025-porsche-911...
    - _yb2s 2y ago
      It is not a correction, but additional context. Indeed Porsche cares about efficiency- but there are different ways to then leverage that efficiency- for either a more powerful car, or a more fuel efficient car. Porsche will choose the more powerful car, because they sell sports cars, not economy cars. Also see my other reply in this thread.
nikanj 2y ago
You can overfill the cylinder for the first stroke, because the unspent fuel will burn on the next cycle instead of being exhausted. High power engines exhaust a lot of unburned fuel, because you can't guarantee an exact 100% fill for the cylinder, and there's more power to be had at 120% fill than 80% fill. Oversimplified of course.
- ethbr1 2y ago
  But you don't have an additional intake stroke, so there's limited oxygen in the second power stroke to burn. It sounds more like they're running fuel-lean, then possibly adding more fuel before the second compression stroke.
Neil44 2y ago
Maybe the first cycle is super lean, leaving lots of O2 and CO still to burn.
Szpadel 2y ago
that might be something similar to why diesels mix exhaust gas with fresh air, but that might be just to purify exhaust gases better - I'm no expert
Maledictus 2y ago
Given there is enough oxygen left, they can inject more fuel.
HPsquared 2y ago
Sounds like EGR
yobbo 2y ago
Might also be possible to inject water into the compressed exhaust gasses. The water evaporates and creates the second power stroke, while lowering the temperature of the exhaust gasses. There's quite a lot of energy left in the exhaust gasses otherwise. This is not a new idea but it creates mechanical complexity and higher requirements on the materials of the piston and cylinder.
- Ccecil 2y ago
  6 stroke diesel prototype. https://www.autoweek.com/news/a2063201/inside-bruce-crowers-six-stroke-engine/ https://www.autoweek.com/news/a2063201/inside-bruce-crowers-... edit: Description before link
labcomputer 2y ago
It looks like the patent describes a weird hybrid of a conventional 4-stroke and a uniflow 2-stroke. At the bottom of the first power stroke, the cylinder drops lower to expose scavenging ports. That both forces air in (at the bottom of the cylinder) and helps push exhaust out (through conventional exhaust valves). Uniflow 2-strokes tend to have high thermal efficiency, but poor emissions, especially particulates. So the idea here might be to gain some efficiency without another emissions-gate.

It says the goal is efficiency, so I assume the point is that if the first does say 80% combustion, then another cycle eeks out another 80% of 80% or whatever. (Brb, have an 8 stroke engine to patent.)

OJFord 2y ago
Oops, another 80% of the remaining 20%, I mean. (But also I would guess it is probably less efficient than the initial one, not another 80%.)
_yb2s 2y ago
When Porsche says efficiency they mean making more power, not using less fuel. Porsche has a long track record of adopting efficiency tech and using them to make fast cars that still use a ton of fuel.
- dahart 2y ago
  What’s the difference between getting more power out of a given quantity of fuel, versus using less fuel to achieve a given power output?
  - serial_dev 2y ago
    Extremely simplified, when you drive a sports car, you want to maximize power (work per unit of time), period, you don’t care about fuel. If you want to go the farthest with a full tank, you want to maximize the total work (proportionate to traveled distance) for unit of fuel. Reality for practically all cars are between these two extremes, you want to enjoy driving, go relatively fast, and still not wasting 25 liters for traveling 100 km.
    - dahart 2y ago
      Those are correct statements that don’t answer the question I asked. You’ve explained the difference between not caring about efficiency and caring about efficiency. The article said the 6-stroke design is for “efficiency” and did not say Porsche doesn’t care about fuel and only wants to maximize power, contrary to the comment I replied to above. If an engine gives you more power with a fixed quantify of fuel, then it must also give you less fuel for a given quantity of power, right? There’s no such thing as more efficient only for power. BTW Porsche makes consumer vehicles, not just race cars. And they make engines for other types of vehicles, not just cars. It’s ridiculous to claim that Porsche doesn’t care about fuel just because they happen to make some race cars. Nothing in the article suggests this design is for a race car, nor would it; a patent is designed to be broadly applicable and if a 6-stroke design is shown to be more efficient than a 4-stroke design for fuel-efficient consumer cars, you can bet Porsche will be happy to sell you the engines or license the design.
      - _yb2s 2y ago
        Porsche cares a lot about efficiency, and their cars are generally designed to be very efficient- but they use the extra efficiency to sell a more powerful car, not a more fuel efficient car. Beyond some historical agricultural tractors, Porsche has only ever made high performance cars, they don't make general purpose "commuter" or "family" cars. Even their large SUVs like the Cayenne are very high performance vehicles.
        dahart 2y ago
        The base model Cayenne takes almost 6 seconds to get to 60mph when floored. That’s not particularly fast, even by family SUV standards, it’s comparable to a Honda Passport, and slower than SUVs from Audi, BMW, and Ford, and quite a few others. The Cayenne is an SUV in the first place. What exactly is a publicly available SUV if not a general purpose family commuter car? One of my friends bought a Cayenne to shuttle his kids to school and soccer practice. Porsche absolutely does make a general purpose commuter/family car, and you named it. Porsche may well care often about high performance, I’m not disputing that at all. The problem with your repeated statement is claiming they don’t care about fuel efficiency. That’s not what “efficiency” means. They absolutely can get more power out of an engine and sacrifice fuel efficiency, and some of their models do, but if the intent of the 6-stroke design is “efficiency”, then by definition they care about fuel efficiency. Whether they use that to achieve higher power, or lower fuel consumption relative to some other car is irrelevant to what is meant by efficiency. Also you’re just assuming that their 6-stroke design is intended for high performance. You might be right, but there are other possibilities you’ve ignored or haven’t thought of.
  - Ccecil 2y ago
    My assumption is there is a context difference. Efficiency in fuel/mile. Efficiency in Power output/liter of displacement. But that is just my assumption. You can have a relatively small engine and force a ton of air/fuel into it under boost and get tons of HP but it tends to lose the ability to maintain fuel economy. Tune it for fuel economy and it tends to lose power. It is very difficult to have both in the same package for many reasons. Adding mods like discussed in the article start to allow for the overlap to be wider.
  - _yb2s 2y ago
    Porsche cares a lot about efficiency, because with higher efficiency they can make more power. They are a sports car company, and ultimately are building high performance vehicles. That is in contrast to other less performance focused car companies, which would use efficiency gains to allow them to use a smaller engine- thereby making it both more fuel efficient and cheaper/lighter, but not faster. The Porsche 918 Spyder for example is a plug in hybrid supercar, which uses the hybrid system together with a massive gasoline engine- to make it really really fast.
    - dahart 2y ago
      Porsche can get more power without higher efficiency. That they’re choosing efficiency means they’re looking for higher power with lower fuel consumption. How they choose to use that efficiency is their business, I’m just pointing out that they do, in fact, care about fuel consumption, and claiming otherwise just because they sell high performance cars, is incorrect.
- OJFord 2y ago
  I'm not sure if that's supposed to be a correction, but if so I don't understand. The description of the two new strokes is as an addition to the normal four, one of which is the fuel intake, I was not assuming that decreases in quantity or anything. It could do, it's just orthogonal to the point - if you don't entirely combust whatever amount you inject in the first ignition , then the idea here aiui is to compress & ignite again to, yes, get some more 'power' out of it.
  - randerson 2y ago
    A recent example of what (I think) the parent is saying, is the new 911 GTS which is now a T-Hybrid [0] engine. But the electric motor doesn't give it better gas mileage than its predecessor, it is just used to eliminate turbo lag which allows them to use a bigger turbo, giving it more horsepower, and using a leaner fuel mixture at full throttle to meet the latest emissions standards. [0] https://www.caranddriver.com/news/a60914997/2025-porsche-911-gts-t-hybrid-engine-details/ https://www.caranddriver.com/news/a60914997/2025-porsche-911...
  - _yb2s 2y ago
    It is not a correction, but additional context. Indeed Porsche cares about efficiency- but there are different ways to then leverage that efficiency- for either a more powerful car, or a more fuel efficient car. Porsche will choose the more powerful car, because they sell sports cars, not economy cars. Also see my other reply in this thread.

nikanj 2y ago

You can overfill the cylinder for the first stroke, because the unspent fuel will burn on the next cycle instead of being exhausted. High power engines exhaust a lot of unburned fuel, because you can't guarantee an exact 100% fill for the cylinder, and there's more power to be had at 120% fill than 80% fill. Oversimplified of course.

ethbr1 2y ago
But you don't have an additional intake stroke, so there's limited oxygen in the second power stroke to burn. It sounds more like they're running fuel-lean, then possibly adding more fuel before the second compression stroke.

Neil44 2y ago

Maybe the first cycle is super lean, leaving lots of O2 and CO still to burn.

Szpadel 2y ago

that might be something similar to why diesels mix exhaust gas with fresh air, but that might be just to purify exhaust gases better - I'm no expert

Maledictus 2y ago

Given there is enough oxygen left, they can inject more fuel.

HPsquared 2y ago

Sounds like EGR

yobbo 2y ago

Might also be possible to inject water into the compressed exhaust gasses. The water evaporates and creates the second power stroke, while lowering the temperature of the exhaust gasses. There's quite a lot of energy left in the exhaust gasses otherwise. This is not a new idea but it creates mechanical complexity and higher requirements on the materials of the piston and cylinder.

Ccecil 2y ago
6 stroke diesel prototype. https://www.autoweek.com/news/a2063201/inside-bruce-crowers-six-stroke-engine/ https://www.autoweek.com/news/a2063201/inside-bruce-crowers-... edit: Description before link

labcomputer 2y ago

It looks like the patent describes a weird hybrid of a conventional 4-stroke and a uniflow 2-stroke. At the bottom of the first power stroke, the cylinder drops lower to expose scavenging ports. That both forces air in (at the bottom of the cylinder) and helps push exhaust out (through conventional exhaust valves). Uniflow 2-strokes tend to have high thermal efficiency, but poor emissions, especially particulates. So the idea here might be to gain some efficiency without another emissions-gate.