But isn't the chamber full of exhaust at the beginning of the second power stroke? What will burn?
Given there is enough oxygen left, they can inject more fuel.
Porsche's idea for a six-stroke internal combustion engine
191–200 of 367 posts
Re: Porsche's idea for a six-stroke internal combustion engine
#192Earlier quoted context omitted.
On top of all the other replies debunking this, one thing left is that they're not the greener option for everyone. Auke Hoekstra has been pretty active (on Twitter etc) debunking this - electric cars' additional footprint gets paid off under 20k miles even at the emission levels of electricity grids of yesterday. As the grid decarbonizes further it will become even less. The number of cars driven less than 20k miles…
Did you actually read my comment and the replies? Because most of the replies didn’t even address the points I was making, let alone debunk it. Just like with your post. I never actually made any claims about mileages. However as it happens, I do specifically fall into that uneconomical bracket. That’s why I ended up buying petrol despite wanting an EV. I work from home and thus rarely drive. EV isn’t yet ready for m…
I read it carefully. Your claim was it's not greener for everyone. It is because the additional costs in terms of emissions are paid off in less than 20k miles. This is a little bit more than the average per year. It's possible a car travels less than that during its life span, but it's so small it's irrelevant. That's like saying it makes financial sense playing the lottery just because someone occasionally wins.
Re: Porsche's idea for a six-stroke internal combustion engine
#193But isn't the chamber full of exhaust at the beginning of the second power stroke? What will burn?
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.)
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%.)
Re: Porsche's idea for a six-stroke internal combustion engine
#194But isn't the chamber full of exhaust at the beginning of the second power stroke? What will burn?
Sounds like EGR
Re: Porsche's idea for a six-stroke internal combustion engine
#195But isn't the chamber full of exhaust at the beginning of the second power stroke? What will burn?
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.
Re: Porsche's idea for a six-stroke internal combustion engine
#196I'm a programmer, not an engine guy. From the description in the article, they do one intake stroke, two pairs of compression-power strokes, followed by an exhaust stroke.
Also, it seems the initial compression-power strokes are done with the piston moving lower, ie both lower top dead center and bottom dead center, hence would have lower compression, and the second moving higher so with higher compression.
From my understanding of more fuel means less compression is tolerated before knocking[1], and vice versa.
So do I understand it correctly that their idea then to make the first power stroke rather rich with lower compression ratio to eliminate knock, and the second at a higher compression ratio to burn the remaining unburnt fuel? Or the other way around, ie lean with high compression first?
If so, it seems like an evolution of variable compression ratio engines[2].
edit: my morning-brain is having issues with thinking about how air-fuel ratio change in rich-burning vs lean-burning scenarios. So perhaps they aim for a good stoichiometric ratio and rely on the exhaust gasses to avoid knock when increasing compression the second time around?
[1]: https://en.wikipedia.org/wiki/Engine_knocking
[2]: https://en.wikipedia.org/wiki/Variable_compression_ratio
Re: Porsche's idea for a six-stroke internal combustion engine
#197But isn't the chamber full of exhaust at the beginning of the second power stroke? What will burn?
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.
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.
Re: Porsche's idea for a six-stroke internal combustion engine
#198Not to say that modern IC engines are any sort of "simple"...but there appear to be a lot more high-precision moving parts, under load, in their clever new crankshaft assembly. (Vs. traditional 4-cycle IC engines.) Obviously, Porche's target market isn't likely to care about that. But for possible down-market uses of this technology - are there any mechanical engineers in the house, to comment?
I drive a 24 year old Porsche and the engine already has a lot more mechanical complexity than most other engines- especially for their variable camshaft timing system. You’re right that Porsche and their target customers don’t care much. I’d say German engineering culture in general is to make things work better (when new), and not worry about complexity.
Re: Porsche's idea for a six-stroke internal combustion engine
#199But isn't the chamber full of exhaust at the beginning of the second power stroke? What will burn?
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.)
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.
Re: Porsche's idea for a six-stroke internal combustion engine
#200Earlier quoted context omitted.
>I'm an enviromentalist and I'd still buy an ICE Porsche. Environmentalists walk or ride bikes.
https://en.wikipedia.org/wiki/No_true_Scotsman
Where do you draw the line then? If I spend the week jetting across the Atlantic but then take a reusable bag to the supermarket am I an environmentalist?