Porsche's idea for a six-stroke internal combustion engine • Hacker News Board

Re: Porsche's idea for a six-stroke internal combustion engine

#201

Post by i_am_jl » Sat, Sep 21, 2024, 1:29 PM UTC

magicalhippo wrote: post #196

I'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 u…

>more fuel means less compression is tolerated before knocking

Generally, no.

Knocking happens from pre-detonation, that's usually caused by heat from compression causing the fuel/air mix to ignite before it's triggered by spark.

To avoid this engines will run a fuel/air mix that is not stoicheometrically ideal, to make the mixture less likely to ignite early.

It is safer to run a fuel rich mix than to run a fuel lean mix as it keeps combustion chamber pressures low (unburned fuel takes heat out of the exhaust). It is more economical and more ecologically friendly to run fuel lean since you paid for that unburned fuel and it's kinda gross.

In general, more fuel than ideal means more resistance to knock. But these things are complex.

EDIT: Knocking happens from pre-detonation. Knocking can also happen from predestination, like in the case of turbocharged Subarus.

Re: Porsche's idea for a six-stroke internal combustion engine

#202

Post by throwaway48540 » Sat, Sep 21, 2024, 1:29 PM UTC

squarefoot wrote: post #94

throwaway48540 wrote: post #24

Earlier quoted context omitted.

Lol, I really want to see a 150-year old EURO6 200kw diesel engine coupled with a 150-year old 9-speed automatic dual-clutch allowing me to drive on the 150-year old roads for 4 liters per 100 km at German highway speeds. BTW, electric cars are older technology than ICE cars.

The main innovation in modern electric cars isn't just about swapping fuel with electricity, but eliminating all junk in between that wasted power only to overcome ICE inherent flaws. More simple electronics aside, clutch, gearbox, then driveshaft are all gone, and they contributed to a huge waste of power, which burned a lot of fuel for nothing. This is so bad that where possible and economically feasible (trains an…

That's not entirely true, most electric cars sold today have a driveshaft, clutch and gearbox.

Re: Porsche's idea for a six-stroke internal combustion engine

#203

Post by tonyedgecombe » Sat, Sep 21, 2024, 1:30 PM UTC

tirant wrote: post #165

tonyedgecombe wrote: post #110

Earlier quoted context omitted.

>I'm an enviromentalist and I'd still buy an ICE Porsche. Environmentalists walk or ride bikes.

According to whom? I am also an environmentalist and burn some fuel from time to time, I’m not a zealot. For me to operate and support the environment the best I can I also need to be mentally fit and have life enjoinment. And riding my old classic carbureted Triumph helps me with that.

According to my dictionary an environmentalist is "a person who is interested in or studies the environment and who tries to protect it from being damaged by human activities".

I can't see how buying a Porsche (or any car really) is compatible with that.

Re: Porsche's idea for a six-stroke internal combustion engine

#204

Post by magicalhippo » Sat, Sep 21, 2024, 1:32 PM UTC

uluyol wrote: post #52

ttwwmm wrote: post #2

[flagged]

ICEs have a lot of advantages that make them much better suited than EVs to certain tasks (extreme climates and remote locations, for example). They will likely stick around for niche use cases (at least) for quite a long time. As for why Porsche is spending money on ICE engines...well, no one really buys a Porsche because it's a "practical car", do they?

Here in Oslo, Norway, they got BEV busses for a lot of lines, and last year was a really cold winter. Somehow, the ones in power were shocked to discover the range dropped to half due to the electric heaters needing a lot of power, causing a public transportation chaos as busses queued up for charging instead of transporting passengers.

Now the busses are getting retrofitted with fuel-based heaters, which will be running on bio-diesel... better than nothing I guess.

Re: Porsche's idea for a six-stroke internal combustion engine

#205

Post by MrDunham » Sat, Sep 21, 2024, 1:32 PM UTC

i_am_jl wrote: post #201

magicalhippo wrote: post #196

I'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 u…

>more fuel means less compression is tolerated before knocking Generally, no. Knocking happens from pre-detonation, that's usually caused by heat from compression causing the fuel/air mix to ignite before it's triggered by spark. To avoid this engines will run a fuel/air mix that is not stoicheometrically ideal, to make the mixture less likely to ignite early. It is safer to run a fuel rich mix than to run a fuel lea…

Friendly correction for others because your auto correct failed you...

"predestination", pretty sure parent meant "pre-detonation"

A.k.a. Autoignition aka "it goes boom before you planned on it"

Only adding this as it's a pretty crucial word for understanding the comment.

Re: Porsche's idea for a six-stroke internal combustion engine

#206

Post by magicalhippo » Sat, Sep 21, 2024, 1:39 PM UTC

i_am_jl wrote: post #201

magicalhippo wrote: post #196

I'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 u…

>more fuel means less compression is tolerated before knocking Generally, no. Knocking happens from pre-detonation, that's usually caused by heat from compression causing the fuel/air mix to ignite before it's triggered by spark. To avoid this engines will run a fuel/air mix that is not stoicheometrically ideal, to make the mixture less likely to ignite early. It is safer to run a fuel rich mix than to run a fuel lea…

Ah yes, read that engine knock article the wrong way around, guess my mind was drawing on intuition from things like gun powder where more stuff crammed more tightly together is worse.

So then, if they're doing a non-ideal initial burn it would have to be a lean lower-compression burn, followed up by a higher-compression secondary burn?

Re: Porsche's idea for a six-stroke internal combustion engine

#207

Post by LightBug1 » Sat, Sep 21, 2024, 1:41 PM UTC

tonyedgecombe wrote: post #200

chromatin wrote: post #168

Earlier quoted context omitted.

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?

https://www.logicallyfallacious.com/logicalfallacies/Appeal-...

https://en.wikipedia.org/wiki/Reductio_ad_absurdum

Re: Porsche's idea for a six-stroke internal combustion engine

#208

Post by rpmisms » Sat, Sep 21, 2024, 1:43 PM UTC

MrDunham wrote: post #205

i_am_jl wrote: post #201

Earlier quoted context omitted.

>more fuel means less compression is tolerated before knocking Generally, no. Knocking happens from pre-detonation, that's usually caused by heat from compression causing the fuel/air mix to ignite before it's triggered by spark. To avoid this engines will run a fuel/air mix that is not stoicheometrically ideal, to make the mixture less likely to ignite early. It is safer to run a fuel rich mix than to run a fuel lea…

Friendly correction for others because your auto correct failed you... "predestination", pretty sure parent meant "pre-detonation" A.k.a. Autoignition aka "it goes boom before you planned on it" Only adding this as it's a pretty crucial word for understanding the comment.

That fuel is totally depraved, and has no hope of salvation.

Re: Porsche's idea for a six-stroke internal combustion engine

#209

Post by dahart » Sat, Sep 21, 2024, 1:57 PM UTC

_yb2s wrote: post #199

OJFord wrote: post #69

Earlier quoted context omitted.

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.

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?

Re: Porsche's idea for a six-stroke internal combustion engine

#210

Post by labcomputer » Sat, Sep 21, 2024, 2:09 PM UTC

teo_zero wrote: post #51

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

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.