4 ms·

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 exha

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 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 https://en.wikipedia.org/wiki/Engine_knocking [2]: https://en.wikipedia.org/wiki/Variable_compression_ratio https://en.wikipedia.org/wiki/Variable_compression_ratio

i_am_jl 2y ago
>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.
- to11mtm 2y ago
  > EDIT: Knocking happens from pre-detonation. Knocking can also happen from predestination, like in the case of turbocharged Subarus. Edit of the week IMO.
- MrDunham 2y ago
  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.
  - rpmisms 2y ago
    That fuel is totally depraved, and has no hope of salvation.
    - cout 2y ago
      This is why TULIP oil makes a great fuel additive.
      - rpmisms 2y ago
        I totally, unconditionally, agree. My own limits do not account for the irresistibility of this combination. I hope you persevere with this message.
  - i_am_jl 2y ago
    Ah you're right, thank you!
- magicalhippo 2y ago
  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?

i_am_jl 2y ago

>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.

to11mtm 2y ago
> EDIT: Knocking happens from pre-detonation. Knocking can also happen from predestination, like in the case of turbocharged Subarus. Edit of the week IMO.
MrDunham 2y ago
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.
- rpmisms 2y ago
  That fuel is totally depraved, and has no hope of salvation.
  - cout 2y ago
    This is why TULIP oil makes a great fuel additive.
    - rpmisms 2y ago
      I totally, unconditionally, agree. My own limits do not account for the irresistibility of this combination. I hope you persevere with this message.
- i_am_jl 2y ago
  Ah you're right, thank you!
magicalhippo 2y ago
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?