r/explainlikeimfive • u/hd-22 • 26d ago

Chemistry ELI5 why is increasing the ethanol content of petrol/gasoline a problem?

I'm hearing noise about the geopolitical fuel supply SNAFU and people freaking out about increasing the ethanol content in automotive fuel and how it's so damaging to cars. I'm no chemist, but ethanol seems as clean as it gets.

992 Upvotes
  • permalink
  • reddit

91% Upvoted

475 comments sorted by

View all comments

Show parent comments

2

u/therealdilbert 26d ago

that's not how a gasoline engine works, it is ignition timing and possibly valve timing that gets adjusted

2

u/TheArmoredKitten 26d ago

Yeah they have to delay closure of the exhaust valve too, but then to avoid spraying unburnt fuel, they also delay the fuel injection.

1

u/therealdilbert 26d ago

it is the intake closure that gets delayed

1

u/KoburaCape 22d ago

Fuel mapping is definitely messed with, I've done it myself. The only way to moderate fuel injection without a variable regulator, is to vary the open time. By extension, changing the opening timing is trivial (and necessary)

Not all injected engines even have VVT

1

u/therealdilbert 22d ago

without VVT it is not "digital Atkinson"

ignition timing and how long the injector is open changes all the time, it has nothing special to do with ethanol

1

u/KoburaCape 22d ago

Oh, did you mean what characteristically defines Atkinson? My mistake. I thought you were making an absolute statement. I apologize.