Why is engine vacuum necessary? Are there other ways to run an engine?

[@mikebruegger8654]

I learned a bit about diesel engines.... 😊

[@bitsofwisdom460]

Yes, diesels have some significant differences that aren't obvious. Diesel combustion science is much different than gas engines.

[@nowayjose596]

I would add BMW's Valvetronic system as a unique approach to removing the throttle body/valve from a gas engine. And yeah, if it weren't for NOx we could already be running our engines a good bit leaner and getting better MPG. GM even has a lean cruise setup programmed into many of their ECUs but in the US it's completely disabled for emissions reasons (NOx specifically).

[@bitsofwisdom460]

I wasn't aware of that system before. You're right it is a unique solution. It uses wide control of valve lift along with variable valve timing in place of the throttle. Others have used lift and timing control, but not to that degree. And yes, lean burn is much better for efficiency (and CO /HC emissions), but the NOx regulations have that restricted.