Quote:
Originally Posted by jeff88
So what you are saying is that with a higher back pressure, the throttle plate opens up a little more, thereby lowering manifold vacuum?
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That may happen, but the lower intake manifold vacuum would primarily result from having a larger volume fraction of inert gas (exhaust) in the intake manifold.
For a gasoline engine, the main purpose of the intake manifold and throttle is to meter the amount of oxygen that goes into each cylinder. The mechanism by which this is accomplished is by creating a volume whose pressure is lower than ambient, so as to lower the amount of oxygen in the intake manifold that is compared to ambient. This takes engine work (therefore, fuel) that would otherwise be spent in pushing the vehicle forward. A higher intake manifold vacuum requires more work, and more fuel, to maintain, than does a lower intake manifold vacuum. Similarly, given the same intake manifold vacuum, it takes more work to maintain that vacuum in a large volume intake manifold, than in a small volume intake manifold.
If oxygen could be metered into a given engine without having to vary intake manifold vacuum, such as by increasing the percentage of inert gas (such as exhaust gas) being sucked into the engine, then that engine would have to work less to maintain an intake manifold vacuum. Such an engine would consume less fuel than a similar engine that did meter oxygen via the use of an intake manifold vacuum. Production gasoline engines do exist that do not depend on a intake manifold vacuum - they instead use variable valve lift/duration to meter the amount of oxygen into each cylinder.
Diesel engines, not needing to meter oxygen to begin with, do not need to have a power-robbing intake manifold vacuum. Placing a pure exhaust restriction on a Diesel powerplant will just lower the efficiency of that powerplant.
Quote:
Originally Posted by jeff88
I would love to see this in action and see the associated FE improvements. I wonder what the comparable numbers would be compared to a turbo. He gained 10%, I wonder if just a pure restriction like you talk about would have a higher or lower increase in FE.
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Heh -
my EGR experiment that I did earlier this year took me into the realm of MPGuino. Soon, hopefully, I can go back into EGR.