Quote:
Originally Posted by wwest40
"..buffer the pressure pulses...."
At WOT how do you "buffer" the pressure pulses in a way that prevents a pressure wave from travelling back up the intake path...??
With a 4 cylinder engine you will have ACTIVE SUCKING of the "opposite" cylinder to neutralize the pressure wave....
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You have the same thing with a 6 or 8 cylinder engine. Even 5 cylinder engines, and 10 cylinder engines will always have a cylinder on intake at the same time that one or more cylinders is on power/exhaust/compression. The only exception to the rule is the single cylinder engine, and any variant of rotary engine.
The only difference is the speed and timing at which the next piston draws back the unused (expelled) intake mixture.
2 cylinder engine, pistons are working 180 from each other (normally)
3 cylinder engine, pistons are working 120 from each other (normally)
4 cylinder engine, pistons are working 90 from each other (normally)
5 cylinder engine, pistons are working 72 from each other (normally)
6 cylinder engine, pistons are working 60 from each other (normally)
8 cylinder engine, pistons are working 45 from each other (normally)
10 cylinder engine, pistons are working 36 from each other (normally)
12 cylinder engine, pistons are working 30 from each other (normally)
In every iteration of a standard balance multi piston engine, each cylinder is working opposite another one such a way that the expelled intake mixture would be recovered by another cylinder.
MechEngVT - What I meant by bunk was more like "Wasteful". I mean this because the cam causes outflow of intake mixture back into the exhaust manifold. This causes issues with intake harmonics, etc, and screws up ideal mixtures in just about any gasoline engine. What's to say that the mixture pushed out wasn't the richest part of a layered homogenous mixture? Now the mixture in the cylinder is lean! Subsequently, the engine has had another pulse of air through the induction system, which in carb'd apps already has gas in it, or in FI apps has fuel added as it flows into the cylinder, but either way - the new cylinder's mixture is ideal, but it's sucking in the richest part of the last cylinder, so now it's rich! Now you have a lean cylinder, and a rich cylinder. Who knows what part of the rich cylinder will end up in the outflow from the second piston's compression event, and so on/so forth. See what I mean? In the Atkinson Cycle engine, this isn't a concern, as there is no outflow.
Ideally, to use the Atkinson cam in place of the Atkinson engine, the outflow would either have to be precisely controlled, or fuel precisely metered AFTER the ouflow event. This is where GDI comes into play. Gasoline Direct Injection engines are similar to diesel engines in that they can directly inject the fuel into the compressed air already in the cylinder. Therefore, the Atkinson cam's outflow event would only expel unnecessary air, and the mixture could be leaned by the GDI computer (ECU) to account for the outflow from the Atkinson cam, so that each cylinder could be individually fed it's own fuel supply without an outflow of fuel from the previous cylinder to suck in.
In that sense, the Atkinson cam is less complex, and easier to create/manufacture, and wins. In any other type of engine, I don't see it being a very reliable system. (Apparently, neither do many auto mfgrs.)
wwest40 - Turbocharger exhaust turbines don't require exhaust gasses to expand to reach full spool. They only require the flow of exhaust gasses. Regardless of the expansion ratio being too large or too small for the engine, the expansion of the exhaust gasses being complete, etc... there will still be exhaust
flow and heat energy (not expansion, heat... the exhaust flow will still be hot.), so the turbo will still spool and create the feedback loop that turbochargers create in order to reach maximum speed.
Guess what happens if you have a turbo running off an engine's exhaust, but feeding it's compressed air to something other than the engine that it's leeching exhaust gas pressure from? The turbine will never reach full speed, and the compressor will never reach max potential boost. Turbochargers
require a feedback loop to reach their full potential, except in extreme circumstances. (Obviously, if you put a T3/T4 hybrid on a submarine engine, it's going to hit 100,000+ RPMs without the feedback loop.) So I guess I should restate to include the obvious - a turbocharger sized properly for the engine will not fully spool without the feedback loop it creates.
That essentially means that your theory on why you don't see Atkinson Cycle or Atkinson Cammed engines with turbos is a myth, and holds no water in logical thinking or applied science.
If you don't believe that turbos don't require expansion of gasses (as opposed to flow) to operate, put a vacuum cleaner nozzle on one some day. I bet you a dollar it starts to spool up.