Quote:
Originally Posted by christofoo
Yes, this is about throttle loss in particular. 'Pump cycle losses' as t vago discussed will increase or be about the same with DCD but throttle losses will decrease.
|
Well, true-believers, go ahead and give this a try. Nobody's really stopping you from attempting to turn pi into exactly 3, make water run uphill, or make this DCD idea work.
Throttling losses are actually a fairly minor component of pumping losses described here. You can define throttling losses are the aerodynamic losses incurred by trying to push air past a really huge aerodynamically ugly shape (the throttle plate).
Lean burn works precisely because it causes intake manifold vacuum to lower. It takes a rather large amount of energy to create a vacuum, and it takes an even larger amount of energy to create and maintain this vacuum in an open system such as an intake manifold.
Throttle opening controls intake manifold vacuum, but it is not of primary importance.
Quote:
Originally Posted by christofoo
My argument in #185 was elegant and perfect.
|
and wrong.
Quote:
Originally Posted by christofoo
I can quickly rephrase it and simplify it even further: You only have to believe three principles:
|
Are we talking real-world, or are we talking religion? Belief has nothing to do with this - in the real world, things either work or they don't. All the belief in the world won't change that.
Quote:
Originally Posted by christofoo
1) DCD results in higher air mass per cylinder per revolution to produce same torque with fewer combustion cylinders. This is a fixed AFR system, where DCD requires more fuel per combustion cylinder per revolution.
|
This is an observation. So what?
Quote:
Originally Posted by christofoo
2) Higher air mass per cylinder requires higher throttle position. That's how the throttle works, by design. If that correlation isn't there, then just remove your throttle and drive without it.
|
No, higher air mass per cylinder requires lower intake manifold vacuum. That's how a basic Otto-cycle internal combustion engine works, by design.
Oh, and I think that BMW did away with the throttle body altogether, and they still manage to effectively vary the air mass per cylinder in their engines. However, even BMW could not get rid of throttling altogether -
their engines that lack a throttle body still have throttling losses.
The throttle only controls intake manifold vacuum. It is intake manifold vacuum that actually controls the amount of air going into the cylinders, and it is intake manifold vacuum that is represented in those graphs.
Don't confuse the two. You could have the most efficient throttle in the world, with zero aerodynamic drag, and zero throttle losses, and you'd still have to put up with intake manifold vacuum, which represents the pumping losses you so cavalierly dismiss.
Quote:
Originally Posted by christofoo
3) Throttle loss dominates over 'pump cycle loss' (defined between intake and exhaust valves as t vango illustrated). If this were not true then lean-burn would not work. It is exactly the same.
|
And... how is that "pump cycle loss" defined in that graph? The area created by the volume difference of the piston in the cylinder, multiplied by the pressure difference between the intake and exhaust manifolds?
Sound familiar? And why is there a pressure difference? It's the pressure difference that matters, not the fact that there is a throttle. As stated before, BMW managed to get rid of the throttle plate altogether - however, there's still throttling going on, with all of its losses associated with throttling air flow. The fact that they can still produce more efficient engines in this way shows that there is something besides throttling losses to consider.
Also, do you know how much power is needed to maintain a 7 psig vacuum in an intake manifold of, say, 4 liters of volume, at 2000 rpm? It's a bit under 5 HP - just to do this. That's not including the power that's also required to drive engine accessories, overcome powertrain friction losses, or overcome other internal engine losses - let alone the power needed to propel the car forward.
Get my name right. It's not exactly hard to do.
Today
Other popular topics in this forum...
