Misc pumping losses questions

[tasdrouille]

I have a couple questions in regards to intake flow and resulting pumping losses.

Anyone knows why the throttle is typically a butterfly valve? I clearly remember from Hucho's book that a gate valve has a significantly smaller impact on the flow. Why don't we see throttle bodies equiped with gate valves? (or maybe I should just look at more cars..)

Also, I was always told that what had the most impact on pumping losses was the throttle plate, but now I read that CVVT can reduce pumping losses at light loads by 80%, so it looks like the valves timing would be the main culprit, no? I'm a bit confused.

[fabrio.]

both valve create an restriction flow.

The problem came from the throttle isnt' full open.
Power is needed to create flow, and this power is loss.
The valve (in the head) create its power loss, but at certain RPM the acustic effects on intake runners (or exaust) minimize this one.
So, at the full throttle, in the Otto engines, the power loss caused from the throttle it is at the minimum.
Only when the throttle it is at the minimum or partialized the its powerloss is bigger.
A way to eliminate the throttle losses is to eliminate the throttle
In this case, the engine power can be regulated from an valve lift and timing electronic controlled system.
This one, permit to create required torque limiting air inlet in the combustion chamber whitout a lot of pumping losses symply, because the acusti effect (resonance and pulse effect) has calibratet in order at an lower pumping losses.

[fabrio.]

another way to reduce the pumping losses from an Otto engine, is the control the AFR (air fuel mixture) it allow, to make to work the engine in region of lean burn.
In the lean burn, for the same torque of a normal engine, it is obteined from an greater opening of the throttle .
This one, minimize the pumping losses

[Duffman]

I know around the area of the year 2000 BMW was experimenting with throttleless gasoline ingines that used EGR to control the amount of O2 for combustion. Not sure if they are in production now or not. I'm sure someone else here knows for sure.

As Fabrio said, when you dont want WOT, it doesnt matter what valve you have in front becuase you want a restriction anyway. With the advent of FI, manufacturers can make bigger throttle bodies so that would reduce the restriction of the valves at WOT, slide valves are best used for carbs I guess.

[fabrio.]

I konw that a lot engine use the EGR valve to recirculate a quote of exhaust gas.
This one, reduce the amount of O2 and hel to reduce the pumping losses.

sorry, I not understand: wath is the "WOT"?

[tasdrouille]

Wide Open Throttle

[Peter7307]

Slides have two distinct drawbacks for production cars.

The first is costs. Simply put a disc pivoting on a shaft is cheaper to make than a sliding block which needs precision machining to wort properly.

The second is slides have a notorious habit of sticking if there is a build up of dirt / grit or any other rubbish on the slide.
Most car makers simply don't want to know about that sort of potential problem.

By the way the SU carb dating back to the very start of car manufacture was a slide type.

Cheers , Pete.

[fabrio.]

[Duffman]

Fabrio,
Can you translate the bottom line please.

[fabrio.]

wow..this one is a big problem!

the image above, is scanned from a magazine.
I can to tray to serch it.

[fabrio.]

Duffman, I have serch in my memory
The pic posted by me, it is a comparation of extimated fuel consumption between the same engine with throttle operation and WOT, the dashed line is the BSFC reduced by throttle loss.
Bottom axis, is the engine RPM; that one written in Italian isnt' relevant.
Note, the discendent curve of the dashed line from 1000 to 5000RPM...I think that is caonsequently of reverse flow in the intake runners and loss of air intake through the exhaust because overlap cams

[Big Dave]

The lack of a throttle is part of the reason why a diesel is more efficient than a spark-ignition engine.