ringo wrote:
really now? Where have you seen this before?
Why should the throttle be kept normally open?
what is the impact on the brake booster?
Its not something I've seen. Its an idea I've been advocating since last summer.
Ill try to explain. As I said the throttle plates only help regulate the air going into the engine because the air/fuel mixture in a petrol engine is critical. When off throttle there is no combustion going on (besides in idle condition). So regulation of the air entering the engine is unnecessary. But when the throttle plate is closed there is a vacuum build-up between the throttle plate and the piston during the intake stroke. The piston has to work against this vacuum and that is what causes pumping loses. This is mechanically braking the engine and increases engine braking. When you have a MGU-K harvesting energy during braking there is no reason to waste some of that energy into mechanical work. So the less engine braking the more energy there is for the MGU-K to absorb.
Another thing is in a turbo engine when you close the throttle bodies theres is almost no air running through the engine. So there is almost no exhaust flow which is driving the turbo so the turbo rpm will fall quickly. If the throttle is left open a lot more air is travelling through the engine giving a better flow through the exhaust meaning the turbo rpm doesn't fall as quick. Its not much but every little thing in an efficiency formula counts.
A third thing is that in a turbo engine when closing the throttle plate when the turbo is in max boost creates a huge pressure spike between the throttle plate and the compressor side of the turbine. It also creates a shock impulse that travels backward into the compressor. This both brakes the turbine and put strain on the turbine axle and the blades. That's why you run blow off valves to bleed out this pressure build up. If the throttle doesn't close you don't get this pressure spike so you wont need a blow off valve.
When it comes to the brake booster I don't believe F1 cars uses those? Otherwise you could just run a auxiliary vacuum pump. That's what diesel road cars do because they don't use throttle plates and therefore don't have this vacuum in the intake plenum.
n smikle wrote:
Yes. I do know. And I am showing you that in spite of that fact Audi still uses a blow off valve on their R18 turbo diesel engine. So we will not know for certain what we will see come testing.
I believe most diesel race engines use throttle plates. But I'm not sure that the R18 is running a blow off valve. What I hear sounds like turbo chatter which happens when not running a blow off. So the air is forces backwards through the compressor stalling the compressor blades.
