321apex wrote:Some thoughts on the subject of MGU-H:
- MGU-H is intended to "load up" the spinning turbo, resulting in the choking effect upon the exhaust gases (there is no wastegate)
- all is fine until the exhaust backpressure starts to exceed the inlet manifold pressure at which point internal EGR takes place which usually reduces pumping losses (good for fuel efficiency) as well as power (bad for performance)
- high revving racing engines utilize a lot of valve angle overlap, often well over 100 deg crank angle, at which point internal EGR will become a real issue
- the internal EGR phenomena is not desirable in a racing engine which is designed to harness maximum resonant tuning effects of inlet/exhaust cylinder gas scavenging
- it should not be excluded, that the iEGR effect may/will become a design parameter of this new system
- in my view, this exhaust backpressure will be the limiting factor of how much electrical power the MGU-H will be able to deliver
- gearing down from turbo speed will allow some design freedom to balance out it's power capacity and low inertia
I believe a change of thinking has occurred within the engine development teams. Normally racing engines have really aggressive cams because they're trying to squeeze every last gram of air into the cylinders.
This is no longer the case!
Internal EGR only reduces power in a traditional ICE setup because the power is effectively constrained by how much oxygen is in the cylinders.
With the fuel flow limit and a turbocharger, it's quite easy to get the required oxygen mass to match the limited fuel mass without employing the traditional aggressive cam profiles. I actually wouldn't be surprised if the intake valves are nearly the same size or smaller than the exhaust valves.
The cam timing will most definitely be optimized for the high levels of exhaust backpressure that will be seen during normal operation. Efficiency is king; with a limited amount of energy flowing through the fuel injectors, better efficiency means more power to the ground.