TinoBoost wrote:
one can have backpressure lower than manifold pressure. Would you call that ICE pumping gains?
Pumping losses is an "average" of energy losses having to pull vaccum, or "suck" air in an N/A engine. It really is a combination of thermodynamics and kinetic energy. There is no "pumping" energy. With a turbo pumping through the ICE is irrelevant. The turbo defines it.
Pumping losses are a significant factor in Otto cycle, internal combustion engines for 2 main reasons.
1. Throttling - being the worst contributor at part throttle - not exactly of a particular concern in racing engines which operate mostly at WOT
2. Valve restriction especially costly at WOT - specifically the air/gas has to overcome the small curtain area passage of a of a valve, inlet or exhaust. It takes
shaft power to move the gas past this restriction each and every time.
TinoBoost wrote:
you cannot gear down the turbo. There is a clear rule about that, mentioned multiple times.
Apparently the MGU-H can be geared to a fixed non 1:1 ratio
TinoBoost wrote:
backpressure will define how much power the MGUH can make. But lets look at massflows. You would want to run the higher backpressure you can before you lose mass flow through the engine. That would maximize turbine power.
In my opinion, the exhaust backpressure will be a key design factor determining how much kW power can practically be harnessed from MGU-H. The exhaust turbine housing and turbine wheel will be sized to attain the necessary balance. I would not be surprised, if Renault's problems have to do with that particular area. In about 2 years, some concrete info may start to leak out.
MGU-H device is an uncharted territory for all engine makers in F1. There is NO PRIOR DATA to fall upon and steep learning curve while the rules will soon fix the specification not to be altered till the end of the season.
TinoBoost wrote:In specific scenarios, it might be worthwhile to "throttle down" the engine by letting higher backpressure limit airflow while harvesting the turbo power.
Throttling means a restriction to flow, such as a throttle valve or VVT effect causing pressure differences across the restriction. The exhaust backpressure effect however while it may have a detrimental effect on the gas exchange process doesn't result in pressure differences so calling it "throttling" is imprecise, but it does have an effect of limiting the net oxygen amount in the pre-combustion content.
TinoBoost wrote:
valve overlap in turbos is usually very different from N/A. Less overlap seems to be usually the case, but it depends how engines use variable valve timing.
Not really. The required valve timing to achieve needed performance, was up until now, traditionally, in relative sense - "blind" to whether you had turbo or not (supercharging is yet different). The key factor in turbo engine valve timing has always been operating speed RPM. The reasons being was that at operating range the inlet manifold pressure and backpressure were usually closely balanced. How? Thru careful selection of turbine/compressor wheels and housings.
I said up until NOW. Because the new F1 specification may rewrite turbo boosted engine science somewhat due to new design parameters introduced in the rule book, namely the effect of MGU-H.
TinoBoost wrote:
EGR helps efficiency, because especially when running rich, you can run less rich, "reusing" fuel from a previous cycle, and using the exhaust to soak up some heat, and inject a little bit less fuel on that cycle. The temperature right after the combustion will still be much higher than the exhaust, and the exhaust could carry more heat that clean air, saving the piston.
In addition high overlap could mean you blast fresh air/fuel past the exhaust valve.
Gasoline powered racing engines usually make peak power at 12-12.5:1 air/fuel ratio. So while that is "richer" than theoretical stoichiometric ratio, it is never called "rich", because that is a design optimum. It is also true, that combustion gases may contain a lot of unburned hydrocarbons. In my view no racing performance potential exists in trying to tap those unburned particles and burn them again.
EGR was the trick that helped fuel efficiency and emissions in passenger vehicle technology since the onset of CAFE and emissions regulations. Specifically, it was reducing pumping losses at part throttle (fuel savings) as well reducing combustion temperatures and reburning some small amount of unburned particles still contained in the exhaust, which helped emissions. EGR is considered to be hot and chemically inert, so it was "taking up space" inside the cylinder and by virtue of being hot, it was "soaking up" very little heat from the chemical energy of combustion.
Much different things are demanded of a racing engine. So while I admit, that some amount of internal EGR due to the combination of technical optimization of MGU-H/turbine housing/turbine wheel may enter the picture. Not necessarily by deliberate design, but by a balance of certain technical circumstances.
Apologies for such a long read
