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Re: Mercedes Power Unit
Posted: 11 Nov 2017, 02:14
by PlatinumZealot
We can work it backwards knowing the boost pressure and air fuel ratio and fuel flow to find the volumetric air flow rate then divide by the plenum cross sectional area to get the air speed.
Re: Mercedes Power Unit
Posted: 11 Nov 2017, 03:19
by MrPotatoHead
PlatinumZealot wrote: ↑11 Nov 2017, 02:14
We can work it backwards knowing the boost pressure and air fuel ratio and fuel flow to find the volumetric air flow rate then divide by the plenum cross sectional area to get the air speed.
I have a pretty good idea of the numbers but I'm curious to see the numbers that gruntguru used
Re: Mercedes Power Unit
Posted: 11 Nov 2017, 10:29
by henry
MrPotatoHead wrote: ↑11 Nov 2017, 03:19
PlatinumZealot wrote: ↑11 Nov 2017, 02:14
We can work it backwards knowing the boost pressure and air fuel ratio and fuel flow to find the volumetric air flow rate then divide by the plenum cross sectional area to get the air speed.
I have a pretty good idea of the numbers but I'm curious to see the numbers that gruntguru used
I would guess gruntguru used:
800cc , 100 times per second through an 80 cm2 hole. Which gives 10m/sec
Re: Mercedes Power Unit
Posted: 11 Nov 2017, 12:51
by gruntguru
I couldn't have put it better myself. Enjoy your up-vote henry.
Re: Mercedes Power Unit
Posted: 12 Nov 2017, 19:37
by MrPotatoHead
The numbers above would be correct for constant flow in an open pipe.
Which is not the dynamics in an intake manifold where the cylinder filling time is roughly a third of a cycle.
So while the average flow velocity might be that, the actual instantaneous velocity during the cylinder filling event is much higher.
An engine is incredibly complex and dynamic. I have done CFD on many Intake manifolds as that’s one of the many engine parts I’m involved in the design and engineering of.
Re: Mercedes Power Unit
Posted: 12 Nov 2017, 19:54
by MrPotatoHead
Every intake that I design and run through CFD I do both a static flow simulation through all of the runners open and then a dynamic simulation with a true time based simulation of per cylinder intake valve opening time.
It’s amazing the differences in flow that you will see between the two.
Re: Mercedes Power Unit
Posted: 12 Nov 2017, 22:44
by toraabe
Re: Mercedes Power Unit
Posted: 12 Nov 2017, 23:19
by Edax
Zynerji wrote: ↑09 Nov 2017, 03:04
thedutchguy wrote: ↑08 Nov 2017, 21:47
Interesting story by Matthew Carter (former team Lotus F1 CEO) on Missed Apex Podcast about Spa 2015, when Mercedes "gave Lotus a different engine mode" in order to have Grosjean finish ahead of Vettel. According the Carter, Grosjean told him after the race that the car had nevert felt like that (good) before. Lotus were neven 'given' that engine mode again.
You can watch the whole clip here:
https://youtu.be/xBQA9eABkpc?t=27m10s
What I wonder is how Mercedes can 'give' or unlock an engine mode for the driver to use, when pit-to-car telemetry is forbidden? I understand how Mercedes can keep certain engine modes from their customer teams, but I'm a bit puzzled as to how they can choose to unlock them for a driver to use during a race when the car is on track.
This is by far the most interesting question... hidden switch combinations? Should the FIA 2021 rules include all software and disclosure of modes to the customer teams as well?
This seems to be a crazy advantage to overcome. And provably why Ron Dennis dropped Mercedes in favor of the factory Honda deal.
Doesn’t necessarely have to be the case. It sounds very complicated to built in secret performance which can be accessed via customer software and interface, without the customer knowing it is there.
When we ship out equipment we give our customers an operating envelope. This contains a margin to what we know they are capable off, simply because we don’t want failures in the field. However with proper supervision you could take them further, and we regularly do in our own workplace.
I can imagine that something like that happens with customer engines as well. In this case that Merc provided Lotus the engineering oversight to allow to run the engine a bit harder and hotter than normal using the conventional engine mappings.
Re: Mercedes Power Unit
Posted: 12 Nov 2017, 23:19
by godlameroso
MrPotatoHead wrote: ↑12 Nov 2017, 19:54
Every intake that I design and run through CFD I do both a static flow simulation through all of the runners open and then a dynamic simulation with a true time based simulation of per cylinder intake valve opening time.
It’s amazing the differences in flow that you will see between the two.
Do pressure waves from valves closing affect mean flow velocity?
Re: Mercedes Power Unit
Posted: 12 Nov 2017, 23:21
by amho
MrPotatoHead wrote: ↑12 Nov 2017, 19:54
Every intake that I design and run through CFD I do both a static flow simulation through all of the runners open and then a dynamic simulation with a true time based simulation of per cylinder intake valve opening time.
It’s amazing the differences in flow that you will see between the two.
What do u mean by"static flow simulation"? U mean steady state flow...
Re: Mercedes Power Unit
Posted: 12 Nov 2017, 23:35
by amho
PlatinumZealot wrote: ↑11 Nov 2017, 02:14
We can work it backwards knowing the boost pressure and air fuel ratio and fuel flow to find the volumetric air flow rate then divide by the plenum cross sectional area to get the air speed.
U mentioned that wanna to know a/f ratio to know volumetric flow, here u know that there is direct fuel injection , do u know when fuel is injected? In intake phase or compression phase?
Re: Mercedes Power Unit
Posted: 13 Nov 2017, 00:11
by godlameroso
amho wrote: ↑12 Nov 2017, 23:21
MrPotatoHead wrote: ↑12 Nov 2017, 19:54
Every intake that I design and run through CFD I do both a static flow simulation through all of the runners open and then a dynamic simulation with a true time based simulation of per cylinder intake valve opening time.
It’s amazing the differences in flow that you will see between the two.
What do u mean by"static flow simulation"? U mean steady state flow...
Static flow as in no interruption, people forget combustion events aren't continuous, the valves close and open and this interrupts flow, this is dynamic.
Re: Mercedes Power Unit
Posted: 13 Nov 2017, 00:13
by godlameroso
amho wrote: ↑12 Nov 2017, 23:35
PlatinumZealot wrote: ↑11 Nov 2017, 02:14
We can work it backwards knowing the boost pressure and air fuel ratio and fuel flow to find the volumetric air flow rate then divide by the plenum cross sectional area to get the air speed.
U mentioned that wanna to know a/f ratio to know volumetric flow, here u know that there is direct fuel injection , do u know when fuel is injected? In intake phase or compression phase?
Fuel is injected in both, the turbulence during intake phase promotes mixing, as does EGR left over from the previous combustion cycle(by helping fuel vaporize). The ideal timing is in between intake and compression.
Re: Mercedes Power Unit
Posted: 13 Nov 2017, 00:58
by PlatinumZealot
Going by experiments a 17:1 air fuel ratio can be assumed? Then what about the boost pressure? Any confirmed telemetry on boost pressure?
Re: Mercedes Power Unit
Posted: 13 Nov 2017, 04:47
by MrPotatoHead
godlameroso wrote: ↑12 Nov 2017, 23:19
MrPotatoHead wrote: ↑12 Nov 2017, 19:54
Every intake that I design and run through CFD I do both a static flow simulation through all of the runners open and then a dynamic simulation with a true time based simulation of per cylinder intake valve opening time.
It’s amazing the differences in flow that you will see between the two.
Do pressure waves from valves closing affect mean flow velocity?
They do for sure but the effect is less on an engine as the plenum pressure gets higher and the air more dense.
This is the reason that intake runner length tuning has less effect under forced induction.