mzivtins wrote: ↑Mon Sep 09, 2019 10:32 amHi all!
Dry sumps have popped up a lot in life recently, and i wondered, what challenges do F1 cars have with using dry sumps?
From a performance perspective I think that difficulties arise from balancing rotor tip shear losses with tip leakage (regardless of rotor type).
Another important factor is sizing the orifices (orifi?) between the crankshaft bays. While it is widely reported that the bays are isolated, in practice they do communicate through small orifices. It can be shown that for a given engine speed there is only one orifice size that gives the smallest pumping loss. Too large an orifice and the compression work (within the bay, not the cylinder) cannot be recovered as efficiently, too small an orifice and the pumping losses associated with blow-by flow across it increase.
Determining the bore of these orifices usually requires complex 1D gas dynamics models as well as engine tests.
How to they remove air from the oil quickly?
As mentioned by SS, centrifugal separators are used. For nose-fed crankshafts, additional separators within the crank nose were used which use the crank angular velocity to centrifuge some more air out (I think this system was used as far back as the RR Merlin - I'm sure the warbird engine buffs will know more).
What are the size restrictions (through packaging) of the sump tank?
Is it possible to have a shallow tank (issues with removing air)?
First off, the oil tank must fit within the FIA-defined PU boundaries. A tall, narrow tank has two distinct advantages:
It is less sensitive to sloshing and it can provide a higher hydrostatic pressure head at the pump inlet (reducing risk of cavitation) for the same oil mass.
Scavenge points, number of scavenge pump sections vs weight/efficiency?
Quick guess for current engines:
3 (1 per bay) + 2 (1 per head valvetrain) + 1 per timing gears + 1 for turbo = about 7
Gear and roots type pumps have been used in the past. Normally the section capacity is calculated based on the flow rate + blowby in that section. For simplicity all rotors are normally the same outside diameters and the widths are adjusted to achieve the required capacity.
In terms of weight - the rotors tend to be relatively light and are typically made of aluminium alloys since the loads are relatively low. The material is also chosen such that it has a similar thermal expansion as he cover (which is almost invariably aluminium and in maybe 90% of cases 7075 or 2618). For example a steel rotor would lead to excessive tip clearance at operating temperatures.
Also any NSFW pictures of pumps more than welcome!
How about this - you can even buy your own! The green coating is xylan. This was used such that the rotor starts off by being in interference with the coating and machines it away when bedding in, ensuring minimal tip clearance.
https://www.racetothefinish.co.uk/mecha ... pump-body/
Isn't this dependant on the type of oil used oil temperature and surface finish of the agitating parts and the speed of the rotor?saviour stivala wrote: ↑Mon Sep 16, 2019 4:09 pmContrary to many claims development results shows a rapid increase in friction occurring at a gap of less than 3.0mm (from a gap of 3.0mm or less). A test result development graph in front of me shows (1.0mm = 4KW. 1.3mm = 3.2KW. 2.6mm = 0.2kw. 3.0mm = 0KW.)