Tommy Cookers wrote:
http://naca.central.cranfield.ac.uk/rep ... rt-822.pdf
the combined power is always best around best bsfc
best bsfc is with -20" Hg on the engine used (probably -15" Hg on an engine with more liberal valve timing)
ie the loss at the crank is the same or less than the gain via the MGUH as the delta P becomes more negative
so 120 kW recovered power might cost 100 kW crankshaft power without any fuel rate limit
but the bsfc as reported is 14% better at 10000' than the same engine with turbo
extrapolation suggests 10% better at sea level
so under a fuel rate limit there's 10% more combined power with this level of compounding
but the F1 engine 'boost' will be much higher, so the best bsfc delta P might be more, maybe close to -1 bar ?
so the bsfc gain over an equivalent turbo engine should be maybe 15%
(because recovered power is largely due to the pressure difference between exhaust pressure and ambient)
giving 15% more combined power with this 'best bsfc' level of recovery
of course a suitably big MGUH and related electrical system is needed
a lower level of recovery such as Wright actually used would according to this report give only maybe 7% bsfc gain
(at lower recovery levels the bsfc gain comes from recovery that costs very little crankshaft power)
and so only 7% more combined power under a fuel rate limit
but would use a much smaller capacity MGUH and related electrical system
with a turbine-electric recovery system as in new F1 .......
in a low recovery level system the electrical power can reasonably described as free
as the efficiency improves in proportion to the electrical power
at maximal recovery level as in NACA 822 only about half the electrical power can be regarded as free
because the efficiency gain is 'only' about half the recovery level
so we should resist the inevitable media and PR attempts to tell us that eg a 120 kW MGUH recovers that much 'free'
NACA 822 is based on running at pressure (loosely, 'boost') of 40" Hg Abs (about 1.35 bar Abs)
the supercharger power is rather low, around 3 % of output power