ok by me
for this you might find helpful Wright's p9-p13 in the paper linked below
reposting this as had given the wrong page number
Tommy Cookers wrote:@ she
as one who has also questioned the fashion for the buzzword 'heat'
in my steam-age way I reposted yesterday at 2030 on p402 of the Formula One 1.6 thread earlier references to exhaust recovery
particularly the position by Wright that their recovery cost no crankshaft power, this a hot topic in that thread
they sold 14000 such engines
there is also a reference etc to energy balance for these engines
regarding impediment to exhaust flow
to avoid the losses you mention, all piston engines necessarily create other losses in 'blowdown' (choked) from around 7 bar
ie much of use is lost in the exhaust before any recovery turbine
1940s work by the NACA showed (compounded) efficiency highest at high mean exhaust pressure, due to less KE loss in blowdown ?
(also around 5-6 Aug 2013 I posted in the above thread including a link to this (NACA 822) and commented on NACA 1602)
this operation, even into actual backpressure, is relevant to current F1
(of course for most aviation propulsion applications exhaust can be better used in other ways)
F1 mgu-h units are 80 kW or more, most of their output would be used real-time (near-continuous mgu-k motoring), not stored
reminding me that Wright's energy balance values showed ......
that only about 35% of the exhaust heat was in a form (KE) useable by an expander type recovery device (the turbine)
65% being nonuseable sensible heat (only good for cooking etc)
the 2014 CR will be maybe double the Wright's CR
improving ICE efficiency, reduced total exhaust heat but also reduce the % of that reduced total that's useable by the turbine ?
the Wright brochure (thanks to the original poster) shows on its p9 p12 p13 in a way that's priceless to us ......
and states that 'the cylinders are relatively unaware of the existence of the turbines'
12 of the 18 exhaust pipes are necessarily longer than normal 'stacks', IMO helping to lower exhaust pressure after BDC
IMO large losses in blowdown are unavoidable in any intermittent-combustion (eg piston) engine, even a Mazda rotary
this from the Wright SAE transactions shows a best BSFC at altitude of 0.325 lb/hp-hr (more recovery at low ambient pressure)
despite Avgas having a significantly lower heat value/lb than good road fuel
another revelation is the large amount of Carbon Monoxide and Methane in the exhaust even with (sea level) lean cruise mixture
(not to mention takoff mixture)
suggesting substantial dissociation (chemical reabsorbtion of combustion heat) due to the high temperatures in-cylinder
a loss of thermodynamic efficiency and of power, presumably unavoidable by Wright
this seems 2014 relevant
though the 2014 high CR/ER would allow re-association in-cylinder due to the greater temperature drop with greater expansion
and there may be a 2014 way to reduce dissociation, possibly in the fuel chemistry
dissociation implies that a CR lower than ideal cannot be well compensated by the resulting increase in available recovery
and apparent gains suggested by (physical) thermodynamics seem to be subverted by the chemical thermodynamics
the right kind of lean-mixture running would also help with dissociation ? but seems unviable with the current fuel quanties