Smokey's motors

[Martin Jackson <mjackson@vcn.bc.ca>]

  Roger Stockton comments:

"I think you'll find that the volumetric efficiency losses which you predict
are negated due to the boost from the turbo."

  At higher power levels, yes. But at low throttle setting, the turbine 
  back pressure and low compressor pressure rise causes the filling to 
  be less than normally aspirated. 

  Heating the intake air is worse for a centrifugal compressor than the
  bare engine

"I agree that it is not the use of waste heat to heat the intake charge in
itself which is likely responsible for the performance Smokey achieved, but
more likely that the hotter charge was beneficial with respect to allowing
him to achieve more complete combustion without detonation while running
mixtures in the 24-26:1 range."

  Performance includes part throttle fuel consumption and full throttle 
  power; I'm perhaps not separating the arguments well enough. 

"As far as exhaust heat being lost and unable to be usefully recovered, you
are neglecting that this is exactly what a turbo does. An important
advantage turbos have over supercharging is that while a supercharger
consumes additional hp (it places another accessory load on the engine) the
turbo is driven using otherwise wasted energy from the exhaust."

  This is a common argument. At low boost, the rotating elements don't 
  do much which is basically good since moving more air around like a 
  supercharger is useless. There are pressure drops which mean a higher 
  throttle setting at low power. 

  But at higher settings, the turbine has a pressure drop that back 
  pressures the cylinders and reduces the expansion cycle inside the 
  cylinder. The exhaust valve-turbine inlet temperature goes way up and a
  back pressure is created at the higher flow level which drives the 
  turbine. Since the compressor efficiency is much less than a piston
  compressor efficiency and the net intake and exhaust efficiencies are
  less, the power produced/lb fuel is lower than unturbocharged. 
  
  The net mission can be improved with part power efficiency of a smaller 
  engine and Maximum power is up due to overfilling the basic 
  displacement. Turbine energy is Not free. Shaft power produced by the
  piston is reduced by the amount of turbine back pressure. If the exhaust
  temperature was significantly reduced, the catalytic converter wouldn't
  operate properly.

"But either approach (turbo or supercharging) strictly improves volumetric 
efficiency:" 

  Only at high power. By the way, 30 years of my career has been spent
  working on aircraft and industrial turbine engine performance 
  calculations, test, compressor design and installation losses.
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