gruntguru wrote:ringo wrote: .......I guess the FIA just wants it to look super fancy and hitech when they say MGUH. lol
If you examine the stream of exhaust gas coming from the ICE there are four types of energy embodied in it. In descending order of magnitude (for hot ICE exhaust gas) they are:
1. Internal energy. (heat)
2. Pressure-volume energy. (can "push" and release energy by expanding the gas)
3. Kinetic energy. (mass of gas times its velocity squared x 1/2)
4. Potential energy. (gravitational. i.e. mass of gas x height x g) Negligible for ICE exhaust.
When the exhaust gas exits the engine, the greatest of these is heat energy. After passing through the turbine the one that has reduced the most is also heat energy, so what has been extracted is primarily heat energy. The method of extracting this heat energy (expanding the gas in a nozzle to increase the kinetic energy then using the kinetic energy to push on the turbine blades) creates the illusion that the energy to drive the turbine is present as pressure or kinetic energy in the exhaust gas.
@gg .... if the exhaust is very hot but only at ambient pressure it cannot drive a turbine ??
presumably then expansion across the turbine means a drop in pressure
ie a mean exhaust pressure above the turbine significantly above ambient ie a raised mean pressure
recovery does not need a raised mean exhaust pressure eg the 14000 Wright Turbocompounds had blowdown turbines
Wright showed that mean exhaust pressure was not raised
(btw Wright stated that 35% of the exhaust energy was of a form potentially useable by the turbines)
@ gg ..... is the pressure energy less than the heat energy at the start of exhaust valve opening ????
'steady-stateist ' visions of a 'stream of exhaust coming from the ICE' as above ignores the basic nature of the piston engine
ie intermittent release by the exhaust valve from a high pressure around 8 bar above ambient
much of that intermittent (pulse) pressure energy is lost as increased heat (the gas flow goes supersonic)
a way to conserve pressure energy is to raise mean exhaust pressure even to true back pressure (ie greater then induction pressure)
presumably the greater downstream gas density and inertia limits acceleration and more of the flow will remain subsonic
the NACA proved this in WW2
that true backpressure gave very high recovery and the best BTE (but only when exhaust valve closure was suitable)
this all suggests that preserving pressure energy 'pulses' works well without any raising of mean exhaust pressure
.... or with raising it to extremes ....... and at positions in between
Mercedes has designed its exhaust system to destroy pressure pulses
this surely raising mean exhaust pressure 'at source' (with their good conservation of heat)
in addition to any other raising they may have chosen from their turbine and its loading