X-Mozilla-Keys:                                                                                 
Jeff Spitzer wrote:

It works!!  My engine model with the fixed area bypass for turbo.  I have
entered the turbine model and all gas dynamics equations and it solves for
MAP and mass flow based on many fixed variables such as ambient conditions,
RPM, intercooling, etc.  

I've just started playing with it so it's not
quite ready for prime time yet but here's what I know so far: Paul Yaw
mentioned that he had about 1.2 sq in of bypass on the engine he did in
addition to the wastegate.  He later reduced the area to get more boost.
When I used 1.2 sq in for my bypass the result (boost, power) agreed very
well with what PY saw on the dyno.  My answer was about 5 psi boost at 6500
RPM without accounting for any friction losses yet.  

(You can design for
any level of max power by choosing bypass area, RPM and turbo design)  As
the ambient pressure is reduced the turbo "normalizes" quite nicely right
on up to 12K.  It also works nicely at reduced speeds.  At 5500 RPM, WOT,
12Kft I'm getting about 145 hp.  I'd say that's right nice.  

 I also ran 30K
just for PL.  It only gives about 100 hp and PR 2.2.  The (non-existent)
wastegate needs to close at the higher altitudes as I suspected.  

The only
issues I've come up with so far are:  Power is sensitive to intercooling.
If the air is allowed to get hot then airflow goes down, turbine power goes
down, and MAP drops too.  So, power is reduced.  On the upside, this is a
stable system and power is somewhat controllable with MCT.  On the
downside, in a "high and hot" situation power is lost kinda like a NA
engine.  At 5000 ft, 100 deg ambient I was showing about 150 hp WOT, 6500
RPM. 

Another concern would be overboosting on a cold morning unless the
intercooler is blocked off (the cooling air that is).  PY showed me some
pictures of how he cut a bypass hole right in the turbine housing and it is
extremely elegant.  This is definitely a workable system.

Upcoming improvements to the model include throttling capability, better
gas D model for sonic flow in bypass, and addition of losses.  Yes, I
intend to share the model when it's done...it's just an Excel spreadsheet
using the built in solver.  More to come.

Jeff Spitzer

good work Jeff and Paul Yaw. It is great to have dyno results to
correlate
math models.

Paul Lamar
 
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