Does anyone have the formula or method to calculate the total CFM air
flow for rotary engines?I need to figure it out to make the
appropriate selection for a blower. I plan on cnc my own roots
blower, seems to fit my needs for the rotary.
david jr.
The tuning has a large effect and the type of intake ports. Tuned
p-ports can give you 120% VE.
Paul Lamar
That is going to be a unique roots blower. It will have to produce
enough air at low speeds and not rip itself apart at high speeds due
to centrifugal force. The roots blowers on Detroit Diesels and drag
cars are 2/3 the size of the rotary. A 6-71 turning 2400 uses about
600 CFM which is what the line on the attached chart goes to for the
rotary at 8500. You could maybe shrink it down and turn it faster
but that is a lot of mass to be slinging around that fast. Lots of
inertia.
Do you have any size parameters in mind so far?
Kevin Alderman
Roots blowers are a big hit on the BSFC. Turbo's use otherwise waste
energy in the exhaust.
Here are a couple of super charged rotaries. The Bobby Hughes version
is being changed to a turbo. Sorry I don't have better pictures.
Paul Lamar
Detroit Diesel used different blower drives depending on whether
NA or turbocharged. The NA engines were designed to spin the
blower at a higher RPM to push more air into the engine. The two
stroke Detroit Diesel engines require the blowers just to scavenge
the cylinders as they have no other way to move air into the cylinder.
For racing trucks using the 6V92 engine they would use a NA drive
and use a Scotch pad to wipe the sealing ridges of the blower rotors.
If you did not wipe the ridges off the rotor would expand under
centrifugal force and score the blower housing. With the increased
drive ratio and running the engines to 3500RPM the blowers were
really spinning.
Guys drag racing like to use the 6L71 blower as it fits on a small
block engine but requires a slower blower drive. It makes big power
at higher RPM. For motor homes or towing a 4L71 blower works
better as you use a higher blower drive ratio and get boost right off
idle. A 6V53 blower also works well for a street 350.
When I worked for Detroit Diesel distributor, I got sent out one Monday
to work on two Terex TS-14 scrapers. These are twin engine units.
One engine and transmission to drive the front wheels and another
engine and transmission for the rear wheels. Over the weekend
someone had stolen the four blowers. They were costly to buy new
and we needed them immediately.
Dale Davies
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