[Diy_efi] RE More ECU progress

Adam Wade espresso_doppio
Wed Feb 28 09:56:33 UTC 2007


--- Ian Molton <spyro at f2s.com> wrote:

> It will take CAS and cam angle inputs, and use them
> to compute the crank angle to better than one
> degree. how much better will depend on how good 
> our interpolation algorithms work).

One thing to keep in mind if we want to get the rotary
engine crowd.  No cam, rotors have 3 "combustion
chambers" per, and they rotate at 1/3 "crank"
(actually called an eccentric shaft) speed.  So in
practice, the fuel and spark events are equivalent to
a 2 cylinder two-stroke engine (one spark and one fuel
event per "crank" rotation).  To complicate matters a
bit more, there is a set of trailing-edge spark plugs
that fire substantially later.  They contribute very
little to power or fuel economy, but clean up
emissions a good bit by getting some of the unburned
mixture at the trailing edge of the combustion
chamber, which is a long, narrow rectangle that in
profile looks not entirely unlike a set of cat-eye
tail lights joined in the middle.  Many rotary owners
will want to be able to drive these plugs as well. 
Early Mazda rotaries used twin distributors (one for
the leading and one for the trailing plugs); 1st gen.
RX-7s used a single distributor with a complicated
rotor to get the same effect (single coil and two
plugs on each circuit).  2nd gen (and I believe the
3rd gen and RX-8) use 3 coils (one of each leading
plug and one for both trailing plugs) triggered by
ignitors, no distributor.  A common conversion for the
1st gen (and possibly earlier rotaries as well) is to
use something like an MSD 6A on the leading plugs,
using the two coils from a 2nd gen motor, and leaving
the trailing plugs run off the distributor with their
original coil.  We'll probably want to make several
options available.

What's the status of closed-loop spark control?  Is
this do-able under the current ion sensing setup?  I'd
very much like that option; I believe at least one of
the research papers I uploaded speaks to the practical
application of ion sensing for that very purpose, and
I believe it includes ion sensing traces for both
over-advanced and over-retarded spark timing.  Of
course there should be a regular open-loop map, both
for a base for the ion sensing to work from and in
case of ion sensing failure, as a backup.  The idea of
having the ECU determine optimal spark timing on the
fly, automagically compensating for engine and air
temps, humidity, fuel mixture, etc. is something I
find very desirable, not least of which is because it
is very difficult for a typical DIY-er to be able to
optimize a spark map without some high-dollar
equipment most don't have ready access to.  A
closed-loop setup would eliminate the need, as well as
allowing compensation for things that cannot be
adjusted for any other way (most notably humidity;
this would even allow water injection on any engine
without the need to figure out how much to adjust
stock timing to make best use of it -- and I have data
showing that it's quite possible for a typical
gasoline-powered engine to make the same power with
lower fuel consumption with a combination of water
injection, spark advance over base, and a leaner
mixture -- even under full throttle).

| Kawasaki Zephyr 615 (Daphne)       Kawasaki Zephyr 550 (Velma)|
| "It was like an emergency ward after a great catastrophe; it  |
|   didn't matter what race or class the victims belonged to.   |
|  They were all given the same miracle drug, which was coffee. |
|   The catastrophe in this case, of course, was that the sun   |
|     had come up again."                    -Kurt Vonnegut     |
| M/C Fuel Inj. Hndbk. @ Amazon.com -  http://tinyurl.com/6o3ze |


 
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