From: bowers@rigel.dfrf.nasa.gov (Al Bowers)
Subject: Re: bmw FI systems (was Re: Cheap Gas in BMW K-100 RS?)
Organization: NASA Dryden, Edwards, Cal.
	<2204@devnull.mpd.tandem.com> <1992Aug12.045741.2800489@locus.com>
Date: Wed, 12 Aug 1992 18:32:25 GMT

In article <1992Aug12.045741.2800489@locus.com> dana@locus.com (Dana H. Myers) writes:

>In article <2204@devnull.mpd.tandem.com> joe@mpd.tandem.com (Joe Senner) writes:

Dana:
>>> >The fuel injection system on the more
>>> >recent BMW K-series bikes senses both engine fuel octane and altitude
>>> >to adjust the mixture. Older K-series bikes had an optional air
>>> >sensor plug for high altitude that had to be inserted at the approriate
>>> >elevation range.

Joe:
>>> How does the Bosch injection on the recent bikes sense fuel octane? I've
>>> never heard of a fuel octane sensor. Remember, the octane rating of a fuel
>>> is simply a rating of fuel performance compared to iso-octane, and does not
>>> imply the content of any particular compound.

Joe:
>>the new K bikes no longer have Bosch injection systems. they now use
>>the Motronic system which monitors the exhaust with an oxygen
>>sensor, and which uses a "hot wire" system instead of the older gate
>>style system for monitoring intake flow, density, etc. I suppose 
>>you could say it monitors the octane in that it monitors the exhaust
>>for proper combustion emissions and adjusts the mixture accordingly.

Dana:
>(1) Isn't the Motronic EFI just one particular kind of Bosch system?
>    (The old Bosch EFI was something like LE-Jetronic?)

True.  Motronic is actually a total engine management system.  It does
both ignition and fuel injection.  The older ones were simply fuel
injection systems.  Like L-Jetronic, ot K-Jetronic, etc.

>(2) How does an O2 sensor sense the fuel octane? I thought O2 sensors
>    were ceramic semiconductors which are sensitive to the amount of
>    free O2 molecules. How do they sense octane rating in the exhaust?
>    I wasn't away that, under normal circumstances, octane rating has
>    a significant effect on O2 emissions.

Octane is not sensed by an O2 sensor.  O2 sensors simply measure the
relative content of free oxidizer (not necessarily oxygen, though it
usually is in most common applications).  By using this to feed back
into the computer that controls the fuel injection, you can enrichen
or lean the mixture for best power/economy/emissions.

The device that measures octane is simply a knock detector, a simple
microphone.  These on started becoming common on cages in the mid
1980s (the FORD SVO Mustang being one of the first in a mass produced
application, some others were Saab 900 and 9000 Turbos and Maserati
Biturbos).  Usually these are only used on turbo aor supercharged
applications (yes, I know a turbo is a special case of a supercharger,
but lets not get into all that, shall we?).  I don't know if the
Japanese turbo'd bikes had knock sensors or not, I believe that Yamaha
and Suzuki did (I can't believe that Honda did not), but I don't know
for a fact.  I don't believe that the Bosch Motronic incorporates a
knock sensor...

--
...ignoring the fact that most Alfas spend their time cruising for
chicks, most Datsuns being washed and most Porsches in parking spaces
marked "Doctor"...              -Henry N. Manney III, Road and Track
Al Bowers                                 bowers@rigel.dfrf.nasa.gov