a/f ratio with LPG

[Seth Allen]

On Thu, 16 May 1996, Darrell Norquay wrote:

> Date: Thu, 16 May 96 21:21 PDT
> From: Darrell Norquay <dnorquay at awinc.com>
> To: diy_efi at coulomb.eng.ohio-state.edu
> Subject: Re: a/f ratio with LPG
> 
> At 01:31 PM 5/16/96 +1000, you wrote:
> >Hi everyone,
> >
> >I was wondering if it is possible to use a normal (i.e petrol) O2 sensor 
> >when running a car on LPG, as opposed to unleaded fuel.
> >
> >Thanks in advance,
> >
> >		Bruno.  (u933234 at student.canberra.edu.au)
> >
> 
> I've been running O2 sensors in my Camaro on LPG for a year or so now,
> but I'm still not sure they read back any useful info.  The Stoich A/F ratio
> for propane is around 23:1, and although Stoich is Stoich no matter what the 
> fuel (at least in theory), they seem to read lean most of the time.  I'm 
> reasonably certain that my mixture is not as lean as indicated, but I have the
> sensors mounted in the header collectors which is fairly far from the engine,
> so it may be a problem with location rather than the sensor itself.  I want
> to try some heated sensors to see what difference it makes, I'll let you know
> what happens.  By the way, O2 sensors do read oxygen content, at least in
> that they are proportional to the difference between the exhaust O2
> concentration and the ambient air.  They are unaffected by concentrations of
> other gases, and generate a voltage by pumping O2 across an electrochemical
> cell.
> 
> Regards
> dn
> 
Heated O2 ensors are a good idea as the cold combustion characteristics 
of gaseous fuels tends to let them cool off and "drop out of the loop" at 
idle.  Or stuff them right up in the manifold. But you still may need a 
heater. Just my opinion. Incidently we got a Neon on CNG to meet ULEV 
emmisions. We were pleasantly suprised when we did the federal test.

Seth Allen
Vehicl Research Institute