WB 02 op. temp.

[Bernd Felsche]

Brian L Massey wrote:
> Most of what is posted there is taken from public Bosch literature. The
> Bosch LSU appears to have a working upper limit of 850C (judging from the
> LSU datasheet uploaded to incoming by BertB & JorgenK), but this is not

There's later Bosch data. It says that the heater must be
turned off at 850C; the standard sensor operates to 930C.
Absolute maximum temperature for short periods (250 hours
accumulated over life) is 1030C.  The accuracy of the sensor
decreases when the heater is turned off because the Nernst effect
depends upon the cell being hotter than the gas,

> the spec for the NTK sensor. Nobody within the DIY community has

US Patent 6,120,677 (NTK) provides some insight to temperature
ranges and regulation.

> demonstrated or claimed to have built any working hardware for the LSU,
> either. Note that the circuit posted on the page you cite is clearly
> stated to be a 'paper tiger', and not an actual working circuit.

It's a work-in-progress.

> 900C IIRC is at the high end of EGTs even for boosted recip
> engines. And just a short distance down the pipe the gases have
> cooled significantly.  These sensors don't ever seem to get placed
> immediately after the exhaust valves anyway; no need to. On rotary
> engines, perhaps you might want to use EGT probes to pick a
> suitable place downstream that is sure to keep within the sensor's
> upper limit.

On the contrary. The LSU is installed before the NOx absorption
cat on lean-burn engines. The NOx cat is placed as close as possible
to the exhaust valves to heat as rapidly as possible to its high
operating temperature. An EGT probe is often placed after the NOx
cat so that the engine management system can tell when it's "safe"
to go into lean-burn mode.

Although temperatures in excess of 850C don't appear to be common in
road-going vehicles (it'd be interesting to peer under the skirts of
a Porsche Turbo), competition engines could exceed those
temperatures; given that the material used are suited to the higher
temperatures.

-- 
Bernd Felsche - Innovative Reckoning, Perth, Western Australia

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