Propane/water/alcohol injection and O2 sensors

[Greg Hermann]

At 10:23 AM 4/9/02, Eck, Joel wrote:
>I understand the desire to inject water in an attempt to stave off
>detonation, especially under high boost, advanced timing, etc. However,
>something bothers me about it.
>
>1. If the water vapor cools the exhaust gas temps, then how bad (overall
>bad, that is) will that be for the whole combination? By cooling the
>exhaust, you are inhibiting the O2 sensor from reaching it needed
>temperature (unless you're using a heated one, and then, does the cooling
>effect of the water vapor then pose any problem to the actual heating of
>the sensor?), so will the O2 sensor read right?

You pretty much answered your own question. The heater in the sensor will
take care of the problem. There is no such thing as a UEGO (WBO2) sensor
without a heater, anyway ! The standard EGO (unheated) and HEGO (heated)
sensors aren't worth discussion in this context anyway.

>2. Also, the cooling of the exhaust gases will keep the cat from reaching
>its proper temps also, so how will that be affected?

CAT ?? Whazza CAT??? That shell that used to have some ceramic stuff inside??

>3. On top of all that, I've also been told that for optimal performance of
>the exhaust system, you want to keep the temperature of the exhaust gases
>as high as possible;

Somebody (whoever has been doing the talking that you have been hearing)
has got their urban legends mixed!

Higher temp exhaust gasses means higher velocity exhaust gasses (in the
same size pipe for a given HP or mass flow level) means a higher Reynolds
number means higher pressure drop means higher backpressure.

Yes, the additional water vapor adds to the mass flow through the exhaust
for a given HP level, but the NET effect is likely equal or slightly lower
backpressure when all factors are considered.

Higher EGT's _ARE_ good for turbocharger performace, but this is something
that can be compensated for in turbine and housing selection. Higher
exhaust velocities are also good for exhaust tuning effects.

 does the benefit of the added power from not backing off the timing or
boost just a little outweigh the detriment of the added backpressure?

Per the above, there is no additional backpressure.

What WI does, if done RIGHT, is lower the temperatures throughout the
compression, power and exhaust strokes by a _SIGNIFICANT_ amount--like 500
to 600° F !! The lower temps have a significant effect on engine
durability. WI also lowers the peak combustion pressure, and the loading on
the engine's bearings for a given HP output level--which is QUITE a bit
more than just "staving off detonation" !!!

Greg


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