How can one convert actual AFR to Bosch narrowband sensor voltage (usvkl...).

For example:
If AFR is 14.7 then this voltage is 450 mV
With increase in AFR, this voltage increases and vice versa.
But what would be exact voltage for fuels with diff AFR, like ethanol blend, Gaseous fules etc.

Voltage would be the same at stoich afr for whichever fuel you are using, and follow the same pattern you describe for rich/lean.

If you want to use narrow bands to tune, its a bad idea.   If you don't care that it's a bad idea, then shoot for around 900mv on boost, and make note that ITS A BAD IDEA.

I want to run my vehicle with ethanol25%.
That's right about sensor not being fuel specific. but why are narrowbands accurate only for 450mV, are they designed for 14.7 AFR.

No they are designed for Lambda = 1, which is the same for ALL fuels.  Oxygen sensors do no read for fuel specific, neither to ECU's.  They all read lambda and not AFR Gasoline.

Just only a few ECU reads the value of narrowband sensors, tipically they use it as a limit, upside 450mV it´s rich and in closed loop ECU decrease lambda steps (STFT - LTFT), when it goes low then 450mV became to increase lambda steps agains

So the value is not considered...

Some new Multec fuelflex systens in Brasil are closed loop all the time, in this case it converts mV in some lambda value...you can enrich the misture and after 2 pass in dinamometer the moisture goes all to 750mV agains untill rev limiter.

Here's an article about narrowband O2 sensor -> http://www.innovatemotorsports.com/resources/news3.php and graph of it's voltage characteristics -> http://www.innovatemotorsports.com/resources/images/n32.jpg
It's characteristics is highly dependant on EGT. So it could be usable taking into account estimated EGT value.

Regards
Lobuziak

All of you are going off topic and confusing the OP