So true Sal what I did as for a test using the tube tell you about the burn and thats it.As for the length that it burns that is correct.Look at a nitro car they run so much timing because it takes so long to start the burn and it burns so deep so you have pressure on the piston dome for almost the entire lenght.Timing compression and such have far more to do with octane than anything.But keep in mind,or some of you might remember back in the 60s' Your car would run hot it you used sunoco 260 unless it was a muscle car.That was due to the fact that the burn lasted longer so more of the cyl wall was exposed to the flame or heat of it.Stan

 

So the bottom line is that what I am doing is safe and not skewing my numbers.

Ruslow, Coldie, Sal, Thank you.

White,
These boards are about sharing information and learning. You obviously have some expertise in chemistry and physics, others do not. Others may have information you desire but do not know. We meet here and share. It's not a test to see who know's what. I even found my answer without opening a book.

 

Sal

You confused me.. Even after I ignored the questionable Gerbil comment...

If you have a misfiring cylinder ( cylinder that doesn’t combust its contents ) you have BOTH excess fuel AND Excess air in the exhaust stream. It may be that the sensor reads the excess O2 (which is why they call it an o2 sensor) rather than the fuel. BUT the mixture wouldn’t be leaner - Couldn’t be leaner. The excess o2 is an indication of rich a/f.

'99 White Lite

This confuses me too When I follow an old beater carbureted pickup running PIG rich and I smell the raw fuel coming out the tail pipe. That is CLEARLY fuel that DIDNT burn in the cylinder. For that matter when my tail pipes turn soot black, that is also from partially burned fuel that made it unburned out of the cylinder..

What am I missing here ???

Doug

 

Doug, my point was when people talk about A/F readings, it's not a measure of hydrocarbons, it's a measure of oxygen. Most people know the "value" is a ratio of air to fuel, but many people are not aware how certain situations affect the reading. The sensor reads nothing but O2. So if you have no combustion in a cylinder, it's going to show up as a leaner A/F ratio on either the stock or wide band HEGO. You are correct that there is a also unburned HCs, but that's not being read, O2 is, and A/F is what's being questioned here. If you had a 4 gas in the pipe, that would be different, and you would easily see the excess HCs. Also keep in mind that a vehicle that is running extra LEAN, can also emit black smoke. When there is so much air as opposed to fuel, then the fuel molecules are not close enough to ignite each other, and the unburned HCs go out the pipe.

 

This is wrong, wrong, wrong. A/F is the mass of air over the mass of fuel. Air to Fuel ratio. That is its definition. If you want to know what it is you measure the airflow and the fuel flow and divide. Now since you don't have a means of measuring fuel flow, you have to substitue an oxygen sensor reading. Note the direction. Mass flows = ideal measurment. Exhaust reading = not ideal measurement.

A tailpipe sniffer like dyno's use or an oxygen sensor like the computer uses looks at oxygen content in the Exhaust. The good sensors (i.e. UEGO's, not switchers like factory) have a membrane and measure current needed to pump oxygen into or out of the sensor (for rich or lean). Since you get no measure of CO2 or CO, your measuring an incomplete sample of the exhaust products and therefore only have an estimate of the air-fuel ratio.

Like I said, A/F is a measure of MASSES not volumes. A/F is a chemistry situation. Things like adibatic flame temperature (the thing that blows stuff up), lamilar flame speed (which will effect timing), and charge cooling (which will effect inlet densities) are based on the chemistry. If incomplete combustion screws up your oxygen sensor readings, it just proves that's a crappy way to measure A/F ratio.

Again, not true. You may change what your exhaust gas sensor "sees", but that is because of the combustion efficiency changes. Just another reason why tailpipe sniffing is less that ideal. In my work, I have not even seen this happen, but I won't discount that it could since you have obviously done a lot of work in this area.

A possible cause of seeing that change could be that you are using race fuels which are heavy in Toluene and Xylene which change not only the octane, but the stoich A/F ratio and have a different density. Since injectors are volumetric flow devices, the change in density with equal pulse widths could show a change in A/F ratio.

[QUOTE]Look at a nitro car they run so much timing because it takes so long to start the burn and it burns so deep so you have pressure on the piston dome for almost the entire lenght.[/QUTOE]

They run so much timing because they run a very very rich mixture (for the cooling from compressing the air so much with an inefficient blower). When the mixture is that rich, it burns very slow. The lamilar flame speed peaks at about an equivalence ratio of 1.15 or so. Equivalence ratio is [(A/F stoich)/(A/F)]. They are probably running somewhere around 1.5. Since it burns so slow, you spark way early. When you spark way early, you do a lot of negative work on the piston before it reaches TDC which hurts power. But since they need the cooling for reliable operation of the engine, they do what they have to do.

 

Whoa, can some send me the





Now this is some good information. Gonna have to re-read everything when my brain is functioning.


Sal - I sent you an email, did you receive it?

 

In about 2 weeks I WILL findout.In the exhaust system I am building it is going to have extra bungs for wide bands.That way the factory O2s will stll be reading and the wide bands will be down stream of them.So not to affect the flow getting to them.I can run straight 102 unleaded [fresh,less than 2 weeks old]Will be picking it up Thrus. then mix it with reg unleaded and we will see.For a thread that had no replies for a day and now.boy things change quick.
Silver you will be ok should not effect your a/f ratio to the piont of damaging your engine if all you are changing is octane now timing and changing the injector time.............. all bets are off.Stan

 

I should have at least provided Silver with an answer.

If you are tuning your truck, I would strongly recommend using the worst fuel you would ever use in your truck. That way any mistakes can be caught at the tuner instead of after you blow it up using worse fuel than what you were using when you did your tuning.

Just keep in mind these aren't the end all be all of measurements. You need a 4-gas to be precide with your measurements. Since the UEGO only looks at Oxygen, you are only getting part of the answer. As long as your engine is running alright, it won't be a problem. If your misfiring, then you might see questionable results.

 

so true but its hard to keep a 4 gas sniffer in the tail pipe at 150!! Plus it is reading the effectiveness of the cats so i don't feel that that is a true reading either needs to be BEFORE them.Stan

 

That is true, best to be before the cats. But if you are running rich, there is no available ozygen to oxidize the hydrocarbons or the CO, so you will still get accurate readings (assuming rich running for long enough to deplete the oxygen in storage).

A 5-gas will measure NOx, and that will be reduced to N2 and O2 going through the cats while rich. But that doesn't matter for A/F measurements.

 

Ummm you are in violation of the licensed use of my name !!!

Cliff


PS... NOW YOU KNOW THE REST OF THE STORY !!! I WROTE
ALL THOSE BOOKS THAT YOU USED IN HIGH SCHOOL !!!

 

Your right about the cliffnotes!!!

 

White,
This is scary. I am actually understanding some of this. Much more indepth than I was looking for, but very good information. Now if I just had some of the high tech toys to accurately measure my A/F. Makes the information I get from the dyno seem so first grade.

 

Bill, you need one of these :

 

White you are somewhat correct on the nitro part BUT it does burn slower they do run them rich but if you look they start them on alcohol and do their burn out on it then they switch to nitro.Before they switch its not spitting raw alcohol out.But after they switch its is spitting raw nitro out.so it does burn slower since that was their only change.Hence more timing.Stan