hxtasy

This is something i have been wondering about for a while. Since gasoline is refined inconsistently, I'm guessing an average chemical make up would be C6H18 (seems to be decent average for gasonline).

with this being said, If i balance the chemical equation i get the following:

C8H18 + 02 -->CO2 + H20


2C8H18 + 25O2 --> 16CO2 + 18H20

and this gives me 12.5 parts of oxygen to fuel.

12.5:1 AFR


I know that there are some things missing in the equation, the Nox gases in the reactents, Nitrogen and other gases in the air, oxygen enrichers such as MTBE, but I don't see how this is even close to 14.7 parts of air to one part of fuel.

Can someone explain this please?

might I add I lack chemistry skill and knowledge.

thanks.

Schister66

for as late as it is, you're putting a little too much thought into this...lol

....in for answers and some in-depth thought at midnight

hxtasy

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Schister66 &raquo;</TD></TR><TR><TD CLASS="quote">for as late as it is, you're putting a little too much thought into this...lol

....in for answers and some in-depth thought at midnight</TD></TR></TABLE>

ha ok thanks.

postscript: its 1 am here :-P

and yes finals are frying my brain beyond repair.

BEST1TUNING.COM

Well...what your doing is determining the actual content of O2 in the chemical makeup of the fuel. This is already taken into consideration when determining an efficient ratio of air to fuel when the actual BURN occurs. The most efficient mixture, after the vaporization process of the fuel, has been determined for gasoline to be 14.7 parts O2 to 1 part fuel. This stoichiometric number represents the ratio at which the burn will occur most efficiently and the least fuel is wasted. This is why the ratio changes when we change fuels because of the burn characteristics of that specific fuel relating to its chemical makeup. We understand that there are inefficiencies in the refining process but not enough for it to effect the burn characteristics to the point that we would have to change this number.

It is an important number when taking fuel consumption and fuel efficiency into consideration especially for emissions purposes.

P.S. ...Its 4:30 AM here


Modified by BEST1TUNING.COM at 1:33 AM 4/30/2007

HiProfile

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by hxtasy &raquo;</TD></TR><TR><TD CLASS="quote">C8H18 + 02 --&gt;CO2 + H20</TD></TR></TABLE>

That's isooctane, just ONE of the MANY hudrocarbons that gasoline is made up of. Actually, its more of an additive in terms of it's percentage. Gasoline is made up of toluene in the highest amounts, up to 35%. Its C4H8 with an octane of ~114, so have fun with those numbers. There's also other impurities and a noticable % of lubricants which burn a bit. FYI 93 octane will differ in % of each hydrocarbon from station to station, but the octane ((R+M)/2) will end up the same.

Trying to find the exact stoimetric number will be virtually impossible, as there's a shitload of factors. Additives, normal swings in AFR (given constant load/rpm), in addition to the error/delays of o2 sensors, inefficient combustion, NOx/CO production, etc. It doesn't really matter how exact it is, just that when a calibrated O2 sensor sees 14.7:1, you get the best split between production of CO, CO2, H2O, NOx, and unburnt fuel.

Its almost like trying to see exactly where an atom is - we see reflected light, so its not technically possible.

hxtasy

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by HiProfile &raquo;</TD></TR><TR><TD CLASS="quote">

That's isooctane, just ONE of the MANY hudrocarbons that gasoline is made up of. Actually, its more of an additive in terms of it's percentage. Gasoline is made up of toluene in the highest amounts, up to 35%. Its C4H8 with an octane of ~114, so have fun with those numbers. There's also other impurities and a noticable % of lubricants which burn a bit. FYI 93 octane will differ in % of each hydrocarbon from station to station, but the octane ((R+M)/2) will end up the same.

Trying to find the exact stoimetric number will be virtually impossible, as there's a shitload of factors. Additives, normal swings in AFR (given constant load/rpm), in addition to the error/delays of o2 sensors, inefficient combustion, NOx/CO production, etc. It doesn't really matter how exact it is, just that when a calibrated O2 sensor sees 14.7:1, you get the best split between production of CO, CO2, H2O, NOx, and unburnt fuel.

Its almost like trying to see exactly where an atom is - we see reflected light, so its not technically possible. </TD></TR></TABLE>

Ok so from what I understand 14.7 is a de facto industry standard car manufactures try to base the average components around, such as making the catalytic converter operate best at this number, etc.

But what I do not understand, or am more confused about now, is how this number is even close to accurate with different types of fuel. It seems more as a baseline, and if that is the case then are we not losing a lot of power potential tuning it to this baseline?

Even if your O2 sensor is calibrated, it is only registering the amounts of oxygen passing through it, so if you had a plug not fire and the combustion didn’t happen, the O2 would read a lean reading even though it is soaking with fuel, because more oxygen has passed the sensor (along with the extra gasoline).

So different fuels burn at different stoichometric ratios, so I am still not understanding how this standard is efficient - it is an efficient way to design a catalytic converter around, but since we are trying to maximize power and efficiency, shouldn’t we be finding the exact number? If not for a street car that gets different fuels everyday what about a track car?

BEST1TUNING.COM

Because it is the standard for gasoline, since it has been researched that at this mixture of air to fuel, a GASOLINE/AIR mixture will burn most efficiently...a slightly richer mixture of about 13.5 will produce the best power with all other aspects remaining the same anything varying richer from this mixture will either waste fuel or decrease the combustion force. 14 .7 takes fuel consuption as well as power into consideration...therefore being the most efficient for GASOLINE. Also, yes the cat will be most efficient as well in its conversion of hydrocarbons. The number represents an efficient burn ratio.

suspendedHatch

By "different fuels" he meant different as in ethanol compared to gasoline. He wasn't comparing 87 to 91, or Chevron to Arco. Those small differences don't affect the stoich ratio.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by hxtasy &raquo;</TD></TR><TR><TD CLASS="quote">

Ok so from what I understand 14.7 is a de facto industry standard car manufactures try to base the average components around, such as making the catalytic converter operate best at this number, etc.</TD></TR></TABLE>

No, it's not a choice made by the industry. It's a laboratory measurement. It's not a result of cat converter design, but vice versa. Car manufacturers would rather not run cat converters if they didn't have to. Cat converters are a band-aid solution to real world conditions. Not just engine and parts wear, but the fact that rapid throttle changes cause unburned fuel to be exhausted, and the fact that manufacturers intentionally run your car rich under high load conditions for engine safety. But that's beside the point. Stoich is not something so much invented as discovered.

No car should ever run 14.7 under all conditions. Cars should idle and cruise as lean as possible, not spray fuel at all under deceleration, and should run rich under high load conditions to protect the motor. Under heavy acceleration the mixture should be slightly rich or whatever gives you the best power, and under normal driving conditions the mixture should be roughly 14.7 depending on combustion chamber design.

BTW 14.7 is a rounded figure.

You are correct in that your O2 sensor will read lean when under some conditions there is too much fuel. You can actually spray so much fuel that it can't ignite and thus you're running lean.

hxtasy

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by HiProfile &raquo;</TD></TR><TR><TD CLASS="quote">

Gasoline is made up of toluene in the highest amounts, up to 35%. Its C4H8 with an octane of ~114, so have fun with those numbers. There's also other impurities and a noticable % of lubricants which burn a bit. FYI 93 octane will differ in % of each hydrocarbon from station to station, but the octane ((R+M)/2) will end up the same.</TD></TR></TABLE>
What did he mean by this then? I would love if someone would just show me from a chemistry standpoint what stoichiometric equation yields an Oxygen to fuel ratio of 14.7:1. Or is it an Air to fuel equation?

Obviously we all know what the ratio means, that wasn’t the question. 14.7 was a scientifically proven number, but it was probably an average of various fuels, I would imagine. And I meant and said that the manufacturers make their cats to operate best at this ratio.

Anyways, we know that 14.7 is a stoich average and that at this lean of a mixture the modern internal combustion engine is not efficient enough to burn it with high engine loads, because it will produce a lot of thermal energy. I just want to know what equation this number came from. I don’t have a good knowledge of fuels, (which after this I am going to have to pick up some books or something) but I know that there are different additives at every gas station, and that MTBE and other oxygenators should affect the equation a noticeable amount. Most of your local fuel stations all get their fuel from the same local refinery, then there are different additives and detergents added, but there must be a huge (as in change this ratio by a noticeable percent) difference of the fuel from one refinery to another across the country.

If I was right that if you put a known fuel in your car and make it burn cleaner by figuring out how much AFR it actually needs, then there will be some kind of efficiency gains, whether or not it is too insignificant to measure, I really just want to know for expletive’s sake.

hxtasy

[QUOTE=BEST1TUNING.COM]...a slightly richer mixture of about 13.5 will produce the best power with all other aspects remaining the same QUOTE]

A ration under stoich will not burn completely thus not producing maximum power, am I wrong?

The only reason we don't tune WOT at 14.7 is because the heat factor is high enough that the fuel has a better chance of preigniting and causing detonation, reducing reliability.

99_GS-T

Although gasoline is made up of a bunch of different components, for this conversation, we are talking about a figure that is based on simply Octane.

Gasoline = Octane = C8H18

You just need to keep going with your calculations. You have the correct MOLAR combustion balance equation. But A/F ratios are MASS ratios...

Don't forget, you aren't burning O2 either. You are burning air, which is 78% Nitrogen...

14.7:1 isn't some random number. When you get 14.7, you have done the chemical balance correctly. Remember, this is IDEAL COMPLETE stoichiometric combustion that these ratios come from as well. You can ignore any of the incomplete combustion by-products. To get it perfect, you will need to use the true composition of air though. If you approximate it as only oxygen and Nitrogen, you should end up around 15.0:1.


Modified by 99_GS-T at 4:22 PM 4/30/2007

nickromeo

one teacher in school told me that 14.7:1 ratio comes from 5% oxygen left in the exhaust

hxtasy

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nickromeo &raquo;</TD></TR><TR><TD CLASS="quote">one teacher in school told me that 14.7:1 ratio comes from 5% oxygen left in the exhaust</TD></TR></TABLE>


my physics teacher once told me coefficient of friction of a drag tire doesn't change with surface area.

(kinetic friction not static)

im going to try balancing it again like 99_GS-T said.

bluedlude

it doesnt. coefficient of friction is based on the two materials in contact. not to be confused with the frictional forces. and im trying to come up with your 14.7:1. i think i figured that one out before.

99_GS-T

Your physics teacher is right...Watch out on the coefficient of friction one when it comes to tires. It doesn't change with the width of the tire. Basic friction does not rely on surface area.

The tire has molecular adhesion and conformity capabilities and this is where the added grip comes from. This is why traction sucks in the rain. The molecular adhesion stops happening and all you get is the basic friction and the force associated with the rubber deformation holding you to the road. The molecular adhesion is a BIGGY. From what I've been told, burn outs have more to do with getting the temperature up to where stronger adhesion occurs, and it is not to make the tire "softer."

hxtasy

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 99_GS-T &raquo;</TD></TR><TR><TD CLASS="quote">Your physics teacher is right...Watch out on the coefficient of friction one when it comes to tires. It doesn't change with the width of the tire. Basic friction does not rely on surface area.

The tire has molecular adhesion and conformity capabilities and this is where the added grip comes from. This is why traction sucks in the rain. The molecular adhesion stops happening and all you get is the basic friction and the force associated with the rubber deformation holding you to the road. The molecular adhesion is a BIGGY. From what I've been told, burn outs have more to do with getting the temperature up to where stronger adhesion occurs, and it is not to make the tire "softer."</TD></TR></TABLE>

Coefficient of frition is constant and does not change with surface area with static friction, but because the tires are addhesive they do not have the same type of friction just like how a piece of scotch tape sitting on a table is not static friction, it is kinetic, even though it is not moving it has addhesive properties and in this case surface area does matter.

this is why drag tires are wider, that and to disperse the pressure more evenly (Pressure = force/area), burning out on them heats them up and enhances the addhesive properties.


tire science is heavy and misunderstood and i dont think anyone that is intrested in debating this has any free time right now because of finals.



anyways thanks for the input guys, and thanks for balancing that for me 99_GS-T.

david@didrace.com

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by hxtasy &raquo;</TD></TR><TR><TD CLASS="quote">But what I do not understand, or am more confused about now, is how this number is even close to accurate with different types of fuel. </TD></TR></TABLE>

All oxygen sensors are lambda sensors, not air/fuel sensors. An air/fuel ratio is derived using lambda and the assumption that the fuel being used is gasoline.

hxtasy

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by david@didrace.com &raquo;</TD></TR><TR><TD CLASS="quote">

All oxygen sensors are lambda sensors, not air/fuel sensors. An air/fuel ratio is derived using lambda and the assumption that the fuel being used is gasoline.</TD></TR></TABLE>

we are using a lamba of 1 which is 14.7 for gasolilne, so a lamba of 1 is 14.7, a higher lamba is a leaner AFR, but 1 is our target area.

This does not change the fact that the O2 sensor only reads oxygen, just how we interpert the data. if i put 50% gas and 50% ethanol the AFR is going to be different at stoich, but my O2 sensor is still only going to read parts Oxygen.

david@didrace.com

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by hxtasy &raquo;</TD></TR><TR><TD CLASS="quote">

we are using a lamba of 1 which is 14.7 for gasolilne, so a lamba of 1 is 14.7, a higher lamba is a leaner AFR, but 1 is our target area.

This does not change the fact that the O2 sensor only reads oxygen, just how we interpert the data. if i put 50% gas and 50% ethanol the AFR is going to be different at stoich, but my O2 sensor is still only going to read parts Oxygen.


</TD></TR></TABLE>

I think you're confusing yourself.

Lambda ~ 1 = 14.7:1 A/F Ratio for Gasoline
Lambda ~ 1 = 9.765 A/F Ratio for E85 (85% Ethanol/15% Gasoline)

If you have E85 in the tank and hookup a wideband and adjust the mixture to Stoich/Lambda it'll show 14.7:1 unless you calibrate the wideband for a different fuel.

Now you questioning how having a misfire or some other issue will cause the air/fuel to be off is a valid concern. That is what 5-gas analyzers are for.

hxtasy

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by david@didrace.com &raquo;</TD></TR><TR><TD CLASS="quote">

I think you're confusing yourself.

Lambda ~ 1 = 14.7:1 A/F Ratio for Gasoline
Lambda ~ 1 = 9.765 A/F Ratio for E85 (85% Ethanol/15% Gasoline)

If you have E85 in the tank and hookup a wideband and adjust the mixture to Stoich/Lambda it'll show 14.7:1 unless you calibrate the wideband for a different fuel.

Now you questioning how having a misfire or some other issue will cause the air/fuel to be off is a valid concern. That is what 5-gas analyzers are for. </TD></TR></TABLE>


hmm i think i might be a little confused on this, as most wideband controllers display 14.7 numbers and not lamba digits.

thanks

bluedlude

my innovate LM1 displays lambda and AFR and takes about 30 seconds to calibrate it to a different fuel. including custom settings. and only at idle would you EVER think to tune an engine to be at 14.7.

hxtasy

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bluedlude &raquo;</TD></TR><TR><TD CLASS="quote">my innovate LM1 displays lambda and AFR and takes about 30 seconds to calibrate it to a different fuel. including custom settings. and only at idle would you EVER think to tune an engine to be at 14.7.</TD></TR></TABLE>

yes, as i stated. idle and no load cruising conditions, just how stock computers are set up.

alex_s817

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by suspendedHatch &raquo;</TD></TR><TR><TD CLASS="quote">
No car should ever run 14.7 under all conditions. Cars should idle and cruise as lean as possible, not spray fuel at all under deceleration, and should run rich under high load conditions to protect the motor. Under heavy acceleration the mixture should be slightly rich or whatever gives you the best power, and under normal driving conditions the mixture should be roughly 14.7 depending on combustion chamber design.
</TD></TR></TABLE>

yes,
I was just learning about this today in my auto class and the teacher said if you could watch it on a graph it would be going up and down and never just sitting at 14.7.

ProJectCvic

The chemical reaction contains N2 also. Start with the following and do chemical balance again.

CxHy + as(O2 +3.76N2) ---&gt; CO2+H2O+ N2

You will find that the molar stoichmetic ratio (as) for Octane, simpified as C8H18, is 12.50 but the As (mass basis) is 15.03. However is you take into account for the the other chemical makeup of today's gasoline it is about 14.7. Interesting topic..I like to see more of this stuff on Honda-tech.

hxtasy

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ProJectCvic &raquo;</TD></TR><TR><TD CLASS="quote">The chemical reaction contains N2 also. Start with the following and do chemical balance again.

CxHy + as(O2 +3.76N2) ---&gt; CO2+H2O+ N2

You will find that the molar stoichmetic ratio (as) for Octane, simpified as C8H18, is 12.50 but the As (mass basis) is 15.03. However is you take into account for the the other chemical makeup of today's gasoline it is about 14.7. Interesting topic..I like to see more of this stuff on Honda-tech.</TD></TR></TABLE>

I would like to see more of this as well! anyawys, GST and the link i posted pretty muched summed it up very well.