Safe lean mixture for family car ?

[ducatisti]

My peugeot 307 1.6 16v was running at 12.3 AFR from 4000rpm. I dont want performance i want economy. What is the safe leanest mixture ?

[camil]

The leaner mixture the hotter your EGT. With all its side effects. Without measuring EGT, i think is difficult to tell how much you can lean the mixture.

And if you don't need performance, i guess you can reduce fuel and also boost, and continue 12.3@4000 and you will gain economy loosing power but keeping safeness.

[oem]

You can make maximum AFR 13.2:1 after 4000 rpm and retarding advance with -2 deg. from 4000 to 5500 rpm's and -3 deg from 5500 to rev limiter. You will lose ~5 hp. But i think that if you rise AFR & spark advance in maximum torque engine rpm moment, you will save fuel in this rpms more than if use lean mixtures.

[warrior888]

Interested in this too.

[camil]

You can make maximum AFR 13.2:1 after 4000 rpm and retarding advance with -2 deg. from 4000 to 5500 rpm's and -3 deg from 5500 to rev limiter. You will lose ~5 hp. But i think that if you rise AFR & spark advance in maximum torque engine rpm moment, you will save fuel in this rpms more than if use lean mixtures.

I'm far to be an expert, but... leaning mixture, and also retarding spark advance will not increase even more the EGT?

[mislav88]

no, increasing spark advance increases EGT, with retarding it you are compensating lean mixture effect on EGT

[camil]

I must be mirssreading then most of the times, or missunderstanding what i read.

If you advance spark combustion ends earlier and less chance to continue burnung when exhaust valves are open, this last is what i thought make egt grow.

Contrary, if you retard spark you have more chance to incomplete combustion into cylinder and burning flame go to exhaust raising EGT.

Leaner mixture means faster burning flame, so you retard spark not to being near knock point, not for EGT means.

That's my inexpert understanding of the case.

[easytech]

Agree with Camil.
Increase advance will lower the EGT.
Increase the AFR will increase the EGT.
It is the basic for the cumbsution engine.
Sure there are much more variables that will effect the EGT. Such as compression ratio. Valve timing.

AFR 12.4 is pretty rich for a simple NA engine.
AFR 13.2-13.4 will help on economics.
But it will not be much.

[oem]

Increase advance on petrol engines will increase EGT becouse maximum cylinder pressure will be in moment where piston is in GMT. Gas pressure in this moment will be very compressed and this will increase temperature in combustion chamber.

Retarding will reduce EGT, becouse you do not have maximum cylinder pressure as when you have more advance. And temperature will small as another situations.

Lean mixtures will burning very fast and will increase EGT as same theory as you have more advance.
Rich will reduce. :)

And the best fuel economy an engine is in currently has the highest efficiency. Currently around peak torque. There are several ways to increase the maximum torque. Whatever you do in this range will have fuel economy.

[Stanton]

Lots of misinformation in this thread.

EGT REDUCES as mixture goes leaner. Simply, thermal efficient increases with a leaner mixture, and since we are talking about a "heat engine" this means less losses through exhaust heat ie cooler EGT.
The effect of fueling on EGT is bell-mouth, it increases with a richer mixture since more chemical to heat energy conversion is taking place. Beyond peak power EGT drops with extra fuel sinice the non oxidised fuel cools the gas.

As for ign advance, RETARDING ign increase EGT since we are moving point of 50% mass fraction burned closer to BDC, therefore peak heat release and therefore gas temp is hotter as exhaust valve is opened.

For the question of afr when cruising 12.3:1 is way too rich. I would suggest you check adaptions and check closed loop lamba function.
The limit of lean burn is only lean burn misfire. The onset of this is mostly dependent on Cr and other geometry which affects cylinder cgwtge motion and gas homogeneity. On a manifold injection system, i tend to target around 15.5:1 and on high Cr stuff maybe a tad leaner.
The effects on ign on fuel economy, increasing ign advance when cruising reduces BSFC, since up until negative work becomes an issue, we can increased conversion efficiency due to increased cylinder pressure.

[mexanico1971]

yes I agreed width you three !
I have bin made same test"s on mine xantia XUD7 1.8 8v"JPZ" PSA motor!
full stock part"s !
and he bring a REV cut at 6400 RPM, the maximum torque by the book is at 6000RPM and if sometimes I want to get some joy the motor end"s early !
so I increase RPM to 7500 rpm , give some enrichment in acceleration, and spark advance in charge to !
no knocking until now ! before sometimes I have knock sound because the bad fuel quality "95 oct"
and no fuel increase, still make 7,5 litres medium !
"this is a normal stock engine "
next step was increse fuel and spark start from 3000RPM to have a economy drive city !
in open road at 3500 or 4000 if I step on it at 4? gear or 5? e goes much more free and esyaly !
now I have to find "VE and O2 sensor" maps !

BR

[Stanton]

Lean mixtures will burning very fast and will increase EGT as same theory as you have more advance.
Rich will reduce. :)
.

Lean mixtures burn slower....with a richer mixture the fuel molecules are closer together, this means less time for flame to propagate. Also less energy required to oxidise each fuel molecule so less delay.

[J_amb_o]

Stanton is 100% correct.

I think you should all stick to "tuning" diesel engines...

[oem]

Stanton, you tell for flame speed. lean mixtures - slow flame speed and rich mixtures - fast flame speed. But lean mixtures burns fast and rich burns slow.

Lean - ignites fast or pre-ignites by high compression (high temperatures)
Rich - ignites slow with small risk from pre-ignites (normal tempertures)

On petrol and diesel engine effect of EGT is same only in ignition advance. More advance - more maximum pressure in GMT. More temperature.

Ofcourse if you have less ignition advance, mixtures will burning to late and this will increase EGT.

[oem]

You would first need to clarify the differences between the temperature of the combustion chamber and the temperature of the exhaust gases. We have high temperature of gases at the same time the temperature in the chamber at TDC is the norm, or otherwise.

[OVERSPEED]

As said before... there is no sense to talk about economy in WOT conditions... and in partial load the closed loop is supposed to lambda 1 everytime.

[Stanton]

Stanton, you tell for flame speed. lean mixtures - slow flame speed and rich mixtures - fast flame speed. But lean mixtures burns fast and rich burns slow.

Lean - ignites fast or pre-ignites by high compression (high temperatures)
Rich - ignites slow with small risk from pre-ignites (normal tempertures)

On petrol and diesel engine effect of EGT is same only in ignition advance. More advance - more maximum pressure in GMT. More temperature.

Ofcourse if you have less ignition advance, mixtures will burning to late and this will increase EGT.

This is where the mis information is at its biggest, around detonation.
To start, here we are talking about CRUISE conditions only, hence better fuel economy. Detonation will not occur at cruise as simply VE is very low, therefore cylinder filling is low, therefore pressure and temps are lower. Also consider a lower amount of fuel mass=lower energy available....the route of detonation is too much energy available.

For flame speed, you have it the wrong way round as i explained in my pprevious post. Its the same for gasoline and diesel, this is the exact principal that a diesel runs without a throttle....more fuel=faster flame propagation=higher engine speed. Conversely less fuel=less engine
sloped....hence how engine speed is governed in a diesel.....very lean at idle ;)

[oem]

It is wrong to make comparisons between diesel and gasoline. You have not right that at part load can not be have detonation. This shows that you are not familiar with petrol engines. In the attachment you can hear the recording of detonation sensor from car that makes detonations in all loads.

[Stanton]

On petrol and diesel engine effect of EGT is same only in ignition advance. More advance - more maximum pressure in GMT. More temperature..

I made this comparison like you have :)

Ive not listened to your sound clip, but the only time I have ever experienced detonation at part load was on high Cr NA with high duration cams, and cam timing was incorrect....exhst cam was too retarded, causing ex gas reversion after TDC....this must have been heating intake charge sufficiently to cause detonation. Correcting cam timing cured this and added 30odd bhp.
SO....check cam timing ;)

So I guess its fairer to say: in most instances, in a properly configured engine, det shouldn't occur at part load.

ANYWAY this wasn't about det :) I think you were about to explain your logic behind the affects of AFR flame speed; seen as Im too unfamiliar either gasoline combustion.

[Stanton]

I think you should all stick to "tuning" diesel engines...

LMAO I love "tuners" :P

[oem]

I made this comparison like you have :)

Ive not listened to your sound clip, but the only time I have ever experienced detonation at part load was on high Cr NA with high duration cams, and cam timing was incorrect....exhst cam was too retarded, causing ex gas reversion after TDC....this must have been heating intake charge sufficiently to cause detonation. Correcting cam timing cured this and added 30odd bhp.
SO....check cam timing ;)

So I guess its fairer to say: in most instances, in a properly configured engine, det shouldn't occur at part load.

ANYWAY this wasn't about det :) I think you were about to explain your logic behind the affects of AFR flame speed; seen as Im too unfamiliar either gasoline combustion.

I think too much deviated from the topic. It would be better to clear up misunderstandings between us in direct conversation :) You picked up an interesting topic for timing. Something that we can talk very long :) I can share with you their experiences and problems in this area. :) If you want to talk about this, my skype: oemotorsport

[mexanico1971]

Stanton, you tell for flame speed. lean mixtures - slow flame speed and rich mixtures - fast flame speed. But lean mixtures burns fast and rich burns slow.

Lean - ignites fast or pre-ignites by high compression (high temperatures)
Rich - ignites slow with small risk from pre-ignites (normal tempertures)

On petrol and diesel engine effect of EGT is same only in ignition advance. More advance - more maximum pressure in GMT. More temperature.

Ofcourse if you have less ignition advance, mixtures will burning to late and this will increase EGT.

OEM ! is right !

[oem]

GMT - TDC (translation) :jiggin:

[Stanton]

OEM ! is right !

We agree, advancing ignition timing increases pressure/temp; this doesnt mean EGT rises. As we know, the reason pressure increases with an increase in ign adv is because you produce peak heat release closer to TDC. In doing this there is greater crank angle until exhaust valve opens, this means MORE TIME for expansion to take place. And what happens when we expand a gas? It cools.
This is basic thermodynamics.

Conversley, if you retard ign, peak heat release occurs further from TDC i.e closer to E.V.O. THEREFORE less time for expansion = hotter gas. Again, simple, basic thermodynamics.

If you want to try and EXPLAIN and expand on the reasoning behind your input then please do so. Simply saying "so and so is right" or "no, this happens", has no grounds. Everything needs an explanation.

As for burn rate, Ive explained how AFR affects flame propogation and structure, and its affects on flame speed. This backs up MY statement. If you want to disagree, thats fine, but please explain the reasoning behind your thoughts.
This is the beauty of open discussion....we explain our thoughts and logic!

[mexanico1971]

ok! now I have understand your point !
yes ! hight pressure / low air density ! and vice versa !
more density more speed flame !
sorry ! the problem for me it"s the time I have to read careful the post"s and the hours that I read"it ! like tonight 03:00 AM !
it"s possible to have pre detonation at part load !
the danger zone is bet-win the 2800RPM to 3500RPM ,
there are a lot of variant"s to take in count, about AFR efficiency and is exactly relation !
sorry I did mean to unkind !

PS : what do you mean width E.V.O ?!

BR

[oem]

E.V.O - Exhaust Valve Opening :)

So far there is nothing wrong said by anyone in this thread. And i think there are enough answers to the main question.

There are two options to gain fuel economy:
1. Fuel mixtures near stoichiometric and retard ignition angle to prevent too early peak pressure in the cylinder and pumping losses.
2. Fuel mixtures and advance settings for maximum torque (an engine as generally speaking has the highest fuel economy in the range of maximum torque or the moment when we have the greatest cylinder pressure)

No need much explanation. The details are there in the books. There are some basic rules in internal combustion engines, fuel combustion and thermodynamics. Result over all, there are some simple and rigorous conclusions. Even if one is not very large professional he need follow these rules and will go in the right direction.

And the other important thing in this topic! We're talking about unmodified naturally aspirated engine. Do not worry about the temperature of the exhaust gases. You must think about temperature in combustion chamber. :)

[mexanico1971]

yestarday I tuned a opel corsa 1.4 8v from 1993 !
today the guy call me and tell me that the medium fuel is now 7,5 litre at 100km"s before it was 10litre !
almost 3 litre economy !
I can believe that is really true !
this is my secund gasoline tuned car !
my on car was the first, ! and now I have shore that is possible to keep economy !

BR

PS. i can not change the file in winols !
first it dosen"t have the CKS for DELCO "BDLU" and wen I try to correct cks in the mod file I made in winols , in a little program 8bits cks I have the file was corrupted, do not know why !
I use ECM 2001 and it work, I could not rise the RPM"s limiter and it only mod the first map group !
I have to use a free and very good program "FASSICHIP " to mod the second map group

I gonna left the file I read width willem PCB3 , it"s a 27c512 !

numbers are !

16163449
BDLU 6964

does anyone knows how to set for 6800rpm !
thank"s in advance
BR

[oem]

Limit-6800 RPM :)

[mexanico1971]

Limit-6800 RPM :)

yes ! you are right ! it was invert ! I search by hand but I was not shore !
and the costumer was watching I made the maps ! is not easy to do this under some pressure !

does this mean that all maps are inverted to ?!

thank you very much !

BR

[oem]

Yes :) But not all maps are inverted.