Fordmods Logo

RUNNING LEAN & RICH? WHATS IT ALL MEAN? 

 

Page 2 of 2 [ 25 posts ] Go to page Previous  1, 2

 
 Post subject: Re: RUNNING LEAN & RICH? WHATS IT ALL MEAN?
Posted: Mon Feb 21, 2005 7:51 pm 
Getting Side Ways
Offline

Age: 35

Posts: 533

Joined: 12th Jan 2005

Location: Melbourne
VIC, Australia

raiki wrote:
Lukieman wrote:
The risk of detonation from running too lean is PARTLY because the valves and plugs are glowing white hot. This lights the fuel before the plug has a chance to fire.

Anyway thats enough of my Physics lecture, I am sure you get the picture.


Really hot engine parts is associated more with pre-ignition. The pre-ignition LEADS TO detonation, but hot valves don't directly cause detonation.... not from what Trevor Thom has taught me anyway.

Fo those of you who don't know, pre-ignition is where the charge in the cylinder ignite before the spark plug fires. Obviously this is exactally the same effect as advancing the ignition, so it causes detonation.
Top
 Profile  
 
 
Posted: Mon Feb 21, 2005 7:56 pm 
Getting Side Ways
Offline

Age: 35

Posts: 533

Joined: 12th Jan 2005

Location: Melbourne
VIC, Australia

4.9 EF Futura wrote:
Rich certainly does not equate to power gains. The leaner the better. Take a stock falcon and lean it slightly via fuel pressure and watch kw increase on dyno.... very cool.

Too much fuel basically chokes the combustion process and hurts power. Richer fuel mixtures at WOT more a matter of safety... as shane mentioned... lean engine condition is conducive to detonation under high load... high load + detonation = broken engines. But of course, air/fuel cannot (shouldnt?) be considered in isolation of spark timing....


I have to agree with Spork. Leaner certainly does not mean better.

Actually, a leaner maxture 'chokes' the cumbustion process. Not the other way round... not untill you get really rich and start blowing copious amounts of black smoke out the exhaust.

And spark advance directly affects AFR. A more retarded spark, a richer exhaust. ARF directly affects spark advance aswell.

The thing about engines is, everything in an engine relys on at least one other thing to work properly. Basically, you cannot change one thing in an engine without affecting something else. If you could, tuning would be easy!
Top
 Profile  
 
 
Posted: Mon Feb 21, 2005 9:03 pm 
Stock as a Rock
Offline

Age: 41

Posts: 115

Joined: 6th Nov 2004

Ride: EF XR6

Location: Dalby
QLD, Australia

SVO XR6 wrote:
@ decell = 16.3-15.5
@ idle = 14.4-14.7
@ cruise = 15.5-16
@ accel = 14.2-13.8
@ WOT = 13.3-12.8

this is a general estimate that i found works quite well.

these are form the general revs that the style is used.
ie, cruise=1200-2500 rpm
accell= 2500-4000 rpm at a medium map pressure

ect...



at what fuel pressure when idleing would give 14.4 - 14.7 afr?
Top
 Profile  
 
 
 Post subject: Re: RUNNING LEAN & RICH? WHATS IT ALL MEAN?
Posted: Mon Feb 21, 2005 9:15 pm 
Getting Side Ways
Offline
User avatar

Age: 42

Posts: 452

Joined: 21st Dec 2004

Gallery: 1 images

Location: Adelaide
SA, Australia

unclewoja wrote:
raiki wrote:
Lukieman wrote:
The risk of detonation from running too lean is PARTLY because the valves and plugs are glowing white hot. This lights the fuel before the plug has a chance to fire.

Anyway thats enough of my Physics lecture, I am sure you get the picture.


Really hot engine parts is associated more with pre-ignition. The pre-ignition LEADS TO detonation, but hot valves don't directly cause detonation.... not from what Trevor Thom has taught me anyway.

Fo those of you who don't know, pre-ignition is where the charge in the cylinder ignite before the spark plug fires. Obviously this is exactally the same effect as advancing the ignition, so it causes detonation.


Uncle,

Thats why I said partly. I needed to dumb it down for the non pilots and the lower IQ'd people among us.

 

_________________

Adrian
EF Fairmont, 5.0Lt, Pacemaker Headers, Sports cats, Redback muff, T5 manual, 16" Tickford rims, Tickford "Body Styling", DBA Gold Rotors, Heritage Green, JVC MP3
XB Coupe, 351C, twin system, C4 shift kitted auto, 9" LSD, Eccose Blue, very loud !!!!

Top
 Profile  
 
 
Posted: Mon Feb 21, 2005 10:20 pm 
Getting Side Ways
Offline
User avatar

Age: 33

Posts: 1680

Joined: 5th Nov 2004

Gallery: 1 images

Ride: 220kw 1600 Datto

Location: Scaaabz
WA, Australia

gravelrash wrote:
SVO XR6 wrote:
@ decell = 16.3-15.5
@ idle = 14.4-14.7
@ cruise = 15.5-16
@ accel = 14.2-13.8
@ WOT = 13.3-12.8

this is a general estimate that i found works quite well.

these are form the general revs that the style is used.
ie, cruise=1200-2500 rpm
accell= 2500-4000 rpm at a medium map pressure

ect...




at what fuel pressure when idleing would give 14.4 - 14.7 afr?


im sorry, i couldnt tell you. I found these A/F's to work well from playing with a aftermarket ecu and fuel maps.

 

_________________

Image

Top
 Profile  
 
 
Posted: Tue Feb 22, 2005 5:59 pm 
Getting Side Ways
Offline

Age: 35

Posts: 533

Joined: 12th Jan 2005

Location: Melbourne
VIC, Australia

gravelrash wrote:
SVO XR6 wrote:
@ decell = 16.3-15.5
@ idle = 14.4-14.7
@ cruise = 15.5-16
@ accel = 14.2-13.8
@ WOT = 13.3-12.8

this is a general estimate that i found works quite well.

these are form the general revs that the style is used.
ie, cruise=1200-2500 rpm
accell= 2500-4000 rpm at a medium map pressure

ect...



at what fuel pressure when idleing would give 14.4 - 14.7 afr?


Any fuel pressure @ idle will give 14.7:1 AFR. If the fuel pressure goes up, the pulse width and duty cycle (the amount of time the injector is open) decreases and vice versa.

EFI engines typically run about 15-20psi @ idle and 36-45 psi @ WOT.

Don't be too fooled by people telling you about 'rising rate' fuel pressure regulators. ALL fuel pressure regulators are rising rate. The more manifold pressure, the more fuel pressure.

The after market 'rising rate' fuel pressure regulators rise at a faster rate than standard. i.e a standard regulator might run 20psi @ idle and 40psi @ WOT. A 'rising rate' regulator might run 20psi @ idel, but 60psi @ WOT.
Top
 Profile  
 
 
Posted: Tue Feb 22, 2005 8:13 pm 
Technical Contributor
Offline
User avatar

Posts: 2799

Joined: 6th Nov 2004

Gallery: 7 images

Ride: Falcon

Location: Sydney
NSW, Australia

lol, poor guy asks what rich/lean means, and he gets a whole science on fuel and air...lol... good read but.


Cheers

 

_________________

;++JustForDimSim++;

Cheap, fast and reliable.. choose 2.

Top
 Profile  
 
 
 Post subject: Re: RUNNING LEAN & RICH? WHATS IT ALL MEAN?
Posted: Thu Feb 24, 2005 5:21 am 
Smokin em up
Offline
User avatar

Age: 36

Posts: 258

Joined: 7th Nov 2004

Gallery: 6 images

Ride: '98 EL XR8

Location: Katherine
NT, Australia

raiki wrote:
Close, but not quite right. Too rich actually keeps the cylinder and valves cooler. Once the oxygen in the cylinder is burnt, the rest of fuel cannot be burnt. This evaporates and flows out the exhaust. Evaporation = cooling

In piston aircraft we use exhaust gas temperature (EGT) as an indicator of mixture, becuase we control our mixture manually. High EGT = too lean. Add more fuel, EGT goes down.

The risk of detonation from running too lean is PARTLY because the valves and plugs are glowing white hot. This lights the fuel before the plug has a chance to fire.

Anyway thats enough of my Physics lecture, I am sure you get the picture.

So, your saying that an engine won't run as hot if you run it rich, than if you run it at stoichiometric mixture... and if its too lean it will run hotter with more likelyhood of pre-detonation.

When I did science at school (basic), fuel needs oxygen to burn, and every fuel only has a certain ammount of energy / heat which can be released with a certain volume of air.

Hence why jet engines compress large quantities of air use a mixture of kerosene and alcohol as those fuels have the highest energy rating and have the power to produce an excess of 35,000 kW of thrust... yeah, and I thought the 290kW GT was impressive!!!.

The way I see it, its pointless adding more fuel to volume of air as there is not enough oxygen, so your wasting fuel... There is an increase in power, as this is one process on how jet engines spool up their turbine/compressors.

And if you run it lean, then your not getting the full energy release potential from the fuel. So I dont know how a lean engine can produce more energy?

Also, can see by SVO XR6 figures, a high reving engine decellerating on no fuel injection will run a lean mixture... obviously... how safe is it though? Compression braking would increase heat into the engine...

Quote:
Don't be too fooled by people telling you about 'rising rate' fuel pressure regulators. ALL fuel pressure regulators are rising rate. The more manifold pressure, the more fuel pressure.


Im not sure how the fuel regulator works, does that mean when there is a high vacume in the manifold (idle)... that vacume opens the valve in the regulator to let bypass pressure through? And when there is no vacume (WOT), the valve is closed for highest fuel pressure???

 

_________________

"...we can rebuild him, we have the technology... we just dont want to spend a lot of money."
SIX MILLION PESO FALCON

Top
 Profile  
 
 
Posted: Thu Feb 24, 2005 8:55 am 
Getting Side Ways
Offline
User avatar

Age: 42

Posts: 452

Joined: 21st Dec 2004

Gallery: 1 images

Location: Adelaide
SA, Australia

An over lean engine does not produce more power, infact it produces less.

Jet engines are way different than piston engines. They don't have a carby or EFI. Their fuel is dumped directly into the combustion chamber. They always run a little lean so there is excess oxygen not burned. This way when you add fuel the extra air burns, producing more thrust which spools up the turbine/compressor providing more air. This is how afterburners can work. All they do is dump more fuel after the turbine. The excess oxygen is burnt increasing thrust, but not spooling up the turbine.

In piston planes we add a little more fuel than required. Not to get more power, but to preserve the engine. A stalled engine in a plane is a little more nasty than a car with a d**k engine. I'd prefer to use a little more fuel than to to risk burning out valves.

Also running an engine rich doesn't really effect the heat of the engine as a whole. It does cool down the exhaust valves.

As for the high reving engine with no throttle, the fuel is actually switched off above 1500rpm. No fuel = no fire = no heat.

PS thrust is measured in pounds, kilograms, newtons. It cannot be measured in kW. The turbine does produce a huge number of kilowatts to turn the compressor which supplies the air. This burns to prodce thrust and spin the turbine.

 

_________________

Adrian
EF Fairmont, 5.0Lt, Pacemaker Headers, Sports cats, Redback muff, T5 manual, 16" Tickford rims, Tickford "Body Styling", DBA Gold Rotors, Heritage Green, JVC MP3
XB Coupe, 351C, twin system, C4 shift kitted auto, 9" LSD, Eccose Blue, very loud !!!!

Top
 Profile  
 
 
 Post subject: Re: RUNNING LEAN & RICH? WHATS IT ALL MEAN?
Posted: Thu Feb 24, 2005 9:15 pm 
Getting Side Ways
Offline

Age: 35

Posts: 533

Joined: 12th Jan 2005

Location: Melbourne
VIC, Australia

Lukieman wrote:
So, your saying that an engine won't run as hot if you run it rich, than if you run it at stoichiometric mixture... and if its too lean it will run hotter with more likelyhood of pre-detonation.


The engine as a whole doesn't run hotter or colder in response to AFR.... but things like valves which temps aren't measured, do get hotter or cooler in response to AFR

Lukieman wrote:
Hence why jet engines compress large quantities of air use a mixture of kerosene and alcohol as those fuels have the highest energy rating and have the power to produce an excess of 35,000 kW of thrust... yeah, and I thought the 290kW GT was impressive!!!.


Not really as simple as that, and there are differences b/n turbo fan engines and turbo jet engines. Then you got your turbo props which are a hybrid b/n a jet engine and a piston engine. Also, put a jet engine in a car and just watch the 290kW GT leave you for dead. Ya see, a jet engine takes about 8 seconds to spool up from idle to full thrust.

Lukieman wrote:
The way I see it, its pointless adding more fuel to volume of air as there is not enough oxygen, so your wasting fuel... There is an increase in power, as this is one process on how jet engines spool up their turbine/compressors.


Don't forget that fuel also lubricates the inside of the cylinder. If you reduce the friction, you increase the available power @ the flywheel. The engine doesn't produce any MORE power, it's just that lees of the power it's producing goes into overcoming the frictional losses.

Lukieman wrote:
And if you run it lean, then your not getting the full energy release potential from the fuel. So I dont know how a lean engine can produce more energy?


Yes you are actually. All the fuel in the cylinder is being burnt. It's just that you're not getting all the potential from the oxygen in the cylinder.

Lukieman wrote:
Also, can see by SVO XR6 figures, a high reving engine decellerating on no fuel injection will run a lean mixture... obviously... how safe is it though? Compression braking would increase heat into the engine...


Running lean only buggers stuff up when the engine is under load.

Lukieman wrote:
Im not sure how the fuel regulator works, does that mean when there is a high vacume in the manifold (idle)... that vacume opens the valve in the regulator to let bypass pressure through? And when there is no vacume (WOT), the valve is closed for highest fuel pressure???


In a nut shell that's exactally how a fuel pressure regulator works. You have a rubber diaphram in the housing. One side is connected to an engine vacuum line, the other side is connected to a valve and fuel passes through that to either the fuel rail, or back to the tank.

If there is high manifold vacuum, it sucks up the diaphram and lets more fuel go back to the fuel tank. If there is low manifold vacuum, the opposite happens. Also there is obviously a spring in there to make everything work too.
Top
 Profile  
 
Display posts from previous:
Sort by  
 Page 2 of 2  [ 25 posts ]  Go to page Previous  1, 2

Who is online

Users browsing this forum: No registered users and 11 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

 

 

It is currently Tue Dec 19, 2017 12:08 am All times are UTC + 11 hours

 

 

(c)2014 Total Web Solutions Australia - Australian Web Hosting and Domain Names