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TDI Power Enhancements Discussions about increasing the power of your TDI engine. i.e. chips, injectors, powerboxes, clutches, etc. Handling, suspensions, wheels, type discussion should be put into the "Upgrades (non TDI Engine related)" forum. Non TDI vehicle related postings will be moved or removed. Please note the Performance Disclaimer.

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Old March 11th, 2008, 10:04   #16
GoFaster
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You will start getting smoke somewhat lean of stoichiometric due to imperfect mixing of fuel and air.
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Old February 2nd, 2014, 02:31   #17
Feinstaub_CH
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Default Please confirm

Hi Mates

Sorry for digging out this old "fred"

I am going to re-adjust my chip. After reading and studding a lot about AFR, can someone pls confirm my mind?

LEAN means: More air is added than for the Stoichiometric is "needed" - lets say: 17 air to 1 fuel is LEAN? (Stoich is 14.7 : 1) - right?

LEAN means LESS EGT?

But why? Is it because not all air is burned and so the un-used air keeps the EGT down?
If so, why not the opposite way? More unused fuel should IMO better help keep the EGT down?

Under WOT target should be at least AFR of 17:1?

Sorry for my English, Swiss-German is still my mother-language


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Old February 2nd, 2014, 08:22   #18
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With lean you can burn all the fuel at the right moment during diesel combustion. Going rich means that the rest of the fuel will burn piston going down or even in ex manifold.

Gasser won't burn the residual fuel, diesel does. That's why excess fuel is raising EGT/EMP in diesel.
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Old February 2nd, 2014, 10:03   #19
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Quote:
Originally Posted by shadowmaker View Post
With lean you can burn all the fuel at the right moment during diesel combustion. Going rich means that the rest of the fuel will burn piston going down or even in ex manifold.

Gasser won't burn the residual fuel, diesel does. That's why excess fuel is raising EGT/EMP in diesel.
This a patently incorrect. Diesel fuel is injected just before combustion is supposed to take place and within that very limited period of time, the atomized liquid jet of fuel must evaporate, diffuse in the air and form a combustible mixture within a local fuel-air ratio not far from stoichiometric. Whether at idle or full-load, combustion in a properly designed engine should be substantially complete within a span of no more than about 45° crank angle from the beginning of noticeable heat release. Combustion duration is more of a function of the engine design and development (swirl, fuel properties, charge temperature at end of compression, bowl/spray geometry, injection pressure/multiple injections (rate shaping) and less about whether the mixture is lean or rich in a global sense.

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Old February 2nd, 2014, 10:11   #20
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On a ve TDI you can usually get down to 17:1 Afr with little to no smoke but timing plays a big role. You can make more smoke at 20:1 Afr than 17:1 if you have too much timing. CR TDI can do 14.5 with little to no smoke.
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Old February 2nd, 2014, 10:20   #21
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Funny to see this thread come back. I barely even recall what I was doing with my wagon when I started it in '08.

Last time Jeff tuned my car he told me the timing was too advance (100 in block 2). In the past he liked it set high to make sure the pump had its full timing advancement available. I've moved it back to 75 or so, and based on the low smoke and FE I'm getting I guess it was a good idea.
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Old February 2nd, 2014, 13:55   #22
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Quote:
Originally Posted by Feinstaub_CH View Post
Hi Mates
Sorry for digging out this old "fred"
I am going to re-adjust my chip. After reading and studding a lot about AFR, can someone pls confirm my mind?
LEAN means: More air is added than for the Stoichiometric is "needed" - lets say: 17 air to 1 fuel is LEAN? (Stoich is 14.7 : 1) - right?
LEAN means LESS EGT?
But why? Is it because not all air is burned and so the un-used air keeps the EGT down?
If so, why not the opposite way? More unused fuel should IMO better help keep the EGT down?
Under WOT target should be at least AFR of 17:1?
Sorry for my English, Swiss-German is still my mother-language
Cheers all
Feinstaub
I will answer with a combination of what I know and what I am assuming. Counting on TDIMeister and others to crtique my answer - just doing so because it seems nobody else replied to you.

First of all, yes, "lean" mixture means excess air and "rich" means excess fuel beyond stoichiometric.

On a gasoline fired, spark ignition engine, peak EGT happens very close to stoichiometric conditions...with the possible exception that the EGT downstream of lean mixture is seeing a bit of burning still taking place as a lean gasoline/air mixture burns more slowly (thus why lean mixtures burn valves - lot of temp on the exhaust valve seat and excess of oxygen). But, you comment about "unused air" is spot on for gassers - the lack of oxygen to be used to burn fuel means less energy release when lean of stoich - thus lower EGT when lean. For why richer lean of peak - see below.

Air does not burn...well, I guess in a way it does. The oxygen in the air combines with hydrogen and carbon in the fuel in an exothermic reation that in turn heats the other 80% of the air (nitrogen) in the chamber - which will expand to drive the piston. When we use forced induction in a diesel to keep the mixture very "lean", or if we simply deliver less fuel to use the air that is in the cylinder, the ratio of mass of reagents to nitrogen (and some remaining oxygen) means that the greater mass has absorbed the fixed (for reference purposes) energy from combustion, thus gaining less temperature from the same amount of heat (energy). THAT is why the engine makes less power with more air (less temperature to expand the gasses that push on the piston = lower MEP - mean effective pressure - that in turn shows up as a lower EGT when it is released into the exhaust tract.

Oh, the comment about air burning "in a way it does" is because at combustion temperatures, some of that nitrogen combines with some of the available oxygen to make oxides of nitrogen (which is what truly erks me when people in my business routinely refer to nitrogen as "inert"). That is the "burning air" part.

I would assume that the deeper you get into smoke and when you finally DO reach stoichiometry with a diesel, you will also see EGTs decrease - but to get there, you need to keep adding fuel thus an engine seeing very rich mixtures while burning less efficiently could still to a great degree be burning more fuel than another reference point of measurement - thus showing a much higher EGT (to a point).

Remember that the fuel supply in a gasser can only burn over a very narrow range (thus more responsive EGT vs. mixture measurement) whereas a diesel can operate over a VERY wide range of mixtures - thus experience these results.
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Old February 2nd, 2014, 14:57   #23
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Quote:
Originally Posted by JFettig View Post
On a ve TDI you can usually get down to 17:1 Afr with little to no smoke but timing plays a big role. You can make more smoke at 20:1 Afr than 17:1 if you have too much timing. CR TDI can do 14.5 with little to no smoke.
Higher quality of nozzle atomisation and multi injection per cycle are the key of complet combustion and CR are far better on this than VE pump system.




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Old February 6th, 2014, 04:43   #24
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Quote:
Originally Posted by TDIMeister View Post
This a patently incorrect. Diesel fuel is injected just before combustion is supposed to take place and within that very limited period of time, the atomized liquid jet of fuel must evaporate, diffuse in the air and form a combustible mixture within a local fuel-air ratio not far from stoichiometric. Whether at idle or full-load, combustion in a properly designed engine should be substantially complete within a span of no more than about 45° crank angle from the beginning of noticeable heat release. Combustion duration is more of a function of the engine design and development (swirl, fuel properties, charge temperature at end of compression, bowl/spray geometry, injection pressure/multiple injections (rate shaping) and less about whether the mixture is lean or rich in a global sense.

I wasn't talking about engineering side of diesel combustion. I was talking about AN engine with either lean or rich of its optimal operation point. It doesn't matter IDI, VE, PD or CR, they all behave identical when nothing else in certain engine, but fuel quantity (=injection window, injection pressure stays the same), is changed. Rich means more EGT, lean means less EGT. Optimal operation point can vary between these very different engine types, but I wasn't talking about that as I didn't see any question about that either (from Feinstaub).

And yes, when most of the combustion happens within 45 degrees crank angle, there's always unburned fuel present after that (as can be seen from Meister's chart above). The amount of that residual fuel is the key for EGT temperatures. Bigger amount means that more fuel is still burning after "optimal" crank angle and the heat of that burning can't be converted efficiently to work -> EGT goes up, power doesn't.

And like Meister said there are many ways to get more fuel be burned in that 45 degree crank angle window, but that's a whole other story - even though very important one here in "TDI Power Enhancement"-section.
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Old February 6th, 2014, 05:35   #25
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Ideal AFR also depends on RPM and injection window.
For example, in my current tune, .234 inj w 11mm pump calibrated pump voltage to 80 mg/s and smokemap used to limit fuel (not torque limiter like some tunes do above 851 mg/s maf)
RPM AFRsmokefree
5500 18.8
5000 18.65
4500 18.5
4000 18.2
3500 17.9
3000 17.6
2500 17.2
2000 17.1

BUT what I am seeking now is what is the best AFR to set the target boost map, for cruising conditions, aka 10 mg/s 20 mg/s 30 mg/s?
I currently use reduced boost from stock boost map based on advice from ecuconnections, but I hear that higher afr than 17 is more economical to a point, due to better mixing etc...??? (tdimeister- is there an optimal part load afr- or is "enough air" better???)

assuming 1 bar absolute is around 480 mg/s maf (when EMP is not too high)
IQ AFR BOOST@2k BOOST@5.5k
10 48 1000 1092
20 28 1167 1274
30 24 1500 1638
37.5 22 1718 1876
45 21 1968 2150
Higher fueling goes closer to the afr from smoke map due to boost limits of the turbo itself (1749vb-vnt17)

Quote:
Originally Posted by IndigoBlueWagon View Post
Funny to see this thread come back. I barely even recall what I was doing with my wagon when I started it in '08.

Last time Jeff tuned my car he told me the timing was too advance (100 in block 2). In the past he liked it set high to make sure the pump had its full timing advancement available. I've moved it back to 75 or so, and based on the low smoke and FE I'm getting I guess it was a good idea.
I don't know why the change in opinion.... setting static to 100 only makes it so that the pump can't go below xx BTDC. 75 for example, you see you get 3 btdc at idle irrespective of timing duty cycle. More timing than that is done by the SOI map, which adapts to whatever static you set it to. (example: asks for 10 btdc@ 3000 rpm: with timing at 75, the solenoid would be 60%, but with 100, it would be 30% - example!)

Anyway, with 75, run output tests, the first one does the timing solenoid. Then go to group 04 measuring blocks and see how even at 75, you can get up to 22 or so BDTC at idle! If you rev it to 1200 rpm or so (not too high or it stops the output test) you see it goes to 25 or so!
So this original advice of 100, is kind of overkill in the first place. Maybe it was a fix for the pumps that couldn't get proper case pressure or feed of fuel?

Last edited by robnitro; February 6th, 2014 at 05:39.
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Old February 6th, 2014, 06:31   #26
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When i cruise on highway, my AFR are between 28:1 to 40:1, change fast with wind, road angle and throttle.




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Old February 7th, 2014, 07:11   #27
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Default Big thanks to your replies!

Thanks for your replies, i can nothing add/write because i need first to understand what i am reading

Cheers
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Old February 7th, 2014, 08:48   #28
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Quote:
Originally Posted by dieseleux View Post
When i cruise on highway, my AFR are between 28:1 to 40:1, change fast with wind, road angle and throttle.




Dieseleux

Same here, I tuned mine to stick around 30AFR cruising to keep the vanes as open as possible and still efficient burn. It drops down to 25-28 up hills sometimes.
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Old July 24th, 2015, 05:47   #29
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Don't have a TDi but a CRDi.

I have an 'extreme' wideband running in my car which can read AFR upto 230:1. At idle the AF goes as down to 200:1




Video:
https://www.youtube.com/watch?v=_DiM...ature=youtu.be


Wideband Controller - Ecotrons ALM
Digital Gauges - Auber Instruments

LED Gauges:
Left green - Intake Manifold Air Temperature
Center orange - AFR (Air Fuel Ratio)
Right red - EGT (Pre-Turbo Exhaust Gas Temperature)

LCD Gauge: Scangauge reading OBD Coolant Temperature, Boost, Intake Temperature & Fuel Rail Pressure (XGauge code)

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Old July 24th, 2015, 10:00   #30
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Nice!
Auber make nice 12v panel display, i use on other projet.
On my ALH engine, idle is 40 to 60:1 on cold engine and 85 to 96:1 on hot engine.


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