EGR - to be, or not to be, or et tu, brute

gmctd · **Posted:** Mon Jan 05, 2009 7:50 pm

There seems to be some universal confusion as to correct functional operation of that mysterious, much maligned and
oft-hated emissions device, affectionately known as the EGR, or Exhaust Gas Recirculation valve. Therefore, some
little-known, mostly ignored information vis a vis infernal combustion engine function, for your consideration -

Your KJ CRD 2.8L engine is little more than a large air pump - as the crankshaft rotates, the pistons travel bottom to
top in open-ended\valved cylinders, displacing cylinder volume to the tune of 2.8 liters, or pumping roughly 3/4 gallon
of air every two rotations (3.79L = 1USgal), being a 4-stroke pump: intake - compression - (power) stroke - exhaust - that results in output from two cylinders per crankshaft revolution - add fuel to suit, and we have an infernal combustion construct, whereby, when sufficient fuel is combined with the 20% O2 in the atmosphere, it is rapidly oxidized, providing
sufficient heat to quickly expand the remaining gas components, increasing pneumatic pressure in the cylinder,
thereby forcing each piston\rod downward, thus rotating the crankshaft - under normal circustances, the rapidly-
expanding combustion flame-front never touches the surface of the piston because the equally-rapid cylinder-
pressure increase keeps the piston moving ahead of the flame front - which is why aluminum pistons do not melt
at combustion temperatures greater than the melting point of aluminum: the pistons, obeying the maxim that discretion
is the greater part of valor, beat a hasty retreat ahead of the flame front - or, as Monte Python's Knights of Camelot
succinctly stated it: "Run away!!"

At idle, fuelrate is minimal, oxygen content is high, cylinder temperatures are low, EGT is low - sometimes too low, cold weather resulting in white unburned fuel vapors until engine block, heads, pistons come up to operating temperatures

At cruise, loading is low, fuelrate is minimal based on light demand, unconsumed oxygen levels are normal, cyl
temps are normal - cyl temps increase as cruise speeds increase, particularly when approaching 100mph and
greater

At high loading, fuelrates are increased commensurate with load demand, remaining oxygen levels are lower and
varying according to demand, cylinder temps can rise to max levels as fuelrate demand increases on grades, hills,
mountings (that's yankee for mountains!), and such

At full wide open throttle, fuelrates are maxed out, post-combustion oxygen levels are lower but not overly diminished
because Diesel air intake is not restricted by a throttle plate, and often enhanced by that magic puffer, the
gas-turbine driven supercharger, and full-power cylinder temps are maxing out

A major problem exists when fuel rapidly converts to other forms in the presence of O2: the hotter the flame and the
greater the remaining, unburned oxygen in the cylinder, the greater and more noxious the resultant oxides (NOx),
when some of the remaining oxygen molecules combine with the nitrogen molecules, not to mention the btu-
converted other components in simple atmosphere - high combustion chamber temperatures freely convert, render,
and distribute those combustion by-product emissions, as deemed offensive by yer casual, societally non-productive
tree-hugger - and, because they far outnumber Joe, the plumber, their vote calls the shots

In those other engines, cylinder temps also increase drastically under long-deceleration scenarios resulting in
high intake vacuum, such as exiting freeway ramps from hiway speeds, reduced throttle to maintain speed on long
grades, deceleration under heavy loading such as towing - this is due to the throttle plates being closed at high rpm,
where the normal scenario would be closed-plate idle fuel\air mixtures resulting in idle rpm, but vehicle speed keeps
the crank turning at greater than idle rpm, forcing greater-than-idle fuel\air rates into the cylinders - modern EFI
systems handle this much better than did the old carbureted systems (not)

Hence, the creation of that wunnerful-a wunnerful-a device we've all come to know and love as the EGR (valve) -
intense governmentally mandated (read: under duress) R&D showed that high cylinder temps could be easily
controlled by simple introduction of already-been-burned combustion byproducts into the intake system, reducing
available oxygen content, reducing the efficient conversion of fuel and oxygen into usable btu's, thus reducing peak
cylinder temperatures and emissions of those noxious oxides (NOx)

So, it may be seen that there is
- no demand for EGR insertion at idle, as cylinder temps are already low, some-times too low - the confusion is
likely that EGR is required at idle position of the throttle plates\TPS at high crankshaft rpm, as in extended
deceleration events
- no-to-little demand for EGR in most low-speed traffic scenarios
- no-to-little demand for EGR in cruise, demand increasing based on increased fuelrate to meet speed\load
- varying demand in loaded scenarios
- high-demand in various fwot scenarios

ECM-estimated max cylinder temperatures, based on rpm, mass airflow, Manifold Air Pressure, Throttle Position
Sensor angle, Engine Coolant Temps, altogether determine any requirement to stifle that soul-satisfying
conflagration taking place in the cylinders of yer fav greenhouse-polluter

Very high EGT's and high ECT's are good indicator of high cylinder temps requiring EGR assassination

Need proof?

For those with vacuum-operated, diaphragm-operated EGR valves, start your engine, pop the hood, reach back and
gently apply pressure to the EGR diaphragm, such that the valve opens slightly, noting resultant idle quality and idle
rpm

That's my story, and I'm stickin' to it..........................

With insincere apologies to Lawrence Welk, and heart-felt accolades to Sarah Palin and Monte Python

UFO · **Posted:** Mon Jan 05, 2009 9:36 pm

Hmm, if you've got high EGTs, EGR would be the solution? NOx is high there too, but does the ECM add EGR to correct for the high EGT or does it add it at times when it's not needed? I don't think the ECM directly measures EGT, but my "solution" would be to level off the fuel.

Death to diesel EGR!

gmctd · **Posted:** Mon Jan 05, 2009 9:43 pm

EGR reduces available O2, reducing flame temperature - as to whether correct solution or not, that is the universally chosen method, noting the mass proliferation of EGR valves, these days

ECM cannot measure EGT without a thermocouple - however, combustion temperatures resulting from various fuel\air ratios at all operating condidtions are known and programmed into ECM for reference - ECM response is based on those matrices, much to our dismay - that's one advantage of the INMOTION tunes, where the matrices can be permanently altered for increased performance

Ranger1 · **Joined:** Mon Oct 17, 2005 7:40 pm **Posts:** 1137

Quote:

So, it may be seen that there is
- no demand for EGR insertion at idle, as cylinder temps are already low, some-times too low - the confusion is
likely that EGR is required at idle position of the throttle plates\TPS at high crankshaft rpm, as in extended
deceleration events
- no-to-little demand for EGR in most low-speed traffic scenarios
- no-to-little demand for EGR in cruise, demand increasing based on increased fuelrate to meet speed\load
- varying demand in loaded scenarios
- high-demand in various fwot scenarios

Interesting observations, but I do see a couple of areas where real world monitoring of my CRD shows somewhat different behavior.
If you monitor the OBD/voltage signals at idle listed below, on a fully warmed up CRD (05 in my case), you can see that EGR is indeed consistently active at idle. On mine, it will activate for 75 to 90 seconds, then deactivate if the accelerator pedal is not touched at idle. If you touch the accelerator pedal even slightly and then let off, EGR will again activate for 75 to 90 seconds, then deactivate. It will do this as long as you care to monitor it on my CRD.

MAF signal
IAT signal
EGR activate on SEGR cable
AFC activate on SEGR cable

MAF readings ~ 2.2 - 2.5 lbs/minute with EGR off, then drops to 1.15 to 1.25 lbs/minute the instant EGR activates. Almost simultaneously with EGR activated, IAT rises 75* to 90* F, then drops by nearly the same amount with EGR deactivated. In hot summer temps, I've seen IAT rise as much as 140*F with EGR active.

If you graph these two readings at idle, you can see the inverse action of both signals: EGR ON --> MAF flow reduced by ~ 50%: EGR OFF--> MAF flow increases by ~ 50%. Monitoring the EGR and AFC activate voltages/ground will verify EGR activity. I've done this for several years at idle in the driveway, with the engine up to operating temperature of 160* F coolant temps. When the engine is first started, before reaching operating temp of 160* or higher, EGR does not activate. But EGR does indeed activate at idle, whether in my driveway or at a stoplight for several minutes. I graphed this using AutoTap software and observed very similar readings on an Innova Equus handheld OBD scanner.

Once the accelerator pedal is touched, EGR activates again, but at this point, I cannot determine from MAF/IAT readings alone if its active or not on acceleration. Reading the voltage/ground on the SEGR cable EGR/AFC pins will show values that represent an averaged voltage of the PWM signals being applied and may provide some insight.

There used to be a partial Bosch engineering article out in late 2004, early 2005 describing EGR operation at that time, or around the time the CRD egr controls were designed. They stated that EGR was deactivated at WOT, when other inputs indicated high engine loads, to prevent loss of power in high demand situations. It also mentioned that EGR was active in low load, low fueling, high airflow conditions, with medium to high engine rpm, where O2 to fuel ratio is higher, such as highway speed cruising or some deceleration events. Under full heavy engine load conditions such as WOT, they indicated that EGR was off because heavy fueling conditions decreased the air-fuel ratio and conditions were less optimal for NOx creation. If the CRD had EGR activated during WOT, high boost would be bled out the egr valve and into the exhaust pipe, setting a code and CEL/MIL for low boost, just as it does when the egr valve sticks open. This is one time when the laws of physics kept the enviro-twiddlers in check.

Whether that has changed since late 2004, I don't know. Another reason for EGR lockout at WOT might be high boost levels present. It would be difficult if not near impossible to get relatively low pressure EGR gas to flow into the intake plenum with 20-25 lbs of boost present, even with an AFC valve. If they were to close the AFC down during WOT/high boost conditions, it would cause excessive back pressure in the IC and turbo compressor and cause a severe loss of power, not to mention turbo compressor problems. If they drop turbo boost during WOT to achieve EGR flow, WOT might as well be limp mode. Certainly, during high loading encountered during towing/wot/high boost conditions, egr flow is going to be very, very difficult to achieve.

While I can no longer find that online Bosch document, I did find an old Chrysler description of WOT EGR lockout on a gasser here(http://www.dodgedaytona.nl/pdf%20files/egr%20system.pdf) so apparently WOT EGR lockout is somewhat present on both diesel and gassers for the same performance reasons.

I suspect that the early violent "lurching/bucking" behavior noted in February/March 2005, when accelerating to 60-65 mph, then letting off on the throttle was partly due to excessive activation of EGR flow, once cruise speed was attained, wot ceased and light engine load, high airflow(O2) conditions existed. I know I had several flashes which reduced this violent behavior.

With the SEGR cable, monitoring the EGR/AFC wire voltages/ground signals could be mapped to determine how much approximate EGR is being applied at light versus heavy loads. Idle situations where maximum O2 to fuel ratios exist are likely ideal air fuel ratios for NOx creation, but the burn temp info isn't available via OBD readings. In higher fuel states, the burn temp increases but the air to fuel ratio decreases.

Of course, none of this is a problem with an ORM or SEGR mod.

nescosmo · **Joined:** Sat Jul 14, 2007 11:17 pm **Posts:** 202

gmctd wrote:

EGR reduces available O2, reducing flame temperature - as to whether correct solution or not, that is the universally chosen method, noting the mass proliferation of EGR valves, these days

ECM cannot measure EGT without a thermocouple - however, combustion temperatures resulting from various fuel\air ratios at all operating condidtions are known and programmed into ECM for reference - ECM response is based on those matrices, much to our dismay - that's one advantage of the INMOTION tunes, where the matrices can be permanently altered for increased performance

The CRD with the egr came about when the egr is not worth a dime. I could care less for the egr if it work properlly and with no essue.
I have an 05 Dodge Sprinter with an egr and with it work fine with no essue, I do not even know that it exit.

gmctd · **Posted:** Mon Jan 05, 2009 10:37 pm

Good input, Ranger1, as was hoped for - this will require several readings to assimilate the data, but initially, I can see slight EGR at idle in cold ambients, where atmosphere in cylinder way in excess of that needed for combustion would allow slight ~295* EGR dilution as method of increasing IAT for warmup, but insertion at normal operating temps would seem to be problematical, even supposing it was being used as idle-speed regulation based on IAT - much easier to control idle speed under varying loads by comparing crankshaft angular position and velocity to alter individual cylinder fuelrate

FYI, nescosmo - the Dodge Sprinter is a Mercedes Benz 5cyl Diesel classified as medium-duty, not subject to the same operating emissions parameters as our lite-duty KJ 1500 passenger-series Diesel

Turbo Tim · **Posted:** Mon Jan 05, 2009 11:25 pm

If one wanted a better signal to monitor EGR functions, just obtain a SEGR module, and connect a “Test Wire” on the comparator inputs on the circuit that is fed “From CPU EGR Output,” measured to ground. This is a nice DC voltage to watch. The higher the voltage, the more EGR is being asked for by the computer.
(Back in the design days of this, I used a circuit that had LED’s that made a bar graph. The more bars, the higher the voltage.
Same for the AFC too. This is how I could visually watch the relationship between the two as I drove around.

You too could add this little visually cool circuit to impress your friends with.

nursecosmo · **Posted:** Mon Jan 05, 2009 11:38 pm

Ranger1; did you post that you do or do not see EGR operation during warm up? I sometimes can get EGR activation during warm up but usually not. There seems to be no rhyme or reason when it decides that it will or will not activate. I also get EGR for 90 seconds or so then it goes off but will come back on after about 90 more seconds without touching the accelerator. I have not monitored what it does during driving.

Ranger1 · **Joined:** Mon Oct 17, 2005 7:40 pm **Posts:** 1137

I do not see EGR operation during warm-up in cold ambient temps. The ECT temp generally reaches somewhere in the vicinity of 160* before I see any EGR activate signal. I've spent many hours monitoring the MAF/IAT values and have never seen the EGR reactivate without touching the accelerator after a 90 second off period. I'm wondering now if there are several variants of emissions code installed via different flash upgrades.

Quote:

If one wanted a better signal to monitor EGR functions, just obtain a SEGR module, and connect a “Test Wire” on the comparator inputs on the circuit that is fed “From CPU EGR Output,” measured to ground. This is a nice DC voltage to watch. The higher the voltage, the more EGR is being asked for by the computer.

Exactly! This is what I validated EGR operation with during non idle conditions where it wasn't possible to distinguish between MAF and EGR flow. What I don't know is how those values correlate to egr volume.

Uffe · **Posted:** Tue Jan 06, 2009 3:32 am

When will they make a NOx sensor dirt cheap, tug it in the diesels and apply EGR to suit? I mean, they already do that sort of thing on the gassers (lambda) for emissions and performance control.

As a control engineer, this is what I'd do - control the variable directly instead of using feed forwards of questionable nature.

If I had it my way (in my dreams and fantasies) I would put an EGT in there too, to reduce fuel before doing permanent damage to the engine.

...and I'd probably not be able to push that through, I think lots of automotive engineers already did try this thing and the pen pushers sacked the idea.

Oh what a great world - economy vs. engineering. I bet sometimes the economists want to push more savings through, but the engineers won't allow them to.

fastRob · **Posted:** Tue Jan 06, 2009 9:11 am

Just got back from Corning, NY and saw the 2 new catalytic converter plants. One for gass and one diesel.
You only need connections to get regulations passed that require massive investment in new plants and equipment.
Whala, jobs!
How silly you say?
GMCTD is not just a pretty face, he be smart too.
Political contributions make the difference. It is for the environment, even if it is not really, silly.

gmctd · **Posted:** Tue Jan 06, 2009 2:20 pm

I'm still perplexed at the supposed need for EGR at idle - pre-INMOTION monitored idle EGT's were ~250* at startup and in cool ambients and low ECT's, then ~295-325* after driving and ECT is normalized at operating conditions, indicating cool combustion temps - EGT's at 30-35mph were only ~425*, measured in the exhaust manifold, pre-turbine - iirc, NOX doesn't start forming until combustion chamber temps are over ~1500*, which would result in EGT's of ~1100* - wonder what Bosch was thinking - maybe it's the EGR at decel, where, as Ranger1 indicated, EGR began soon as he released the accel pedal at idle

Too cold and damp, at ~40*F, for me to start messin' around outside today, but I surely need to get back on this investigative stuff - I've got the INMOTION tune in the KJ, and a spare oem-tune ECM on the bench, just need to do the VIN and key swappo to do comparisons with Ranger1's input - plus, Turbo Tim's solid-state LED bar-graph addition to his SEGR module is a very good EGR-demand quick-check, and very easy to do

UFO · **Posted:** Tue Jan 06, 2009 2:52 pm

I'd be willing to bet EGR is not needed at many points in the operating curve, although it may be commanded by the ECM. Something having to do with covering your stupid?

mackruss · **Posted:** Tue Jan 06, 2009 3:18 pm

gmctd wrote:

Too cold and damp, at ~40*F, for me to start messin' around outside today, but I surely need to get back on this investigative stuff - I've got the INMOTION tune in the KJ, and a spare oem-tune ECM on the bench, just need to do the VIN and key swappo to do comparisons with Ranger1's input - plus, Turbo Tim's solid-state LED bar-graph addition to his SEGR module is a very good EGR-demand quick-check, and very easy to do

You're sure you don't want to part with that ECU knowing my current plight :wink:

Ranger1 · **Joined:** Mon Oct 17, 2005 7:40 pm **Posts:** 1137

I'm perplexed at the need for EGR at any engine speed. EGR defines the term 'reverse engineering' to a whole new level. Filter the air to micron range on the intake filter and then pump sooty exhaust back in on the backside.

nursecosmo · **Posted:** Tue Jan 06, 2009 4:23 pm

gmctd wrote:

I'm still perplexed at the supposed need for EGR at idle - pre-INMOTION monitored idle EGT's were ~250* at startup and in cool ambients and low ECT's, then ~295-325* after driving and ECT is normalized at operating conditions, indicating cool combustion temps - EGT's at 30-35mph were only ~425*, measured in the exhaust manifold, pre-turbine - iirc, NOX doesn't start forming until combustion chamber temps are over ~1500*, which would result in EGT's of ~1100* - wonder what Bosch was thinking - maybe it's the EGR at decel, where, as Ranger1 indicated, EGR began soon as he released the accel pedal at idle

Too cold and damp, at ~40*F, for me to start messin' around outside today, but I surely need to get back on this investigative stuff - I've got the INMOTION tune in the KJ, and a spare oem-tune ECM on the bench, just need to do the VIN and key swappo to do comparisons with Ranger1's input - plus, Turbo Tim's solid-state LED bar-graph addition to his SEGR module is a very good EGR-demand quick-check, and very easy to do

What should be remembered about combustion temp in a diesel engine is that it does not necessarily correlate with EGTs. Consider what happens with a single compression stroke. Assume that the ambient temperature is 80 degrees Fahrenheit, which is 299.666 kelvin or "absolute" degrees. compress those 300 degrees 17.5 times for rise of 5250 degrees. Now of course the compression temp in the cylinder does not even come close to that because as the temperature rises, much of it is lost through radiation and conduction into the cylinder walls and many of the gases in air have specific heat values which increase with compression which also absorb a large amount of the total available heat. The generally accepted temperature of the un-boosted compressed air in a diesel engine before the fuel is added to absorb more heat is ~1000F. It has to be that high because before the injected diesel mist can ignite, it absorbs a significant amount of additional heat which can drop the temperature several hundred more degrees to the point where the Diesel could be difficult to auto ignite, thus the need for glow plugs, grid heaters or Ether.

Now, once fuel is added to the hot air, combustion occurs which drives the temperature well over the 1500 degrees required to produce NOx (to get an idea of how high the temp of diesel combustion actually is, point an IR thermometer at a saucer of burning diesel). This all occurs at approximately TDC when compression is at max. As the piston moves down through it's stroke the pressure spike is decreased significantly and so is the temperature of the gases which were generated. About 30 percent of the heat generated by the flame is turned into mechanical energy and another 20-30 percent or so is lost into the engine through conduction and radiation. That leaves another 30 percent or so left to go into the turbo charger or out the tail pipe. However because of the high amount of CO2 and H2O created by combustion the actual amount of remaining heat in the exhaust is much less because both CO2 and especially H2O have a very high specific heat value.

So; the EGT is not an accurate indicator of cylinder combustion temps. The EGTs are usually but not always linearly correlated to actual peak combustion temperatures which would indicate that at full boost and fueling rates the combustion temperature could exceed 3000 degrees F, and it does. Every engine is unique but especially in some engines with small displacements and long crank throws, EGTs can be lower at high RPM medium load conditions than they are at idle because of higher air flow. The peak combustion temp however is higher than at idle. So why is maximum NOx not generated at high engine loads? Because temperature is not the only factor involved in NOx production.

The other two ingredients necessary for NOx creation during combustion are excess O2 and dwell time.

When the engine is at idle or low load conditions, there is an excess of O2 for complete combustion. This leads to high NOx production. But when the engine is under load, the ratio of O2 to fuel is much lower thus making the production of NOx more difficult.

The final factor for NOx production is Dwell time. NOx takes several milliseconds at high temperature and O2 levels in order to form. Max dwell time at these conditions naturally occurs at idle. At higher RPMs the dwell time under NOx generating conditions is insufficient for significant NOx production, thus little to no use of EGR at higher speeds.

The EGR valve is one of the dumbest creations of modern man (Coprophagia is the scientific term for it), but it does what it was intended to do, that being to reduce NOx. Whether or not NOx is as harmful to the environment as the EPA would like us to believe is a topic for another day.

UFO · **Posted:** Tue Jan 06, 2009 6:29 pm

Interesting stuff nursecosmo!

nescosmo · **Joined:** Sat Jul 14, 2007 11:17 pm **Posts:** 202

Then if that is the situation why they do not reduce the o2 at idle some how to reduce the nox. I think that the way to reduce nox in not by changing the temp on the combustion chanber but by changing the quimistry of the nox. Mercedes has the right approche with their bllue liquid.

nursecosmo · **Posted:** Wed Jan 07, 2009 3:29 am

nescosmo wrote:

Then if that is the situation why they do not reduce the o2 at idle some how to reduce the nox. I think that the way to reduce nox in not by changing the temp on the combustion chanber but by changing the quimistry of the nox. Mercedes has the right approche with their bllue liquid.

nes; I debated even responding to your post but got sucked in anyway.

How do you propose that the 21% of O2 present in the atmosphere be altered?

Both BlueTec and AdBlue piss injection add unnecessary complication to the exhaust system with the use of a very expensive catalytic converter as well as an even more expensive DPF. Of course the auto makers are not complaining about adding more gizmo's to their cars because for every dollar which is added to their production cost they add three dollars to the sale price because of the "Government Mandated" equipment.

The very same reduction in NOx is easily achieved through intake water injection, which incidentally also increases HP and fuel mileage. But neither the auto makers, the Government or the oil industry make money off of that.

Do you realize that the US tier 2 NOx restrictions are about 1/8th of what the EU allows and they have a vastly higher number of diesel "polluters" on the road. Are their Ozone levels higher than ours? Of course not, because NOx is a mostly harmless chemical.

BTW, please invest in a spell checker.

Uffe · **Posted:** Wed Jan 07, 2009 5:59 am

nursecosmo wrote:

The very same reduction in NOx is easily achieved through intake water injection, which incidentally also increases HP and fuel mileage. But neither the auto makers, the Government or the oil industry make money off of that.

Are you sure it can be done so simple?

Adding water injection requires additional injectors and pumps, right?

EGR - to be, or not to be, or et tu, brute

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