Cooler EGR Charge

Has anyone done the math to calculate whether or not hot EGR gasses elevate the overall intake charge temperature? If so how much? How about a way to cool the EGR gas off somewhat, before it's introduced into the intake stream? Would there be a benefit to introducing cooler more dense EGR gasses into the intake? Thoughts?

The only reason to modify anything about the EGR system would be to save weight (by removing it), or if you're building a full blown race engine. The engine is designed and programmed to run perfectly with the EGR system as it is. If you tried screwing with the EGR "charge" temperature at all, you'd screw up the Fuel Trims and idle. The car would run funny as hell unless you knew what to change in the programming.

I "deleted" my EGR system once. I made sure the EGR was closed, and unplugged the valve. I then "turned off" EGR functions with my DHP. The car didn't run noticeably different at all. The only thing I did notice was that the car got hotter faster at idle...like stopping for a red light.

There really is no benefit to modifying the EGR system. Even if you did manage to cool the EGR "charge", how would you tune for it? The system is in place to help control NOx emissions. At WOT, the EGR is generally closed. Only under special circumstances would the EGR actually be open during WOT, given that emissions are way out of whack at that particular moment. If anything, just remove the whole system.....

Boy oh boy people really do not like EGR for some reason. Just leave it be. It's part of the whole package. It has a purpose. It works.

The only time you "need a cooler intake air temp" is at heavy/WOT. At those throttle levels, the EGR is closed anyway.

I realize the system only works while cruising and at part throttle. I'd like to continue using the system but, I think there could be some mid-range torque benefit from a cooler stream of the EG going into the intake stream.

ironclyde wrote:

I realize the system only works while cruising and at part throttle. I'd like to continue using the system but, I think there could be some mid-range torque benefit from a cooler stream of the EG going into the intake stream.

Run the EGR tube to a heat exchanger!

Seriously, a hotter combustion chamber makes for a more thorough burn. So you want it hot, within limits (which the EGR is). More efficiency = more power.

Unless you are building a track only car, just leave the EGR the way it is. It works so well you don't even notice it.

What makes you think there is more power available? More power comes from more fuel, which also means more air. So you open the throttle blade a little more, and you get more air and more gas, and more power.

Another point is that when it actually matters for performance, the EGR is closed, period. Trying to cool an EGR charge is a complete waste of energy, time, and money. If it were the other way around, if there were any benefit, you'd be able to buy an EGR Intercooler, and every Ricer in the country would own one and have it installed on their Civic.

  

Given how misunderstood the EGR system is, you and I should make an "Universal EGR heat exchanger" and start selling it. There's money to part with some fools out there.

So a hotter intake charge doesn't contribute to detonation?

ironclyde wrote:

So a hotter intake charge doesn't contribute to detonation?

You're completely missing the point dude. The Intake charge has nothing to do with EGR. The EGR is CLOSED during WOT, so what's the point of modifying anything on it? It's only open mostly during cruising speeds where RPM is constant.


Right from GM's mouth......

"The Exhaust Gas Recirculation (EGR) system is used to lower Oxides of Nitrogen (NOx) emission levels caused by high combustion temperature. It does this by decreasing combustion temperature."

"The main element of the system is the linear EGR valve. The EGR valve feeds small amounts of exhaust gas back into the combustion chamber. With the fuel/air mixture diluted by the exhaust gases, combustion temperatures are reduced."

"The linear EGR valve is designed to accurately supply EGR to an engine independent of intake manifold vacuum. The valve controls EGR flow from the exhaust to the intake manifold through an orifice with a PCM controlled pintle. During operation, the PCM controls pintle position by monitoring the pintle position feedback signal. The feedback signal can be monitored with a scan tool as ACTUAL EGR POS. ACTUAL EGR POS should always be near the commanded EGR position ( DESIRED EGR POS). The PCM uses information from the following sensors to control the pintle position:"

•Engine Coolant Temperature (ECT) sensor.
•Throttle Position (TP) sensor.
•Mass Air Flow (MAF).
The linear EGR valve is usually activated under the following conditions:

•Warm engine operation
•Above idle speed

"Too much EGR flow at idle, cruise, or cold operation may cause any of the following conditions to occur:"

•Engine stalls after cold start.
•Engine stalls during closed throttle conditions.
•Vehicle surges during cruise.
•Rough idle.
•DTC P0300 (misfire detected).

"Too little or no EGR flow may allow combustion temperatures to get too high. This could cause the following symptoms:"

•Spark knock (detonation).
•Engine overheating.
•Emission test failure.
•DTC P0401.
•Poor fuel economy.

Hmm. Well I'm having all three of these issues after warm-up, with no DTC and trying three different EGR valves...:

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•Engine stalls during closed throttle conditions.
•Vehicle surges during cruise.
•Rough idle.

Anyway, the last time I was under my hood, the exhaust was much hotter than the intake air. So, apart from some very strong endo-thermic chemical reaction, caused by the introduction of HOT exhaust into the theoretically cooler INTAKE stream, I'm not certain how any amount of HOT exhaust can COOL the intake stream simply because the GM propaganda states:

"The EGR valve feeds small amounts of exhaust gas back into the combustion chamber. With the fuel/air mixture diluted by the exhaust gases, combustion temperatures are reduced."

Moreover, the air charge temperature on a supercharged engine tends to run much hotter than on N/A engines. So, given the possibility that some massive endo-thermic reaction occurs from the addition of even a small amount of some very hot recirculated exhausts gas, is it not intuitive to conceptualize that cooling off the EGR stream would be beneficial, even at cruise, since the SC is still operative, dude?

Further, if the GM propaganda is really really actually factually true, then it could be surmised that given all of the possible environmental conditions (i.e. supercooling the EGR gases) could mean that there would be no need for any additional fuel, if the system could be closed loop?

It doesnt cool the intake stream, just the combustion temps. You cant reburn most EGR gases so it takes up some of the cylinder space so less energy is available and less potential to create heat and knock. Thats how it is able to increase efficiency at cruise. I think I understand your idea though. If you were able to introduce a colder egr charge, I agree it would help intake temps stay cooler but I think EGR relies on the high temps to make sure there is a complete burn. If the EGR temps are not high enough, it would likely hurt economy and you would be better off just shedding the EGR system altogether! EGR is a compromise that helps maintain most performance and increase MPG.

Now you're talking some sense. EGR wasn't even introduced until the 70's, so they could make up for the lower octane fuels and the elimination of lead from gasoline. You have some bad ass wheels btw.

What about putting an AC evaporator in the airbox? That wouldn't necessarily cool the EGR but, it might be a theoretical 30 degree or so drop in the intake airstream...

We can chase colder intake temps and minor gains all day, but is it worth it? We have a more limited aftermarket on our 95s so we need to get creative. You could set up a liquid to air intercooler in the airbox, and see what kind of a temperature drop you get with it.

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What about putting an AC evaporator in the airbox? That wouldn't necessarily cool the EGR but, it might be a theoretical 30 degree or so drop in the intake airstream...

This has come up before. An intercooler will work better, because you're cooling the air after it's supercharged. The air dumping from the blower into the LIM will pick up ~150ºF just from being compressed. THAT'S where you want the core to be. Compared to that superheated air, ambient air hitting the heat exchanger is ice cold, so no need to waste energy cooling it.

Cooler inlet air ought to be able to equal cooler compressed air on the outlet side of the SC. Though I would agree that putting an evaporator below the SC would be more efficient overall. The problem would be preventing back-pressure on the SC outlet.

With the extra weight, cost, and complexity of an intercooler system I doubt there would be any actual overall performance superiority over an AC cooled intake. I live in Arizona AC is not an option with leather seats. Also, a compressor will not have to work any harder to compress the refrigerant. The condenser might get hotter, depending on the location of the evaporator, though.

Can you find the thread where this has been covered before?

It was brought up a few years back. Maybe in the intercooler thread? Not sure.

A ZZP full-size IC core claims temp drops up to 160º. The heat exchanger has the effect of lining the manifold with dry ice relative to the superheated air. No AC pump can keep up with that. But you're right, every degree helps. That's why the custom FWI mod is so popular. I see between 10-20º drops depending on the weather and vehicle speed. Usually if I'm over 20 mph IAT is same as ambient.

Dropping the cooler intake charge gains you what, exactly? Are you concerned about WOT power or cruise efficiency?

The combustion temp is going to be whatever the combustion temp is, no matter if your intake air is 85 or 110 or 180 degrees on the way in - it's still going to be 1500 degrees inside (or whatever it is). By filling some of the combustion chamber that would otherwise be an empty vacuum with exhaust gas, the combustion temp is lowered a little bit because there is some air in there that won't burn (and some unburned gasses that will now get burned). That's all the EGR does. Yes, the intake air is hotter, but to the combustion it doesn't matter that much.

If you are concerned about WOT, an intercooler after the supercharger is the only thing that's going to make a difference.

Well apart from the normal laws of physics when mixing two masses of gas that have a higher and lower temperatures, a derived temperature is achieved that is not as high as the original high temperature and not as low as the low temperature. So, if the air charge is reduced say 20 degrees in the input side of the supercharger that should mean roughly a 20 degree drop on the output side of the SC. So, while the combustion temperature may remain the same, the combustion process might be delayed slightly, by a cooler intake charge, and perhaps thereby, some detonation might be reduced. On the other hand, a denser air/fuel charge would contain more calories...I dunno just sayin'. Anyway, I can build an airbox evaporator set up and my A/C is always on. So, I don't think I have that much to lose by trying.

Since when is a Factory Service Manual propaganda?

I certainly didn't read any misleading information there.....

deekster_caddy wrote:

Dropping the cooler intake charge gains you what, exactly? Are you concerned about WOT power or cruise efficiency?

The combustion temp is going to be whatever the combustion temp is, no matter if your intake air is 85 or 110 or 180 degrees on the way in - it's still going to be 1500 degrees inside (or whatever it is). By filling some of the combustion chamber that would otherwise be an empty vacuum with exhaust gas, the combustion temp is lowered a little bit because there is some air in there that won't burn (and some unburned gasses that will now get burned). That's all the EGR does. Yes, the intake air is hotter, but to the combustion it doesn't matter that much.

If you are concerned about WOT, an intercooler after the supercharger is the only thing that's going to make a difference.

so youre saying a FWI/cold air intake has no performance value?  We should just mount our filters right to the throttle bodies?

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so youre saying a FWI/cold air intake has no performance value? We should just mount our filters right to the throttle bodies?

Not that I agree, but there are people out there pushing this very idea with seemingly solid evidence to support. The important factor we need to consider is forced induction. Engines with turbos almost always get an intercooler. Engines with blowers always source fresh, ambient air. These are knock-fighting measures that can always be improved upon, especially when adding boost mods.

Cold air is good for N/A engines too, but in certain cases you can actually run a cone right off the TB without consequence. If the engine is big enough, air flow becomes priority over air temp. On turbo cars with IC, I can see how CAI might not make much difference, but for blown engines w/o IC, it becomes more important.

Cold air is always better. In my mind there is always too much underhood heat. The evidence for that is the 40 to 50 degree difference between the IAT and the MAF air temp. Today in Tucson it was a balmy 85 degrees. My IAT reflected that. However, the MAF was saying 130 degrees. So, I think a cone on the TB just above the hot ass cross over pipe is not the greatest way to get cooler air into the TB. I can only imagine what the air temp in the MAF would go to with a cone above the crossover.

Turbo diesels come with EGR coolers and they effectively lower intake and exhaust temperatures while still effectively reducing NOX emissions. One of my friends owns a tuned 2013 Duramax that runs high 12s in the 1/4 mile and he is deleting his EGR system. The coolers fail on these trucks between 50-100k miles and need to be replaced so they don't start leaking coolant into the engine. Deleting the cooler and not the EGR altogether can cause Exhaust temps that damage the turbos. Obviously, these guys are running 40lbs of boost on 6.6L engines so it's a completely different setup but lower EGTs would allow you to advance timing without knock most likely if the same result were available on the Riv.

I suspected as much. So, as I stated earlier, GM can produce propaganda. There's usually more to the facts than the theory.