EGR - Would anyone want it?

[The Speaker Guy]

Is there any advantage to adding an EGR system? Does it extend fuel economy? Does it reduce engine temperature?

Is it worth adding if modernizing to EFI and electronically controlled spark?

 

[xctasy]

I'll speak up right now and say it should be included for the sake of investment in emission reduction. Okay for me to say so 'cause we don't have mandatory emission controll in NZ. I run propane because I get better performance and less $$ per mile, and don't use any EGR.

EGR does wipe off open road fuel economy a little, but as a system, it does more good than bad. If you can included it, do so. Sure, it lookes ugly, but everythings designed around it, as a whole package.

If you are thorough enough for EFI, then adding all the systems from the donar vehicle is a lot of work. Leaving one system out may hurt the lean cruise cycle (closed loop), and cause some problems.

EGR and emissions gear is taken off because people just don't see the point in it. Some of it is expensive to replace, some ias no longer available, and some is better left out for performance or economy. In the early 70's, smog gear could loose 20% of usable power, and increase fuel consumption. From 1975 to 1985, things improved as the systems improved, but EGR gained extra systems to run it.

All I'll say is the emission engineers spent heaps getting it sorted, the latter the system, the better, and it should be used unless you've got a cast iron guarentee that your not breaking the law or you've got some other means of moping up photochemical smog.

 

[Asa]

i plan on keepin mine for the first couple reasons X mentioned, not for any emissions compatability, but because i want to "do my part"

In the early 70's, smog gear could loose 20% of usable power, and increase fuel consumption. From 1975 to 1985, things improved as the systems improved, but EGR gained extra systems to run it.

but i was wondering about the above, how much power do the newer systems rob? has there been any research done into modding the system so that they work correctly, but don't rob as much power?

 

[Anonymous]

The Ford '70s EGR systems mostly operated during 'venturi vacuum' throttle phase, which is approximately the RPM zone of 1200-3300 RPM under load. When the EFI computers got more sophisticated, they add EGR only under lightly-loaded conditions, like cruising and certain deceleration modes, cutting it off entirely during high acceleration and hard braking. (GM and Chrysler systems vary from this approach.)

EGR will reduce power when it's running, period. It does so by reducing the amount of oxygen available in the combustion charge, so as to reduce peak combustion temperatures (this lowers NOx production). Lowered temperatures=lower thrust against the piston crown, hence lower power. BUT - if the timing of the engine is altered (i.e., advanced) during the ingestion of the EGR, the power drop is not very noticeable - which is done in the modern multi-port EFI systems. The timing must back off when the EGR drops out or ping results - this is the computer's busy little task.

The older systems usually introduced too much EGR. I've had good luck with inserting smaller orifices into the EGR valve(s) to help the situation at high altitude, where I live. This reduces the power (and MPG) losses while still keeping the NOx emissions within legal limits. Some of the EGR valves I have obtained from NAPA parts come with these differing orifices in the box - you pick the one that matches your car. I used the one that fits the Buick 4-cylinder engine instead or the larger one, and accidentally made improvements. Then I went out to study the whole EGR thing so I could be (dangerously) informed about it all. I want to be legal, just not visiting the gas pumps so often..

By the way, some cars with catalytic converters require air pumps be used to add air into the converter. The reason? The EGR was too much under certain conditions, so the exhaust contained unburned fuel because it 'ran out' of oxygen before it was burned up in the cylinder. The converter then has to burn it off to reduce the hydrocarbons at the tailpipe. This inefficiency translates directly to lost power and lower MPG, because the burning is not happening in the cylinder.

But, it makes it pass emissions. :!: :arg:

 

[podboy3]

now i could be wrong but we would not be having this argument at all if Honda made the deal that was made up to Ford. i had a good article about honda from his humble beginings until his death and he had some great ideas for the automotive industry (all of which seem to be lost now).

funny that ford said no because a ford would never have a japanese engine or parts. i guess that worked out for him.

as for EGR providing a noticabledifferance in pollution i am not quite sure. i could of sworn that i read somewhere that all the good that is being done a little at a time is being wiped out everytime a shuttle is launched into space, i love the shuttle launches and what not so i am not complaining about them. i just am making the point that when all of our little actions are being wiped out by a larger sum that does not have to worry about such things like we do that we are doing just as much harm as good.

dan

 

[Anonymous]

EGR isn't reducing the amount of air getting into your motor. As it only works during part throttle, your foot is restricting the air that goes into the motor. The EGR just feeds the intake charge with inert exhaust gas, which lowers combustion temperatures, which lowers NOx. It also helps reduce pre-ignition (by keeping the chamber cooler).


-=Whittey=-

 

[Anonymous]

Execute
Who made that quote in the above "for DEATH awaits you all with big pointy teeth". It wasnt me as it is alledged. I do agree with the statement I just cant see its funny side or its real relevance to the Forum (except maybe for careless speed freeks who may like to meet it sooner).

Perhaps I am the only one who is not enlightened here?

Cheers Tim

 

[Asa]

heh
go pick up some old Monty Python man
never said it was you, that's a direct quote from Tim the Enchanter
MP & the Holy Grail

 

[Anonymous]

Whittey;
You're coorect in the comment that EGR doesn't reduce the air going into the engine. What it DOEs do is reduce the OXYGEN going into the engine, after the carb. The irony of these older systems is that the fuel charge didn't change, just the amount of oxygen. So, although the mix was still about 14:1, the depleted oxygen made it as bad as 11:1 in combustion terms. This necessitated the catalytic and air pumps into the exhaust manifold, so there would be enough oxygen to burn up the leftover hydrocarbons, since the chamber already used the little oxygen that was left after EGR was fed.

This is why the spark plugs have to be hotter, typically, 1 step hotter than the 1960s versions of the same engines: they run a little too rich in the EGR phase, so the plugs get dirty. At full throttle and idle, it cleans the plugs back up.

If the carb is accurately calibrated and the EGR is left in place, removing the cat oftens leaves emissions reading the same as if it were left in place!

 

[Anonymous]

Please tell me how adding exhaust gas after the intake restriction (throttle blades) is taking away oxygen?


-=Whittey=-

 

[Anonymous]

Think of it this way; if you have a gallon of air at 20% oxygen concentration, then add 25% of inert gas to the mix, letting the combined mix escape to become 1 gallon of mix, you will have:

.20-(.20*(.25*.25))=.1875, or 18.75% oxygen by volume left. This causes early termination of the combustion for lack of oxygen, relative to the fuel load that was mixed by velocity in the venturi, because the pressure drop across the venturi lowers after the EGR starts. This variability in the venturi speeds is what gives the engine it's drop in power when the EGR valve opens, which is usually noticeable unless the valve opens very slowly. Unfortunately, on late 70s versions of the Fairmont I6, the valve opens quite suddenly, being switched into a vacuum cannister by a WOT switch, used in reverse.

If you drive under ideal conditions, on flat, level roads with no acceleration or deceleration, the mix "flattens out" after a few seconds and the oxygen content rises close to normal (19.2%, say the experts, in a 20% environment). But, as soon as you decelerate, it goes momentarily rich, then lean. And as you accelerate, it goes lean (after the acel pump dries out), then the EGR pops open and the oxygen drops off, so leftover, unburned fuel ends up in the exhaust manifold. After settling back into 'steady mode', this balances out again.

Overall, the result is that the cat has to burn off the unburned fuel or it will end up as hydrocarbons in the exhaust. That's what the AIR systems do: add oxygen to the exhaust to burn fuel in the cat. All this unburned fuel is lost power and gas mileage.

Since documentation and experimentation from the period 1970-1988 show losses of 10%-22% in fuel mileage with the old-style emissions controls, it's easy to understand why America had such a fuel shortage during that period. Today we have more cars than ever, but the MPG is better, even on an SUV, than the average family sedan in the mid-to-late 1970s. We actually use less oil per capita now than we did back then.

 

[Anonymous]

Think of it this way; if you have a gallon of air at 20% oxygen concentration, then add 25% of inert gas to the mix, letting the combined mix escape to become 1 gallon of mix, you will have: .20-(.20*(.25*.25))=.1875, or 18.75% oxygen by volume left.

That's all well and good, but you're not letting extra escape. You still have the same amount of oxygen , but you also have more of other gasses as well.

This causes early termination of the combustion for lack of oxygen, relative to the fuel load that was mixed by velocity in the venturi, because the pressure drop across the venturi lowers after the EGR starts. This variability in the venturi speeds is what gives the engine it's drop in power when the EGR valve opens.

Two things:
1) Combustion doesn't stop because of lack of oxygen. When the proper amount of air and fuel are in close enough contact with one another, with proper heat, they will ignite. Only those 14.7 oxygen and 1 fuel molecules will burn together. That air/fuel group will burn just like normal regardless of it's surroundings.

2) Any variability in the carb causes mix variability. EGR should come on off idle (any effects can be tuned out with the carb at that point) and turn off at WOT.


-=Whittey=-

 

[Anonymous]

I think what MarkP is saying is that after everything is said and done, the percentage of oxygen in the mix is less than when it began. If I had a half gallon of orange juice and poured it into a glass, it would be 100% oj. If i pour a half gallon of apple juice in with the half gallon of orange juice, and pour it into the same glass, you get 50% oj and 50% apple juice. There is still a half gallon of orange juice, that didn't change. But when it is pured into the glass, there is less in the glass. The EGR allows exhaust into the air charge. This will not change the absolute amount of oxygen, but will change the percentage of oxygen relative to all other gasses. The cylinders will draw in a certain amount of air each intake, and each of them sees less oxygen because the exhaust "thinned out" the mix.

 

[Anonymous]

That's exactly what I am saying is wrong. When you're at part throttle, you're drawing in less air/fuel than at WOT. That is the problem with your analogy. To fix it you'd have to say:

You have a 5 liter jug. You have 1 liter of air in it. Now add 0.1 liters of exhaust to it. How much oxygen do you have?


-=Whittey=-

 

[Anonymous]

Exactly the same amount, however, you now have a smaller percentage of it. Let's say air is 20% oxygen 80% nitrogen by volume, that way the math is simple. You have a given amount, say 1 liter. That gives us .2 liters oxygen and .8 liters nitrogen. Add 10% inert gas. You now have 18% oxygen 72% nitrogen 10% inert gas and 1.1 liters, .2 liters oxygen, .8 liters nitrogen, and .1 liters inert gas. As far as absolute amount, you have the same. The relative amount has changed. The EGR adds volume the the air charge. The "container" in our engines is the intake manifold, not the cylinders. If you change the rotio of gasses in the intake, The cylinders will draw in gas according to that ratio. Of course, the fuel will be "thinned out" by the same ratio that the air is, so fuel air ratio is (theoreticaly) 14.7 to 1. However, with more inert gasses in the cylinder, the combustion is slower and less efficent. That is why computer controlled engines advance when using the EGR.

 

[Anonymous]

Slantsickness's analogy is certainly easier to understand than my engineer-bred math approach. It also makes me want to mix OJ and Jose' Cuervo for breakfast!

Whittey, even at part throttle, the mix physics remain the same. The purpose of EGR is to dilute the amount of oxygen available in the charge that enters the chamber during the intake stroke. At peak EGR introduction, 7% EGR by volume, the charge in the chamber becomes 92% fresh mix (of which 6.8% is fuel by volume) + 7% burned-out air. This means that the total oxygen available for combustion inside the chamber is 7% less than that required for complete combustion, leaving behind 0.48% unburned fuel by volume. Since the fuel burned up the 18+% of oxygen until the oxygen ran out, the fuel will be left unburned.
No oxygen = no further combustion (firefighting also teaches this: to stop gasoline fires, halon is spread across the top of it. This blocks oxygen from reaching the gas, and the fire instantly stops. It's impressive to watch!).
The only fuels that will combust in the absence of oxygen are called 'hypergolic' fuels. Rockets use these, as do some electric turbines. These fuels combust by eating one another very rapidly, like a slow explosion, creating solid materials and a few spurious gases as a result.

 

[Anonymous]

so is there any way to change the ratio without using the EGR cause ive seen plenty of custom and stock intake without any EGR, and to pass air care they have to be compensating somehow, right?

 

[Anonymous]

Trueslayer;
As far as the 'tailpipe sniff' test is concerned, the EGR system typically doesn't even get tested! Truth is, if your catalytic is working good and your spark advance (static setting) is close to where the underhood sticker states it should be, the typically-tested items like CO and Hydrocarbons will be fine.

The EGR really helps lower combustion temperatures to reduce oxides of nitrogen, called NOx emissions. These are responsible for photochemical reaction smog in geographical areas where air inversions trap the pollutants over the metro areas. Denver, CO, Salt Lake City, UT and Los Angeles, CA are 3 strong bad examples of this phenomenon. Although reducing it is the goal of EGR, the use of EGR causes loss of HP and MPG. Oddly enough, the catalytic had to become reality to control the extra bursts of hydrocarbons that EGR can produce on sudden acceleration and deceleration! I have never seen an emissions test for pre-1990 cars that included the NOx test, but some areas require the equipment be present and functional under the hood - although I've also never heard of anyone actually looking to see if it worked. I got busted for it being missing when I bought my car - the previous owner took it off. Cost over $200 to put it back on. I only paid $500 for the car!

If you live in a flat geography, like Kansas, USA, and are willing to spend the time fine-tuning it with water injection, theory says that the EGR-water combination can actually INCREASE fuel economy by increasing the compression ration while cooling the engine. It has been successfully done on several dual-boosted industrial engines I worked with, big 1500 cu. in., supercharged AND turbocharged (both at once!) engines on electrical generator systems. We got about 9% better fuel consumption. BUT - that is a very steady-state environment. Those engines run at only 2 speeds: idle or 1800 RPM, period. It wasn't too hard to control the EGR-water mix in that situation.

With the normal driving situation, all EGR does for you is keep you within the law or your conscience, if you 'think green'.

 

[Anonymous]

It's alright MarkP, being in the machine tool industry, I spend alot of time turning engineer gibberish into understandable speach.

 

[Anonymous]

thanks for the info MarkP. up here it BC they dont even look under the hood anymore so i dont have to worry about them finding a missing part, all i have to do is make sure my engine runs fairly clean. Air Care up here still checks under the car though so i wont pass without a cat. So what i'm understanding is that i can take of my EGR, put in a good cat and tune my carb and adjust my timing for good economy, and i might even notice some sort of power increase?