Thread: EGR kits,, do not buy!!!

this debate has opened up a whole new can of warms

so it is to stop the particulates from contaminating the intake charge (and subsequently the oil) and to remove the inlet restriction (butterfly) where the gas is fed into the inlet side of the engine.

My understanding is that in petrol engines when the engine is cold more fuel than that required for the stoichiometric ratio has to be pumped into the cylinders to ensure reliable ignition, that is why the O2 sensor has to be bypassed until the engine warms up. In diesels, is there a similar issue? glow plugs and very hot air due to compression would reduce this problem. Therefore I don't know that EGR is really to overcome problems when the engine is cold (not wormed up).

Originally Posted by slug_burner

this debate has opened up a whole new can of warms

....................the stoichiometric ratio has to be pumped into .

You're not kidding. I use phrases like this at 1:43 am, SWMBO just belts me and rolls over...........................

Deano

Originally Posted by slug_burner

... My understanding is that in petrol engines when the engine is cold more fuel than that required for the stoichiometric ratio has to be pumped into the cylinders to ensure reliable ignition, that is why the O2 sensor has to be bypassed until the engine warms up. In diesels, is there a similar issue? glow plugs and very hot air due to compression would reduce this problem. Therefore I don't know that EGR is really to overcome problems when the engine is cold (not wormed up).

Diesels run with much more air than the stoich... ratio.

I do know for some mechanical injection pumps, the governor goes to a maximum fuel position for starting, but when the engines starts, it goes to normal.

lets get this sorted.

EGR is done in both petrol and diesel engines for similar reasons in similar ways to pacify the greenies.

in a naturally aspirated petrol engine it mainly comes into effect under light throttle settings and overrun. Heres why.

when you're off the noise the throttle butterfly is closed and in theory so is the fuel supply. In reality whats happening is you're in a rich running situation with more fuel than air available so you wind up with unburnt fuel (and other nasties) heading for the exhaust. This is where EGR for petrols comes into play by opening up a port between the exhaust and the intake some of the gasses recirculate thus burning off some of the unburnt fuel(and other nasties)

A good enough reason in and of itself. but wait theres more and Im not talking a free set of steak knives and a stapler.

With the ERG open and exhaust gasses winding up back in the intake manifold the pressure in the intake manifold behind the throttle butterfly increases which does 2 things for you. First off it reduces pumping losses in the engine because theres now a lower pressure differential across the the engine so at light throttle settings less of the available power is used to draw air into the combustion chamber, Secondly (and which way this works depends on if you're talking carbies or injectors but its the same result at the end of the day) it slows the speed of the gasses in the intake manifold which in the case of a carbied engine means theres a "lesser" vacuum behind the butterfly so less fuel is drawn out of the main jet and in the case of an injected engine less air passing the air flow meter which means the injectors are turned way down on duty cycle so less fuel goes in. Oh as a bonus on the injected engines you have a higher manifold pressure so the fuel pressure regulator ups the pressure behind the injectors meaning A) the fuel that is going in is going to atomize better and therefore burn cleaner and when you do get round to opening the throttle you're going to get a nice dose of fuel from the get go to get things happening in a hurry.

Whatdya mean thats not enough, you still want more? Ok heres one last thing it does for ya.

IT makes the combustion process run cooler by displacing some of the fuel and some of the air(read oxygen) theres less stuff in the cylinder to burn which means less heat and a cooler running engine. This has long term advantages in terms of fuel efficiency, cylinder head/gasket life (especially on ally heads), valve life and your exhaust system.


Now I know that has bugger all to do with the TD5 cause its a diesel and its a turbo and and and... Thats just to give you the background of WHY we have EGR in the first place.

Now lets talk diesels.

A diesel engine at the end of the day is the same as a petrol engine fuel and air goes in exhaust, torque and heat come out. Same end result Very very different execution. With every variation on a theme comes its own set of problems each problem has its own solution and for once the same problem (emissions) once arrived at has the same solution (EGR).

With a petrol engine we use EGR to reduce the amount of unburnt stuff thats going out the exhaust in a diesel its the other way around when you're on a light throttle setting you have gobs of air (again read as O2) to burn but not much fuel, for those of you not familiar with the difference read on for those who are feel free to skip ahead a bit.

With a diesel every time the crank goes round the same amount of air gets drawn into the engine and spat out the exhaust, why? cause theres no throttle butterfly to vary the airflow and therefore the fuel/air mix ratio. Remember a petrol engine varies the total amount of air AND fuel thats in the combustion chamber keeping it, ideally, at a 14.7:1 ratio of Air/fuel by mass. (it cant so thats part of why we have EGR anyway) where as a diesel just changes the amount of fuel being injected into the combustion chamber. Which leaves us with the problem of lots of free air to be burnt, good for combustion and fuel economy bad for the production of oxides of nitrogen.

No, its not what you're probably thinking, Its not Nitrous Oxide that gets produced if It was I guarentee not one person would ever complain about EGR. We're talking about Oxides of Nitrogen which are far nastier to the environment and nowhere near as much fun to have in the engine.

Heres how it happens.

When youve got your diesel (turbo or not) humming along at full noise all things being as designed youve got nearly the perfect air fuel mix for diesel burning off producing a few hydrocarbon emissions (which get delt with by a catalitic converter) some nitrogen, water and lots of CO2 which is all good..

When you back off the situation changes and with less fuel but the same amount of air you wind up with lots of oxides of nitrogen and the easiest way to prevent that is to replace some of the air (21%O2 79%N) with something that not, say Exhaust gasses. The first benefit is that any unburnt gasses get another go round and the second is that you lower the oxygen and nitrogen content getting in in the first place which means lower output of nastie Noxies at the tail pipe.

Unlike the petrol engine the EGR on a diesel should only be passing gasses from the exhaust to the inlet under light throttle conditions when the potential for the production of nasties is highest. The fuel mapping that should be on a diesel (more accurately small turbo diesels) and the reasoning for having the EGR should lead to the EGR being closed off under all the following conditions, Over run and normal driving the reasonings simple.

Firstly If the engine is on over-run then the fuel rack or injector cycle should be at 0 because you dont need the engine running as its being pushed along by inertia, If the engine is being pushed along by inertia and its got no fuel theres no combustion process, if theres no combustion process your engines a compressor and you're making neither exhaust gasses or any oxides of nitrogen. If theres no exhaust gasses or oxides of nitrogen then A, you dont need EGR because the problem you're trying to solve is already solved and B, even if you did need it there's no point in having it because All you're recycling is air and why? Because on over-run a properly tuned diesel is just an aircompressor. Simple yeah.

Second situation is under power. Its a turbo diesel you put in x amount of air y amount of fuel and bingo perfect combustion. If you're making any boost then you have above atmospheric pressure to work with which means there is no reason to have anything other than perfect combustion happening in the pot come bang time. This leaves us with only one other throttle condition, A trailing throttle.

how often do you drive your small diesel on a trailing throttle?

on a trailing throttle you're in pretty much the opposite boat to a petrol engine more air than fuel with a lot more combustion temperature so you get a lot more oxides of nitrogen with very little additional heat (diesels combustion process is a lot hotter than petrols to begin with) and no unburnt fuel so you really only need the EGR to open up enough to replace the unrequired oxygen and nitrogen with something else

All good yeah, all simple and all benefits. Well yes, so long as its all working properly and designed properly in the first place.

First off Engine manufactures don't like putting this stuff in in the first place because it costs money look at the TD5 (if you have one) especially the EU3 version you've got an extra bit of casting on the exhaust manifold, a cooler, the valving, the control mechanism, more joints to make, more bits of piping and a partridge in a pear tree.... Compare it to someones TD5 whose pulled the lot off all you have is a bit of pipe, and a flange blanking plate. A lot simpler and a lot cheaper.

So why do it?

Because of the greenies.

now given that theres some benefits to be had and they can be had at no loss to performance theres no reason why we shouldnt appease the greenies. Well right up until something goes wrong.

when something goes wrong you wind up with an inefficient running engine that at best burns more fuel to do the same amount of work and at worst not only does the same amount of work burning more fuel but polluting more as well. That doesnt even take into account the increased long term wear rate on the engine which then leads to increased oil consumption. This is especially true of a diesel.

usually the first thing to go wrong is the recirculating valve sticks open or becomes sluggish which means that you wind up with spent combustion gasses getting into the combustion chamber when all you want is nice clean air and fuel. But thats not the worst bit, well not in my opinion anyway, the worst bit is that unless you do some very expensive filtering you will always be putting dirty air into the engine and this causes what I'd call premature wear.


Ok spieling done.

At the end of the day.

A correctly functioning EGR costs you nothing in terms of power nor performance especially in a turbo'd engine. Before you try the argument of "intake restriction" remember the turbocharger is forcing air past it and the MAP sensor is after the EGR valving. If the engine needs more air the turbo just pushes it in and the velocity of the air past the EGR valving increases to compensate for it. (no don't try the volume argument either if you think that way I'm going to get you to explain a carburettor to me).

What a correctly functioning EGR costs you ultimately is engine life.

When it starts to go wrong is when it starts to cost you power and performance. Honestly would you have even known that your engine even had an Exhaust Gas Recirculator on it if it hadn't gone wrong and started to cost you power/performance/fuel economy?

If your EGR is working right your only gain by bypassing it is engine longevity. If its not then you start to get some gains But they're not really gains because all you're doing is getting back to the original performance. Its a bit like saying "I fitted silicon intercooler hoses and it improved my engines performance". It might have but only because you took out an old worn out delaminating rubber hose that was restricting flow and replaced it. You'd have got the same effect by simply putting in a new rubber piece but you make a long term gain from only having to replace the hoses once as the silicone hoses last practically forever as opposed to the 3ish year life of the rubber ones.


Questions?

Originally Posted by Tombie2

Chipped TD5s with removed EGR still pass all MOT testing and would pass testing in AU on emissions too.

Yes, they WOULD pass the very limited MOT and AU emissions testing, BUT - car manufacturers have to comply with MUCH more stringent testing regimes, which have to be valid for the projected life of the engine, assuming proper servicing. If this were not so, they would certainly not spend money on EGR valves!

Removing a properly working EGR valve WILL increase the NOx emissions over some part of the normal working range of the engine, (in the case of the TD5, probably on trailing throttle.)

If you are happy about this, well and good, but personally, I have no desire to adversely affect the environment unnecessarily, so I won't be removing mine.

Your above statement is a little like drinking drivers who worry more about being caught, than the real point, which is the danger they cause themselves and other road users.

BTW, I'm NOT suggesting you drive when drunk!!!

Cheers,

Lionel

Originally Posted by Blknight.aus

lets get this sorted.
...... .... .... ...

Questions?

None that I can think of.

Originally Posted by Blknight.aus

on a trailing throttle

Questions?

OK I'll ask the dumb question. What's a trailing throttle ?

Deano

not a dumb question...

before I get to answering that it needs to be pointed out that round these parts the only dumb question is the one you think of but dont ask. Guaranteed theres no fewer that 5 other people who are thinking exactly the same thing but havent asked.

A trailing throttle is essentially a light throttle application in an over run condition.

Its order of applicability is (as far as this thread is concerned at any rate)

• Petrol engines
  
  • Carbied
  • Early injected
  • Modern injection
• Diesel engines
  
  • Naturally aspirated
  • Forced induction

the reason behind that applicability in this instance is the nature of the fuel delivery control systems ability to deal with Exhaust emissions in its own right. as mentioned in the diatribe the diesels governor in its own right if all things are perfect should take care of unwanted emissions.

an example of a trailing throttle is when you're coasting down a hill and rather than lifting your foot right the way off the accelerator pedal you maintain a little throttle application.

What it causes to happen (as applicable to diesels) is a combustion condition where there is more air than fuel and a lowered combustion temperature, this is because of a change in the conditions of the combustion chamber. Instead of the bang initiating, raising the temperature and the pressure thus forcing the piston down you wind up with the bang initiating and then burning on against a lowering pressure (and therefore temperature) resulting in raised nasties being produced. (A practical example of this is if you build a fire in a fan forced hearth then put some very green wood on the top. Once the green wood starts to burn remove it from the hearth and observe how much more smoke is made.)

on very very old school engines a trailing throttle was important as it prevented the antiquated carburetors from massively overfuelling the engines and causing fouling (carbon deposits forming, oil dilution, backfiring, excessive fuel consumption yada yada yada) when on extended downhill grades which could then take up to a couple of Ks to clear up if it cleared up at all.