EGR - Anybody here mechanical minded?

lee678

Notmyrealname wrote: »

You should. All they are there for is to reduce emissions by recirculating exhaust gases back through the engine. They serve absolutely no other purpose. They don't improve performance or fuel economy.

At the risk of repeating myself the result of blanking off the egr will be much higher combustion chamber temperatures. This will a) stress the valves and seats much more, and b) cause pinking, which the ECU will deal with by retarding the ignition, so the engine will not be working at it's optimum designed parameters. You probably won't notice this until a valve burns out, a piston or spark plug melts or you get overheating problems. in fairness the problems are less prevalent in a diesel engine as the running temperatures are quite a bit lower to start with, the engine internals are tougher, and by definition they don't suffer from pinking, so removal is much more risky in a petrol engine, in my garage if asked to blank off a egr the answer if you cant afford a new egr then you shouldnt be running a car, imagine the scenario if a plug melts and they come back "well you blocked the valve" ! its not all about performance and economy and a lot of you need to recognize that fact .

Joe_Horner

Notmyrealname wrote: »

You should. All they are there for is to reduce emissions by recirculating exhaust gases back through the engine. They serve absolutely no other purpose. They don't improve performance or fuel economy.

It really isn't that simple anymore. It can't increase power but it can (and generally does nowadays) improve economy.

In the early days it was only there to reduced NOx emissions but those very clever people in their very expensive labs soon found that it can also boost economy. How it does so is quite complicated but well proven and well understood.

Part of the improvement is it effectively gives you a smaller engine capacity at low load by filling some of the cylinder with inert gas. That makes you use a wider throttle, which reduces pumping losses and improves economy. Part is because it slows combustion, allowing greater ignition advance to be used without knock occurring.

Just about any new-ish car will have it's ECU programmed to take advantage of these factors and disabling it will leave the engine maps less than optimum.

There's also the question of material specs for valves, pistons and so on, which are designed by the manufacturer to be adequate for the designed running conditions of the engine. Because EGR substantially reduces combustion temperatures, especially at part-throttle where most engines spend most of their time, that allows the manufacturer to specify lower grade (and cheaper) alloys than they would without it.

That doesn't mean the engine will explode if you blank it, but the higher temperatures will reduce the life of components and might cause catastrophic failure.

Like anything other deviation from the designed spec, you pays yer money and takes yer chance.



eta: As for "lots of people have done it and found better power / economy" - over the years, lots of people have fitted over-priced magnets to their fuel lines to "align the (completely non-magnetic) molecules", "Browns gas converters" to split water into H2 and O2 then combibne it again in some magically >100% efficient reaction, and all sorts of other "performance improvers".

And they almost all swear blind that these snake-oil contraptions actually worked

Apples2

lee678 wrote: »

At the risk of repeating myself the result of blanking off the egr will be much higher combustion chamber temperatures.

Repeat again if you will.

An EGR pushes the hot exhaust gasses back into the inlet to be re-combusted.

Withouth the EGR, fresh air enters, gets combusted and disappears out the exhaust.

Why is it hotter without the EGR?

Joe_Horner

Apples2 wrote: »

Repeat again if you will.

An EGR pushes the hot exhaust gasses back into the inlet to be re-combusted.

Withouth the EGR, fresh air enters, gets combusted and disappears out the exhaust.

Why is it hotter without the EGR?

Because of two factors.

The (hot but much cooler than burning petrol) exhaust gas takes the place of a certain amount of the mixture. That means that less fuel is burnt on each combustion stroke, so the combustion temperature is lower.

Also, the charge burns more slowly with EGR, so the heat that IS produced has more time to be dissipated into the cooling system through the cylinder walls, again reducing the temperature in the cylinder (and greatly reducing exhaust valve temperature as a result)

jaydeeuk1

But if the the valves and cylinder walls were made of the same material from previous gen diesel engines that didn't have EGR's (quite likely imo - why change a component that works), they therefore would haven been designed to work at these temperatures anyway?

colino

The egr valve wasn't added to any engine to make it any more efficient, economical or "better" in any way. It is a crude device to reduce emissions to get under arbitrarily invented limits. It works on two levels, re-burning off the exhaust emissions and strangling the efficacy of the engine.
This can be equated to California "leading the way" in reducing airborne pollution in the 70's by bolting catalytic converters to very inefficient V8 gas guzzlers to protect the US motor industry, causing Honda and the like to all but give up their progress on lean burn technology. Now we all have cats and engine development was set back decades.

By all means disconnect them as your car will run better, but once they've stopped dithering about the MOT changes, if your eml is on, it might fail.

Notmyrealname

lee678 wrote: »

At the risk of repeating myself the result of blanking off the egr will be much higher combustion chamber temperatures.

How? The air/fuel mixture would not be weakened which is what would need to happen to increase the combustion chamber temperatures.

Part of the improvement is it effectively gives you a smaller engine capacity at low load by filling some of the cylinder with inert gas.

No it doesn't.

That makes you use a wider throttle, which reduces pumping losses and improves economy.

No it doesn't. Wider throttle on a petrol means more air intake into the engine which means more fuel has to be added to maintain the air/fuel mixture required.

Part is because it slows combustion, allowing greater ignition advance to be used without knock occurring.

No it doesn't.

You seriously don't have the first clue what you're on about. But thank you for demonstrating how looking at the results from Google for a technical subject when you haven't got a clue about it usually results in epic fail.

lee678

i think you should go top up your su, and put a drop on the felt that lubes the cam that opens your points, seems about your knowledge,seen the latest engine that you can sit on a piece of a4 paper ? go block your egr up, its not my engine your stressing .

atrixblue.-MFR-.

EGR feeds lower oxy gasses not high temp no2 gasses wich makes combustion less efficient inturn makes for less MPG by feeding a extremely small portion of the pre combustion mixture ratio removing the EGR will not affect ignition timing, the EGR valve on a diesel is primarily to reduce NO2 OUTPUT for EU regs. however, the EGR will increase soot output, can produce a tar like residue on valves and valve seats, decrease the life of a cat converter (excess acidic soot) decrease the life expectancy of a diesel unit due to contaminants from the EGR valve.

by removing the EGR you get a better combustion, wich will better your MPG and throttle response, less production of soot and contaminants such as acidic oil deposits and abrasive soot contaminating valveseats DPF amd cat converters, so you effectivly prolong your engine life.

EGR's reduce performace and reduce econemy and longetivity.

coupled with under tuning with ECU, low blo turbo with bigger intercooler, manifold flaps and a EGR, DPF cat conveter you arrive with a lower throughput of NO2 for EU regs.

Joe_Horner

Notmyrealname wrote: »

How? The air/fuel mixture would not be weakened which is what would need to happen to increase the combustion chamber temperatures.

No, burning more fuel will also increase chamber temperatures. I suspect you're getting confused between flame temp and chamber temp.

Flame temp depends mostly on AFR, chamber temp depends on the quantity of heat produced during combustion (which depends on the quantity of fuel burnt) and how quickly the cooling system can remove it. So aspirating and burning more fuel (by NOT having part of the chamber filled with exhaust) will increase the chamber (though not the flame) temperature.

Don't worry, it's a common mistake amongst the amateur tuning brigade

Notmyrealname wrote: »

No it doesn't.

Yes it does. If you have a cylinder capacity of, say 400cc on a 4 cyl 1600, and you recirculate 100cc of exhaust gas then, in simplistic terms, there is only 300cc available to be filled with air and fuel on each induction stroke. Smaller capacity.

Notmyrealname wrote: »

No it doesn't. Wider throttle on a petrol means more air intake into the engine which means more fuel has to be added to maintain the air/fuel mixture required.

Another common novice misconception. That only applies all other things being equal. But, as I explained above, by recirculating exhaust, even on full throttle, there is less capacity available to be filled.

So an engine at a certain throttle opening will consume LESS air an fuel with EGR. That means you have to open the throttle further in order to restore the same amount of air and fuel. So you end up with the same fuel and air consumption, but with the throttle plate wider open.

Basic thermodynamics says that an open throttle is more efficient than a close one because it reduces the pumping losses of the engine. It's the same reason people spend lots and lots of money having heads ported and flowed - less restrictive = better.

Notmyrealname wrote: »

No it doesn't.

Yes it does.

EGR slows combustion and reduces chamber temperatures, both of which reduce the likelihood of detonation. Most cars now employ knock sensors to dynamically adjust timing and having the engine less likely to knock allows the ECU to advance timing further than it would with a hot chamber and fast burn before the sensor stops it.

Notmyrealname wrote: »

You seriously don't have the first clue what you're on about. But thank you for demonstrating how looking at the results from Google for a technical subject when you haven't got a clue about it usually results in epic fail.

That really doesn't deserve a reply - the amateur errors in your understanding are fair enough, everyone has to start somewhere, but the misguided attempt at summing up my knowledge of engines and combustion processes is just laughable