DPF / EGR Removal - Advantages / Disadvantages?

discombobulate

on doing a bit of research on the car i'm looking to buy at the moment i've seen a lot of people have talked of how they've increased mpg, bhp and reliability by having the DPF / EGR removed.

In the couple of forums I looked at I could only see positives to having it done but presume there are obviously side effects also as it was put there for a reason. I was wondering if anyone could explain the disadvantages to me. Thanks.

Plug

There are no side effects once the ECU is remapped and knows that there is no EGR valve or DPF. If its a new car it will effect warranty but if its under warranty in the first place you won't have to worry about it.

discombobulate

Plug wrote: »

There are no side effects once the ECU is remapped and knows that there is no EGR valve or DPF. If its a new car it will effect warranty but if its under warranty in the first place you won't have to worry about it.

And would it have any effect on emissions for an NCT test?

Plug

No it shouldn't unless they start bring out new regulations.

discombobulate

Plug wrote: »

No it shouldn't unless they start bring out new regulations.

Thanks for the info. Just need to find the car now!

Nissan doctor

The purpose of a properly functioning EGR is to cool the combustion chamber so while removing them, depending on the car, may seem to have no ill effects in the short term, the hight combustion chamber temperatures can lead to long term issues. If the car you buy has an EGR cooler, like some modern cars do, then the effect of removing it would be more pronounced.

discombobulate

Nissan doctor wrote: »

The purpose of a properly functioning EGR is to cool the combustion chamber so while removing them, depending on the car, may seem to have no ill effects in the short term, the hight combustion chamber temperatures can lead to long term issues. If the car you buy has an EGR cooler, like some modern cars do, then the effect of removing it would be more pronounced.

Yes it does have an EGR cooler. Are the DPF and EGR seperate i.e. can you remove the DPF but not the EGR?

dgt

discombobulate wrote: »

can you remove the DPF but not the EGR?

Yes you can

Nissan doctor

discombobulate wrote: »

Yes it does have an EGR cooler. Are the DPF and EGR seperate i.e. can you remove the DPF but not the EGR?

Yes they are two completely separate systems on any current car(won't be the case with Euro 6 compliant engines though). The DPF serves no function in the actual operation of the engine so once removed, and the ECU programmed not to throw a DPF fault after its removal, then the only side effects are a little more soot which would be almost invisible at low/mid revs on a modern common rail diesel anyway.

Plug

Nissan doctor wrote: »

The purpose of a properly functioning EGR is to cool the combustion chamber so while removing them, depending on the car, may seem to have no ill effects in the short term, the hight combustion chamber temperatures can lead to long term issues. If the car you buy has an EGR cooler, like some modern cars do, then the effect of removing it would be more pronounced.

The idea of an EGR cooler is to reduce Nox gases further iirc.

jackofalltrades

Removed the EGR on my Rover 75 diesel.
The engine is a lot more responsive in the 1500-2000 rpm range.
There was no noticeable effect on the cooling system after it's removal.
Haven't noted any significant change in MPG.

The EGR was fairly caked in sludge when I removed it. The air flow would have been restricted by it.

Also planning to remove the inter-cooler and air intake manifold to inspect them to see if they're covered in sludge as well.

discombobulate

As a side i'd presume the parts would then be ok to sell on after removal. Would they have much worth if from a newish car?

dgt

Nissan doctor wrote: »

The purpose of a properly functioning EGR is to cool the combustion chamber so while removing them, depending on the car, may seem to have no ill effects in the short term, the hight combustion chamber temperatures can lead to long term issues. If the car you buy has an EGR cooler, like some modern cars do, then the effect of removing it would be more pronounced.

Plug wrote: »

The idea of an EGR cooler is to reduce Nox gases further iirc.

I'm pretty sure it's both tbh

EGR really gives trouble when people don't look after them and become sooted, jamming open etc. It needs attention now and again!

Ronnie Beck

Is a cooler combustion not more of a side effect of EGR rather than the purpose. That's the way I look at it. It's taking up valuable space in the cylinder. A well built engine should be well able to cope.

jackofalltrades

Ronnie Beck wrote:

Is a cooler combustion not more of a side effect of EGR rather than the purpose.

That's exactly it. If it was essential for reducing combustion temperatures then it would work when the engine was under heavy loads. But it doesn't. It only works till about 60% load.

Nissan doctor

Plug wrote: »

The idea of an EGR cooler is to reduce Nox gases further iirc.

Yup, Higher combustion temperatures increase NOX output, so cooling the combustion chamber reduces them.

Ronnie Beck wrote: »

Is a cooler combustion not more of a side effect of EGR rather than the purpose. That's the way I look at it. It's taking up valuable space in the cylinder. A well built engine should be well able to cope.

Too hot a combustion temperature is as bad for components, economy and emissions as too cool. On modern, high power, diesels running very high fuel pressures and capable of higher RPM's, the EGR is essential to helping control the cylinder temperatures. Hence why coolers are now being fitted to further reduce the temperatures as the fuel pressures and power outputs increase.

Diesel engines running 2 EGR systems, both high(current system) and low pressure systems will be used on the coming generation of engines, both with coolers. The very latest Euro 6 Renault engines have this already.

jackofalltrades wrote: »

That's exactly it. If it was essential for reducing combustion temperatures then it would work when the engine was under heavy loads. But it doesn't. It only works till about 60% load.

Modern electronically controlled EGR's on diesel engines can operate over 100% of the load range, depending on engine temperatures and ambient temperature. The reason they often appear not to operate at higher RPM here is normally due to our climate. The intake air temperature is often low enough that at high RPM the rapid movement of low temperature air though the cylinders keeps the cylinder temps where they need to be for optimum efficiency.

Ronnie Beck

Nissan doctor wrote: »

Too hot a combustion temperature is as bad for components, economy and emissions as too cool. On modern, high power, diesels running very high fuel pressures and capable of higher RPM's, the EGR is essential to helping control the cylinder temperatures. Hence why coolers are now being fitted to further reduce the temperatures as the fuel pressures and power outputs increase.

Do peak's on temperatures advance the ignition to far or make it burn to quick? Why is too hot less efficient?

Nissan doctor

Ronnie Beck wrote: »

Do peak's on temperatures advance the ignition to far or make it burn to quick? Why is too hot less efficient?

There is no ignition timing on a diesel engine. There can only be injection timing which on modern engines is electronically controlled.

The reason that hotter combustion temperatures are less efficient is because of the NOx mentioned earlier. The creation of NOx also uses oxygen which can then not be burned with the fuel, so the combustion is incomplete, hence lower efficiency

On the very latest diesels the EGR also directly controls the air/fuel mix by working in conjunction with a lambda sensor. The sensor reads the oxygen level in the exhaust gasses, the ECU then uses the EGR to adjust the level of oxygen that enters the cylinder. More EGR = less oxygen in the cylinders, less EGR = more oxygen.

Ronnie Beck

You get an ignition lag between the start of injection and the start of combustion. There was also time between the start and end of combustion. EGR's by cooling the chamber increased the ignition lag and slowed the release of energy. Basically retarding the timing a bit. That's what I was getting at above. Never heard about the positive effects of an EGR before. I suppose fuel systems particularly the modern ones are designed with all this and more taken into account.

Nissan doctor

Ronnie Beck wrote: »

You get an ignition lag between the start of injection and the start of combustion. There was also time between the start and end of combustion. EGR's by cooling the chamber increased the ignition lag and slowed the release of energy. Basically retarding the timing a bit. That's what I was getting at above. Never heard about the positive effects of an EGR before. I suppose fuel systems particularly the modern ones are designed with all this and more taken into account.

On modern Diesels, and ones with piezo injectors even more so then solenoid injectors, the problem you describe is solved by the use of pilot injection during the combustion process.

To smooth out the ignition lag you mention, a small amount of fuel(pilot) is injected before TDC which begins to burn so that when the main injection(actually several injections within the one stroke)takes place, the mix is already up to temperature, reducing the lag or knock zone, meaning smoother running and better combustion.




This thread is getting nerdy:P