role of EGR/EGR bypass

[pondweed]

doing a bit of research on the EGR, and whilst I was thinking that it was a pointless EU-officials-efficiency-improving figures device, I also note that the role of drawing in the exhaust gases is part of providing inert gases that keep temperatures down at cruising speed - i.e. CO2 just a bulking agent, if you like. (which thus also keeps the NOx down by keeping under a temperature threshold)

Any comments/thoughts on this, in relation to the EGR bypass on the diesel? I know it runs quite cool anyway, but are there hidden things we are going to miss....?

[Spanky]

I have removed/blocked EGR valves on various cars over the years and have never once had any negative side effects. If I was being critical, the time it takes for the car to heat up in winter could be one, but thats scraping the barrel a bit.

There are products for this for various cars manufactured by various companies and test over periods of time, if there were any issues by removing/blanking an EGR valve, it would be known.

All IMO.

[r44712]

The EGR valve has nothing to do with efficiency or reducing temperate, it is soley there as a means to re-circulate exhaust gasses back into the inlet manifold for subsequent re-burning, and to reduce emissions as a result.

I can remember when they first started fitting these to diesel Montegos in the mid-90's and it was well explained in the sales brochure of the time.

[Roverron]

Any temperature reducing effect is only going to be relevant at part throttle when the load on the engine is low.
On full throttle, the egr valve is closed anyway so there is no advantage from the point of view of reducing combustion temperaures when the engine is under heavy load.

Ergo, disqbling or removing the egr valve will not affect engine longevity.

Ron

[pondweed]

Originally Posted by r44712

The EGR valve has nothing to do with efficiency or reducing temperate, it is soley there as a means to re-circulate exhaust gasses back into the inlet manifold for subsequent re-burning, and to reduce emissions as a result.

All the threads are helpful - Rons most so (and, I should mention, I've paypalled for mine already!) but this was the quote I found on fordscorpio.co.uk, which gives a good explanation of the role of temperature reduction in the process! -

"Why would anyone want to dump exhaust back into the intake of a perfectly good engine?

Unfortunately, the internal combustion engine is not `perfectly good.' The modern multi-valve, high compression engine can create NOx (Nitrogen Oxides) during the high temperature combustion process. NOx reacts with sunlight to create atmospheric problems such as smog and so comes into the category of 'not a good idea'.

EGR is considered a `metered intake leak' and was developed to reduce the combustion temperatures to below 2,500 degrees, the threshold where NOx is created. Not unlike putting a brick in your lavatory to lower the volume of water used, the EGR valve meters a readily available inert gas (actually exhaust gas which contains a lot of very inert Carbon Dioxide) into the combustion chamber to effectively reduce the volume. Smaller effective displacement means less fire, and less heat and thus lower temperatures, thereby controlling NOx emissions.

Obviously we don't want to `reduce' the volume of the combustion chambers (effectively reduced engine displacement) during hard acceleration, so EGR is turned off when you need full power (WOT (Wide Open throttle) conditions). At idle, the engine is very sensitive to air/fuel mixture ratios and swirl in the combustion chamber, so introducing EGR at idle is not on either. However at cruise the Fuel/Air mixture is set as lean as possible for maximum economy and this in turn generates the highest temperatures, and so the EEC-V uses these conditions to inject exhaust gas into the inlet manifolds to reduce emissions. Older vehicles used vacuum devices to control the EGR valve whereas the Scorpio uses the EEC-V and it's sensors to control it.

If EGR is on during idle, stumble and even stalling will likely result. If EGR is on during hard acceleration, low power (from reduced air/fuel volume) is the result. At part load, lean mixtures for economy create high combustion chamber temperatures and without EGR, these conditions not only create Nox, they also foster pre-ignition and pinking."