Disconnect EGR valve ?.

[wemyss]

In commom with others on this site I have disconnected the tube which operates the EGR valve which gives continous clean air to the the combustion process on my TD.
Have just read this interesting comment on HJs Daily Telegraph agony column.

Quote:
In a different context, another reader explained why diesel turbochargers sometimes fail: "The Exhaust Gas Recirculation valve should open to allow carbon dioxide (which acts as a cooling gas) into the combustion chambers when the engine is under load (more than 30 per cent boost). This allows the combustion chamber temperature to drop and thus the temperature of the exhaust gases. If it sticks in the closed position the exhaust gas temperature will rise, causing the turbo bearings to fail and eventually allowing engine oil into the induction system. This can cause the engine to run on its crankcase oil until it is either stalled or goes bang. Problems with EGR valves are also often the cause of rough running when the valve is stuck in the open position as well. In several cases turbos have blown but the EGR valve has not been replaced. Inevitably the new turbo unit will not last long." The most common cause of the EGR valve sticking is dirty, sludged or otherwise contaminated engine oil.
Unquote:
Any comments on this as I had personally never heard of the cooling effect and thought that the EGR valve was purely used as an aid to cleaner emissions and reduced CO2.

wemyss

[E_T_V]

Absolute rubbish. Exhaust gases are REALLY hot and so increase the temperature of the gases in the combustion chambers. The EGR valve is only open at cruising revs and small throttle openings and so low/no boost situations. The exhaust gas temperatures at this point are relatively low anyway, (lots of excess air to dilute and cool the intake charge).

If the valve sticks open then you have a problem with high exhaust gas temperatures, poor performance and lots of smoke. If it sticks closed then the engine takes longer to warm up, produces more NOx emissions and may be less efficient (not usually the case for maestros and montegos).

[wemyss]

Dan, The lads on HJs site would generally agree with you.
You might be interested in having a look,
http://tinyurl.com/2zg79w

wemyss

[G Force]

Any comments on this as I had personally never heard of the cooling effect and thought that the EGR valve was purely used as an aid to cleaner emissions and reduced CO2.

wemyss

The main reason for manufacturers fitting EGR systems is that it reduces oxides of Nitrogen emmisions, these NOx emmisions form the basis for photo-chemical smog. NOx is only produced at very high combustion temperatures so to reduce combustion temperature exhaust gas is recirculated into the engine intake.

Although exhaust gas is hotter than intake air it still cools the combustion process because it is mostly CO2 and does not support combustion. The exhaust gas that is introduced effectively takes up the room in the cylinder that could be taken up by fresh intake air which includes oxygen which does support combustion.

I can see where the man is coming from when he talks about the turbo temperature running higher than normal with the EGR valve stuck closed, but when he talks of turbo failiure I would imagine that he is referring to more modern diesel turbos. Modern turbo diesels are using more sophisticated EGR systems which use a variety of different methods to introduce EGR at most running conditions including high load and rpm, to balance emmisions and power and drivability such as variable geometry turbos. In theory I can see that disconnecting the EGR on such engines could damage the turbo.

In the case of our reletively humble maestro montego turbo that does not employ EGR at high load and rpm the disconnecting of the EGR should not cause any such problems.

Gary:)