Does an egr help that much?

[COcyclist]

Originally Posted by Dieselman

Not quite correct. An open EGR valve reduces pumping losses due to the restriction caused by the throttle flap, without allowing any more oxygen into the cylinders.

We are talking about a gas (petrol) engine here right? as the diesel technically does not have a throttle plate because it does not need to operate at a specific air fuel ratio. Therefore both posts may be correct. EGR hurts mileage in some diesels but may help low load mpg in gasoline vehicles due to reduced pumping losses.

[oil pan 4]

EGR can help diesels get better FE by warming them up faster.
Once up to temperature EGR gets cut off.

[mwebb]

Originally Posted by oil pan 4

EGR can help diesels get better FE by warming them up faster.
Once up to temperature EGR gets cut off.

EGR reduces combustion pressure and
thereby reduces Combustion temperature

so
warm up time will NOT be reduced if EGR is used when cold
EGR could possibly be used to heat the incoming fuel air charge ....
a little bit . possibly to improve fuel atomization a little bit

heating intake air from drawing it across the exhaust manifold would do the same thing , better .

EGR does not get cut off when the system is at normal operating temperature because the primary reason there is EGR
is
to reduce
NOX emissions

[Piwoslaw]

+1
I'll add that according to my engine's technical manual, EGR is off until the engine reaches a certain temperature. This may be to reduce condensation of exhaust gases on the cold metal elements?

Originally Posted by oil pan 4

EGR can help diesels get better FE by warming them up faster.
Once up to temperature EGR gets cut off.

[serialk11r]

I believe part of the reason for that ^^^ would be to improve startup combustion stability. When the engine is started and cold the ECU retards the spark to increase exhaust gas temperature and warm the catalyst. EGR would cause misfires/torque fluctuation/etc.

As far as the coolant and block temperature goes, dunno.

[oil pan 4]

If I add my own EGR system it will do what ever I make it.
No way I am waisting time/money on a WAI that will reduce FE.
I could care less about NOx reduction.

EGR delete guys all report lower coolant temperatures.
This is for a diesel.

[jtbo]

You don't need to make full time WAI, you could make similar flap like old carburettor cars had, exhaust heated air came from pipe and fresh air from another, mechanical temperature sensing element adjusted flap so that there was constantly around +20C air going into intake manifold at cold weather.

One could do that so that he gets full heated air during warmup phase and then flap would change to fresh air?

I remember reading from some study that it was around X% (maybe 4%) increase in fuel consumption because of EGR, but I can't remember if that was diesel or petrol. In that study there were three methods compared, one being EGR, at least one other was injection of something which I can't recall by name, those other methods did not increase fuel consumption and were better at controlling emissions too. However because of my poor memory I can't now locate that document, can't even remember if I linked it here some thread.

It might be saved to my other computer as it can't show PDF documents unless I save them first, if I find it, I post it here, that might provide some interesting points again.

From my experience, when driving longer distances, if I disconnect EGR wires, it improves economy small amount, certainly under 5%, in my mechanical turbo diesel, which has catalyst installed. That I have tested with thousands of kilometers on and off, so I'm sure that it has effect. Another test would be to clean it up as it probably has not been cleaned for 300 000km, that might change things a bit, I guess.

[COcyclist]

Originally Posted by mwebb

EGR reduces combustion pressure and
thereby reduces Combustion temperature so warm up time will NOT be reduced if EGR is used when cold.

On the VW TDI is does help warm up times. The Exhaust Gas goes through a stainless steel EGR cooler which is tied into the coolant loop. As the exhaust gas is cooled it heats the coolant flow.

Originally Posted by mwebb

EGR does not get cut off when the system is at normal operating temperature because the primary reason there is EGR
is to reduce NOX emissions

Agreed. Unless it has been modified (tuned).

[oldbeaver]

Yes, I inhibited the EGR working by simply disconnect the vacuum pipe that makes it work. Last tank complete was without it and fuel yield was significantley lower.

You can see it in my fuel log.

Oldbeaver

[oil pan 4]

Was your coolant temperature lower on your diesel with no EGR?