Some thoughts on the 2.2 C5 EGR SYSTEM (Long)

[cachaciero]

Something else I have just found:

There was an interesting article in Wikipedia some time ago regarding problems caused by EGR but it appears the article has been rewritten as below quoted information has been edited out:

EGR deletion in diesel engines is considered justifiable by a wide range of people, including the environmentally conscious. Although deleting the EGR system results in increased NOx level; hydrocarbon emissions, particulates, carbon monoxide and carbon dioxide are drastically reduced. Furthermore, EGR deletion results in an increase in fuel economy as high as 25%. Exhaust gas recirculated back into the cylinders adds wear-inducing contaminants and increases engine oil acidity, which can result in an inefficient, poorly running engine. The increased level of soot also creates the need for diesel particulate filters to prevent environmental contamination.

I would regard most of the above as true in most cases although the claimed 25% improvement in economy is probably over the top for most EGR systems without FAPsI wonder who deleted it and why?

cachaciero

[xmexclusive]

What does a MAF sensor actually measure?
If it just measures air pressure how about adding a short devider baffel plate in the pipe leading up to it. Plate to finish just past the sensor. Taper the plate slightly towards the sensor to increase the pressure it reads. Taper it the other way to reduce the reading.

John

[Deanxm]

MAF measures the flow of air rather than pressure, im sure the same sort of thing could be done by remapping the ecu to fuel at your desired ratio?????

D

[cachaciero]

The MAF actually measures air flow and air temperature so if you know the flow and you know the temperature the actual mass of the air going through the sensor into the engine can be calculated.
In a diesel engine there is no requirement to know the Mass flow for fueling, unlike a petrol engine. In a diesel fueling depends on throttle position and engine revs, as an aside the ECU turns throttle position and revs into a demanded torque value,.more demanded torque=more fuel less demanded torque = less fuel. The only function that I can see the MAF being used for in a diesel is control of the EGR and possibly an outer monitoring loop to compare mass flow into the engine against revs for failure detection purposes.

cachaciero

[CitTone]

Surely the ECU on a diesel balances supply and demand, though? If you give it more throttle, and thus demand more fuel, but the MAF reports there isn't enough air to burn that amount of fuel, will the response not be a reduction in the fuel input to ensure the mixture stays correct?

[Paul-R]

but the MAF reports there isn't enough air to burn that amount of fuel,

That would be a fault condition as there is ALWAYS more air than is needed.

There is no throttle valve to limit the air in a diesel engine - only in petrol engines.

[cachaciero]

Paul-R is basically correct.
The volume of a cylinder is a constant so IN A THEORETICALLY PERFECT ENGINE the cylinder charge mass of air will be a constant whether the engine is turning over at 1 RPM or 10000 RPM.
Given that the mass of air is known then the maximum amount of fuel that can be burnt is also known, when this fuel has burnt in theory the residual gas mixture in the cylinder will have no oxygen. Any amount of fuel less than the max limit will burn completely.
I would expect that the maximum possible amount of fuel would be a limit within the ECU model on an HDI engine. With modern electronics and calibrated injectors it is possible to very precisely meter the fuel injected.

If there is a failure of the injector such that too much fuel is injected the system has no way of knowing this as Andy (corsehf} can attest to.

Now something I have said in the second paragraph tends to suggest that something I said in my original discurs is not quite true


cachaciero

[corsehf]

I would expect that the maximum possible amount of fuel would be a limit within the ECU model on an HDI engine. With modern electronics and calibrated injectors it is possible to very precisely meter the fuel injected.

If there is a failure of the injector such that too much fuel is injected the system has no way of knowing this as Andy (corsehf} can attest to.

Now something I have said in the second paragraph tends to suggest that something I said in my original discurs is not quite true


cachaciero

Quite true, in fact i would have thought that the 'Anti-Pollution' lights would have thrown a wobbly but when the car failed - with a dead battery, an injector delivering 109% more fuel than was necessary and a piston that has quite a bit of it missing, i am quite surprised that i didn't get a single warning light on?
Stick a tiny hole in a vacuum pipe somewhere and the whole bloody car throws a wobbly and the dash lights up like a Christmas Tree with musical Bongs! to boot!!!!

[CitTone]

Paul-R is basically correct.
The volume of a cylinder is a constant
cachaciero

But the amount of oxygen available for combustion isn't, is it?

Air temperature and altitude (or barometric pressure) alter the density, with typical changes of about 9% by my calculations over the range of winter-to-summer temps and seafront-to-mountain-pass altitute limits in the UK.

As pollution control is demanding ever more delicate adjustments to injection, the closer to approach optimum burn, I find it hard to believe that the MAF (in combination with the MAP, to correct for the boost provided by the turbo) would not be providing data to contribute to this. 9%'s a big difference in combustion chemistry.

http://www.engineeringtoolbox.com/air-a ... d_195.html

Unless I've done some duff maths, that applies to EITHER temp OR altitude....what you get at 32degC and 800m ASL together, I wouldn't like to say, and on a good day in the Lake District, it could be possible.

Admittedly, when I've been there it's been perishing and pouring, but there you go.

Mind you, I think I'm just looking for a reason to believe that we aren't all paying for a bunch of pointless gubbins that (a) go wrong too often (b) don't do anything useful and (c) cost a shedload of money to fix!

[CitroJim]

Mid you, I think I'm just looking for a reason to believe that we aren't all paying for a bunch of pointless gubbins that (a) go wrong too often (b) don't do anything useful and (c) cost a shedload of money to fix!

I fear you may be looking for a very long time! As far as I can see the devices are indeed pointless, do go wrong frequently, do nothing of benefit and are almost beyond reasonable repair.

They're good only for maintaining built-in obsolescence and keeping the car manufacturers and their main dealers rolling in it...

Oh, and keeping a few politicians in their jobs formulating so-called emissions regulations...

[CitTone]

Air temperature and altitude (or barometric pressure) alter the density, with typical changes of about 9% by my calculations over the range of winter-to-summer temps and seafront-to-mountain-pass altitute limits in the UK.

Oh yes...and anybody know what the other weather conditions (wet-bulb temperature and changing barometric pressure at static altitude) do to all this?

[cachaciero]

But the amount of oxygen available for combustion isn't, is it?

As a proportion of the total Airmass yes.

Air temperature and altitude (or barometric pressure) alter the density, with typical changes of about 9% by my calculations over the range of winter-to-summer temps and seafront-to-mountain-pass altitute limits in the UK.

You are correct both temperature and pressure will alter the density of air but the Mass Flow sensor measures the temperature of the air and differences in ambient pressure will affect the flow through the sensor i.e assuming a constant -ve pressure on the "suck" side of the MAF the flow through it will vary with ambient pressure high ambient equates to higher flow lower ambient pressure lower flow.

As pollution control is demanding ever more delicate adjustments to injection, the closer to approach optimum burn, I find it hard to believe that the MAF (in combination with the MAP, to correct for the boost provided by the turbo) would not be providing data to contribute to this. 9%'s a big difference in combustion chemistry.

Ask yourself is there a MASS flow sensor on a traditional old style diesel engine system?. If not why would you need one on an HDI engine ?
The last of the old style injection systems got pretty good fuel metering with just a pump and springs.
Having said that although in an ideal engine air flow through the engine will be directly proportional to RPM in a real engine, valve and valve timing plus other things may upset this relationship so I concede that it may be possible that data from the MAF may be used as a correction factor for injected fuel but if so it will be a very minor correction term as the main control loop will be a software version of the old mechanical fuel pump / governor /accelerator posn setup.

Mind you, I think I'm just looking for a reason to believe that we aren't all paying for a bunch of pointless gubbins that (a) go wrong too often (b) don't do anything useful and (c) cost a shedload of money to fix!

As has been said I think you will have to look long and hard. The more I look at this the bigger crock of smelly stuff it becomes, if you didn't need a FAP before fitting the EGR system you do after because of the extra soot produced.
For my money if we have to limit Nox and I believe we do, then AdBlue set up makes far more sense, the engine runs more efficently at higher temps produces less soot and the clean up of Nox is done in the exhaust pipe as a separate exercise, the only disadvantage is extra space required for another tank and the cost of the liquid itself which is used I believe at a rate of 3 litres to every 100 litres of fuel burn at a cost of about 80P a litre. I hav'nt done the sums but at todays diesel cost I suspect that the cost of the additive could be re-couped by the reduction of diesel used due to improved combustion efficiency.

cachaciero

[CitroJim]

How does the AdBlue system work then?

I see many garages sell the stuff very freely in 5 litre cans...

[Sid_the_Squid]

If I'm reading the Wiki article correctly AdBlue is merely distilled water and p**s??
http://en.wikipedia.org/wiki/AdBlue

[CitroJim]

AdBlue is merely distilled water and p**s??

So it is!

Well, they're certainly taking it on these modern engines....

So basically, yet another cat with precious metals in it.

the Wiki article (onward from your link Sid) on Selective Catalytic Reduction (SCR) speaks well on how the system works chemically...

On the basis of the article that N2 is the end result along with water and CO2 then the grass verges should grow a treat and look very green as a result of all that N2 coming out of lorry exhausts...