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I've no idea when it comes to these things but always curious.
I've just had my 320d EGR replaced under a recall, during which they've also replaced the inlet manifold because it was damaged by the faulty EGR.
I'l love to know how all this works, is related and therefore got damaged. and how I might feel the difference when driving it home later 🙂 OK maybe forget the last bit.
Thanks!
NOx is formed at high temperature/pressure in the engine from excess O2 and N2.
N2 has a high ratio of specific heats, which means when you compress it, it gets much hotter than other gasses, the psychical chemistry behind this is simply that N2 is a very rigid molecule (diatomic with only a triple bond), which means any energy input to it appears as temperature rather than deforming that bond.
So it's not good if 80% of air is N2 because that both makes the engine hotter and produces more NOx.
The EGR solves this by diverting exhaust gas which has much more CO2 and Water back to the inlet manifold and therefore dilutes the N2. Which then lowers the temperature in the engine and reduces NOx emissions.
The downside of this in a diesel engine is the soot tends to coke up the inlet manifold.
Petrol engines didn't traditionally suffer from this as
a) didn't need an EGR as compression and therefore temperature is lower
b) the liquid petrol droplets from plenum / manifold injectors do a really good job of cleaning the manifold.
Later petrol engines can have the same issues as they are also going to direct injection like a diesel, and also have EGR's as emissions laws are tightened.
Generally you won't notice any performance change. The manifold coking up restricts airflow, but you won't notice until near wide open throttle and max boost from the turbo, if at all, forced induction is largely immune from intake restriction issues.
And the less scientific (and less accurate) version is that the dirty exhaust gas (the EG bit) get pumped back (Recirculated for the R bit) through the inlet manifold when the EGR valve is open. If the EGR valve malfunctions then the crappy exhaust gas can clog up the inlet manifold.
When you drive it home it will feel no different what so ever but you will be 7.32% smugger knowing your exhaust gas is killing fewer Easter Bunnies.
EGR Doesn't necessarily clog up the pipes with soot. But it can do, particularly if something else goes wrong which causes your engine to smoke more. If you have a DPF you wouldn't see the smoke but it could be being recirculated.
The one on the Passat had a thin film of soot on the inside after 150k or so.
Thanks all. Turns out that BMW give you a £100 and a bottle of engine oil for the inconvenience of a major recall, so my major service was less painful at the same time. Add that to finding my Thermos (see the Shito thread) I've had a good day.
You're right, the car didnt feel any different, just cleaner after the free valet. 🙂
Interestingly though I see the service interval has gone from the normal 15/20k miles to 13k. With that and the oil I'm suspicious of something, I've never had to top up the oil before.
If I understand this recall correctly it's an EGR <cooler> failure, with the recall being officially due to fire risk. BMW use a glycol based coolant so it's combustible, though in practice pretty damn hard to set on fire. But maybe exhaust conditions are enough, or it can evaporate just right, or something?
But either way shouldn't be anything to worry about once fixed.
A leaky cooler could in theory put a LOT of water into the intake and hydrolock a piston or more likely just drain the engine of coolant and cause overheating issues, but I think it's got to have been a pretty small leak- any amount of water in the intake is pretty obvious as it steams out the exhaist, don't arsk me how I knows, I just knows.
Had the same issue with a 2016 320d, it's a clear problem for them I guess.
I think the benefit is ledd about performance, and more that it doesn't self-combust on the hard shoulder
Turns out that BMW give you a £100 and a bottle of engine oil for the inconvenience of a major recall
I didn't get this the two times my bmw has had the egr valve replaced!
Did you buy yours new from BMW?
First time it started smoking out of the air vents and cost £3000 for new egr valve and all the stuff the egr broke as it broke.
Me "Does this car have any recalls?"
BMW service department "No"
1 month later....Letter through the door- this car needs a recall for egr valve!
BMW paid me back for most of the work.
Second time letter through the door "this car needs an (third) egr valve"
Me "what's different about this third egr valve"
BMW service department- clearly didn't know " fundamentally it's less likely to break".
Be happy if you have had it done before black smoke starts pouring out the exhaust and the air vents!
Not bitter about not getting to ride at fort William for half a week. No, no no!
The only difference I noticed after the third cooler was the car had been washed.
fundamentally it’s less likely to break
Thats what they told me today, together with the fact the new part effectively had a lifetime warranty due to the know issues. I couldn't get him to say "lifetime warranty" but he did say "if ever there was a problem, bring it and it'll be fixed". I bought the car from BMW yes as an ex demonstrator, I'm the only owner.
The only difference I noticed after the third cooler was the car had been washed.
Same, although I've just noted they haven't update the interval service history, grrrr...
<failed quote> tall_martin
Full Member
Me “what’s different about this third egr valve”
BMW service department- clearly didn’t know ” fundamentally it’s less likely to break”. </failed quote>
They couldn't meet demand for the updated replacements because of the sheer number of cars that got recalled, but they had new stock of the old one, so for a while they were fitting those as the failures are age related, a new "bad" one was as safe from failure as a new "good" one at least for a while. But everyone who got one of those was entitled to the redesigned one when it became available
My understanding of them was at WCA's level.
TINAS explanation kind of makes sense, but surely if the recirculated exhaust gases reduce the proportion of nitrogen by increasing the proportion of carbon dioxide and water then it is also reducing the proportion of oxygen at the same time? How does that help?
They couldn’t meet demand for the updated replacements because of the sheer number of cars that got recalled, but they had new stock of the old one, so for a while they were fitting those as the failures are age related, a new “bad” one was as safe from failure as a new “good” one at least for a while. But everyone who got one of those was entitled to the redesigned one when it became available
sigh, that’s interesting becuase they told me when I dropped it off that they didn’t have any in stock and if found faulty they’d order one on an emergency basis, might be a few days. When I picked the car up they’d “found the last one in Parts…”. So either I have a new old one, or they are spinning a line on availability to stop people demanding the new part is fitted immediately. 🤷♂️
[i]exhaust gases reduce the proportion of nitrogen by increasing the proportion of carbon dioxide and water then it is also reducing the proportion of oxygen at the same time? How does that help?[/i]
The computer knows and can adjust the mix while this is happening.
Did any of you BMW drivers get the 'indicator switch' fix recall notice?
😉
surely if the recirculated exhaust gases reduce the proportion of nitrogen by increasing the proportion of carbon dioxide and water then it is also reducing the proportion of oxygen at the same time?
In a diesel, or in a direct injection petrol engine, there is usually way more oxygen than is needed to burn the fuel. There's always a full cylinder's worth (at least), the injector just squirts in however much fuel you've asked for via the pedal. That burns in the air around the injector and the rest of the air in the cylinder just gets hotter and the nitrogen and oxygen in it react to form NOx. The only time you need all the air in there is when you are at full power. That's why you have an EGR valve - to vary the amount of exhaust gas that goes in according to the engine load. There won't be any EGR at full power, when it's cold or when you start it.
In a diesel, or in a direct injection petrol engine, there is usually way more oxygen than is needed to burn the fuel. There’s always a full cylinder’s worth (at least), the injector just squirts in however much fuel you’ve asked for via the pedal. That burns in the air around the injector and the rest of the air in the cylinder just gets hotter and the nitrogen and oxygen in it react to form NOx. The only time you need all the air in there is when you are at full power. That’s why you have an EGR valve – to vary the amount of exhaust gas that goes in according to the engine load. There won’t be any EGR at full power, when it’s cold or when you start it.
Not completely accurate...
A diesel is fuel quantity driven, whereas a petrol is fuel quality driven. As you rightly say, a diesel will generally have air far in excess of what is required for combustion - you just fill the cylinder up and then inject as much fuel as you need for the power you want. If EGR fills some of that air space in the cylinder then, unless the ratio of egr to air is REALLY high, you still inject the same amount of fuel as you still have more air than is required. At full load on a diesel you will still have an excess of air, but not much and so it can't really tolerate much EGR. Modern diesels run EGR as far up the load range as possible though.
In a petrol, you are always targeting lambda 1 which is 14.7 times more air than fuel. This is why you have a throttle for a gasoline as you limit the amount of air going in to the cylinder and then inject the correct quantity of fuel to match that amount of air. As you require more power you allow more e air in and so more fuel. As such a petrol engine power is governed more by the amount of air you can get in whereas on a diesel it is the quantity of fuel.
Whilst petrol engines produced NOx and can use EGR to reduce it, in reality NOx emissions are very small compared to a diesel. EGR is more used in petrols to aid fuel economy. As mentioned above, you use the throttle to limit the amount of air in the cylinder, but closing the throttle introduced large pumping losses which make the engine less efficient. Ideally you want to run the throttle as open as possible. So, if you can fill up some of the cylinder with I ert exhaust gas, you can open the throttle more and still have the same level of fresh air in the cylinder. As a side note, this was the same reason for the shift to smaller, turbocharged petrol engines - at low loads you have the throttle open much more and then use the turbo at high loads to provide the air you need. EGR is also used in petrols to lower combustion temperatures at high loads where you would normally inject more fuel to cool the exhaust gas - clearly this is a waste of fuel so much better to use EGR and run at lambda 1 at full load.
EGR is more used in petrols to aid fuel economy
Cool didn't know this.
As a side note, this was the same reason for the shift to smaller, turbocharged petrol engines – at low loads you have the throttle open much more and then use the turbo at high loads to provide the air you need.
Similar to hybrids, I think - run the throttle more open at low cruising speeds and slow the car down by applying load to charge the battery.