Adjusting driving style to avoid clogging inlet and EGR?

[peterposh]

The  DPF has a finite life so will block up sooner or later  , If you're getting 55 mpg you're obviously not giving the car stick. Long  motorway journeys at 73 mph on the speedo = 70 mph seems to do my car good , engine is at optimum temperature , DPF and EGR will be red hot and burn off most  deposits

[WesBrooks]

12 minutes ago, peterposh said:

The  DPF has a finite life so will block up sooner or later  , If you're getting 55 mpg you're obviously not giving the car stick. Long  motorway journeys at 73 mph on the speedo = 70 mph seems to do my car good , engine is at optimum temperature , DPF and EGR will be red hot and burn off most  deposits

 

I mentioned the 55mpg as what I was getting in my first post. I also said I swapped from GPS 65 to 70 as there were issues, the cause of which couldn't be identified. I'm aware of the difference between speedo and GPS, and as it happens so is the car! Plug in a OBD2 device and the speed that reports will be far closer to the real speed. The difference is introduced by the manufacturer to ensure there is minimal chance of a speedo under reading. It's a result of the way teh Construction and Use requirements are worded and you end up needing todo a very similar thing with kitcars when you try to get them through the IVA, or spend a lot of time calibrating.

 

Anyway when your journey involves long stretches of motorway and 50mph road there is only so much stick you can give it without being a real hindrance to other traffic by yo-yoing your speed.

[WesBrooks]

12 hours ago, chimaera said:

The engine's idle speed will increase to around 950 rpm during regen and you might notice the gear suggestions being lower than usual e.g. 5th when it might normally suggest 6th. Otherwise there's no telltale.

 

I've not noticed it, but guess this could be that it has plenty of chance to do it while I'm on the motorway, or simply because it is a motorway mile muncher the DPF hasn't suffered too bad. No gear change indicator in my car but happy without that.

[jafo]

12 hours ago, chimaera said:

The engine's idle speed will increase to around 950 rpm during regen and you might notice the gear suggestions being lower than usual e.g. 5th when it might normally suggest 6th. Otherwise there's no telltale.

Smell of burn rubber most noticeable when unloading shoppings from the boot

[essexalan]

So as I understand it the EGR recirculates exhaust gases via a cooler system back in to the combustion chamber, purpose to cool down the combustion temperature. I fail to understand how these cooled exhaust gases can be be anywhere near as low as the temperature of the clean air being delivered via a normal intake system. If it's real purpose is to allow the engine to have another go at burning unburnt fuel present in the exhaust gas at certain throttle openings then that would make more sense. Whatever such a device must mean the car takes a performance hit IMO but I am not an expert.

[WesBrooks]

There is loads more info here than I can relay in a form:

 

https://en.wikipedia.org/wiki/Exhaust_gas_recirculation

 

...but in essence it is not there to improve performance, rather to reduce cylinder combustion temperatures to reduce the production of oxides of nitrogen. Nitrogen is largely inert, but if you get it hot enough it will react with oxygen. I guess the exhaust gas is largely inert, or at least is far more inert than a fuel-air mix and so when some of the mass of gasses in the cylinder is exhaust gas then this reduces the total amount of energy that can be released in a combustion event, and hence lowers the ultimate combustion temps.

[chimaera]

52 minutes ago, essexalan said:

So as I understand it the EGR recirculates exhaust gases via a cooler system back in to the combustion chamber, purpose to cool down the combustion temperature. I fail to understand how these cooled exhaust gases can be be anywhere near as low as the temperature of the clean air being delivered via a normal intake system. If it's real purpose is to allow the engine to have another go at burning unburnt fuel present in the exhaust gas at certain throttle openings then that would make more sense. Whatever such a device must mean the car takes a performance hit IMO but I am not an expert.

It's not cooling the intake air - it's going to be quite a bit hotter than it even after going through the cooler.

 

Diesel engines have very low levels of unburned fuel compared to petrol engines since they always run lean.

 

What EGR does is dilute the intake charge, reducing the concentration of oxygen. This reduces combustion temperatures. Like Wes said above, lowering combustion temperatures lowers the level of NOx formation.

[essexalan]

Thank you for the answer, kind of used to the concept of colder air means denser charge leading to bigger bangs and more power. I suppose something simple like water injection would not have the same effect as an EGR. My car suffered an early life failure of the EGR plus cooling system leaks in that area so advice concerning avoiding this again is most welcome.