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What the software actually did was stop the mixing of DEF[0] into the exhaust gases. DEF is a consumable catalyst that reduces NOx emissions[1]. If they had mix
by tyho 10y ago
What the software actually did was stop the mixing of DEF[0] into the exhaust gases. DEF is a consumable catalyst that reduces NOx emissions[1]. If they had mixed it in properly as they did when the car was under test, then fuel consumption or performance would not change, but the resovwair of DEF inside the car would be depleted more quickly.
My theory is that they reduced the consumption rate of DEF so that it could be filled up during regular services without being depleted before one was due. They could instead just provide a larger reservoir of DEF, or schedule more frequent maintenance. Either solution would not impact fuel consumption or performance but would fix the issue. Remember DEF is injected into the exhaust gases and does not interact with the engine at all.
[0] https://en.wikipedia.org/wiki/Diesel_exhaust_fluid https://en.wikipedia.org/wiki/Diesel_exhaust_fluid
[1] https://lwn.net/Articles/670488/ https://lwn.net/Articles/670488/
- cr3ative 10y agoMy car is affected by this recall (as confirmed by a letter from the VW group to my registered address) and does not have a DEF / AdBlue system.
- paol 10y agoMaybe that's the case for engines that use DEF, but the cheating was done in engines with no DEF injection systems too. In those engines at least I doubt very much "the fix will not affect the performance or fuel economy", unless they resort to extremely expensive changes that seem unlikely (like adding said system to cars that don't have it).
- tyho 10y agoI am not sure, I have no idea what they did in cars that didn't have the urea injection system.
- DannyBee 10y agoSo they'd be dumb to say it just for PR reasons - A bunch of people will test it, if their statements turn out to be false, they'll be a massive class action suit that will be pretty easily won. It's entirely possible, of course, that they are counting on this, and decided by then things will have died down enough PR wise that making the PR statement makes sense.
- JorgeGT 10y agoThat's applicable to engines featuring DEF, but for the rest my theory is that they will just increase EGR to lower combustion peak temperature and thus decrease NOx at the cost of engine efficiency. There's no magical software fix that can decrease NOx without affecting the combustion and thus either performance or efficiency. That would be the holy grail of thermal engine research!
- celticninja 10y ago*reservoir, but I enjoyed your spelling of it anyway.
- sathackr 10y agoThe models affected by this do not use DEF[1] I used to understand the system fully but have lost some of that as it's no longer important to me. In short, the CBEA engine line has a complex emissions control system consisting of 3 separate catalytic converters that each must be regenerated from time to time, and two exhaust gas recirculation systems. These regeneration cycles reduce performance and increase fuel consumption. For example, a DPF regeneration cycle closes a valve in the exhaust which increases system pressure and thus system temperature, while also triggering a post-combustion fuel injection -- injects unburned fuel into the cylinder on the exhaust storke -- to increase the exhaust temperature to burn off soot that accumulates in the particulate filter. It is likely a change in the schedule of these regeneration events that is necessary to bring the vehicle into compliance. There is a long PDF[2] that goes into detail how the emissions systems work on these cars. [1] http://www.myturbodiesel.com/images/dpf3.jpg http://www.myturbodiesel.com/images/dpf3.jpg [2] http://www.natef.org/natef/media/natefmedia/vw%20files/2-0-tdi-ssp.pdf http://www.natef.org/natef/media/natefmedia/vw%20files/2-0-t...
- vonmoltke 10y ago> The models affected by this do not use DEF[1] Huh? Some certainly don't, but 2014 TDI Passats like mine use DEF. My reservoir currently lasts about 10000 miles, which is also the manufacturer's service interval.
- sathackr 10y agoOops...my apologies. I was not aware that both versions were affected -- looks like this information came out a bit later. I'll edit the original post. Edit: Or not...looks like too much time has passed.