This weeks issue was about carbon deposits causing running problems on VW and
AUDI direct injected vehicles. Also talked about camshafts wearing due to poor tempering of the camshafts.
Anyway, regarding the carbon deposits, it says that due to fuel being direct injected bypassing the intake valves
That article is about 10 years too late
These have been common issues on these cars for yonks now !
I always thought that was the
Purpose of VVT. Closing the exhaust valve a little earlier traps exhaust gasses in the cylinder- voila!! Am i missing something???
Yes that is ONE purpose of VVT but by far not its only purpose
As you say with VVT it is possible to have some Auto Egr by playing with Valve opening & Closing times. Has been done for years now.
egr is used to reduce nox gasses and vvt to improve performance but as i understand they both have other side affects
The purpose of EGR as Andrew wrote is 1. to be a nuisance & 2. lower combustion temperature to prevent the formation of NO2, NO3 .... NOx as we all call them.
VVT is for Improved efficiency at different engine speeds & loads but some bright spark discovered it can be used for Auto EGR. The EGR Valve is fitted as well as VVT for more EGR, hence less NOx, than valve timing alone can achieve.
VVT (Auto EGR) plus EGR valve is still not enough to get NOx low enough to satisfy the emission targets. (VW Scandel)We can only have EGR on a warm Engine at low / moderate loads.
At times of high power demand, EGR will be closed & VVT may do the opposite with valve timing and encourage full excavation of exhaust gasses with an efficient inrush of cool air in to the chamber actually preventing any Auto EGR. Swirl Flaps, Manifold Design, Forced Induction .... .... ....
All the above Prevent NOx formation but not effectively enough, so now we have NOx Catalysts, SCR, Adblue ..... etc. to deal with the NOx formation that could not be prevented.
We have now come full circle with technology trying and failing with emission reduction, someone has now finally realised that all these nasty emissions are a result of burning fuel and by burning less we will get less emissions. That would be a big reason behind new cars now using smaller CC engines to manage emissions but have Superchargers and/or turbo's bolted on to satisfy performance requirements.