VNT turbo doesn't have a waste gate because its VNT, also what throttle on a Diesel engine are we talking about? Are you aware the EGR is fully closed higher up the rev range?
Egr blanking plates
- Thread starter Ibiza2000
- Start date
VNT turbo doesn't have a waste gate because its VNT, also what throttle on a Diesel engine are we talking about? Are you aware the EGR is fully closed higher up the rev range?
xpro
Guest
When i said throttle i meant when you let off.. I fully understand how the egr works, but what im saying is that egr is also used to relief excess turbo pressure on deacceleration. ( one reason not to blank it)
Pd or most vag engines run over 2.5bar turbo boost and when you let go that pressure has to be vented somewhere. Do you get what im saying?
Have a quick browse on google and you will find the principle. I have presonally tested the complete Egr system on the bench so i have a fairly good idea on how it works.
xpro
Guest
I will dig out a vw technical bulletin on egr valve, that says about increased turbocharger noise due to blocked egr valve as the intake pressure is trapped because it has nowhere to go.
That will also explain that Egr on some diesel engines, especially those fitted with VNT turbos also acts as blow off valve.
Cheers
That will also explain that Egr on some diesel engines, especially those fitted with VNT turbos also acts as blow off valve.
Cheers
xpro. Diesels have no throttle plate. There is no excess pressure that needs to be vented when you lift off the accelerator.
The VNT system controls the boost by varying the exhaust gas speed across the turbine. It doesn't need to dump this fictitious excess pressure, because it is already controlling boost by means of the vanes. If a sudden pressure increase were to occur, the ECU would simply open the vanes further to stop the turbo overspeeding.
What do you think will happen if you open the EGR valve when you lift off to change gear i.e. at high revs? Do you think that the exhaust system or the inlet system is at higher pressure - which way will the gas flow? Remember that the exhaust system is tapped for EGR before the turbocharger.
The EGR system is designed to add exhaust gas into the inlet charge. That isn't going to happen if the exhaust is at lower pressure, which it would have to be for the EGR to do double duty as a dump valve.
One of the failure modes of the EGR system is to stick partly open, and this leads to overpressure in the inlet, as experienced by many people on this forum over the years. The exhaust system is always at higher pressure than the inlet (it's all that hot gas that's just been generated to push your pistons around, being held back to push the turbo around).
What you describe would be trying to use the EGR valve as a dump valve. Dump valves recirculate inlet pressure to the air inlet side of the turbo, or dump it to atmosphere. Here you're proposing a system that tries to dump inlet pressure into the high-pressure side of the exhaust manifold.
Here's a couple of the VAG Self-Study program pdf's that touch on EGR in diesels.
SSP 190 "Adjustable Turbocharger. Design and Function". VNT provides charge pressure control.
SSP 209 "1.9-ltr. TDI Engine with Pump Injection System. Design and Function" p 44 EGR description - it is solely about emission control.
According to your profile you drive a Toyota. Perhaps they do it differently, somehow?
The VNT system controls the boost by varying the exhaust gas speed across the turbine. It doesn't need to dump this fictitious excess pressure, because it is already controlling boost by means of the vanes. If a sudden pressure increase were to occur, the ECU would simply open the vanes further to stop the turbo overspeeding.
What do you think will happen if you open the EGR valve when you lift off to change gear i.e. at high revs? Do you think that the exhaust system or the inlet system is at higher pressure - which way will the gas flow? Remember that the exhaust system is tapped for EGR before the turbocharger.
The EGR system is designed to add exhaust gas into the inlet charge. That isn't going to happen if the exhaust is at lower pressure, which it would have to be for the EGR to do double duty as a dump valve.
One of the failure modes of the EGR system is to stick partly open, and this leads to overpressure in the inlet, as experienced by many people on this forum over the years. The exhaust system is always at higher pressure than the inlet (it's all that hot gas that's just been generated to push your pistons around, being held back to push the turbo around).
What you describe would be trying to use the EGR valve as a dump valve. Dump valves recirculate inlet pressure to the air inlet side of the turbo, or dump it to atmosphere. Here you're proposing a system that tries to dump inlet pressure into the high-pressure side of the exhaust manifold.
Here's a couple of the VAG Self-Study program pdf's that touch on EGR in diesels.
SSP 190 "Adjustable Turbocharger. Design and Function". VNT provides charge pressure control.
SSP 209 "1.9-ltr. TDI Engine with Pump Injection System. Design and Function" p 44 EGR description - it is solely about emission control.
According to your profile you drive a Toyota. Perhaps they do it differently, somehow?
Last edited:
xpro
Guest
Hi. I do drive a toyota aswell
Im not getting into a debate here, but what im saying is what i tested myself on numerous vag diesel engines and some petrol engines.
When i reffered to throttle i meant letting go off pedal as i understand that diesel dont have a throttle plate other then shut off valve.
There is massive missinformation on internet about egr valves and the principle of operation, thats all im gona say.
And thanks for the pdf i will have a look at thrm,
Regards,
Im not getting into a debate here, but what im saying is what i tested myself on numerous vag diesel engines and some petrol engines.
When i reffered to throttle i meant letting go off pedal as i understand that diesel dont have a throttle plate other then shut off valve.
There is massive missinformation on internet about egr valves and the principle of operation, thats all im gona say.
And thanks for the pdf i will have a look at thrm,
Regards,
Similar threads
