60 replies to this topic

[J. Edlund]

to help reduce NOx get rid of the hot exhaust valves in the combustion chamber . there is a solution 

 

Talking poppycock isn't a solution. The exhaust valves have nothing to do with NOx formation in an engine.

[malbear]

Thermal NOx formation describes the process when nitrogen, N2, in the combustion air reacts with oxygen, O2, in the combustion air to produce NOx. This process is best studied and understood. The formation requires very high temperatures and is exponentially dependent on the temperature. Because the process is very nonlinear, so called hot spots, local areas with higher temperature than the average temperature, can give very large effect on the amount of NOx produced. The maximum rather then the average temperature is therefore very important and the process is very hard to model accurately because of this. Other important factors in thermal NOx formation are the residence time, which describes how long time the combustion gas is having the high temperature. The turbulence and the amount of excess oxygen are two other important factors

 

http://www.control.l...s/2006/5769.pdf

[Briancoat]

I'd like to open up the conversation to consider the actual exhaust emissions.

How NOx is formed in the engine not really the key issue.

The disadvantage of lean SI / diesel wrt NOx is nothing to do with raw NOx formation in the engine.

The main challenge is that the highly effective and mature three way catalyst technology only works when the AFR is stoichiometric. And for lean SI / diesel it isn't.

So expensive and compromised alternative aftertreatment systems are required. Urea etc.

For a stoichiometric SI engine the NOx emissions can be reduced to virtually zero once the three way catalyst is up to operating temperature, pretty much regardless of the raw NOx levels. At normal ambient conditions, this takes seconds, even from a cold start. From a warm start it is virtually instant which is why the third bag NOx of an FTP75 test is always negligible.

[gruntguru]

There is a lot of potential for dramatic reduction of engine-out NOx using the same technology as Formula 1 ie ultra-lean spark ignition.

[Briancoat]

There is a lot of potential for dramatic reduction of engine-out NOx using ... ultra-lean

OK ... BUT

The engine-out NOx of the leanest McLeanface GDI on the planet is still way over the USA NOx standards.

There is still a big problem with the high cost and inconvenience of the lean NOx aftertreatment.

It wasn't their inability to run lean which canned/homogenized a load of manufacturers' lean GDI engines programmes in early/mid 2000s it was aftertreatment.

Edited by Briancoat, 05 December 2016 - 21:19.

[gruntguru]

I was referring to TJI not GDI. Engine-out NOx less than 10 ppm has been achieved in the lab.

[Briancoat]

I was referring to TJI not GDI. Engine-out NOx less than 10 ppm has been achieved in the lab.

I know.

You are thinking a GDI engine with TJI could have real-driving BSNOx low enough to surmount the aftertreatment headaches?

I had dismissed it but maybe I should be more open minded :-)

[malbear]

I know.

You are thinking a GDI engine with TJI could have real-driving BSNOx low enough to surmount the aftertreatment headaches?

I had dismissed it but maybe I should be more open minded :-)

here is a link      http://www.f1technical.net/news/20316

[Briancoat]

Thanks for the link, which I read when it was posted on F1T.

I've seen/posted some of Mahle's published dyno results so I appreciate where GG is coming from.

And Mahle's PR team agrees ...

"MAHLE Powertrain’s Turbulent Jet Ignition (TJI) [...] Engine-out NOx emissions are also virtually reduced to zero levels, negating the need for lean NOx after-treatment."


I guess it all depends on how TJI performs under real conditions. In a car with a real-world calibration and a real DF. It will move the game on but will it change the after-treatment game in the way they suggest?

I'm prepared to be open to the idea that it might.

Edited by Briancoat, 08 December 2016 - 08:16.

[gruntguru]

 

I guess it all depends on how TJI performs under real conditions. In a car with a real-world calibration and a real DF. It will move the game on but will it change the after-treatment game in the way they suggest?

Real world? I thought you only had to pass a dyno drive-cycle test?

[Briancoat]

Heh heh.

That is changing, though.

In the EU, forthcoming RDE regs will make actual real-world testing part of the regime.

In the USA the (several) tests are much more real-worldly (and stringent) than the EU.

WLTC aims to harmonise the USA and EU tests with a real-world-like dyno test.

"Doing a VW" will be harder.

(Stable door closing after horses bolted).

Edited by Briancoat, 13 December 2016 - 14:20.