NOx emissions and 205 injectors

When Joe Rappa hooked up is portable emissions tester to my stock ECU TDI with 205 injectors, the amazingly low NOx surprised him. It was the lowest he had measured to date.

The reason is that the EGR map uses an injection quantity value that is calculated based on the stock 184 injectors.

Thus when installing 205s with a stock EGR and ECU you decrease available oxygen and reduce NOx below stock levels, with a corresponding increase in HC emissions --> then soot in the oil as some have observed.

Solution: adapt EGR to suit the 205s. How much? I do not know. But would like to run some tests. Ideally we would want to reduce EGR by 15-20% or so.

Amazing, all these years of diesel study going out the window. You get in the mindset that a diesel is always lean-burn, but on the TDI with electronic EGR there really is to some degree a "mixture" and a semi-closed control loop. (No oxygen sensor downstream but lots of feedback on the intake side; also calculated values.)

It's remarkable how all the systems interact.

As I recall it was 60 mph cruise in top gear.

Hi Ted,
Here is one of those graphs. I can post more of them if you want... I checked quite a few modded cars that day.
Joe



[ May 21, 2002, 22:57: Message edited by: Joe Rappa ]

At what RPM did he measure NOx?

Thanks Joe - are you going to be at the GTG this weekend or at the TDI fest?

Regards,

Ted

I would expect NOx to drop as RPM and power increase, since EGR drops the same way.

Hi Ted,
I'm not going to the GTG this weekend, but I will be at TDI Fest, doing the Biodiesel thing. I'm bringing some pretty cool diesel stuff that I've been collecting too. I've got an 1.6L engine cutaway(lets you see everything inside), some pistons that were scuffed by ether starts, and some cylinders that were eroded by poor coolant. Stuff like that.

Here's the NOx/.205 situation as I see it.
The .205s spray a thicker stream into the cylinder. The thicker the stream, the more fuel begins to burn in an oxygen defecit, increasing the soot level. Anything that increases sooting, decreases NOx formation. I don't believe it is connected to EGR myself. I think it is simply a function of the fuel stream difference.
Your NOx level was also quite a bit lower at full throttle, when EGR is not functioning.
(where's TDIMeister when we need him?)
Joe Rappa

Interesting Joe I had forgotten about the full-load runs. That's great that you're coming to the Fest - its not so far off now. Ted

(where's TDIMeister when we need him?)

That would still be Malaysia i quess......

And VW's excuse for not bringing in the 110hp was ... emissions ? ? ? Go figure!

If your theory is correct, it would be interesting to see what the NOx is like in mine with 0.216 injectors, stock ECU (but with a boost bleed), and EGR present but "reduced".

There is still 2.5 times more oxygen than CO2 according to the display, that's still quite lean operation. Interesting.

Back-of-notepad rough calculations suggest somewhere around 0.2 grams per kilometer of NOx under those operating conditions. What are the EPA exhaust emission limits? What about Euro 4?

Actually, NOx production in a diesel is greatest just off idle and decreases as power increases. This is the opposite of gas engines. It has to do with mixture, which is leanest (more excess O2) at idle/low power and becomes richer as power increases. Gas engines (as you know) have a fixed mixture across their power range. Their NOx production is more temperature related (higher power, higher temps, more NOx).

It's very difficult to compare emissions measurements to each other. I think the EPA test is a cycle, and it's a "bag test" i.e. total emissions during the cycle. Other standards use g/km, etc.

Remember Brian that I was at the time running the standard EGR, not reduced, and that optimization of HC and NOx would have bumped up NOx somewhat.

I think the reason we don't get the 110 is that with very poor fuel it makes a good deal of visible smoke. This of course is not a problem on Premier or B20.

Are you coming to Michigan this weekend?

Ted

I know the official test procedure isn't under these particular conditions, but still, it's an interesting order-of-magnitude comparison. Can't make it to any get-togethers this weekend, got too much else going on.

I know the official test procedure isn't under these particular conditions, but still, it's an interesting order-of-magnitude comparison. Can't make it to any get-togethers this weekend, got too much else going on.