Thread: O2 Sensor in a diesel

The smoke limit is approx 18:1 air/fuel, so 14 - 15 should give lots of smoke and high egt.

Petrol engines can tolerate much higher egt than diesel engines.

Some modern diesels have O2 sensors. AFAIK as part of their emission systems - from memory tied in with the egr, but I stand to be corrected.

Stoich on a diesel is pretty close to stoich on a petrol. 14.55 for diesel, 14.7 for petrol.

However, run a diesel anywhere near that and it's a smokey bomb with very high EGT's.
18:1 is as rich as you want to run a diesel that takes low boost. As your boost levels rise you need more excess air (higher AF ratio) to keep EGT's down.

Stock turbo diesels seem to not go lower than 22:1. With a dilligent driver and the appropriate gauges you can go lower, but I wouldn't recommend going past 18:1.
I've heard of aftermarket tuners going as low as 13:1. IMO people who do that are muppets that're being paid to ruin engines and lungs.

I think a wide band sensor would most of the time be running outside it's range of operation on a diesel. Only at high torque requests would it be working and at that point the EGT guage is the one to watch.

So you would say this TD5 is overfueling?

Post 46 here
http://www.aulro.com/afvb/technical-...ml#post1172308

I remember mine (300Tdi) also on Graham Coopers dyno being this sort of A/F but I can't find the print out at the moment, I have no indication that mine is overfueling, it has low EGTs and rarely any smoke visible in the mirrors.

Or am I miss reading the dyno plot?


Tony

Originally Posted by TonyC

So you would say this TD5 is overfueling?

Post 46 here
Who has had a dyno run on their LR?

I remember mine (300Tdi) also on Graham Coopers dyno being this sort of A/F but I can't find the print out at the moment, I have no indication that mine is overfueling, it has low EGTs and rarely any smoke visible in the mirrors.

Or am I miss reading the dyno plot?


Tony

I don't think you're miss reading the dyno plot.

I do wonder how the A/F ratio is measured/determined for those dyno runs.

Looking at a few of the the other plots some have AFR:P, some AFR:L and that one AFR. Guessing may signify P=petrol, L=lpg, D=diesel

I expect A/F ratio to be mass ratio. Stoic calculation is based upon molar quantities of the carbon and hydrogen molecules in the particular fuel to react with oxygen during combustion - from there, the masses can be determined.