Hi all,
I know this has been a long thread but I have been giving some thought to my original comments on why older vehicles did not need egr. Obviously legislation and enviromental issues have had a large impact but I still think older diesels did run a lot richer than modern variants. As I said, I had never really thought about the AFR on a diesel and took many things for granted, but I don't think the fact that they run on excess air means they all have the same, or similar AFR. I spent many years working on air cooled stationary diesel engines and it is my opinion that altering the volume of fuel delivered does affect AFR, i.e. loads of black smoke when more is injected than the engine can burn. I think many other issues have to be taken into account like the engines ability to "breath" (I think the term is volumetric efficiency?), the ability of the injector to fully atomise the fuel, the compression ratio, the shape of the combustion chamber etc, etc. If modern engines are returning better MPG than the older ones, then surely it must follow that they are burning less fuel and therefore more likely to raise the combustion temp and produce more NOx? Surely getting rid of one gas (smoke in this case) must result in another i.e. less CO = more CO2 = less O2??? Like most I am happy to be corrected but after sooooooo many years it's going to be difficult .
Regards to all, Bryan.