Back when the ALH was a relatively new engine, Bosch pointed out that a cetane number over 50 was a waste of chemistry - it wouldn't make a difference.
So if certain bodies, such as CARB, specify more than 50 as the minimum cetane number, it is, IMO, yet another piece of evidence that they don't really know about diesels. This is nothing new, if you've followed CARB activities and pronouncements in relation to diesels.
Now if they would boost the lubricity requirement, then they'd get my attention.
Cheers,
PH
I wonder if that stance has changed with the large advancements in injection technology since then?
Here in California, we also have 70 cetane 'renewable' diesel. But, it also seems that fuel has less BTUs than normal diesel. With 70 cetane, cars definitely start easier and idle smoother on that fuel, but I do notice a lack of low end torque and loss of fuel economy, which I can only assume is due to lower actual energy content (cetane being how easy/fast the fuel can ignite, BTUs or calories being the actual energy content). BUT, high RPM power seems better than on standard ULSD.
It gets better. The 'renewable' clean burning diesel we have at a few locations here is chemically very very similar to Shell's synthetic, GTL from natural gas diesel, right down to the cetane rating.
When Audi was racing at Le Mans with their R10 TDI starting in 2006 (commonrail 5.5L V12, twin wastegate turbos, AND, equipped with DPFs, interestingly enough) they were using a blend of 70% normal ULSD, and 30% of this 70 cetane synthetic stuff.
They apparently took the time to figure out that was the ideal ratio to retain enough of the energy content of the ULSD and get a very solid cetane boost to make it ideal for the higher RPM running of those race engines (6000+ RPM) as well as a small percentage increase in fuel economy. I can only assume Bosch played a large part of developing the fuel system in the race car as well.
So, given that information, I have actually tried to replicate that mix by blending our 'renewable' diesel and normal ULSD. There is a noticeable difference, I can empirically say that much just by seat of the pants feel as well as USUALLY a small increase in fuel economy... except for when I'm enjoying the added power and response a little too much... especially in the Touareg.
That blend makes the engine feel more responsive and powerful throughout the entire RPM range. It's fun. Particularly fun with 5 liters and 10 cylinders worth of TDI power.