Originally Posted by Giff
So a higher cetane rated diesel will ignite faster, the effect being similar to advancing the ignition of a petrol engine?
The idea is to have a smoother, more complete burn of the atomised diesel. Higher cetane assists this, gets the fuel ignited faster, allowing more time for the fuel to burn efficiently. It is also why we typically have a quieter more refined engine, on the higher cetane fuels. Extra diesel knock is often due to an incomplete burn.
Users often say there is no difference in mpg, a lot will depend on use. The diesel is best suited to steady state running, so drivers who just cruise, mile after mile at lowish revs, (best flame burn) will get the best mpg benefit from better combustion. If we drive with a lot of high revs, then mpg benefits will be less likely.
My car is definitely smoother and quieter on BP Ultimate, compared with the standard BP fuel, feels more responsive and returns more mpg.