Anyone using high octane petrol and notice any benefits?

Goudy

forgotmyname said:

2-EHN can degrade the quality of the fuel and increase emissions. Seem to remember adding too much
has the opposite effect.  It pops up every now and then as a newly found additive that everyone needs
but then the negatives make it not worthwhile for most people.

Yes, that's right.

2-EHN can lower the temperature of combustion slightly which can be a problem for low temperature combustion engines as it does increase the production of nitrogen oxides.

Your diesel engine in your car though doesn't operate as an LTC engine.
Plus modern diesel engines are equipped to deal with NOx via exhaust recirculation and selective catalytic reduction systems. 

Some Japanese manufacturers experimented with homogeneous charge compression engines in the 1970's which ran at lower temps but generally LTC engines are used when far lower engine speeds are required than that in your average car.

There have been studies relating to the oxidisation stability of fuel with the addition of 2-EHN and from those that I have read, they haven't proven anything that isn't already known. Fuel oxidises over time.

Long term studies of fuel with 2-EHN have shown it oxidises slightly faster than normal low sulphur diesel but have resulted in the fuel still meeting the EN16091, the oxidisation and stability standard for liquid petroleum products. So yes it does, but not enough to matter.

The biggest issue with it is using too much by over dosing.
This will reduce the diesel lubricity can cause wear issues within the high pressure system and also takes away what it enhances, the fuel that burns.
Mix it at 1% and you have 99% fuel and it doesn't matter.
Mix it at 20% and you now only have 80% fuel and that will reduce the power significantly. 

In the UK normal diesel has a rating of 51 cetane and your premium diesel around 55 or so.
It's often recommended to add it (99% pure 2-EHN) at around 1% which is enough to bump up standard 51 cetane close to 55.

Obviously, if you buy it in as a commercial available "diesel treatment and/or additive" package, it's dosage will be higher due to the carrier fluid in the bottle, often around 200ml of so will treat a tank full of diesel.

There was a interesting study by a certain Bavarian car manufacturer a few years ago with regards to additives in diesel.
I can't for the life of me find it, but it was quite interesting though a little out of date these days.