From Wikipedia:

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Cetane number or CN is to diesel fuel what octane rating is to gasoline. It is a measure of the fuel's combustion quality.

Cetane is an alkane molecule that ignites very easily under compression, so it was assigned a cetane number of 100. All other hydrocarbons in diesel fuel are indexed to cetane as to how well they ignite under compression. The cetane number therefore measures how quickly the fuel starts to burn (auto-ignites) under diesel engine conditions. Since there are hundreds of components in diesel fuel, with each having a different cetane quality, the overall cetane number of the diesel is the average cetane quality of all the components.

A fuel with a high cetane number starts to burn shortly after it is injected into the cylinder; it has a short ignition delay period. Conversely, a fuel with a low cetane number resists auto-ignition and has a longer ignition delay period.

To measure cetane number properly is rather difficult, as it requires burning the fuel in a special, hard-to-find, diesel engine called a Cooperative Fuel Research (CFR) engine, under standard test conditions. For most practical purposes, fuel-users control quality using the Cetane Index, which is a calculated number based on the density and distillation range of the oil. There are various versions of this, depending on whether you use Metric or Imperial units, and how many distillation points are used. These days most oil companies use the '4-point method'.

There is very little actual cetane in diesel fuel. Diesel engines run just fine with a CN between 45 to 50. There is no performance or emission advantage when the CN is raised past 50; after this point, the fuel's performance hits a plateau.

Diesel at the pump can be found in two CN ranges: 40-46 for regular diesel, and 45-50 for premium. Premium diesel has additives to improve CN and lubricity, detergents to clean the fuel injectors and minimize carbon deposits, water dispersants, and other additives depending on geographical and seasonal needs.

Some fuel additives used to raise the cetane number are eg. alkyl nitrates and di-tert-butyl peroxide.

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So, Amsoil cetane booster is an octyl NITRATE and MEKP is methyl-ethyl-ketone-PEROXIDE. And of course, there's the traditional amyl NITRATE.

But note that there's no performance advantage when the CN number is raised past 50.

As we all know, with ether, we get an improved cetane rating. As we add 2% amyl nitrate to that, we boost the CN a bit more. AND, as we know, over 2% can cause problems. Is the issue too high a cetane number? Or is the issue the MANNER in which too much AN raises the cetane rating. I wish I had some to test 10% in a no ether fuel. When I added way more MEKP in the one test, it didn't help but it didn't hurt.

It would be interesting to test ALL the ignition improvers in various concentrations with various ether and no ether formulas. These combinations could reach into the hundreds though.

But what if you could get this stuff called cetane and play with that? Say, add it to methanol and create a new fuel base. Gasoline? Acetone? With a CN number of 100, it might not take much to raise the cetane rating of these "octane" fuels to 50 for use in diesel engines.