Sunday, January 22, 2017

reaction mechanism - What are the key chemical characteristics that determine the octane rating of fuel?


The octane rating of petrol (gasoline) is a measure of the how much compression a fuel air mixture can have before detonating (which in petrol engines is a bad thing as you want the mix to combust only when the spark plug arcs).


What are the key chemical characteristics that determine this rating? What is the molecular-level explanation? And how do the various non-hydrocarbon additives work to modify the result?




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periodic trends - Comparing radii in lithium, beryllium, magnesium, aluminium and sodium ions

Apparently the of last four, $\ce{Mg^2+}$ is closest in radius to $\ce{Li+}$. Is this true, and if so, why would a whole larger shell ($\ce{...