Things you can measure are oxidized states of each component alcohol, aldehyde, ketone, and acid. Activated intermediates are present but maybe not observed except in specialized equipment.
I want to observe it in CFD study. In one paper i read that CH2O shows the start of consumption of n-heptane and OH shows the start of consumption of iso-octane.
If you want to track the consumption of your fuels in the low temperature regime (i.e. below 750 K), I guess the respective alkenes of each one of your paraffinic fuels could provide some information (e.g. for n-heptane, 3-heptene, for isooctane, 2,2,4trimethyl-3-pentene). For Butanol I guess butanal or butenal would be an option.
In the high temperature regime, C-C beta scissions will be more frequent, so it could be more difficult to pinpoint species that are formed solely by one fuel.