I join robot fire fighting contest. One of the mission is to extinguish candle by spraying it with liquid (water is default option). For spray mechanism I use pump with Venturi effect principle. Is there any liquid substance that is more effective extinguishing fire than water by Venturi spraying mechanism? Homemade is preferred.
You could consider an aqueous film forming foam (AFFF) system, this is water with some additives to form a foam. Originally foam was something intended for class B fires, but there are now foams which are intended for both class A and class B fires. They are even considered to be acceptable for use on gas fueled fires where there is no risk of explosion (class C). Thus there are ABC foams.
A word of warning some ABC foams such as those based on PFOS are horrible and harmful. It might be best if you stick to a water spray system. The PFOS foams are considered to be problem when they enter the environment, if I recall correctly they are very harmful to fish and the perfluoro compound PFOS only breaks down very slowly in the environment.