What would happen, if, under safe conditions, I took my feces, doused it with lighter fluid, and set it on fire? What the neck would burn? And what would be left? What if I threw in some wood twigs?
According to the German nursing profession wiki, the contents of human feces are as follows:
75 % water
10 % (non-digestable) remainder of food (e.g. cellulose)
8 % enteric bacteria
7 % epithelium (cells from your own gastrointestinal tract)
rest = mucus and salts
Given that, initially only the lighter fluid will burn. This will heat up the surface of the mass and evaporate some water from it. As the mass reaches a sufficiently high temperature, organic material with a low boiling point might be set free as well and possible burn.
On a closer look, it turns that the VOCs (volatile organic compounds) in human feces constitute an interesting matter (yes, pun intended).
In a freely available study titled Volatile organic compounds from feces and their potential for diagnosis of gastrointestinal disease, which was published in FASEB J, 2007, 21, 1675-1688 (DOI), the authors identified a large number of of VOCs from asymptomatic donors and patients with different diseases by gas chromatography. Among the compounds found in at least 60% of the asymptomatic donors than were
- 3-carene, limonene, $\alpha$-pinene and other terpenes
- ethanal, acetone, 2-butanal , 2-heptanone and other carbonyl compounds
- toluene, styrene, phenylethyl alcohol
- heterocyclic compounds, such as indole, 3-methylfuran
But given that you chose pyrotechnics, you might not be interested in these details and were looking for less pleasant and productive experiments ;)
If you are simply interested to incinerate and burn feces to leave as little "solid" remains as possible, remember that in some parts of the world (animal) feces are commonly used as fuel. Consequently, you might be better off with dried feces.