Who discovered conservation of energy?
In short it came out of the work of a variety of engineers, scientists and academics.
In many ways it was almost a collaborative effort.
Here is a list of some of those who contributed at various times:
Engineers: John Smeaton, Peter Ewart, Carl Holtzmann, Gustave-Adolphe Hirn, Marc Seguin.
Chemists: William Hyde Wollaston, Karl Friedrich Mohr.
Academic: John Playfair.
Chemist and mathematician: Antoine Lavoisier and Pierre-Simon Laplace.
Polymath: Thomas Young (i.e. he contributed to a wide range of fields).
Engineers / mathematicians: Gaspard-Gustave Coriolis and Jean-Victor Poncelet