Over the years of engine development, several types or configurations have been made. All of them relate to the position of the valves and the camshaft (s) that operates them.
air cooled engine -- An engine which is not cooled by antifreeze but by passing air past external fins.
diesel engine -- An engine with high compression that pressurizes the diesel oil fuel and fires the
charge through compression not by a spark plug.
DOHC -- double overhead camshafts
F-head -- Side exhaust valve and overhead intake valve .
flat engine
four-stroke cycle engine
hemi or hemi-head -- Engine using hemispherical -shaped (half of a globe or sphere) combustion chambers.
horizontally opposed engine
hydrocarbon engine
I-head -- Both valves located directly over the piston . Also called valve-in-head or overhead valve engine.
in-line engine
internal combustion engine
L-head -- Both valves on one side of the cylinder
oversquare engine
pancake engine
radial engine
rotary engine
slant engine
SOHC -- Single overhead camshaft.
square engine
steam engine
stirling engine
stratified charge engine
straight engine
T-head -- exhaust valve on one side and inlet valve on the other side of the cylinder and found on twin-camshaft engines.
traction engine
transverse engine
turbine engine
two-stroke cycle engine
undersquare engine
V-type -- Two sets of cylinders set apart in a V-formation like a V-8 or V-6
valve-in-head engine
wankel engine
X-type