PA-44 flight instructor with student and observers on board reported during engine start that a fire developed on the cowling. Instructor then shut down the engine; stopping the fire; and everyone evacuated the aircraft safely.

Narrative

During a normal hot engine start on the left engine (no primer due to running prior) a fire developed on the left side of the cowling causing a continuous approximately 4-foot tall 2-foot wide fire. An observer in the back seat noticed this and yelled fire; I looked to my left to see what was going on and saw the fire myself. I called for an aborted start and an evacuation of the aircraft. My student in the right seat began to evacuate while I used the time to cut mixtures and secure the aircraft. I evacuated second followed by the two observers in the back as briefed. By the time we had evacuated the aircraft; the fire had externally stopped and I placed a call to our company Maintenance. Soot from the fire was observed on the leading edge of the wing and cowling side. Maintenance arrived with fire extinguishers however the fire was already out and they verified there was no fire inside the cowling still which there was not. The extent of the damage inside the cowling is unknown but external damage was just soot and some burnt paint. I filed an internal company report and discussed the event with our safety team and decided to file this on my own as well externally.