emu means "electric multiple unit". such a train does not have one engine loco, but many engines. there are multiple electric motors located inside some of the coaches. Mumbai locals are emu's. You will see the pantographs touching the overhead electric wires. Whichever coach has a pantograph also has an electric motor - all these motors together power the train.
(also the emu is a flightless bird native to Australia. click here
bit.ly/n6tzT Also see picture attached.)