All the common glow plugs and glow heads use about 1.5 volts. There are a few plugs that will handle 2 volts without burning out, but not many. The Fox should run on 10-15% nitro and a minimum of 20% castor oil fuel. The 09 is not a great running or powerful engine.
The Cox engines are the RR-1 and a common Babe Bee 049.