Diesel Generator produce FE from various cells, like
Nitrofuel Cell. It has internal buffer to store 10 buckets of fluid which is converted to Energy. It is a Medium tier machine with 128E\t output rate and 1M Energy buffer.
Diesel Generator could be created using either
Iron Plate or
Aluminium Plate. Second one looks more expensive in terms of time and materials, but you will have plenty of aluminium in a mid-game.
Put any of cells from list below inside Diesel Generator in order to start FE generation