The fuel value for rocket fuel is removed in xander (i guess for realism):
../prototypes/item/part/rocket.lua:10
If I comment this, it loads:
--Base "rocket-fuel"
--data.raw.item["rocket-fuel"].fuel_category = ""
--data.raw.item["rocket-fuel"].fuel_value = "0J"
--data.raw.item["rocket-fuel"].fuel_acceleration_multiplier = 1
--data.raw.item["rocket-fuel"].fuel_top_speed_multiplier = 1
I don't know, if it'll be changed. But maybe it works, if the fuel value is set very low to achieve the same