Lords of heaven, light my cigarette!

[Durinor]

See below the Celestial sorcerer bloodline power:

Heavenly Fire (Sp): Starting at 1st level, you can unleash a ray of heavenly fire as a standard action, targeting any foe within 30 feet as a ranged touch attack. Against evil creatures, this ray deals 1d4 points of damage + 1 for every two sorcerer levels you possess. This damage is divine and not subject to energy resistance or immunity. This ray heals good creatures of 1d4 points of damage + 1 for every two sorcerer levels you possess. A good creature cannot benefit from your heavenly fire more than once per day. Neutral creatures are neither harmed nor healed by this effect. You can use this ability a number of times per day equal to 3 + your Charisma modifier.

Is the name 'fire' simply flavour, or can I use this fire to set alight to unattended objects?

[Nails]

I'd say no.

Spells like Burning Hands and Fireball note specifically that they set flammable materials on fire. Scorching Ray doesn't mention setting things on fire at all in the spell description but a spell clarification from the Skull and Shackles Player's Guide states that it does not.

In addition Flame Strike notes that half of its damage is fire damage and half is holy damage, but does start fires unless the unattended object rolls a 1 on its saving throw (Again, Skull and Shackles Player's Guide).

Heavenly Fire is specifically noted as divine damage, not fire damage, and is not subject to fire resistance.