Era 4: Sol Supremacy

The Era 4: Sol Supremacy is the crowing achievement of The Mechanist Guild in the 4th century. It is the most powerful fire based engine in existence, capable of sustained flight for roughly 2000 KM. 
The Sol Supremacy uses a fire Attuned Source Crystal for power, requiring a similarly aligned crystal for recharging. The crystal is specially cut in such a way as to be irremovable from the engine, as it is integrated too deeply into the mechanisms of the engine. This means that the entire engine must be moved for charging, a process that takes hours and roughly 10 crew people to accomplish. 
The Sol Supremacy is designed with an optional "nitrous burn" setting, allowing for increased power at the cost of consuming the energy of its Source Crystal at double the usual rate.

Access & Availability

The engine is currently only used to power Vengeance Class: Skycrusher, the most powerful ship in Molten Heart's navy. The method of creating the Sol Supremacy is a closely guarded secret.

Complexity

The engine uses a complex array of Echo Quartz and Magitech Circuits , which allow it to recycle excess heat energy which it can then funnel back into the Source Crystals at the engine's heart. This allows the crystal to maintain its charge much longer than previously thought possible.