The Fundamentals Governing the Operation and Efficiency of a Superheated Liquid Flash, Boiling (S.L.F.B) Cycle Powered Reciprocating Engine for Automotive Waste Heat Recovery

“Flashing” is a process where high temperature liquids held in a subcooled state, explosively release large amounts of stored energy when depressurized. The rapid volume expansion that results from the flashing has been harnessed to drive an expansion engine working on a cycle called “The Superheated Liquid Flash, Boiling” (S.L.F.B) cycle. In cyclic operation, the expansion engine power output was seen to be directly related to the mass and temperature of the injected subcooled water. At low levels of subcooling, smaller masses of water were able to achieve higher levels of efficiency in converting the total enthalpy of injected subcooled water to work, than larger injection masses with the same level of subcooling. However, with higher levels of subcooling, smaller injection masses show a reduction in efficiency. Furthermore, multiple equal small injections of subcooled water at high levels of subcooling were able to achieve higher levels of efficiency than single large injections at the same level of subcooling. With the current design of the engine, residual mass build up during multiple cycle operation result in the reduction of engine efficiency. The effective removal of the residual liquid mass during the exhaust stroke is vital to improving the overall efficiency of the engine.