The necessity of raising Liquid Rocket Engine performance requires combustion chamber pressure even higher than the propellants critical pressure (Pc), that is the highest pressure value where the liquid-vapor equilibrium of the substance still exists.
Close to the critical point it is not a mistake to consider fluids in-between a liquid and a gas; in fact, density is of the same order of magnitude of a liquid, while transport properties are closer to those of gases.
The main consequences are: flow laminarization and reduced ignition times (permitting shorter combustion chambers designs).
Studies about methane-oxygen co-axial igniters were carried out due to the FLPP ESA research project .
Several Documents and 1 Thesis have been produced.