Copenhagen Suborbitals have been continuing their testing of swirl injectors (article here), planned for there BPM-100 rocket engine, the group plan to carry out small scale tests on their BPM-5 engine.
Swirl injectors are most commonly found in Russian rocket engines and more predominantly with a liquid/gas injection scheme (coaxial swirl) where the gaseous propellant is directed down through the centre and the liquid propellant injected tangentially along the element wall, producing a swirl. This fuel swirl produces a cone at the outlet where when the oxidiser is introduced it mixes in this cone thus giving good atomisation of the propellants.
As being investigated by CS, a liquid-liquid coaxial swirl injector has been used in the past with storable propellants but also with liquid oxygen and kerosene as used in the RD-0110/0107 engine which has served as an upper stage in various launch vehicles over the years.
The coaxial swirl injector should not be confused with a shear coaxial injector (also called a coaxial hollow post) as found in the Space Shuttle Main Engine (SSME) or RS-25. This injector element is typically used with liquid oxygen and gaseous hydrogen (phase change after absorbing heat from the cooling jacket). The gaseous hydrogen flows at much higher velocity compared to the liquid oxygen where the differential in this velocity creates a shear action, breaking the liquid oxygen into droplets, hence the name. This injector does not work well with both propellants being liquids as the pressure drop required to achieve the high velocity would become too great.
You can find more info on swirl injectors below or in any liquid rocket book,
Swirl Coaxial Injector Development
Swirl Effect on Coaxial Injector Optimisation
History of Liquid Propellant Rocket Engines in Russia
Combustion Characteristics of Bi-liquid Swirl Coaxial Injectors with Respect to a Recess