The present work discusses a novel oxy-fuel combustion mode named internal combustion rankine cycle utilized in CI engines. Water is heated up through heat exchanger by exhaust gas and coolant before injected into cylinder near TDC to control combustion temperature and enhance thermal efficiency. The added extra work fluid in form of water vapor which is capable to utilize the combustion heat more effectively. ICRC proves to be an effective solution in improving thermal efficiency and lowering emissions for IC engines, the increment of compression ratio can further improve cycle performance. Compare with SI engines, abnormal combustion is better restrained in CI engines which is advantageous in adopting higher compression ratio, both homogeneous charge and heterogeneous charge CI is discussed in this paper. A retrofitted CI engine coupled with port and direct injection is adopted in the test. Water is heated up in a rail with electric heater and injected into cylinder using modified diesel injector. The water injection pressure is amplified through booster up to 15~40MPa. The O2/CO2 intake provided by high pressure cylinders are fully mixed in a surge tank in order to maintain intake pressure and oxygen fraction constant. The experiments with different CI modes under different engine loads were carried out. This study investigates the combustion characteristics of CI ICRC engine. The results indicate the applicable oxygen fraction are greatly expanded under CI compared to SI. The improvement of thermal efficiency is negligible under HCCI even though the limit water injection boundaries have been adopted. The heterogeneous charge CI show great potential in improving thermal efficiency with ICRC concept. The biggest difference between homogeneous and heterogeneous charge CI lies in temperature, with a higher temperature, water evaporation speed enhanced and this implied that in-cylinder temperature plays a crucial role in the cycle performance of ICRC engine.