A novel reciprocating engine version of oxy-fuel combustion cycle combined with water direct injection (known as internal combustion rankine cycle) is presented in this paper. Water is injected near top dead center to control the reaction rate of the oxy-fuel mixture, as well as the peak in-cylinder temperature. The evaporation of the water mist will increase the mass of working gas inside the cylinder, and enhances the thermo efficiency and MEP. Moreover, the injected water is heated up through heat exchangers by both engine coolant and exhaust gas, and the waste heat is effectively recovered this way.
This study investigates the combustion and emission characteristics of ICRC under different engine loads based on a single-cylinder, air-cooled SI engine fueled with propane. An extra diesel injector is employed to inject water with high injection temperature (160°C).
Results show that the water injection process is able to increase the indicated work up to 27%, and the indicated thermo efficiency is improved by 7.8% under higher engine load. However, the same amount of injected water will decrease cycle performances when engine load is lower, mainly because the water injection process has stronger negative effects on the combustion process when the reaction rate of the oxy-fuel mixture and the in-cylinder pressure is lower. HC emissions are notable under lower engine load, but decrease significantly with the increase of the engine load. NOx emission increases slightly with the increase of the engine load, but stay under 20ppm.