Investigation to Charge Cooling Effect of Evaporation of Ethanol Fuel Directly Injected in a Gasoline Port Injection Engine

Ethanol direct injection plus gasoline port injection (EDI+GPI) is a new technology to make the use of ethanol fuel more effective and efficient in spark ignition engines. It takes the advantages of ethanol fuel, such as its greater latent heat of vaporization than that of gasoline fuel, to enhance the charge cooling effect and consequently to increase the compression ratio and improve the engine thermal efficiency. Experimental investigation has shown improvement in the performance of a single cylinder spark ignition engine equipped with EDI+GPI. It was inferred that the charge cooling enhanced by EDI played an important role. To investigate it, a CFD model has been developed for the experimentally tested engine. The Eulerian-Lagrangian approach and Discrete Droplet Model were used to model the evolution of the fuel sprays. The model was verified by comparing the numerical and experimental results of cylinder pressure during the intake and compression strokes. Mesh density and time step sensitivities have been tested. The verified model was used to investigate the charge cooling effect of EDI in terms of spatial and temporal distributions of cylinder temperature and fuel vapor fraction. Compared with GPI only, EDI+GPI demonstrated stronger effect on charge cooling by decreased in-cylinder temperature. The cooling effect was limited by the low evaporation rate of the ethanol fuel due to its lower saturation vapor pressure than gasoline's in low temperature conditions.