Comparative analysis of different heat transfer correlations in a two-zone combustion model applied on a SI engine fueled with wet ethanol

Abstract

This work focuses on modeling the combustion cycle of a SI engine running with both hydrous ethanol fuel, which has about 95% of ethanol in water by volume, and four wet ethanol fuel blends, with water volume fractions of 10% (E90W10), 20% (E80W20), 30% (E70W30) and 40% (E60W40). Thus, a two-zone combustion model was implemented with the mass fraction burned calculated through the Wiebe function and four different heat transfer correlations: Woschni, Hohenberg, Sitkei and Annand. To correctly evaluate the use of these ethanol fuels, a parameter estimation technique was used to calibrate both Wiebe and heat transfer correlation parameters for each simulation made. Experimental pressure trends from a SI engine were used to validate the two-zone combustion model predictions and the influence of parameter estimation. Results showed that Hohenberg’s correlation was the most accurate, being able to predict with high precision the in-cylinder pressure and heat flux through the cylinder walls. The parameter estimation technique had great influence in calibrating the Wiebe equation parameters to match the tests conditions. In addition, the use of wet ethanol fuels has shown stable combustion and engine operation, indicating concrete possibilities of commercial use in the future.