Numerical Analysis of the Performance and Emissions of ICEs Fuelled by Bioethanol

Ethanol is a very interesting alternative fuel for the transportation sector, for both its chemical-physical properties and reduced environmental impact. As a matter of fact, ethanol has a relatively high octane number, about 107, and a high latent heat of vaporization. Therefore, it can be used in Spark Ignition (SI) engines in order to increase the compression ratio, especially in those engines working in direct injection mode. In Homogeneous Charge Compression Ignition (HCCI) engines, ethanol can be used in pure form or blended to conventional fuel to prevent knock occurrence and increase engine efficiency. Besides, as an oxygenated fuel, ethanol oxidation is characterized by lower CO emissions, if compared with combustion of conventional fuels. Finally, ethanol is produced from biomass, thus fitting the requirements of a sustainable energy system, concerning both greenhouse gas emissions and petroleum dependence. In this work, a three-dimensional CFD model is coupled with an accurate kinetic mechanism for ethanol combustion, in order to investigate the performance of engines fuelled by ethanol. The experimental results of a test engine are considered for comparisons. This test engine is a single cylinder engine working in HCCI mode. The numerical results are shown in terms of average in-cylinder pressure, heat release rate, CO and CO2 emissions for different equivalence ratios. They are compared with measurements and very good agreement is obtained. Sensitivity analyses of various initial and boundary conditions, such as initial temperature of the mixture and wall temperature, are performed. Finally, the influence of wall heat loss on CO emissions is considered.