Numerical Analyses of Spray Development and Combustion Process with Diesel-Gasoline-Ethanol Mixtures in Compression-Ignition Engines

Biofuels represent a viable contribution in increasing the energy system sustainability. Since a long time, ethanol has been used as a fuel for spark-ignition engines and, nowadays, it is being tested also in compression-ignition engines. Furthermore, in order to exploit the emulsifying properties of gasoline, small amounts of this fuel can be added to the ethanol-diesel blends. Due to the presence of bio-mass derived fuels, and considering that ethanol is an oxygenated fuel, this kind of fuel mixtures, fired in high efficiency engines, could lead to the reduction of both CO2 and particulate emissions. In order to deeply investigate the behavior of the above mentioned mixtures, when they are injected at high pressure in the combustion chamber of Diesel engines, numerical analyses have been carried out by using the AVL-FIRE 3-D code. First, the spray characteristics of diesel fuel, injected into a quiescent chamber in non-evaporative conditions, have been numerically evaluated and the obtained results have been compared to the available experimental data. Later, in order to obtain useful information on both the combustion process and the engine emissions, the behavior of the ternary diesel-ethanol-gasoline blend, injected and fired in a Diesel engine available at the test bench, has been numerically simulated. Referring to the simulations of the combustion chamber of the compression-ignition engine, the most remarkable result shows the combustion of oxygenated fuel blends leads to an important reduction of soot production. Furthermore, using diesel-alcohol mixtures, lower NOx emissions have been observed at the analyzed operating points.