Experimental Investigation of n-C7H16/Ethanol Blended Fuels on Auto-ignition and Flame Propagation in High Temperature/Pressure Constant-Volume Combustion Vessel

<div class="section abstract"><div class="htmlview paragraph">This study aims to investigate the effect of ethanol blends on flame propagation and auto-ignition under high pressure and high temperature conditions. Experimental investigations are conducted using n-C<sub>7</sub>H<sub>16</sub> / ethanol blends at various blending ratios (0, 5, 10, 20, 40, 70, and 100 vol%). The blends are premixed with air at stoichiometric ratios and ignited centrally in a cylindrical constant-volume combustion chamber (20-mm inner diameter, 80-mm long) under elevated temperature (500 K) and pressure (1.0 MPa) conditions. The results show that auto-ignition occurs at an ethanol blend ratio of 10% or less and ceases above 20%. Increasing the ethanol blend to 70% results in a slight change in flame propagation speed, with a noticeable delay at 100%. The pressure measurements show a peak of about 5.6 MPa at a blend ratio of 5%, which gradually decreases with increasing ratios. High-pass filtering reveals the maximum pressure fluctuation amplitude at the 5% blend ratio, indicating increased knocking intensity at certain ethanol blend ratios. These results clearly indicate that, for the cases of larger ethanol content over 10%, auto-ignition, and therefore, the pressure increase by combustion can be suppressed. On the other hand, for the cases of less ethanol content than 10%, flame propagation can be accelerated, which leads to the rapid compression of the unburned mixture, and thus, the large amplitude strong auto-ignition.</div></div>