A single n-heptane droplet behavior in rapid compression machine

This study investigated the evaporation characteristics of a single n-heptane droplet inside a rapid compression machine (RCM). The RCM is an experimental apparatus used to simulate a single compression stroke of an internal combustion engine to observe the combustion phenomena in homogeneous charge compression ignition (HCCI) environments. During the compression stroke, the temperature inside the RCM increases and the fuel droplet evaporates under unsteady conditions. In this study, a single n-heptane droplet was placed at the center of the reaction chamber. The droplet was suspended from the tip of a fine thermocouple (50 μm), and the transient bulk temperature of the droplet was measured. The evaporation process was recorded by a high-speed charge-coupled device (CCD) camera with a frame rate of 500 frames per second. The initial droplet diameter (450–700 μm) operation time (170 ms and 210 ms), and the compression ratio (14 and 18) were set as experimental parameters. To observe the pure evaporation of the droplet, the reaction chamber was filled with N2 gas. Experimental results showed that the droplet diameter decreased with the constant evaporation rate during the evaporation process, even under time-varying temperature and pressure surrounding the droplet. The evaporation rate of the droplet rose as the diameter of the droplet increased, due to the differences in droplet heat capacity. As the compression rate increased, temperature inside the reaction chamber increased and increase in droplet evaporation rate was observed. The operation time did not appear to affect the droplet’s evaporation rate.