2.2.4 Polarizing optical microscope (POM)
A DM2500P polarizing optical microscope (Leica Microsystems, Wetzlar, Germany) equipped with a Leica DFC420C digital camera was used for observing the wax crystal morphology and crystallization behavior of sample fuels. A drop of samples was putted on a slide, and initially hold at 30 °C for 3 min to eliminate all the crystal memory and subsequently cooled under a fixed cooling rate (0.8 °C/min) down to −60 °C using the liquid nitrogen, and the micrographs were captured in 1 °C increments under a magnification of 100×.