Vegetable oils consist of glycerol and three variants of fatty acid. Each fatty acid gives different influence on ignition process which is important to be studied. Generally, fatty acids are categorized into polar and nonpolar fatty acids. Both of them have straight and bent molecule geometry. Their roles on evaporation and ignition are discussed based on their polarity and geometry. The study was done with a single droplet from various vegetable oils. Results show polar fatty acids are more reactive due to electric charge. Long and bent polar fatty acids are more reactive than the short and straight polar one since the former one has stronger polarity and higher electron mobility. The highest electron mobility in long and bent unsaturated fatty acid makes molecules less tight, thus, evaporation rate becomes the fastest. However, reactivity decreases since the polarity is neutralized by electron mobility. The existence of more than one double bonds in carbon chain of polyunsaturated oil partially blocks electron mobility, therefore, the polarity becomes stronger while electron mobility still high so it becomes more reactive with high evaporation rate. Faster evaporation rate makes ignition temperature lower since heat energy is changed into latent heat for phase change during evaporation. (C) 2019 Elsevier Ltd. All rights reserved.