ABSTRACT
The objective of this study was to investigate the deposit-forming tendency of vegetable oils as a function of fatty acid prole. Vegetable oils were thermally and oxidatively stressed at high temperatures (250°C). The temperature regime of these studies was in the range of crown head and upper piston temperatures in a conventional and high performance spark ignition (SI) engine. Differences in deposit forming tendency of the oils studied were signicant. These large differences in deposit-forming tendency under the same stressing conditions can be attributed to the differences in the chemical composition of the vegetable oils. The amount of carbonaceous deposit left on a stainless steel (SS) 304 strip was found to be directly proportional to the amount of palmitic and total saturated acids present in the vegetable oil. Carbon deposit was found to be independent of the amount of stearic acid present in the vegetable oil. Oxidative stability was found to be dependent on the total unsaturated fatty acid amount. Different deposit morphologies or surface coverages were observed from vegetable oils having different fatty acid compositions. In general, the SS 304 surface after thermo-oxidative stressing was covered more uniformly with higher oleic acid content vegetable oils, whereas a layered surface coverage was seen with vegetable oil containing higher palmitic acid content. A sponge-like deposit morphology was observed with coconut oil, a vegetable oil that is solid at room temperature having 90% total saturates.
