ABSTRACT
Introduction In the pa st, engine performance and durability studies showed that combustion of neat (100%) vegetable oil and vegetable oil/No. 2 petrodiesel (DF2) blends led to incomplete combustion, nozzle coking, engine deposits, ring sticking, and contamination of crankcase lubricant (1-5). Contamination and polymerization of lubricating oil by unsaturated triacylglycerol (TAG) led to an increase in lubricant viscosity. Many durability problems were traced to poor fuel atomization aggravated by the relatively high kinematic viscosity (ν) (6,7). As shown in the tables in Appendix A, ν data for most TAG are typically an order of magnitude greater than that of DF2. Injection systems in modern diesel engines are very sensitive to ν. Although durability problems were less severe for indirect injection engines (1,8,9), the majority of engines deployed in North America are the direct injection type in which heating and mixing with air occur in the main combustion chamber and the design requires fuels with tighter control of properties such as ν and cetane number (CN). In addition, recent studies with preheated palm oil (10,11) suggested that although problems associated with high ν and clogged fuel filters were mitigated by preheating to 100°C, performance was unaffected and emissions did not improve.
