Extending Injector Life in Methanol-Fueled DDC Engines Through Engine Oil and Fuel Additives

Considerable development effort has shown that conventional diesel engine lubricating oil specifications do not define the needs for acceptable injector life in methanol-fueled, two-stroke cycle diesel engines. A cooperative program was undertaken to formulate an engine oil-fuel additive system which was aimed at improving performance with methanol fueling. The performance feature of greatest concern was injector tip plugging. A Taguchi matrix using a 100 hour engine test was designed around an engine oil formulation which had performed well in a 500 hour engine test using a simulated urban bus cycle. Parameters investigated included: detergent level and type, dispersant choice, and zinc dithiophosphate level. In addition, the influence of a supplemental fuel additive was assessed. Analysis of the Taguchi Matrix data shows the fuel additive to have the most dramatic beneficial influence on maintaining injector performance. The base engine oil formulation, which performed well in the 500 hour urban bus cycle, and is currently in use in several field locations, appears to be a good choice in terms of injector performance. While the matrix identified a different lubricant formulation as optimum, the expected improvement is expected to be small in comparison to the effect projected for the fuel additive.