Compatibility studies between an indirect injection diesel injector and biodiesel with different composition: Stationary tests

Abstract

Compatibility between automotive materials and biodiesel is key for engine manufacturers, since failures occur in the medium term and may significantly reduce engine useful life. There are only few studies about compatibility between biodiesel and pure materials, but all agree there is biodiesel degradation and material corrosion beyond desirable values. This manuscript shows results about the compatibility behavior of an indirect injection diesel engine injector, with different types of biodiesel (from rapeseed, soybean, coconut and palm oil). Tests were carried out by static immersion of actual injector parts inside biodiesel, at room temperature, during 1100 h. To analyze elemental composition of each injector part and potential compatibility problems, scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) were used. Visual variations were detected in both biodiesel and metals, showing the need of a further quantification of both piece mass loss and biodiesel acid value increase. Metallic oxides on the surface were detected by X-ray photoelectron spectroscopy (XPS). After immersion tests, mass variation in alloying elements of each piece (behaving differently depending on their composition), besides biodiesel acid value differences, were found. In this sense, pieces with aluminum alloys showed the highest corrosion (mass loss) compared to those without aluminum in their structure, no matter the unsaturation degree and chain length of biodiesel. In sum, there were not conclusive results about the influence of biodiesel composition over injector materials. However, it was found that European biodiesel standard EN 14214 should include other parameters than just copper band corrosion, to determine material deterioration, provided that aluminum alloys and other metals react with biodiesel.