Impact of Biodiesel on Ash Emissions and Lubricant Properties Affecting Fuel Economy and Engine Wear: Comparison with Conventional Diesel Fuel

The increased use of biodiesel fuels has raised concerns over the fuel's impact on engine performance and hardware compatibility. While these issues have received much attention in recent years, less well-known are the effects of biodiesel on engine-out ash emissions and lubricant properties. Significant differences in composition between biodiesel and petroleum diesel fuels have the potential to influence ash emissions, thereby affecting aftertreatment system performance. Further, the fuel also interacts directly with the lubricant through fuel dilution, and may impact lubricant properties.

In this study, a 5.9L, 6 cylinder, Cummins ISB 300 diesel engine was outfitted with a specially designed rapid lubricant aging system and subjected to a set of steady-state engine operating conditions. The lubricant aging system allows for the investigation of the interactions of emissions and combustion products, as well as fuel dilution, on lubricant properties in an accelerated manner. Neat soy-derived biodiesel and a conventional ultra-low sulfur diesel were employed, and both gaseous and particulate emissions were sampled and characterized. The two lubricants used in this study consisted of a conventional CI-4 diesel engine lubricant as well as a CJ-4 oil. Both the fuels and lubricants were subjected to detailed chemical and physical analyses. Following the lubricant aging procedure, changes in lubricant properties were measured and accounted for. Additionally, total ash emissions for each of these fuels were measured and characterized. This study, thus, presents a first step in investigating differences and potential interactions of biodiesel fuels on lubricant properties as well as total engine-out ash emissions. Based on differences in lubricant properties and ash emissions, explanations for the observed results were developed and implications for the compatibility of biodiesel fuels with conventional lubricants and aftertreatment systems presented.