Biodiesel remains an alternative fuel of interest for use in diesel engines. A common characteristic of biodiesel, relative to petroleum diesel, is a lowered heating value (or energy content of the fuel). A lower heating value of the fuel would, presuming all other parameters are equal, result in decreased engine torque. Since engine torque is often user-demanded, the lower heating value of the fuel generally translates into increased brake specific fuel consumption. Several literature report this characteristic of biodiesel.
In spite of the wealth of fuel consumption characteristic data available for biodiesel, it is not clear how other engine performance parameters may change with the use of biodiesel. Characterizing these parameters becomes complicated when considering the interactions of the various engine systems, such as a variable geometry turbocharger with exhaust gas recirculation. This research study follows a systematic analysis of experimental data of neat biodiesel to diagnose how various key performance parameters are affected by the use of 100% palm olein biodiesel (relative to 100% petroleum diesel).
The two objectives of the research study are to 1) identify the engine performance parameters affected by the use of biodiesel and assess their differences compared to petroleum diesel and 2) characterize nitric oxide emissions and smoke concentrations in biodiesel exhaust to those in petroleum diesel. The study identifies that fuel-air ratio and inlet mixture density tend to increase with biodiesel (on average by 4.7% and 6.3% relative to petroleum diesel, respectively, which increases brake torque) while volumetric efficiency tends to decrease with biodiesel (on average by 2.5% relative to petroleum diesel, which tends to decreases brake torque). In net, the competing changes balance the lower heating value of biodiesel (lower by 9.2% relative to petroleum diesel) to yield the same brake torque as petroleum diesel. Furthermore, and consistent with most other literature, brake fuel conversion efficiencies are about the same between biodiesel and petroleum diesel fuels for this study. Finally, and also consistent with most literature, exhaust nitric oxide emissions tend to increase and smoke concentrations tend to decrease with the use of biodiesel. Nitric oxide emissions are 20.5% higher, on average, with 100% palm olein biodiesel than 100% petroleum diesel. Correspondingly, smoke concentrations (which are not necessarily representative of particulate matter emissions, the regulated emission of concern) are 85% lower, on average, with 100% palm olein biodiesel than 100% petroleum diesel. Some of these differences in exhaust species result from controlled changes by the engine controller (i.e., the differences are not completely attributed to property and combustion characteristic differences between the fuels).