Researchers at Purdue University have found that they can extend a flexible control strategy designed better to manage the lower fuel energy density and increased NOx emissions from biodiesel use to also address biodiesel variability due to feedstock and processing differences. A paper on their work is published in the International Journal of Engine Research.
Use of biodiesel—fatty acid methyl esters produced from renewable and domestically available sources—generally lowers carbon dioxide, carbon monoxide and particulate matter emissions. However, biodiesel brings some challenges, including lower fuel energy density; potentially increased nitrogen NOx emissions; and variability in the composition of the fuel due to differences in the feedstock and in processing.
The researchers had already developed a control algorithm incorporating energy-based fueling for torque control and combustible oxygen mass fraction control for NOx regulation. In this new paper, they extend that work to address fuel variability.
The type of oil/fat from which the biodiesel is derived will impact the fuel properties via variation in the fuel’s fatty acid composition. The fuel’s fatty acid composition can also be altered by an additional processing done in order to change certain fuel properties. For example, the saturation level of biodiesel can be reduced in order to lower the fuel cloud point, making it suitable for colder climates. The effect of variation in the fuel fatty acid structure on the previously developed control algorithm is studied in this work.
It is shown both theoretically and experimentally that the proposed control algorithms are robust to variation in the fatty acid composition of biodiesel due to the fact that biodiesels with very different fatty acid compositions exhibit minor changes in heating values and fuel oxygen mass fraction. As such, the control technique is suitable for use with variable blend fractions of biodiesel produced from different feedstocks as well as fuel processed to improve cold weather operation.—Hall et al.
Carrie Hall, Gayatri Adi, Gregory Shaver and Bernard Tao (2012) A Robust Fuel Flexible Combustion Control Strategy for Biodiesel with Variable Fatty Acid Composition during Mixing-Controlled Combustion. International Journal of Engine Research doi: 10.1177/1468087412465276