A robust fuel flexible combustion control strategy for biodiesel with variable fatty acid composition during mixing-controlled combustion

Abstract

Biodiesel is a diesel fuel alternative which is produced from renewable and domestically available sources. The use of biodiesel generally lowers carbon dioxide, carbon monoxide and particulate matter emissions. However, there are certain challenges associated with the use of biodiesel, mainly (1) lower fuel energy density, (2) increased nitrogen oxide (NO_x) emissions and (3) fuel variability due to feedstock and processing differences. In prior efforts, the authors have demonstrated that the first two of these challenges can be overcome for different blend fractions of soy-based biodiesel by using a control algorithm incorporating energy-based fueling for torque control and combustible oxygen mass fraction control for NO_x regulation. However, in addition to overcoming these combustion-related challenges, in this work, the authors consider the extension of these techniques to biodiesel generated from oils/fats of varying composition. 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.

Keywords

Diesel engine biodiesel control emissions robust control

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