Experimental investigation of a butylcyclohexane / propylcyclohexane based naphthenic bio-blendstock surrogate fuel for use in a compression ignition engine

Abstract

Finding fuels derived from renewable sources that can displace fossil fuels is crucial to fight climate change as drop-in replacement fuels can immediately leverage ubiquitous, existing energy conversion hardware such as the reciprocating-piston internal combustion engine. However, any replacement fuel must necessarily maintain or ideally exceed the performance of fossil fuels. There are many possible pathways to obtain renewable fuels from biomass, but one pathway that has demonstrated the potential to meet the necessary thermophysical and performance requirements is the Catalytic Fast Pyrolysis pathway followed by hydrotreating to produce a bio-blendstock oil - rich in naphthenes. Due to the variability of bio-blendstock oil composition and variations in process parameters at such a production facility, developing a representative surrogate fuel is necessary for use in understanding compositional desirability and comparative experimental investigations are required to determine performance and emissions characteristics. This work builds upon past surrogate fuel formulation efforts to represent the naphthenic-rich bio-blendstock oils produced from a one ton per day (1TPD) catalytic biomass pyrolisis facility. Specifically, in this work a new formulation of surrogate fuel (SF), SF1.12, containing butylcyclohexane and propylcyclohexane, to represent the naphthenic hydrocarbon content, was created and produced and further blended (up to 30% by vol.) with research-grade No.2 diesel (DF2). These blends were then tested in a single-cylinder Ricardo Hydra compression ignition research engine. A range of conditions were evaluated by first holding the start of injection constant and varying the injection duration from max load (knock limit) to 40% of the max load value. In addition, experiments were performed by holding the fuel-air equivalence ratio constant while sweeping start of fuel injection, and the results were compared to previous generations of SF. It was demonstrated that increasing the proposed SF concentration in DF2 lead to an increase in load output, as well as to a decrease in sooting propensity without impacting NOx formation. It was also shown that this formulation of SF performs best in increasing load and reducing emissions compared to previously reported generations. This SF formulation in the concentrations evaluated (up to 30% by vol.) was shown to be a feasible candidate for displacing heavy distillate fossil fuels in engines.