Sustainable Aviation Fuels Approval Streamlining: Auxiliary Power Unit Lean Blowout Testing

An underpinning hindrance in the market penetration of sustainable aviation fuel is the approval process for alternative jet fuels. One solution to this is to develop low-cost screening tools that can be implemented earlier in the approval process. Auxiliary power unit combustors historically show the most sensitivity to physical and volatile fuel properties, making it a useful tool in assessing potential alternative jet fuel effects at test conditions representative of operability stability limits. It is hypothesized that these observations can be explained via timescale analysis considering fuel droplet breakup and evaporation, combustor mixing, and chemical reactivity timescales on the progression to lean blowout. This paper combines timescale theory with reduced-order fuel properties and random forest regressions to represent each of the identified timescales. Random forest regressions with only these timescale representative properties account for better than 95% of experimental variance across seven very different test conditions. An additional sensitivity analysis corroborates previous observations in which auxiliary power units are most sensitive to mixing, atomization, and evaporative timescales. Testing of these key timescale representative fuel properties requires 280 mL of fuel and could be used as a new screening tool for alternative jet fuels, reducing the time and cost for their approval.