Evaluation of Reciprocating Aircraft Engines with Unleaded Fuels

摘要

Clean Air Act legislation banned the uses of leaded fuels however, due to significant safety concerns, the EPA has not enforced compliance on the general aviation community. Nonetheless, significant economic pressures will continue to mount concerning the purchase, handling, and shipping of lead containing fuels and the disposal of lead tainted engine oils. This is driving the need to develop a high Motor Octane unleaded alternative to the current leaded stock. The cost to develop this alternatives expected to be exponentially proportional to the motor octane number of the fuel. A Coordinating Research Council Subcommittee has been formed to address the development of an unleaded fuel, with the current focus being the determination of the minimum motor octane number required for knock free operation of the majority of the piston engine fleet. This report details ongoing FAA efforts toward this effort. Data from both ground based engine testing and in-flight testing are included. The findings suggest that greater than 100 motor octane number will be required with lean fuel flow schedule conditions requiring substantially greater motor octane numbers. The data also suggest that significant decrease in octane requirement can be obtained by substantial power deration for the large turbocharged engines.