Search Results

The removal of tetraethyl lead (TEL) from U.S. automotive gasoline has caused concern within the general aviation (GA) community because of possible legislated environmental or supply restrictions on TEL, an essential ingredient in existing high octane aviation gasolines (avgas). At the same time, the GA industry which was besieged by numerous product liability suits in the past has seen a resurgence since the passage of the GA Revitalization Act in 1994. Because aircraft typically remain in service for many years, the survival of the industry may well depend on the availability of a high octane unleaded gasoline that provides a safe level of power and antiknock performance to the existing fleet. This paper describes the tools and techniques used by one team to develop fuels that provide the required antiknock quality while meeting most of the other criteria of the existing specification for high octane avgas: ASTM D 910, Standard Specification for Aviation Gasolines.

Four pressure transducers were installed into a split-head CFR engine to determine the spatial and temporal location of engine knock. The CFR engine was operated for these experiments using a primary reference fuel of 80% iso-octane and 20% n-heptane (octane number of 80). The compression ratio was varied to obtain different intensities of knock in the acquired data sets. Pressure transducer signals were recorded using a high speed data acquisition system and the resulting traces were analyzed to find where knock was occurring within the combustion chamber. A two dimensional triangulation scheme was developed to locate the knock origin based on the time difference between the acoustic signals detected by the pressure transducers. Limitations in spatial resolution due to digital sampling rate and variations in the speed of sound are discussed.