Search Results

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.

The oxides of nitrogen (NOx) produced during combustion in an automobile engine play a major role in atmospheric chemistry and therefore need to be reduced by modifying vehicle engine designs and fuels of tomorrow. In a combustion chamber of a spark ignited engine, NOx is formed as atmospheric nitrogen competes with fuel molecules to couple with oxygen in the extremely hot burned gases behind the proceeding flame front (Zeldovich type) and as reactions occur directly in the combustion flame zone (“prompt” type). Since little nitrogen is present in the fuel, the fuel contribution to the overall NOx emissions is minor. Certain combustion chamber deposits have been shown to increase NOx emissions by thermally insulating the combustion chamber and taking up chamber volume, thus slightly increasing the compression ratio of the engine and raising the combustion gas temperature.