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This study investigated the relationship between the average molecular structures of combustion chamber deposits (CCD), the quantity of deposit formed and the aromatic content of the fuel. Solid-state 13C nuclear magnetic resonance (NMR) techniques developed for the study of coal were applied to CCDs generated in spark ignition engines on dynamometer test stands. Using these techniques, the molecular structures were identified and related to fuel chemistry, cylinder deposit thickness and cylinder deposit weight. With a better understanding of the structure of the deposits formed during combustion, fuel formulations and CCD control-additive development can be greatly improved.

Combustion chamber deposits (CCDs) have been quantified with a variety of methods in the past. Historically, the primary means of quantifying fuel related deposits involved either a visual rating, deposit weight, or an audible method. However, these methods can be time consuming and do not give any indication of actual location or volume of these deposits. A unique method of gaining accurate cylinder head and piston top deposit volumes has been developed and utilized for several years. Data will be shown using the deposit thickness method and its benefits compared to CCD weights, Coordinating Research Council (CRC) visual merit ratings, and an audible method.