The Effects of Fuels and Engines on Intake Valve and Combustion Chamber Deposits

A mileage accumulation dynamometer (MAD) facility capable of running four vehicles continuously has been upgraded to provide a useful tool to evaluate the deposit control performance of fuels and fuel additives. Road cycles were recorded and repeated in this facility consistently. An optimized driving test cycle and testing duration have been developed to represent the field performance of fuels and vehicles.

This tool was used in a large testing program to evaluate the intake valve and combustion chamber deposit control capability of several premium gasolines, produced by major fuel suppliers in the U.S. Four high production volume vehicle models were included in the program. Results indicate that the level of deposits is a strong function of the engine type. Differences in engine design can result in considerable differences in valve and combustion chamber deposits. The study also demonstrates that existing fuels in the market affect the levels of engine deposits significantly.

Combustion chamber deposit (CCD) thickness values were obtained and compared with the corresponding weight measurements. Additional tests were conducted in a 2.3-liter engine similar to the Coordinating Research Council's (CRC) proposed intake valve deposit (IVD) test method. These results were compared to the results obtained using a similar engine in a vehicle. CCD weights also were compared with gasoline unwashed gum values. The correlation between IVD visual ratings and values obtained by a boroscope are also presented.