Richard Eugene Baker

Effects of Combustion Chamber Deposit Location and Composition

Combustion chamber deposits were analyzed for chemical composition in an attempt to explain the octane requirement increase (ORI) and exhaust hydrocarbon (HC) increase observed during mileage accumulation in two vehicle test fleets. Comparisons are made of deposit composition differences within different areas of a combustion chamber, between cylinders, and between engines. Deposits accumulating in the end gas areas, on exhaust valves, and in cylinders with high oil consumption can be distinguished by comparison of H/C atom ratios, carbon content and inorganic compound content. Differences in deposit composition can be observed between engine families and between driving cycles with the same engine family. Composition differences between deposits from two engine families suggest a possible explanation for the ORI trends observed in the fleet test. Chemical composition alone is not sufficient to identify a unique relation between deposits and ORI. The flame end gas region was located with ionization gaps and was compared with deposit mass distribution to examine the influence of chamber geometry on ORI. Similarly, the HC increase mechanism requires a more complete definition than available from chemical characterization alone. A vehicle was tested with fuel containing MMT followed by operation and tests with clear fuel. The results suggest that HC are controlled by the deposits on the exposed surface only and that deposit equilibrium takes place primarily on the exposed surface rather than by massive deposit removal and replacement.

Future Transportation Fuels and the Environment

The selection of fuels for use in transportation has been based upon cost, function, available energy resources and convenience. Petroleum-derived fuels, gasoline and diesel, have consistently been the fuels of choice. Concern for the effects of selected species in the products of combustion of hydrocarbons on the environment continues to increase, and will influence choice of fuels in the future. Fuel properties vary widely among the alternatives worthy of consideration for the future. Utilization of alternative fuels will require innovative approaches in sensors and controls in order to develop vehicles with features and function to rival current vehicles. The fuel composition sensor, on-board computer and related controls used on Flexible Fuel Vehicles have resolved the transition issue to methanol fuel. Sensors and control systems remain to be developed for other fuel alternatives.