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Consumer use vehicle fleet testing is the ultimate test of a fuel additive. This real-world evaluation of how different types of engine designs and various driving conditions react to gasoline additives provides very useful information. A carefully designed employee fleet test consisting of 26, currently in-use, cars from four different makes and five different models was conducted throughout a twelve month period. The vehicles were split into matched pairs to provide two roughly equivalent fleets. Each fleet had the opportunity to run each of the two additives that were being tested. The unleaded base gasoline used throughout the test was similar to a reformulated fuel with 11% by volume MTBE, low aromatics, low T90 and low sulfur and was designed to provide good driveability throughout the seasonal changes associated with an entire year of operation. A fiberoptic borescope was utilized to evaluate intake valve and combustion chamber deposit levels.

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.

Various unleaded gasoline formulations and gasoline components obtained from refinery streams were evaluated for their deposit forming tendencies in several multicylinder automotive engines. A pair of GM 2.0L engines equipped with throttle body fuel injection and a GM 1.8L equipped with an electronic feedback carburetor were utilized to determine fuel property effects on intake valves, cylinder head, and piston top deposits. Engine performance with respect to octane requirement increase was measured. Various analytical techniques were used to study a variety of fuel properties. Analyses of gasoline formulations and related fuel components such as light reformate, motor alkylate, benzene raffinate, and light catalytically cracked refinery streams were accomplished. Gas chromatography-mass spectrometry (GC/MS) and flourescence indicator absorbance (FIA) analysis were performed on these fuels to determine their composition.

To reduce the time associated with fuel additive testing, a quick, reliable and repeatable screening test was necessary for the evaluation of intake system deposit levels. The additive development process has also shown certain additive packages to result in intake valve stickiness at low temperatures. A successful additive screening procedure was developed using a portable generator set. This paper describes an 80 hour test in which different additives and dosage levels can be evaluated for both intake valve deposit and stickiness levels. Test results were comparable to those found in automobile testing.