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The Coordinating Research Council (CRC) Intake Valve Deposit Group is evaluating a dynamometer based test to rank fuels for their relative tendency to form intake valve deposits. The Ford 2.3L OHC, dual spark plug equipped engine was previously selected (1*) for use in the current test program to determine optimum test conditions. A fifteen test design of experiments was constructed to reproduce intake valve deposit weight and morphology, representative of that causing field driveability problems. Test results were analyzed and a two-mode composite test was deduced from deposit weights, visual ratings, observations on the test valves and thermogravimetric analysis (TGA) results. Once the test was optimized, an additional ten test matrix was conducted to assess both repeatability and the performance of the test over a range of deposit levels. Base fuel and base fuel + two additive combinations were tested to provide a range of deposit tendencies.

The 1991 Ford 2.3L engine was selected as a test engine for purposes of developing a standard industry accepted intake valve deposit test. Candidate engine selection criteria and test protocol are discussed. Three 1991 domestic engine types were compared for intake valve deposit (IVD) characteristics using the SwRI/BMW on-road cycle. A composite blend of six, non-additized fuels was chosen for both base fuel and base fuel + additized tests. A test matrix was designed to assess both IVD accumulation characteristics and sensitivity to additive chemistry for each engine. Screening tests were performed using two 1985 BMW 318i sedans to find a suitable additive for additized tests and to use as a reference to the existing database.