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In response to industry demands for a method to qualify fuels for their intake valve deposit (IVD) forming tendencies, the Coordinating Research Council (CRC) has developed an engine dynamometer test procedure. In Phase I, the 2.3L Ford engine was chosen as the focus test engine in comparison testing with two other high volume U.S. manufactured engines.1* A two-mode dynamometer test was developed in Phases II-A & II-B and shown to discriminate among the test fuels at a 95% confidence level.2 In Phase III, both an interlaboratory study (ILS) of the two-mode dynamometer test and a vehicle fleet study were performed. The ILS was conducted to determine the repeatability and reproducibility of the test procedure and also to fulfill requirements for consideration of the test as an American Society for Testing and Materials (ASTM) standard.

Two V-6 engine types were investigated for the physical mechanisms causing combustion chamber deposit (CCD) formation. Experimental techniques and parameters such as combustion chamber deposit weights, thicknesses, thermogravimetric analysis (TGA), inductively coupled plasma (ICP) and solid state 13C nuclear magnetic resonance (NMR) were used to determine both the chemical and physical characteristics of combustion chamber deposit material. An analysis of the results indicated a mechanism for combustion chamber deposit formation consistent with that originally developed by Lepperhoff.1 Lepperhoff proposed that four layers exist in the combustion chamber deposit morphology. In contrast, the investigation described below has led to identification of only two distinct CCD morphologies.

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.