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An investigation of the clean-up effects of a Combustion Chamber Deposit (CCD) detergent additive package on tailpipe exhaust emissions was conducted using (6) 1992 2.3L vehicles. Part one of this program was a deposit build-up phase for all cars and part two included two phases where, in the first phase, one-half of the cars were operated with the CCD detergent package and the other half were run as a control on the build-up fuel. In the final phase, the fuels were switched between the sets of vehicles to compensate for any vehicle to vehicle differences. A gasoline containing a detergent package which provided port fuel injector (PFI) and intake valve deposit (IVD) cleanliness performance in accordance with California Air Resources Board (CARB) requirements was used as the deposit build-up fuel for part one and as the control in part two. This fuel is typical of many gasolines that are in the market place today.

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.

An initial investigation into the effects of combustion chamber deposits (CCD) on tailpipe exhaust emissions has been completed. Four different model vehicles were evaluated for tailpipe emissions at four different deposit conditions. The deposit levels included a baseline clean level, a condition after deposit accumulation, a condition after CCD removal and finally a reevaluation after disassembly and mechanical clean up of the entire intake system. A special rig was developed using a walnut shell blasting device to allow cleaning of CCD without disturbing other engine deposits and without disassembly of the engine. This approach was taken to eliminate numerous time related variables and focus on the effects of CCD removal. The results of this investigation confirm that directionally HC, CO, and Nox all increased after the deposit accumulation period and decreased with the removal of CCD. However, statistically only Nox emissions increased significantly at the 90% confidence level.