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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.

Portable generator sets have been successfully used as gasoline additive screening tools for intake system deposits (ISD) and intake valve sticking tendencies. To assist in the additive development process, a program was undertaken to determine if the generator sets might also be used to examine additive effects on combustion chamber deposits (CCDs). Tests that were performed and evaluated, show that the generator set is capable of discriminating between additives and correlating with engine and fleet testing results with respect to CCDs. This has resulted in a screening test with a single test cycle that can effectively screen fuels and fuel additives for intake system deposits, intake valve sticking and combustion chamber deposits. This paper discusses the engine and fleet tests that are used to show the generator set's ability to satisfy these criteria.