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Detergent additives in automotive gasoline fuel are mainly designed to reduce deposit formation on intake valves and fuel injectors, but it has been reported that some additives may contribute to CCD formation. Therefore, a standardized bench engine test method for CCDs needs to be developed in response to industry demands. Cooperative research between the Petroleum Association of Japan (PAJ) and the Japan Automobile Manufacturers Association, Inc. (JAMA), has led to the development of a 2.2L Honda engine dynamometer-based CCD test procedure to evaluate CCDs from fuel additives. Ten automobile manufacturers, nine petroleum companies and the Petroleum Energy Center joined the project, which underwent PAJ-JAMA round robin testing. This paper describes the CCD test development activities, which include the selection of an engine and the determination of the optimum test conditions and other test criteria.

Worldwide concern about combustion chamber deposits (CCDs) has increased from the viewpoint of fuel and additives technology, which has been developed for the cleaning of intake valve deposits (IVDs), intake port deposits and injector deposits. The research effort described here, focused on the differences between CCDs and IVDs in terms of quality based on analyses of CCDs and IVDs collected from used vehicles from the Japanese market. The CCDs and IVDs were characterized according to weight, benzene-solubles and sulfated ash. Since the sulfated ash in CCDs is a key to understanding the effect of engine oil on CCD formation, the relationship between CCDs and the sulfated ash in CCDs was evaluated under the two typical conditions on a 2.0L engine testing bench. Based on the results, the gasoline-related and oil-related factors were estimated for these conditions. Moreover, the effect of CCDs on exhaust emissions was investigated in a 2.2L vehicle.

Recently, an audible clattering noise has been noticed in some vehicles during cold engine starts, mainly in the U.S. The clattering is referred to by various names, such as “carbon knock,” “carbon rap,” “mechanical knock” and “combustion chamber deposit interference (CCDI).” CCDI is believed to be caused by the deposit formation in the combustion chamber. In the research effort described here, CCDI was successfully reproduced in a 2.5-liter multipoint injection engine with a polyolefin amine gasoline additive. It was determined that the CCDI was caused by mechanical contact between the piston top and the cylinder head deposits. The vibration due to CCDI originated mainly at the thrust side of the piston right after top-dead-center on compression stroke and was characterized by a high frequency response. Combustion chamber deposit (CCD) formation depends on many factors, including gasoline additives.