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We are interested in learning how commercial intake valve detergents contribute to combustion chamber deposits (CCD) in modern vehicles run for higher mileage. It is appealing to use short mileage (<5,000 miles) tests to evaluate the CCD performance of gasoline. However, the ability to extrapolate CCD performance to higher mileage (≥10,000 miles) is uncertain because of changes in CCD formation processes. For this reason, CCD from base fuel and a commercial IVD detergent package were generated in duplicate 10,000 mile tests using four 1996 model-year vehicles. The detergent package used a polyalkylamine detergent combined with a synthetic carrier fluid and achieved 94% intake valve deposit (IVD) reduction averaged across the four vehicles tested. The CCD weights were found to be variable between repeat tests but, when pooled across the four vehicle fleet, the CCD weights were found to be statistically the same for both the additized fuel and the base fuel.

There is continuing interest in understanding how fuel, fuel additives, and lubricants contribute to combustion chamber deposit (CCD) weights and compositions in order to better anticipate the impact of CCD on exhaust emissions and engine performance. For this reason, we have characterized a range of CCDs from bench engines and vehicles using solid state 13C Nuclear Magnetic Resonance Spectroscopy (NMR) and X-ray Photoelectron Spectroscopy (XPS). Differences in CCD composition and structure were related to the fuel, fuel additives, and engine oil used in the test. CCDs derived from most fuels run in modern engines are predominantly organic. The fraction of aromatic carbon ranges between 24 and 74% depending on fuels and test conditions over a test length of 1,000 to 20,000 miles. These aromatic carbons exist in predominantly 1 and 2 ring structures that are independent of the amount of aromatic carbon in the CCD.