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In a 25-car field test, using five different gasoline additives and five car models, differences in IVD and CCD performance were observed. A comparison of IVD levels from the 15,000-mile field test with results from a 100-hour Ford 2.3-liter engine test (similar to the proposed ASTM/CRC IVD test) showed that the engine test generally ranked additives in the same order as cars in the field. IVD weights observed in the engine test were also similar to those in the field test. During the 15,000-mile field test, NOx increased an average of 17% and fuel economy improved by an average of 2.2%, both as a result of accumulation of deposits. A comparison of the increase in CCD with increases observed in NOx emissions and fuel economy did not show a clear relationship between the amount of CCD and the NOx and fuel economy changes observed. A good correlation was apparent between CCD weight and CCD thickness.

In a series of bench engine, road simulation dynamometer and on-road fleet tests various single fuel parameters have been examined to check their efficacy as potential predictors of CCD. Parameters included TGA residue, unwashed gum, T95, sulfur, PNA, and aromatics. The tests show that no fuel parameter acts as a good predictor of CCD thickness (maximum or mean) and that more complex physical-chemical models are required.