Search Results

Both cylinder head deposits (CHD) and piston top deposits (PTD) can be accurately characterized using deposit thickness profiles. Fleet test data using 1994 Lumina vehicles demonstrates the utility of this technique for both the qualitative and quantitative comparison of test results. This particular vehicle is able to differentiate between the relative deposit forming tendencies of different fuel additives. Repeatability of tests measuring deposit formation are discussed. The relative magnitude of deposit profiles and the scatter in such profiles both have to be considered in the statistical evaluation of performance differences.

Cylinder head deposit (CHD) thicknesses and weights were measured for five vehicle types in 16,093 km (10,000 miles) and 24,140 km (15,000 miles) fleet tests and for the Ford Ranger in additional 8,046 km (5,000 miles) vehicle tests. Thickness measurements at 60 locations in each combustion chamber provided an accurate picture of the distribution of deposits. Deposit formation profiles measured by deposit thickness in the cylinder heads were reproducible for pairs of matched vehicles in different tests. Deposit profiles varied little for different test series even though selected test conditions were altered. Similarly, almost all tests showed good repeatability of deposit profiles for the four to six combustion chambers of a given engine. The lack of reproducibility for one vehicle type was related in part to the changing orientation of the combustion chambers along each of the cylinder heads.