Gasoline Type and Engine Effects on Equilibrium Combustion Chamber Deposits (CCD)

The behavior of equilibrium combustion chamber deposits (CCDs) was examined in Honda generator engines. The initial rapid CCD build-up was followed by a slower period of growth until an equilibrium level was reached after about 240 hours. The chemical composition of these CCDs follow the same compositional trends originally established for a range of vehicle CCDs produced up to 20,000 miles. The mean CCD thickness was related to the total CCD weight obtained from end of test samples. Differences were found in the equilibrium CCD thicknesses among base fuel and gasoline additives. The range of the mean CCD thickness was 155 microns to 240 microns. Three different experimental additives gave equilibrium CCD thickness that were 2% below, 1% above and 22% above the corresponding base fuel. The mean equilibrium CCD thickness for a commercial additive package was 8% above the corresponding base fuel. Analyses of equilibrium CCD thickness changes at individual sampling locations identified active regions on the piston tops near the cylinder wall and by the exhaust valve near the cylinder wall. Other selected regions gave individual point thickness changes comparable to calibration measurements. Mean individual point CCD thickness changes with base fuel and with a commercial additive package were not significantly different. This work demonstrates that it is possible to quantify equilibrium CCD performance differences for gasoline by utilizing CCD thickness measurements