Using Intake Valve Deposit Cleanup Testing as a Combustion Chamber Deposit Discriminator 982714
Carefully controlled intake valve deposit (IVD) cleanup testing is found to be an effective method for differentiating the effect of the deposit control additives on combustion chamber deposits (CCD). The IVD buildup procedure produces a consistent initial level of CCD that the cleanup additive, the additive of interest, continues to build on until the end of the cleanup test. This “end of cleanup” CCD is found to be as repeatable and differentiable a measurement as tests run under the more common “keep clean” type operation. While IVD cleanup testing induces a mid-test disturbance in the form of the end of buildup measurement, it aligns well with two key CCD protocols in terms of the higher additive treat rates used and the extended total test length. In an analysis of results from IVD cleanup tests run using four different engine/vehicle procedures on seven different additives, several findings stood out. Variations in end of buildup CCD had a predictable effect on end of cleanup test CCD and additive effects could be assessed conditional on the buildup result. Of the models considered, the best predictor of CCD thickness results at the end of test was one that used the thickness results obtained at the end of IVD buildup as a covariant. The variation in end of buildup CCD and the procedure for obtaining the buildup CCD measurement appears to have had little adverse effect on the end of cleanup CCD variability. End of cleanup variability estimates from this study compare favorably to those of other studies with procedures of presumably lower inherent variability. Finally, the repeated buildup CCD thickness measurements provide a measure of quality control, a first order estimate of variability, and useful correlating data for operational changes. This study also reiterates the difficulty in differentiating the CCD performance of commercial additives under realistic conditions in a cost effective manner. Only the two most dissimilar additives used could have been significantly discriminated in a single test.