DIESEL-ENGINE OILS FORMULATED WITH HYDROCRACKED AND SOLVENT-REFINED BASE-STOCKS HAVE EQUAL EHD FILM THICKNESSES

Change in emissions standards for particulate and NOx have resulted in changes in diesel engine combustion processes and in diesel engine fu els. To meed the standards, injection timing changes and injection pre ssure changes have been made. Higher injection pressures required by t hese changes have been attained by using roller followers in valve and injector trains with Hertzian stresses at the injector-cam roller int erface in the range of 1.72-2.07 GPa (250,000-300,000 psi). As a conse quence, concerns have arisen regarding the oil film thickness in the i njector-cam roller interface. In particular, questions were raised as to differences in film thicknesses of oils formulated with hydrocracke d and with solvent-refined basestocks. Blends of two different commerc ial formulations in hydrocracked and solvent-refined basestocks were p repared. An optical interferometric method was used to measure film th icknesses under EHD conditions for the formulated oils and for the bas estock blends corresponding to each formulated oil. No differences in film thicknesses were found among the fully formulated oils, all blend ed to SAE 15W-40 grade. Differences were found between the basestock b lends for the two formulations due to differences in atmospheric press ure viscosities of the basestock blends.