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To establish a criteria for engine oil requirements for Mack diesel engines, a program was conducted to establish a specification based on the use of a production multicylinder engine. Laboratory engine tests were supplemented by field tests to assure correlation. Subsequently modifications were made to the engine test procedures to accommodate modifications in engines being marketed. Oil monitoring and oil analysis programs were also implemented to further assist in assuring adequate engine lubrication.

This paper describes tests conducted to determine the effect of increased compression ratio on the multifuel capability of a standard diesel engine. The tests included power and cold starting capability checks, and it was found that the thermal efficiency was increased, combustion at full-load was improved, and part-load operation was definitely improved. Although there was no major improvement in cold starting characteristics as a result of increased compression ratio, the warm-up characteristics of the engine were markedly improved.

Controlled laboratory engine tests produced a correlation between the rates of viscosity and oxidation increase and the increase in engine bmep. A multicylinder turbocharged engine test procedure was developed which correlated with field experience of known lubricants. The Mack EO-G oil recommendation was based on results obtained by evaluating representative oils of different additive levels by this test procedure.

Field experience, together with engine laboratory testing, indicated the need for upgrading of Mack's diesel engine lubricant specifications. Field testing and laboratory testing indicated the superiority of several of the newer oil formulations for the Mack engine requirements. The newer type multi-viscosity oils were found to be particularly suited. A modified multi-cylinder engine test (T-5) was developed together with an oil specification based on the use of this test procedure (EO-J).

Heavy-duty natural gas engines available today are typically derived from diesel engines. The biggest discrepancy in thermal efficiency between a natural gas engine and its diesel counterpart comes at low loads. This is particularly true for a lean-burn throttle-controlled refuse hauler. Field data shows that a refuse hauler operates at low speeds for the majority of the time, averaging between 3 to 7 miles per hour. As a result, many developers focus primarily on the improvement of thermal efficiency at light loads and low speeds. One way to improve efficiency at light loads is through the use of a late intake valve closing (IVC) technique. With the increase in electronic and hydraulic control technologies, the potential benefits of late IVC with unthrottled control are realizable in production engines.

More stringent emission legislation has been a driver for changes in the design of Heavy Duty Diesel engines since the 1980s. Optimization of the combustion processes has lead to significant reductions of exhaust emission levels over the years. However, in the year 2002, diesel engines in the USA will have to meet an even more stringent set of emission requirements. Expectations are that this will force most engine builders to incorporate Exhaust Gas Recirculation (EGR). Several studies of the impact of EGR on lubricant degradation have shown increased levels of contamination with soot particles and acidic components. Both of these could lead to changes in lubricant requirements. The industry is developing a new specification for diesel engine lubricants, PC-9, using test procedures incorporating engines with EGR.