ASTM D6894-13

5.1 Background—In the HEUI fuel system, the engine oil from the oil sump not only lubricates the engine, it also supplies a high-pressure oil system that takes oil from the main gallery and pressurizes it up to 20.7 MPa in a plunger pump (see Fig. A1.1). This oil is used to operate unit injectors that, when used in combination with intensifiers, increase the fuel injection pressure up to 145 MPa, independent of engine speed. The electronic controls permit varied injection timing and duration to provide optimum fuel economy and emissions. This system may, however, circulate all the oil in the sump in approximately 8 s; as a consequence, aeration of the oil can occur with some engine oils. International determined that 8 % oil aeration was the limit beyond which engine operation and performance would be impaired in actual service.

5.2 Method—The data obtained from the use of this test method provide a comparative index of the aeration resistance of engine oils used in medium- and heavy-duty truck diesel engines.

5.3 Use—The tendency of engine oils to aerate in direct-injection, turbocharged diesel engines is influenced by a variety of factors, including engine oil formulation variables, oil temperature, sump design and capacity, residence time of the oil in the sump, and the design of the pressurized oil systems. In some engine-oil-activated injection systems, the residence time of the oil in the sump is insufficient to allow dissipation of aeration from the oil. As a consequence, aerated oil can be circulated to the injector intensifiers, adversely affecting the injection timing characteristics and engine operation.