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.

Prior to 1994, the ability of an engine lubricant to resist aeration was measured by Test Method D 892. During the development of the API CG-4 category in 1994, however, it was found that this bench test did not correlate with aeration in the International T 444E engine. The EOAT was developed, therefore, to provide a better measurement of the ability of a lubricant to resist aeration during engine operation. This test has been included in API CG-4, CH-4, and CI-4 categories for heavy-duty diesel engine oils.

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.

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.