LUBRICITY OF DIESEL FUELS BY SLBOCLE: ASTM D6078
EXPLANATION
Diesel fuel injection equipment has some reliance on lubricating properties of diesel fuel. Shortened life of engine components, such as diesel fuel injection pumps and injectors, has sometimes been ascribed to lack of lubricity in a diesel fuel. The trend of Scuffing Load Ball-on-Cylinder Lubricity Evaluator (SLBOCLE) test results to diesel injection system pump component distress due to wear has been demonstrated in pump rig tests for some fuel/hardware combinations where boundary lubrication is believed to be a factor in the operation of the component. The tangential friction force, as measured in the SLBOCLE test, is sensitive to contamination of the fluids and test materials, the presence of oxygen and water in the atmosphere, and the temperature of the test. Lubricity evaluations are also sensitive to trace contaminants acquired during test fuel sampling and storage. This test method is applicable to middle distillate fuels, such as Grades Low Sulfur No. 1D and 2D, No. 1D and 2D diesel fuels, in accordance with Specification ASTM D975, and other similar petroleum-based fuels which can be used in diesel engines. It is not known that this test method will predict the performance of all additive/fuel combinations. Additional work is underway to further establish this correlation. The SLBOCLE and High Frequency Reciprocating Rig (HFRR) Test Method ASTM D6079 are two methods for evaluating diesel fuel lubricity. No absolute correlation has been developed between these two test methods. The SLBOCLE may be used to evaluate the relative effectiveness of diesel fuels for preventing wear under the prescribed test conditions. If a standard SLBOCLE rating has been set, then the single load test provides a more rapid evaluation than the incremental load test. Correlation of SLBOCLE test results with field performance of diesel fuel injection systems has not yet been determined. This test method is designed to evaluate boundary lubricating properties. While viscosity effects on lubricity in this test method are not totally eliminated, they are minimized.
TEST SUMMARY
A 50 mL test specimen of fuel is placed in the test reservoir of an SLBOCLE and adjusted to the test temperature of 25° C. When the temperature has stabilized, 50 % relative humidity air is used to aerate the fuel at 0.5 L/min while 3.3 L/min flows over the fuel for 15 min. During the remainder of the test sequence, 50 % relative humidity air flows over the fuel at a rate of 3.8 L/min. A load arm holding a nonrotating steel ball and loaded with a 500 g mass is lowered until it contacts a partially fuel immersed polished steel test ring rotating at 525 r/min. The ball is caused to rub against the test ring for a 30 s break in period before beginning an incremental-load or a single-load test. Wear tests are conducted by maintaining the ball in contact with the partially immersed 525 r/min test ring for 60 s. For incremental load tests, the test ring is moved at least 0.75 mm for each new load prior to bringing a new ball into contact with the test ring. The tangential friction force is recorded while the ball is in contact with the test ring. The friction coefficient is calculated from the tangential friction force. In the incremental-load test, the minimum applied load required to produce a friction coefficient greater than 0.175 is an evaluation of the lubricating properties of the diesel fuel. In the single-load test, a friction coefficient less than or equal to 0.175 indicated the diesel fuel passes the lubricity evaluation, while a friction coefficient greater than 0.175 indicated the diesel fuel fails the lubricity evaluation.
TEST PRECISION
Repeatability: 900 g
Reproducibility: 1500 g
The procedure in this test method has no bias because lubricity is not a fundamental and measurable fluid property, and thus is evaluated in terms of this test method.
