Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/120548
OIL ANALYSIS BY GERARD A BELLANEDA , PSA PEUGEOT CITROEN, AND DIDIER PIGEON, AD S YSTEMS NEW Method for Evaluating Lubricant Dispersancy O One of the primary functions of a lubricant is to preserve the cleanliness of a combustion engine's mechanical parts. The cleanliness of these parts is facilitated by the introduction of detergency and dispersancy additives to the engine oil. This last property, dispersancy, is the property that allows the oil to suspend and carry away pollutants of diverse sources, such as soot from combustion, metallic particles from wear, corrosion of mechanical parts and insoluble products resulting from the aging of the oil, etc. With the arrival of new fuels (e.g., biodiesel, ethanol blends, etc.), the existing or traditional lubricants present an important variability in terms of durability and resistance to pollutants. Studies show that the dispersancy capacity of certain types of lubricants is significantly degraded by the presence of specific pollutants, in particular fatty-acid methyl esters of biofuels, which have a significant impact. It is therefore important to quantify the degradation of the oil in service (engines or transmission oils) and to monitor the evolution of the oil's dispersancy properties during use to be able to determine steps and intervals for maintenance. Additionally, for the development of new lubricants, it is necessary to define a criterion of acceptance of the oil by its dispersancy capacity. Existing Methods for Analyzing Lubricant Dispersancy To date, no rigorous analytical method makes possible the measurement of the dispersancy capacity of the lubricant. The blotter spot method could provide an answer to this need, but the only method practiced to date is based on a visual evaluation. This subjective visual interpretation is not rigorous and consequently limits the information that could be provided by the method. Engine Test The objective of the engine test (DV4TD – CEC-L-93-04) is to evaluate the effect of combustion soot on engine oil viscosity increase and piston cleanliness. This procedure simulates highspeed highway service in a diesel-powered passenger car. The 28 March - April 2013 | www.machinerylubrication.com procedure fixture is an engine dynamometer procedure stand with a Peugeot DV4TD/L4 four-cylinder, in-line, common rail diesel engine installed. Pistons and rings are future rated for lacquer deposits and ring sticking. Kinematic viscosity at 100 degrees C, soot content and iron content in the used oil are evaluated at 24-hour intervals during the procedure. The final oil drain is used in conjunction with the intermediate samples to interpolate the absolute viscosity increase at 6 percent soot. This approach has the merit of exactly reproducing the behavior of the Figure 1. Dispersancy tester instrument lubricant under definite conditions of the test. However, the evaluation methods on the engine are very long and expensive. In addition, the precision of this test is not at the level of a laboratory method. Blotter Test Method Several versions of this old method exist in industry. Many studies show the value of this method as being rich in practical information on in-service lubricants, but it remains mainly manual and homemade. The interpretation of the blotter spot continues to be subjective and not formalized by a universally recognized method. To conduct the test, a small quantity of a homogenized sample is heated to 240 degrees C (464 degrees F) for 5 minutes. The purpose of this short period of intense heating is to stress any oil that is close to thermal or oxidative failure so that the blotter spot shows a positive response. Any oil that is still in good shape will not be affected by such a short heating period, which will be reflected in the dispersion pattern of the blotter spot.