A capable filtration system for diesel locomotive engines can accomplish a number of things. The primary purpose is to remove soot, air particles and other contaminants and maintain the quality of the oil lubricating the engine. When this happens, the locomotive can travel greater distances and complete more trips between maintenance stops. This should also reduce labor and other operational costs.

The economic benefits depend on maintaining the purity of the oil, so clearly the goal is to remove as much of the contaminants as possible. Since the size of contaminants varies, finer filters would remove more contaminants and thus make for a better system, at least theoretically.

In practice, complications arise. Traditional filters direct the fluid through membranes made of paper or other material. Using this technology, if the filter size drops as low as 15 or 20 microns, hydraulic resistance will begin to drop significantly as contaminants collect. They would need to be removed in order to maintain sufficient oil flow.

This could be accomplished through one of two steps: Either the filter material would need to be replaced more frequently – thereby shortening maintenance intervals and increasing maintenance costs – or the filter area would need to be increased, and this would necessitate increasing the dimensions of the filter.

Since neither of these alternatives is satisfactory, an additional component is added – a centrifuge which removes a large portion of the contaminants. For a number of years, some Russian locomotives have employed conventional centrifuges, designed to remove contaminants by directing the oil through a spinning chamber. Centrifugal force pushes contaminants to the outside of the chamber while the oil exits through the chambers hollow axle.

Such systems are currently installed on approximately 16 percent of Russias diesel locomotives. The rest use just conventional paper filters. A team at All-Russian Railway Research Institute (VNIIZhT) studied five years of performance by combination self-cleaning/ centrifuge filters on D49 locomotives built by Kolomensky zavod, Russias largest producer of train engines. Results were poor. As it turns out, the conventional centrifuges remove little sediment because their rotors turn too slowly. Consequently, the self-cleaning filters again became clogged, causing drops in oil pressure and requiring frequent service. The locomotives in question had service intervals ranging from 25,000 to 50,000 kilometers, instead of 150,000 km as prescribed by the manufacturer.

Locomotives with more than 400,000 to 500,000 km of service are likely to have filter problems, and there are a number of common causes, in addition to inadequate filter performance. Engine oils used in these locomotives typically have a number of shortcomings. Viscosity at high temperatures is too low, and oxidation stability at high temperatures is too low. Detergents and dispersants do not adequately break up contaminants. These oils are also high in ash-forming metals, which further adds to the mix of particles being filtered. Air filtration is often inadequate, further contributing to accumulation of contaminants.

The obvious solution is to use centrifuges that are more effective. However, the question then was what to do with all of the sediment collected. Ships cope with this problem by using automatic separators that clear sediment out of the oil and dump it into large holding vessels. Space and weight constraints made this impractical in locomotives, however.

VNIIZhT found a solution by using self-cleaning filters from Alfa Laval in combination with a Delta electro centrifuge with replaceable containers for automated sediment unloading. These centrifuges capture much more sediment which can then be removed by replacing the containers.

The location of the centrifuge is an important factor. VNIIZhT places it between the first and second pumps because oil exiting the first pump is nine or 10 degrees C hotter than the oil exiting the second pump, which includes an oil-to-water heat exchanger. The higher temperature enables more separation of contaminants from the oil.

The volume of oil in the centrifuge is constant and not dependent on the rate of engine rotations. This allows the power exerted by the centrifuge motor to be held constant at 1.2 kW.

VNIIZhT tested the electro centrifuge by installing it on a shunter, a small locomotive that stays in the rail yard assembling rail cars into trains for a larger locomotive to pull. Monitoring showed that the electro centrifuge separated between eight and 18 grams of contaminants per hour, depending on the level of the oils impurity. VNIIZhT concluded that this pace would keep up with the rate of contaminants being generated in the oil and therefore allow the oil to maintain a level of cleanliness.

We also installed an electro centrifuge in combination with the Alfa Laval self-cleaning, full-stream filter on a 2TE116 diesel engine and then assessed its performance at a repair shop in Rtishevo, in the southern oblast of Saratov. The primary result was that maintenance intervals for the filter system were stretched to 180 days and nearly to the distances recommended by the locomotive manufacturer. This was a significant improvement over the intervals achieved with self-cleaning filters and conventional centrifuges.

The benefits of the new system are clear. As stated earlier, less frequent maintenance events require less work by crews and reduce labor expense. Locomotive engines are also better protected and will last longer because there is a closer balance between the rate at which contaminants enter into or are generated by the oil and the rate at which they are removed. Put more simply, the oil remains cleaner longer.

This is good for Russias rail network and therefore for all of Russia.