The formation of burnt fuel residue is a typical issue with certain types of engines. The incomplete combustion of diesel, for example, results to the formation of a black powders or flakes of amorphous carbon. This residual compound can have significant consequences on the lubrication system.
Many lubricants are developed to help with removing burnt fuel residue and other contaminant particles from the system. The contaminants are absorbed by the lubricant. As the lubricant passes through the filter, the contaminants are trapped and can then be removed.
However, some contaminant particles are too small to be filtered even with fine filters. The particles remain in the lubricant, altering its viscosity and interfering with some of its qualities. Using a fine filter would not work and could cause more harm than good. Lubricants contain additive particles that can also be removed by the finer filter. The smaller holes of the filter can also increase the resistance and slows down the flow of the lubricant within the system.
The best way to deal with burnt fuel residue is to regularly inspect the quality of oil and perform replacement is needed. There are many techniques of detecting burnt fuel residue in oil. A commonly used technique is the FTIR or Fourier transform infrared technology that determines the level of contamination by measuring the infrared spectrum emitted or absorbed by the material.
Another technique is the pentane insoluble test wherein the residue and particles are separated from the oil by mixing a solvent with the lubricant.