Effect of lubricant on particulate emissions of heavy duty diesel engines

Effect of lubricant on particle emissions was studied using two heavy-duty diesel engines. Both particulate mass and particle number distribution were measured. Differences between lubricants were studied by dosing two percent of each lubricant (diesel engine oil) to diesel fuel. This arrangement was seen necessary to get clear differences between lubricants. The lubricant had a clear effect on particulate mass emissions. Two of the lubricants gave about the same emission as pure diesel fuel. The worst result was more than two times higher than without oil added to the fuel. The lubricants were all diesel engine oils with different base oils/additive package. Lubricant ash content presumably affects particulate mass. However, the difference in ash content between lubricants was no higher than 30%. Therefore, ash content can only partly explain the differences. The combustion characteristics and the sulphur content of the base oil are essential, too. All fuels containing lubricant produced higher number of small particles than pure diesel fuel. The lubricant, which gave the lowest particulate mass result, produced the highest number of particles. The reason might be that when the number of large particles decreases (also particle mass decreases), the small particles cannot agglomerate to the surfaces of larger particles. It is also possible that, for example, oxidation of catalyst could reduce the number of small particles.