Inhibition of particle bounce and re-entrainment using oil-treated filter media for automotive engine intake air filtration

Abstract

It is well known that the face velocity is a critical parameter for deciding the capture of airborne dust particles by fibrous filter media. As the face velocity increases, the capture efficiency of relatively large particles increases owing to inertial impaction. This is not true always as found in the current work. Here it was observed that the filtration efficiency of a cellulosic filter media decreased at higher face velocities for relatively large particles. This happened apparently due to particle bounce and re-entrainment phenomenon. Nevertheless, it poses a major challenge to achieve the futuristic target of filtration efficiency with ever-increasing trend of engine downsizing and less availability of installation space for automotive engine intake air filter media. In this work, it was demonstrated that the particle bounce could be suppressed by oil treatment to the filter media, as a result, the filtration efficiency of the oil-treated filter media increased at higher face velocities for large particles, unlike the untreated ones. This behaviour was explained in the light of theoretical and empirical models of air filtration. In case of less oil loading, the initial pressure drop across the oil-treated filter media was found to be almost the same as that across the untreated one. But, when the oil loading was high, the initial pressure drop increased tremendously. This behaviour was discussed with the help of Davies equation by taking into account of the changes in diameter of oil-coated fiber and packing density due to oil treatment. Further, at lower dust loading, the oil-treated filter media exhibited lower pressure drop and lower filtration efficiency at lower face velocities, but, at higher face velocities, the same media displayed higher filtration efficiency but with a similar pressure drop. However, at higher dust loading, the same media exhibited higher filtration efficiency.