Discriminating Tests for Automotive Engine Air Filters 2001-01-0370
Test standards for evaluating filters should provide uniform methods for the quantitative performance evaluation. Currently, automotive air induction filters are tested according to the SAE J726 standard. This standard recommends measurement of the gravimetric initial and final efficiencies. Measurement of gravimetric efficiencies provides limited information on filter behavior, since the information about the size of particles penetrating the filter is not included. In addition, the measurement of the initial gravimetric efficiency does not provide sufficient information on the initial stage of filtration. Determination of the efficiency at the initial stage of filtration is critical, since at this stage filters show their lowest efficiency, which can have an adverse effect on engine wear.
To overcome this problem and to obtain more knowledge on the initial stage of filtration, the initial gravimetric efficiency was measured at different levels of dust loading. The initial gravimetric efficiency measured at the dust loading of 5 grams was in the range of 90%, well below the recommended value of 99%. Additional information about this stage of filtration and the size of particles penetrating filters was obtained from the fractional efficiency measurements. Current filters remove approximately 40% of particles larger than 1 micron and 80% of particles larger than 2.5 microns.