Filtering diesel exhaust gases with ceramic filters

Abstract

Results are given from three test series on a ceramic filter for diesel exhausts. In the first and second series, use was made of diesel fuel (in the summer), while in the third series, we used the Standard Euro-4 fuel. A grain-size analysis is given for the dust. The filtration performance (with hot gases) is compared with experiments on filters made of ceramic materials.Test results have been reported [1] for a ceramic filter used with diesel exhausts for plant in underground locations. In 2007, three new test series were performed that included certification ones with a ceramic filter for handling exhaust from a diesel of type 6Ch 12/14 (without turbocharge) with nominal power of 50 kW [2].Filter parameters: total area of filter surface 7.8 m 2 ; porosity of filter material ε = 0.38 m 3 /m 3 ; thickness of filter h = 1.25 mm; and diameter of the grains used in making the filter components d gr = 22 µm.The exhaust gas flow under normal conditions was about 450 m 3 /h; as in the previous tests, we determined the dust concentration at the inlet to the filter and at the outlet from it by a gravimetric method and based on filters type AFA in accordance with GOST R 50820-95.In the first and second series, we used diesel fuel in accordance with GOST 305-82 (summer). The idling speed of the diesel was 1000 rpm, while in the working state it was 1500 rpm. The current load in the working state in the first series was 30 A, and in the second it was 58 A.The third (certification) series was performed with the Standard Euro-4 fuel. The shaft speeds in the idling and working states were as in the first and second series. The load current in the working state was 70 A (maximum permissible value 90 A). Table 1 gives the results from the three series. During the tests with a jet impactor [3], the dust was examined for grain size at the inlet to the filter with the diesel working on both forms of fuel (second and third series). The dust dispersion analyses (Fig. 1) are of significance because the fractional composition of the diesel fuel determines the unburned residue, i.e., the parameters of the suspended particles formed in combustion [4].When we used diesel fuel (summer), we obtained the following results from the grain size analysis: median particle size d m = 2.0 µm; and mean logarithmic deviation of the distribution in size with log σ p = 0.688.When we used the Standard Euro-4 fuel, the suspended particles were larger: d m = 3.1 µm and log σ p = 0.41. These larger particles were confirmed also by the data on the trapping performance: the mean performance in working states in the second series was 0.922, while in the third series it was 0.951.The grain-size data allowed us to compare the performance results with the ceramic filter with those for ceramic filter baffles [5]. In the comparisons, we used the averaged data from the experiments in each series (Table 1).