PM and $\hbox {NO}_{\rm x}$ Removal for Diesel Engine Emission Using Ozonizer and Chemical Hybrid Reactor

Over the years, we have investigated particulate matter (PM) and NO_x reduction using nonthermal plasma-chemical hybrid processes without using catalysts. Among nonthermal plasma hybrid processes, the ozonizer combined with the chemical hybrid reactor was investigated using a 479 cc (5.5 kW) power generation diesel engine. The PM deposited on the diesel particulate filter can be incinerated by ozone and NO₂ in a wide range of flue gas temperature. The NO was oxidized to form NO₂ by ozone, and NO₂ was reduced by the 3% Na₂SO₃ chemical reactor. As the results, PM deposited on both metal and ceramic filters were successfully removed even at ambient temperature. The rate of PM incineration depends on the amount of ozone injected and was significantly higher than the rate of PM generation. Using 2.4% ozone concentration with a flow rate of 10 L/min, 82% of NO having 720 L/min was oxidized to NO₂, and 78% of NO_x was removed as a chemical scrubber. However, NO_x removal was deteriorated about 10% after 1-h operation. This was attributed to Na₂SO₃ oxidation by air, which was evidenced by the reduction of pH in the chemical reactor.