NOx -SCR over Ag/ Al2O3 catalyst using ethanol (C2H5OH) as a reductant has proven its ability to significantly reduce NOx emission in a simulated engine exhaust gas environment. However the real engine exhaust gas environment is too complicated to be simulated. Therefore, the performance evaluation of the Ag/ Al2O3 catalyst in real exhaust gas environment is necessary. Moreover, the ethanol dosing device and control strategy also need to be validated for the practical use.
In this paper, firstly the catalyst performance and its sulfur tolerance was tested on an engine test bench and the effect of the catalyst on PM emission was investigated. Then the aftertreatment system composed of Ag/Al2O3 catalyst + Cu/TiO2 catalyst + Pt/TiO2 catalyst and ethanol dosing control based on open loop control was designed, and the diesel engine emission with the aftertreatment system was tested according to ESC test cycle. Finally, the whole aftertreatment system was integrated on a bus and demonstrated.
The performance test results showed that under the conditions of fresh catalyst and SV=30,000 h-1, high NOx conversion (up to 90%) can be obtained in the range of temperature 350∼450 °C. The aging test showed that sulfur absorbed on catalyst surface is the main reason for catalyst deactivation.
The Ag/ Al2O3 catalyst can effectively decrease the soluble organic fraction (SOF) in PM, but has little effect on dry soot (DS). The catalyst can also decrease the sulfate slightly when the exhaust temperature is below 410 °C, but dramatically increase the sulfate when the temperature is about 470 °C. Totally, the PM emission can be decreased more than half of the raw engine out when the exhaust temperature is 336 °C, but increased a little when the temperature is over 470 °C.
The emissions based on ESC test cycle showed that the engine with the aftertreatment system can completely meet EURO III regulations. Bus demonstration test result showed that the NOx conversion was less then 15%, which indicated that ethanol SCR has some obstacles to be overcome in vehicle road running.