| Up to now, domestic Ⅳ emission regulation of diesel engine has been implemented fully, and selective catalytic reduction(SCR) is considered as one of the most satisfactory diesel engines aftertreatment technologies to meet the domestic Ⅳ and Ⅴ emission regulation in a short time. However, SCR technology still faces some problems when applied in diesel vehicle, for instance, the problem of poor conversion efficiency. Abroad researchers has solved this problem by installing pre-oxidation device(DOC). However, this DOC-SCR system has strict requirement of sulphur content in diesel, and currently, our country’s diesel commonly has a high sulphur content, which can poison the noble metal catalyst of DOC. Therefore, the problem, that pre-oxidation device loses efficacy in the condition of high sulphur content diesel, must be solved, if SCR is adopted to reduce NOx emission of diesel engines in China.In order to solve the above problems, a double-dielectric non-thermal plasma(NTP) reactor and a new kind of NTP-SCR system were developed. Through air discharge experiment, the performance of NTP reactor was tested and the working parameters was optimized. Through diesel engine bench test, the possibility that NTP reactor can pre-oxide NO of diesel engines was researched. At last, the experiment that NTP-SCR system reduces NOx of diesel engines was carried out. These researches mainly consist of three section as followed.1、A double-dielectric NTP reactor was designed and air discharge test was carried out. The effects of discharge peak to peak voltage(Vp-p), discharge frequency and air flows on the volume fraction of NO and NO2 were researched. Spectral information of discharge region under different air flows and working voltage was collected, and the reaction mechanism of NTP was also discussed. The results showed that air flows doesn’t much affect spectral intensity of the discharge region. When the discharge frequency was constant, the spectral intensity of the discharge region increased with Vp-p. When the Vp-p was constant, the spectral intensity of the discharge region decreased with increasing discharge frequency while the discharge frequency was from 7 kHz to 9 kHz. The regulation of the volume fraction of NO and NO2 changed when discharge frequency changed. The volume fraction of NO and NO2 decreased with increasing air flows into the creator, but the changing regularity that the volume fraction of NO and NO2 varied with Vp-p remained the same when the air flows was the only parameter.2、A engine bench test system of double-dielectric non-thermal plasma(NTP) reactor for pre-oxidizing diesel emissions of NO was established. The effects of several parameters such as discharge peak to peak voltage(Vp-p), discharge frequency, exhaust flows and engine load on the performance of NTP pre-oxidizing NO were studied. The results showed that, exhaust flows had insignificant effects on the performance of NTP pre-oxidizing NO. Under low load condition and different discharge frequencies, a critical value of the Vp-p was all existed, which could make the ratio of NO/NO2 be 1/1. The NTP ability to pre-oxidize NO weakened gradually with the increase of engine load. When the engine load was 0% or 25%, the ratio of NO/NO2 could reach 1/1. In these working conditions, SCR system could improve the conversion rate of the NOx at low temperature zone through quick reaction combined with NTP.3、A test system of the SCR system to reduce NOx emission of diesel engine, combined with NTP reactor, was established. The effects of several parameters such as NO2/NO ratio and catalyst temperature on the NOx conversion rate were studied. The results showed that, under the condition of low catalyst temperature, the NOx conversion rate increased obviously with NO2/NO ratio and reached the maximum when NO2/NO ratio was 1. As catalyst temperature increased, NO2/NO ratio had weaker influence on the NOx conversion rate. When the catalyst temperature was high, the NO2/NO ratio had no impact on the NOx conversion rate. |
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