Experimental Study Of Four-way Catalyst On Diesel Engine Bench

Diesel engines are widely used recently, mostly due to their superior fuel economy, durability, reliability and high specific power output. However, there are more concerns about much NOx and PM emissions, and the NOx and PM in diesel emissions have trade-off relations. It’s difficult to purge NOx and PM simultaneously, for using the strategies of controlling the in-cylinder combustion process only. Four-way Catalyst catalyst can not only purge NO*and PM in diesel emissions simultaneously, but also avoid occupying much space and bringing high engine exhaust back pressure as a result of using of NOx and PM after-treatment devices in series, which is suitable for passenger car powered by diesel engine. Experimental studies of Four-way catalyst on a real engine bench, and simulation studies of detailed mechanism of NO-O2reaction which occurs in Four-way catalyst, were mainly conducted in the paper.Firstly, studies of continuous regeneration effects of Four-way catalyst under steady-state conditions, which was compared with DPF, were conducted in the paper. Secondly, NOx conversion efficiency of Four-way catalyst under transient-state conditions, and forced regeneration of DPF and Four-way catalyst were studied. At last, detailed mechanism of NO-O2reaction occurring in Four-way catalyst and the effect of reactant concentration on NO conversion rate were investigated.Experimental results include as follows:Under steady-state conditions, the pressure drop of Four-way catalyst is obviously lower than that of DPF, which tells us Four-way catalyst could continuously oxidize soot very well. The catalyst activity for soot oxidation increases firstly and then decreases with the increase of diesel exhaust temperature, reaching the maximum when the temperature is at386℃(200N-m). PM filtration efficiency of Four-way converter is above80%, and will be higher and higher with the increase of soot accumulation on Four-way converter. CO conversion rate also improves with the temperature, reaching80%at320℃. NOx conversion rate of Four-way catalyst is approximately3%under the transient state, with93.4%CO conversion rate and46.9%HC conversion rate at the same time.The experimental results of Forced regeneration show the light-off temperature of soot in DPF is at least above550℃. The soot distribution in Four-way monolith is not uniform with more in the middle, which results in damage of monolith because of higher local temperature and temperature gradient during regeneration.The results of simulation studies show detailed mechanism of NO-O2reaction can predict the changing of experimental data with the temperature. NO conversion efficiency increases with the increase of O2concentration in reactant gases, and decreases with the increase of NO or NO2concentration in reactant gases. The oxidation reaction of NO is auto-inhibited because of persistent deactivation of catalyst, which must be attributed to the formation of platinum oxide on the surface of the platinum particles.