Investigation Of Reducing NOx Emission On A Quasi-homogenous Lean Burn Gasoline Engine With SCR Catalyst

The development of the automobile industry has been greatly affected by themore and more severe problems of energy source lacking and environment pollution.As lean burn technology has great potential to reduce emissions and improve fueleconomy, it has become one of the most important developing trends of automotivegasoline engine. But, the rich oxygen exhaust gas caused by lean burn makes itimpossible to reduce the NOX emissions by the three-way catalytic converter. ThoughNOX emission can be effectively reduced by Storage-reduction Type NOX Catalyst,the sulfur in the gasoline will make the catalyst disabled. Therefore, to solve theproblem, the experimental study were conducted on the method of HC-SCR. Based on virtual instrument, this paper put forward a new idea to combine virtualinstrument with electronic control. According to it, a measure and control systemwere set up. Quasi-homogeneous mixture lean burn is realized, and the upmostair/fuel ratio is 22.5. The practices prove that it is a good test platform for SCRexperiments on lean burn gasoline engine. Experiments were conducted on a four-cylinder and sixteen-valve engine. Theflow characteristics of the inlet port are tested on a steady flow test rig with themomentum meter. The results show a rather strong tumble motion exists in the engine,which make lean burn possible. The ion-exchanged zeolite cordierite monolith catalysts are made by usingin-situsynthesized method. Their tokens are investigated by some ways, such as XRD,SEM and ICP. Baced on the simulation experiment, the engine experiments werecarried out, the NOX reduction capability of Cu-ZSM5, Cu-Pd-ZSM5, Cu-Rh-ZSM5and Cu-Ir-ZSM5 were evaluated. The results prove that the Cu-ZSM zeolite selective catalyst is not well active, butits temperature performance is good. So, it can be used as a carrier of multi-metalion-changed zeolite. For the first time, a overall steady NOx transforming rate isfound in the temperature of lean burn exhaust gas under the condition of combinedPd-Rh zeolite catalyst , the efficiency of reducing NOX is about 45%. From thetemperature curve, it can be found that the temperature window is extended withdifferent catalysts. The experiments on Cu-Ir-ZSM5 show CO can reduce NOX,perhaps its effect is obvious. In addition, all experiments found that the sulfur, thetemperature and water cann't affect these catalysts.According to the actual instance of automobile catalyst, a few of big catalystsamples(Ф82x125mm) were make and experiments were carried out, sometimes itcombine with a three-way catalyst. In a typical status of lean burn engine, underconditions of 50,000/h space velocity, Cu-Ir-ZSM5 catalyst can reduce 41.6% of NOXat most. After adding a three-way catalyst, the efficiency of NOX reduction can reachto 51% at 365oC degree. When the space velocity decline to 18,000/h, the maximalefficiency rate can get to 71.6%, which have exceeded the demand of "863" plan inchina.