Research On Four-way Catalyst On Diesel Engine

Because of its excellent power and economy in fuel, diesel is widely applied in recentl years. The main noxious contents of diesel emission are particles, CO, HC, and NO_x, and the concentration of HC and CO is relatively slow and they can easily be oxidized when oxygen is enough. So the focous of diesel emission control is NO_x and particles. At present, internal measures can reduce the emission to be relatevely low, but it can not meet the regulation in future. The after-treatment and combining various technoque together to purify the diesel exhausts are needed.The development of four-way catalyst all over the world is analyzed. Many purifying techniques in diesel have been developed but there still exist some shortcomings. Combine the technology of low-temperature plasma technology with catalytic conversion technology can obtain better effect theoretically, and the main problems existed in other four-way catalyst can be overcome, such as high emission temperature,complex supply equipment for reducer, which is of important value.Then the catalyst the perovskite type La_0.9K_0.1CoO₃ was prepared through bothcalcination and sol-gel method. The purity of La_0.9K_0.1CoO₃ powders can be increasedby raising the calcining temperature, at the same time, the particle diameter increased,BET surface area decrease. Under the same calcining temperature, the charactic properties of the La_0.9K_0.1CoO₃ powders synthesized by sol-gel, method is better than those synthesized by solid state reaction method, such as purer phase, smaller particle diameter, which can be used as a satisfactory catalyst in diesel waste gas cleaning.In small sample experiment, the catalytic performance of the La_0.9K_0.1CoO₃ Perovskite Composite Oxide catalyst synthesized by sol-gel, method sintered at 1050℃is better than that of the catalyst synthesized by solid state reaction method catalyst, such as lower ignition temperature of the diesel soot particulates, lower start temperature of NO_x treatment, creating lower concentration of byproduct CO, so it has better catalyzing effect. By increasing the sintering tempetature appropriately and using the sol-gel method, the effect of catalyst to purify PM and NO_x can be improved. Three measures, i e ,using Pt and La_0.9K_0.1CoO₃ respectively and both as catalyst to clear PM and NO_x were taken. It is indicated that it is not efficient using Pt and La_0.9K_0.1CoO₃ both, the effcet of Pt is a little superior to La_0.9K_0.1CoO₃,but the conversion rate to NO_x is slow and it can not treat with CO and HC, at the same time ,it is expensive. Considering the whole conditions, the better catalyst was chosen as La_0.9K_0.1CoO₃ prepared by sol-gel method and sintered at 1050℃. The working conditions of the catalyst was investigated, which is coincident with the exhaust gas when the engine is in high speed and large load.In the diesel test bench experimental, La_0.9K_0.1CoO₃ catalyst can not only reduce the PM and NO_x, but also reduce HC and CO emission. The conversion rate to PM and NO_x is still low, which is about 15%-20% on the optinum condition, so it is nessissary to combine with low-thermal plasms technique to improve the purifying effect.Then energy, consumption of low-thermal plasma technique was analyzed as focous, and the shunt dielectric barrier discharge plasma reactor was designed, then the corresponding high-pulse power parameters were determined. The power of the reactor was calculated by experiential formula. The calculation results indicate the reactor's power is in the lower range of the diesel engine.The low-thermal plasma technique was combined with the La_0.9K_0.1CoO₃ Perovskite Composite Oxide catalyst for the first time. Compared with using single catalyst, the combined technique can improve the clearing effect, but it reduce the reaction temperature little, which is still at about 300℃.In the emplace bench experimental, the designed shunt dielectric barrier discharge plasma reactor can work well-balanced, and the diesel exhaust can be treated. When catalyst were emplaced behind and low-thermal plasma reactor were emplaced frontal, the temperature was not high enough for the catalyst to work. While When catalyst were emplaced frontal and low-thermal plasma reactor were emplaced behind, the catalyst can work efficiently. Four-way catalyst technique combimed with low-thermal plasms technique can purify PM and NO_x more efficiently, especially for PM, the purifying rate can reach 81.2%. This technique is feasible for improved fixed diesel engine,'and for mobile diesel engine, when the volume of the high voltage pulse power can be reduced and it can be locomotive, the technique may be widely applied in the future.