Experimental Study And Mechanism Analysis On Transforming NO_x Of Diesel Emission And Regenerating DPF Using NTP Technology

Though automobile industry promoted the economic development and social progress, it inevitably brought atmospheric pollution and led to human living environment and health endangered. At the present, the aftetreatrment techniques for controlling NO_x and PM emissions of diesel engine are not yet sophisticated, and need to be improved. In this text, the author presents a technology route using non-thermal plasma to convert NO_x and regenerate diesel paniculate filter from a practical point of view and discusses its feasibility. Firstly of all, main electrical parameters of dielectric barrier discharge have been studied using static experimental system. On this basis, a non-thermal plasma reactor is designed which is suitable for controlling the diesel engine emissions. Secondly, the author studies the changing of NO/C₃H₆/CO₂/O₂/N₂ mixture in the non-thermal plasma reactor and attempts to reveal the chemical reaction mechanisms. Lastly, through building diesel engine bench system, the active substances produced by the non-thermal plasma reactor are injected into the exhaust pipe and its effects for dealing with diesel engine emissions and capacity for regenerating diesel particulate filter are studied. Some researches are made in the text:(1)Based on dielectric barrier discharge theory, a static experiment system is built to research dielectric barrier discharge characteristics, the effect of dielectric thickness, discharge gap, discharge frequency, excitation peak voltage on the working parameters, such as the power, equivalent capacitance, charge transfer value and electric field intensity, are studied using Q-V Lissajous figures. The experimental results show that: adopting thinner dielectric discharge and smaller discharge gap can improve the discharge power and electric field strength, increasing the discharge frequency may also improve discharge power, but its impact on the electric field strength is little.(2)On the basis of the results of static experiments and considering that the non-thermal plasma reactor should meet the long work-time and large gas flow conditions, the key structural parameters are finally determined as follows: quartz thickness is 3mm, discharge gap is 2mm. Its 12-hour endurance test result shows that the reactor can stably run for long work-hours.(3)Through building a simulation gases system, NO conversion efficiency and its influencing factors are studied in detail when O₂/N2, NO/O₂/N₂, NO/C₃H₆/O₂/N₂ and NO/N₂, NO/C₃H₆/N₂ mixture passing the discharge area of the reactor, and the author also attempts to reveal these chemical reaction mechanisms. The experimental results show that: O₃ and NO₂ are produced when the O₂/N₂ mixture passing the discharge area of the non-thermal plasma reactor; when active substances produced by the reactor acting on the NO/O₂/N₂ mixture, NO is mainly oxidized into NO2, and the decrease of O₂ and NO initial concentration can enhance NO conversion rate; In the NO/C₃H₆/O₂/N₂ mixture, NO oxidation and reduction reactions simultaneously exist, the higher C₃H₆ initial concentration is, the easier NO reverts into N₂ through the reduction reaction, at the same time, CO is produced; when the NO/N₂ mixture passing the discharge area of the non-thermal plasma reactor, NO reduction reaction only occurs ,its conversion rate is low and its energy consumption is high, after adding C₃H₆ in the NO/N₂ mixture, NO reduction efficiency can be effectively improved, and CO is also produced.(4)Through building a non-thermal plasma injection system to deal with diesel engine simulation exhaust, the transformation of simulation exhaust components is studied at the different gas temperature when active substances produced in non-thermal plasma reactor are injected into the exhaust pipe. At the lower temperature, the active substance produced by the reactor mainly oxidize NO into NO₂, the NO_x concentration is almost changeless when excitation peak voltage increases; when the temperature increases, the active substance produced by the reactor simultaneously reacts with NO and C₃H₆, NO is converted to NO2, CO is produced because C₃H₆ is oxidized by the active substance; When the temperature continues to rise, the oxidation reaction between the active substance and C₃H₆ plays a major role, and generate a large number of CO, active substance which oxidize NO becomes less, so the NO conversion rate drops.(5)Through injecting active substance produced by the non-thermal plasma reactor into the diesel exhaust pipe, the transformation effect of exhaust componentsand regeneration efficiency of diesel particulate filter are studied under the diesel different operating conditions. The results showed that: diesel exhaust temperature have a significant impact on the transformation efficiency. When exhaust temperature is low, NO oxidation reaction with the active substances will be strengthened, more NO₂ is generated; when exhaust temperature is high, the active substances simultaneously act on NO_x,HC,PM in the emission pipe, at this time, NO oxidation reaction is not obvious. In addition, HC concentration will slightly increases because active substances will oxidize soluble organic fraction into gaseous HC; when exhaust temperature is more higher, the active substance are mainly used for the decomposition of HC and PM, so CO concentration increased and HC concentration decreased.(6) In the Bench test, particulate matter after diesel particulate filter which are fixed in diesel engine exhaust pipe are adsorbed using activated carbon adsorption tube. After Soxhlet extraction, the SOF is analyzed by the use of GC-MS. The results show that: the active substance produced by the non-thermal plasma reactor can strictly regenerate diesel particulate filter. When the diesel engine runs at high speed, big or medium load operating conditions, HC macromolecules in the SOF can be decomposed or transformed by the active composition produced by the reactor and are divorced from particulate matter surface, consequently, diesel particulate filter is regenerated; when the diesel engine runs at low load conditions, the decomposition of SOF by active material becomes weaker due to the low exhaust gas temperature.