| With the development of economy, more serious environmental problems facedby people, and in the nitrogen oxide pollution, vehicle emissions is an importantsource. There are many Measures to reduce vehicle emissions of nitrogen oxides atthis stage, SCR technology is an important means of reducing NOx emissions ofdiesel engine. More mature SCR technology is generally use of32.5%aqueous ureasolution as the ammonia source. However, the SCR technology with liquid ureasolution as a reducing agent also found a number of problems. First, the liquidaqueous urea solution has a low ammonia storage density, requires frequentreplenishment of the reducing agent. Secondly, the liquid solution of urea result inlower NOx conversion efficiency at the lower exhaust temperature, and easily lead tocrystallization problems.The solid SCR system which use solid urea, ammoniumcarbamate, metal ammine such as reducing agent, have high ammonia storage density,the space occupied is small, at low temperature, the NOx conversion efficiency stillhigh, and hardily lead to crystallization problems.To overcome the disadvantages of liquid SCR technology，many domestic andforeign scholars have in-depth study about solid SCR technology with ammonia gasdirect injection. In this study, we propose the working principle of solid SCRammonia gas injection system. Using strontium Ammine chloride as a reducing agent,we designed a solid SCR ammonia quantitative injection system.The feasibility of thesystem were measured. In the case of direct injection of ammonia gas, The catalyticproperties of the catalyst were studied using the solid SCR system which we designed.The main contents are as follows:1. In this paper, using strontium Ammine chloride as a reducing agent, theammonia generator, the volume of the ammonia generator, the diameter size of theinternal heating and layout were designed based on the replacement cycle of thereducing agent and the ammonia generation rate.2. To solve this problem, the ammonia stabilization system has been designed,The pressure signal can be used to control the flow of the coolant flowing through the ammonia generator. In a particular experiment, the system pressure in the surge tankis about2.5bar, through the decompression valve, the ammonia pressure is about2.0bar.3. The electronic control system of solid SCR was design based on Freescalemicrocontrollers, including ammonia quantitative injection control program, ammoniatank pressure regulator stability program, temperature sensors, pressure sensors, NOxsensor signal acquisition program. The data is sent to the pc-detection software whichwas designed based on labVIEW.4. Using high-pressure pump to provide high pressure air instead of ammonia asinjection gas, we have a preliminary study about the spray characteristics of thenozzle. Experiments show that the gas injection flow rate is not only affected by thenozzle aperture size, but also by the gas pressure and the ejection frequency of thenozzle. We choose ammonia injection pressure of2.0bar, nozzle ejection frequency25HZ to test.5. After completion of the test bench, in order to ensure the accuracy of the data,the Smart NOx sensor measurements with HORIBA exhaust analyzer measurementswere compared in the ESC experiment. The maximum amount of fluctuation in theNOx sensor is about6ppm in B25condition. At each operating point, the differencebetween the two measurements is below4%, indicating that the performance of theNOx sensor which we select can meet the test requirements. The test about systemcapacity to build pressure and a reducing agent to absorb heat were carried, After5minutes, the stabilizing system can reach the injection pressure of the ammonia. Thisexperiments show that in this temperature range the NOx conversion efficiency is stillbetween20%-60%,which still maintain a high conversion efficiency. So theconclusion can be show that the solid SCR system for reducing the NOxconcentration at a low temperature has an important role. |
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