Abstract
To solve the problems of low exhaust temperature NO x conversion efficiency of urea Selective Catalytic Reduction (SCR) and easy production of urea crystals during actual vehicle operation, this paper studies the effect of solid SCR on NO x emission on the engine bench. The experimental results show that for a solid SCR carrying the same reducing agent, its volume is only 1/3 the volume of urea SCR. When the exhaust temperature is 160°C, the NO x conversion efficiency of the solid SCR system can reach 40%. Based on the same ammonia-nitrogen ratio setting, the World Harmonized Steady Cycle (WHSC) NO x conversion efficiency is improved by 3.3%, and the World Harmonized Transient Cycle (WHTC) NO x conversion efficiency is increased by 4.5%. When the solid SCR injection temperature is reduced to 160°C, the NO x conversion efficiency is significantly improved, which is 9.7% and 15.5% higher than that of the 200°C solid SCR system and the urea SCR system, respectively, and the number of power base windows is between [0 20]. The NO x emission of diesel vehicles matching the urea SCR system is significantly higher, reaching 2.38 and 1.73 times that of the solid SCR system with a starting temperature of 160°C and 200°C, respectively.
Highlights
As the number of vehicles in China increases each year, people are paying increasing attention to the sources of motor vehicle pollution
Particulate matter (PM) emissions of heavy diesel vehicles account for 78% of total motor vehicle emissions, and NOx emissions account for 57.3% of total motor vehicle emissions[1],[2]
The ammonia storage of the SCR catalyst decreases as the temperature of the catalyst increases, and at the same temperature point, as the storage amount increases, the NOx conversion efficiency increases
Summary
As the number of vehicles in China increases each year, people are paying increasing attention to the sources of motor vehicle pollution. When the exhaust temperature is higher than 380°C, the urea aqueous solution sprayed into the exhaust gas flow may be quickly dehydrated and transformed into melamine deposits, blocking the exhaust line, thereby resulting in increased engine back pressure, reduced power, and increased fuel consumption. These effects often occur inside and outside an engine[13]. Solid SCR can solve the problems of current low temperature activity of urea SCR systems, exhaust pipe crystallization, and low temperature icing and is a highly promising NOx emission control technology for diesel engines. The research results have reference significance for reducing the NOx emissions of urban diesel vehicles in China and have a guiding significance for light diesel vehicles to meet the China VI emission standards[17]-[21]
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