Abstract
With the effectuation of Kyoto Protocol in 2005 February, carbon dioxide has becoming very important problem and carbon dioxide emitted from vehicle becomes serious issue. In point of carbon dioxide reduction, diesel engine has advantages than gasoline engine, but NOx from the diesel engine is still an important issue. There are some way to reduce NOx from diesel engine, such as Lean NOx Trap, Lean NOx Catalyst, HC-SCR (Selective Catalytic Reduction) and Urea-SCR. Among these methods, Urea-SCR technology is well-known to be effective for the reduction of NOx emission from diesel engine in point of fuel economy. Therefore Urea-SCR is becoming increasingly more popular as a cost effective way of reducing NOx. This paper will discuss experiments to optimize the Urea- SCR system in a light duty diesel engine, and result of heavy duty diesel engine test was added to compare with. It is evaluated that injection characteristics of urea injector, NOx conversion efficiency according to specified catalyst temperature, NOx conversion characteristics and temperature changes in different positions such as upstream, downstream and inside of the SCR catalyst. Experiments were accomplished to estimate the effect of urea injection pressure, urea injection position and urea quality. As a result of the test, NOx reduced faster and NOx conversion efficiency was higher at high temperature than low temperature, also when the SCR reaction has occurred, catalyst temperature was raised. It is shown that catalyst temperature is a dominant factor for achieving high NOx conversion efficiency. When injection pressure was increased, urea flow rate was enlarged. So, in the high injection pressure, DeNOx efficiency was increased. When distance between injection position and entrance of SCR catalyst was further, NOx conversion efficiency was increased. And, when the urea quality was dropped, the NOx conversion efficiency and temperature variation by SCR reaction was decreased.
Keywords: Diesel, Urea, SCR, NOx, DeNOx, Catalyst Temperature, Conversion Efficiency, Urea Quality