Studies on Deposit Formation and Entrainment Characteristics of Urea in SCR System for Diesel and Biodiesel Exhausts

The Urea-Selective Catalytic Reduction (SCR) Technology is an after-treatment technique adopted by heavy-duty, diesel-run automobiles to meet stringent emission norms as conventional NH3-SCR has handling problems of NH3 in automobiles. Urea being in a hot environment decomposes and provides sufficient NH3 to reduce NOx into N2. At part loads, the engine exhaust temperature is low, which causes deposit formation in the Urea-SCR system and deposits to form complex non-depleting complexes. The variables affecting this deposit formation find their importance and mitigation of these deposits should be carefully done by controlling those variables. In this context, extensive work has been done earlier by authors using a hot air test rig. As actual SCR systems work with exhaust gases of actual engines, the phenomenological studies are verified using a single-cylinder diesel engine. The results obtained are in line with the trend of hot air conditions when compared with the earlier work of the authors. The SCR technology is presently successful in diesel-run vehicles and methods to evaluate and mitigate the deposits underway. The extension of SCR technology to biodiesel-run diesel engine vehicles is a future challenge as the biodiesel-fueled diesel engine results in higher NOx emissions. A comparative study was undertaken in this work using a medium-duty diesel engine, and deposit formation characteristics are investigated in no-load and full conditions to reveal the quantitative analysis, and nature of deposits. It is found that the absorption of biodiesel by urea deposits inhibits further growth of deposits and entrainment characteristics.