Browse Publications Technical Papers 2014-01-2808
2014-10-13

Urea Decomposition at Low Temperature in SCR Systems for Diesel Engines 2014-01-2808

Selective catalytic reduction (SCR) has been demonstrated as one of the most promising technologies to reduce NOx emissions from heavy-duty diesel engines. To meet the Euro VI regulations, the SCR system should achieve high NOx reduction efficiency even at low temperature. In the SCR system, NH3 is usually supplied by the injection of urea water solution (UWS), therefore it is important to improve the evaporation and decomposition efficiency of UWS at low temperature and minimize urea deposits.
In this study, the UWS spray, urea decomposition, and the UWS impingement on pipe wall at low temperature were investigated based on an engine test bench and computational fluid dynamics (CFD) code. The decomposition of urea and deposits was analyzed using thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC) and fourier transform infrared spectroscopy (FTIR).
The TGA experiment shows that urea decomposition started at about 150°C, and exhibited two stages of rapid mass loss. The off-gas in each stage was mainly NH3 and HNCO respectively.
In tailpipes the decomposition rate of the injected urea was significantly influenced by the exhaust temperature. At 185°C about 20% urea decomposed and produced NH3. The UWS wall film had formed at low temperature and resulted in urea deposits. The TGA and DSC experiments showed that most of the deposits formed and sampled below 180°C were urea crystal, and the urea deposits in the tailpipes could decompose gradually at high exhaust temperatures. The deposits formed after several WHTC tests at the inlet of the SCR catalyst was also sampled and analyzed by TGA and DSC, which proposed to be cyanuric (CYA) acid, and started to decompose at about 300°C.

SAE MOBILUS

Subscribers can view annotate, and download all of SAE's content. Learn More »

Access SAE MOBILUS »

Preview Document Add to Cart
Members save up to 17% off list price.
Login to see discount.
Special Offer: Download multiple Technical Papers each year? TechSelect is a cost-effective subscription option to select and download 12-100 full-text Technical Papers per year. Find more information here.
We also recommend:
TECHNICAL PAPER

Predictive Modeling of Impact of ANR Non-Uniformity on Transient SCR System DeNOx Performance

2015-01-1055

View Details

TECHNICAL PAPER

High Speed Video Measurements of a Heated Tip Urea Injector Spray

2012-01-1747

View Details

TECHNICAL PAPER

Design Improvements of Urea SCR Mixing for Medium-Duty Trucks

2013-01-1074

View Details

X