Formation of Urea-Based Deposits in an Exhaust System: Numerical Predictions and Experimental Observations on a Hot Gas Test Bench

Brack, Wolfgang; Heine, Barbara; Birkhold, Felix; Kruse, Matthias; Deutschmann, Olaf

doi:10.1007/s40825-016-0042-2

Cited by 62 publications

(33 citation statements)

References 12 publications

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“…For the two lowest impact velocities, the numerical values for b max are quite large when compared with Eq. (11). However, this obvious disagreement is plausible.…”

Section: Maximum Spreading Factormentioning

confidence: 99%

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Maximum Spreading of Urea Water Solution during Drop Impingement

et al. 2019

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Droplet impingement of urea water solution (UWS) is a common source for liquid film and solid deposits formed in the tailpipe of diesel engines. In order to better understand and predict wetting phenomena on the tailpipe wall, this study focuses on droplet spreading dynamics of urea water solution. Impingement of single droplets is investigated under defined conditions by high‐speed imaging using shadowgraphy technique. The experimental studies are complemented by numerical simulations with a phase‐field method. Computational results are in good agreement with experimental data for the advancing phase of spreading and the maximum and terminal spreading radius, whereas for the receding phase notable differences occur. For the maximum spreading radius, an empirical correlation derived for glycerol‐water‐ethanol mixtures is found to be valid for millimeter‐sized UWS droplets as well. A numerical simulation for a much smaller droplet however indicates that this correlation is not valid for the tiny droplets of UWS sprays in technical applications.

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“…For the two lowest impact velocities, the numerical values for b max are quite large when compared with Eq. (11). However, this obvious disagreement is plausible.…”

Section: Maximum Spreading Factormentioning

confidence: 99%

“…At transient operating conditions, the spray will inevitably impinge on the exhaust gas pipe. Liquid films will be formed on the wall leading to undesired formation of solid deposits [8][9][10][11][12][13][14]. As a result, NO x conversion decreases while backpressure increases, affecting both pollutant emissions and engine performance.…”

Section: Introductionmentioning

confidence: 99%

Maximum Spreading of Urea Water Solution during Drop Impingement

et al. 2019

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“…However, a minimum exhaust gas temperature is required (around 200 C) before urea solution injection, in order to ensure a complete decomposition and hydrolysis of urea to ammonia and to avoid catalyst deactivation, by-products and deposits (Brack et al 2016;Guan et al 2014). Images of collected PM with and without urea injection showed that urea-injected particles had sizes from 200 nm to 1 lm (Lee et al 2012).…”

Section: Introductionmentioning

confidence: 99%

Effect of selective catalytic reduction on exhaust nonvolatile particle emissions of Euro VI heavy-duty compression ignition vehicles

Mamakos

Schwelberger

Fierz³

et al. 2019

Aerosol Science and Technology

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The nonvolatile particle number (PN) emissions of late technology diesel heavy-duty vehicles (HDV) are very low due to the introduction of Diesel Particulate Filters (DPF). Nevertheless, a large fraction (50%) of particles below the current lower regulated size (23 nm) was recently reported. Moreover, large differences between laboratory and PN Portable Emission Measurement Systems (PN-PEMS) have been observed. In order to better understand such differences, the physical properties of the exhaust aerosol from two Euro VI technology diesel heavy-duty engines were studied. It was found that urea injection leads to formation of nonvolatile particles. The produced particles covered a wide size range spanning from below 10 nm to above 100 nm. As such, they contribute to the regulated PN emissions, with measured concentrations corresponding to as high as 2 Â 10 11 #/kWh over a World Harmonized Transient Cycle (WHTC). However, a large fraction of them was undetected owing to their small particle size. Low-cutoff size (10 nm) Condensation Particle Counters (CPCs) (which are under discussion to be included in the regulations) measured up to twice as high concentrations. Considering the large particle losses in the sampling systems at this size range, the true concentrations can be two times higher from what the low-cutoff CPCs reported. When the temperature of the SCR system exceeded a threshold of 300 C, the produced particles were found to be positively charged, increasing the average exhaust aerosol charge up to þ3 elementary charges per particle. Scanning Mobility Particle Sizer (SMPS) measurements of non-neutralized samples revealed that even the smallest of them can carry more than one positive charge. The findings of this study can explain the differences reported between PEMS and laboratory systems and especially those based on diffusion charging. They also provide insight for a refinement of technical requirements prescribed in the European PEMS regulation to more accurately quantify the PN emissions from such technologies.

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“…With respect to deposit formation and decomposition the problem with the time scales remains. First steps have been done to include reaction kinetics in the CFD method and to run the simulation for a sufficiently long time but must be considered as demonstration at the moment , . A comprehensive modeling approach that embraces turbulent flow, spray, liquid film and the heterogeneous liquid‐solid‐gas reactions over time ranges of several minutes real time is still missing.…”

Section: Summary and Future Challengesmentioning

confidence: 99%

Preparation of Ammonia from Liquid AdBlue – Modeling Approaches and Future Challenges

Lauer

2018

Chemie Ingenieur Technik

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Sustainable mobility is a legal and public demand. An important measure to clean the exhaust gas of diesel engines is the conversion of nitric oxides with selective catalytic reduction (SCR). The development of SCR systems can be strongly supported by numerical methods. This review article is to document the status of the CFD-simulation method with respect to the preparation of the injected urea-water solution, the turbulent transport of ammonia and the assessment of solid deposits coming from liquid film. Comparisons with measurements for realistic sprays and mixing sections are given.

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Formation of Urea-Based Deposits in an Exhaust System: Numerical Predictions and Experimental Observations on a Hot Gas Test Bench

Cited by 62 publications

References 12 publications

Maximum Spreading of Urea Water Solution during Drop Impingement

Maximum Spreading of Urea Water Solution during Drop Impingement

Effect of selective catalytic reduction on exhaust nonvolatile particle emissions of Euro VI heavy-duty compression ignition vehicles

Preparation of Ammonia from Liquid AdBlue – Modeling Approaches and Future Challenges

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