Influence of the Backpressure on Urea Sprays Generated by an Air-Blast Atomizer for Large-Scale SCR-Applications 2019-01-0046
In 2016, the latest step of emission standards for marine ships came into operation. As the emission limit for nitric oxides has decreased to approximately 25% of the former values, selective catalytic reduction (SCR) will play an important role to fulfil those limits. SCR is an established method in the field of trucks and heavy diesel cars, but applying it to ships requires further research and development. The demands on ship engines are different, not only due to the large scales but also because the engineering process is strongly based on numerical simulations. To allow the validation of simulations at well-defined conditions and to investigate the fundamental processes, e.g. of the injection of urea solution for marine applications, a high pressure hot gas test rig was built up at the ITV.
The current work focuses on the injection of urea solution by an air-blast atomizer. The spray breakup is the initial part of the urea decomposition, which is why reliable validation data is needed for modelling and simulating the respective spray and chemical processes. Therefore, a parametric study was carried out, which takes into account injection parameters as well as temperature and backpressure of the hot exhaust gas. The pressure influence is of particular interest, due to the possibility to install an SCR-system upstream the turbocharger of a marine engine. High speed shadowgraphy was applied to investigate the primary breakup of the urea spray. The breakup phenomena are discussed and combined with droplet spectra, which were measured by phase-Doppler anemometry (PDA). Apart from obtaining validation data, the study gives answers to the guiding question how to obtain acceptably fine sprays by using minimal atomization air under various circumstances.
Markus Höltermann, Jan Wichmar, Friedrich Dinkelacker
Leibniz University Hannover
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