A Droplet Size Investigation and Comparison Using a Novel Biomimetic Flash-Boiling Injector for AdBlue Injections 2016-01-2211

Increased research is being driven by the automotive industry facing challenges, requiring to comply with both current and future emissions legislation, and to lower the fuel consumption. The reason for this legislation is to restrict the harmful pollution which every year causes 3.3 million premature deaths worldwide [1]. One factor that causes this pollution is NOx emissions. NOx emission legislation has been reduced from 8 g/kWh (Euro I) down to 0.4 g/kWh (Euro VI) and recently new legislation for ammonia slip which increase the challenge of exhaust aftertreatment with a SCR system. In order to achieve a good NOx conversion together with a low slip of ammonia, small droplets of Urea solution needs to be injected which can be rapidly evaporated and mixed into the flow of exhaust gases. In most of today's solutions this process is enhanced with flow restricting mixers or longer path lengths but if these can be removed and shortened the flow losses can be reduced, leading to higher efficiency and lower fuel consumption as well as a more compact exhaust system.

The μMist^® injector, inspired by nature, takes the concept from the Bombardier beetle which induces flash-boiling in its effective defence mechanism by spraying a plume of hot poisonous fine droplets with great accuracy towards an attacker [3]. By heating up the fluid in a constant volume chamber above the saturation temperature and induce flash evaporation by opening the nozzle, the liquid breaks up into fine droplets which flow out into the target environment.

This paper presents a study comparing the different effects of spray behaviour at different ratios between the saturation pressure and the target pressure. In this study the target pressure is atmospheric. The aim for the study is to gain a better understanding of the droplet sizes and the injector flow rates for different pressures and also present a limited benchmarking study of current market leading AdBlue injectors. Current testing has shown that this novel injector has the ability to produce 33% smaller droplets in SMD and 87% reduction in DV50.