Intermittent multijet sprays for improving mixture preparation with low-pressure injection systems

• Published in: Experiments in fluids 2013-06, Vol.54 (6), p.1-9, Article 1550
• Main Authors: Panão, Miguel R. Oliveira, Moreira, António Luis N., Durão, Diamantino F. G.
• Format: Article
• Language: English
• Subjects: Application of Laser Techniques to Fluid Mechanics 2012; Applied sciences; Droplets; Energy; Energy. Thermal use of fuels; Engineering; Engineering Fluid Dynamics; Engineering Thermodynamics; Engines and turbines; Equipments for energy generation and conversion: thermal, electrical, mechanical energy, etc; Exact sciences and technology; Fluid dynamics; Fluid- and Aerodynamics; Fundamental areas of phenomenology (including applications); Heat and Mass Transfer; Heat transfer; Impingement; Mathematical analysis; Mathematical models; Multiphase and particle-laden flows; Nonhomogeneous flows; Physics; Research Article; Sprayers; Sprays; Standard deviation
• ISSN: 0723-4864; 1432-1114
• DOI: 10.1007/s00348-013-1550-2

In this work, the characteristics of droplets produced by a multijet impingement atomization process are measured with a Phase-Doppler Interferometer and statistically described using finite mixtures of weighted probability density functions. Through this statistical tool, drop size and axial velocity distributions are involved in the physical interpretation of the flow, instead of limiting it to first- and second-order distribution moments. Each group of droplets with similar size characteristics has been modeled by lognormal distributions and normal distributions relatively to drop axial velocity. The analysis based on finite mixtures identified three groups of droplets with similar size characteristics, although the group with smaller sizes is negligibly represented in the statistical finite mixture. Also, the lognormal standard deviation in all groups is well correlated with the corresponding geometric mean diameter allowing to simplify the description of the spray. In terms of axial velocity, mainly one distribution has been identified with a relatively constant standard deviation, and a characteristic velocity slightly dependent on the duty cycle associated with the spray intermittent condition. Furthermore, droplets characteristics are correlated with the heat transfer rate obtained for several operating conditions that maintain the surface temperature in steady-state at 125 °C. The effect of the time between consecutive injections is analyzed. Concerning the potential use of multijet impingement sprays for fuel injection systems, results evidence the importance of an interaction between thin liquid film heat transfer and droplets axial velocity for enhancing heat transfer and promote evaporation. This would decrease the amount of fuel deposited on interposed surfaces, thus, improving mixture preparation in low-pressure injection systems for internal combustion engines.