Miguel R. Oliveira Panão

A real-time assessment of measurement uncertainty in the experimental characterization of sprays

This work addresses the estimation of the measurement uncertainty of discrete probability distributions used in the characterization of sprays. A real-time assessment of this measurement uncertainty is further investigated, particularly concerning the informative quality of the measured distribution and the influence of acquiring additional information on the knowledge retrieved from statistical analysis. The informative quality is associated with the entropy concept as understood in information theory (Shannon entropy), normalized by the entropy of the most informative experiment. A new empirical correlation is derived between the error accuracy of a discrete cumulative probability distribution and the normalized Shannon entropy. The results include case studies using: (i) spray impingement measurements to study the applicability of the real-time assessment of measurement uncertainty, and (ii) the simulation of discrete probability distributions of unknown shape or function to test the applicability of the new correlation.

Visualization and Analysis of Spray Impingement Under Cross-Flow Conditions

Gasoline Direct Injection (GDI) engines are becoming increasingly popular due to the potential to improve power and fuel consumption. The direct injection of gasoline inside an engine is classified in three types: wall-guided; air-guided; and spray-guided (also designated as air-assisted). In the wall-guided, spray impingement on the piston’s bowl head is part of the process to form a stratified charge near the spark plug, as well as to aid in the fuel mixture preparation. In the air-guided (swirl and tumble) and spray-guided, the impingement is undesirable. The interaction between the spray and the surrounding air, as well as the characteristics of the spray, are very important to achieve the benefits of the GDI concept. Although many works have been published which consider the structure of individual sprays, much remains to be known about the interaction between the spray and the wall in the presence of air motion. This is the goal of our work. For that an experimental facility has been built to study the fluid and thermodynamic behavior of a gasoline spray impinging onto a cold/heated surface under cross flow conditions. In a first step of our study we intend to build a fundamental basis on the influence of droplet size and velocity relatively to the cross flow and, therefore, used a PFI injector for easy of experimental analysis. Despite this injector operates at low pressure, images of the spray under quiescent conditions showed a spray quality similar to that of a DI injector, without injection of streams of liquid. Also, measurements obtained with a phase Doppler anemometer showed that droplet sizes range between 10µm and 120µm.

Effect of pre-impingement length and misalignment in the hydrodynamics of multijet impingement atomization

The multijet impingement atomization strategy is proposed as a competitive one in designing atomizers with relatively simple geometries, producing sprays from the impact of multiple jets at low-flow rate conditions (<1.5 l/min). Most theoretical studies have been made for the spray produced by the impact of two jets. However, there are two important geometric issues related with the atomizer design, scarcely approached in the literature, which are the pre-impingement length of jets before impact and jet misalignment. This work analyses the influence of these parameters on the structure of the liquid sheet as well as on drop size. First, the liquid sheet structure has two hydrodynamic regimes: closed-rim and open-rim. The results evidence that higher pre-jet-impingement distances influence only the open-rim regime, namely, producing shorter liquid sheet breakup lengths, smaller drop sizes, and more droplets. The jet misalignment elongates the liquid sheet in the closed-rim regime, and anticipates breakup i...

Assessment of measurement efficiency in laser- and phase-Doppler techniques: an information theory approach

Laser- and phase-Doppler diagnostic techniques provide information on particle characteristics in the form of discrete probability distribution functions. Most methods assess the amount of information required for an accurate measurement through the first- and second-order moments of these distributions. However, considering that a measurement is the distribution and not its moments, a different approach is developed based on information theory (IT) concepts in order to assess if the information provided to the experimentalist is enough to ensure an accurate statistical analysis. The methodology and stopping criteria are presented and used in previously reported measurements obtained with laser- and phase-Doppler techniques. Results show that using an IT approach to assess the reliability of data provided by a measurement means evaluating the degree of stabilization of a discrete probability distribution, where more information acquired does not necessarily imply a more accurate measurement. The statistical analysis performed using the number of samples indicated by the IT method, compared to the total sample size previously measured, shows similar results. Moreover, measurement time is substantially reduced if the IT method is used, thus improving measurement efficiency.

The Effects of Fuel Impact on Mixture Preparation in SI Engines with Port Fuel Injection

An experimental study is reported in a simplified flow configuration aimed at deriving a correlation for the Nusselt number, which can be used to predict the thermal behavior of intake valves in port-fuel injection systems. The analysis is based on simultaneous measurements of droplets characteristics and surface thermal behavior and is relevant for the period of engine warm up. For the engine operating at steady state, an integral method to describe the overall process of heat transfer is devised, which accounts for the heterogeneities of fluid-dynamic interactions induced by multiple and successive droplet interactions within the area of spray impact. The method considers overall boiling curves dependant on the injection conditions and provides an empirical tool to characterize the heat transfer processes on the impact of pulsed sprays. The information is also useful to the development of models for engine simulation.

Micro-cooling constructal design: An application to mold inserts thermal management

Mold thermal performance has a direct influence on part properties, quality and defects, and mold productivity. Through additive manufacturing, inserts can be developed with features that respect the necessary high complex geometries the part requires and that increase thermal performance. Constructal design is explored as a design tool to produce guidelines for cooling channels development.Mold thermal performance has a direct influence on part properties, quality and defects, and mold productivity. Through additive manufacturing, inserts can be developed with features that respect the necessary high complex geometries the part requires and that increase thermal performance. Constructal design is explored as a design tool to produce guidelines for cooling channels development.

Multiple Impinging Jet Air-Assisted Atomization

The growth of the aviation sector triggered the search for alternative fuels and continued improvements in thecombustion process. This work addresses the technological challenges associated with spray systems and theconcern of mixing biofuels with fossil fuels to produce alternative and more ecological fuels for aviation. This workproposes a new injector design based on sprays produced from the simultaneous impact of multiple jets, using anadditional jet of air to assist the atomization process. The results evidence the ability to control the average dropsize through the air-mass flow rate. Depending on the air-mass flow rate there is a transition between atomizationby hydrodynamic breakup of the liquid sheet formed on the impact point, to an aerodynamic breakup mechanism,as found in the atomization of inclined jets under cross-flow conditions. The aerodynamic shear breakupdeteriorates the atomization performance, but within the same order of magnitude. Finally, our experiments showthat mixing a biofuel with a fossil fuel does not significantly alter the spray characteristics, regarded as a stepfurther in developing alternative and more ecological fuels for aero-engines. DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4737

Application of dry-ice for transient spray cooling

The authors would like to acknowledge to the financial support of project EMCool - Efficient Mold Cooling (POCI01-0247-FEDER-011375)