Wall Impingement Model Research Articles

Investigation of the GCI main injection: experimental-numerical analysis of gasoline spray impact at reference engine conditions

This work deals with the experimental and numerical investigation of ultra-high pressure gasoline injection against heated walls in order to characterize the fuel evaporation and distribution in gasoline compression ignition combustion chambers. Spray-wall impingement tests have been conducted in a quiescent vessel and recorded by means of the Mie scattering technique. The test conditions have been set in line with those of a reference benched GCI engine, leading to 500 bar and 700 bar for the injection pressure, 298 K, 423 K, 493 K for the wall temperature, 20 mm and 30 mm for the injector-wall distance. The same test matrix has been reproduced by means of CFD three-dimensional simulations using a proper setting of the wall-impingement model and the joint use of CFD-FEM approaches for the vapour-wall heat exchange. The time evolution of the rebound spray has been recorded and then postprocessed leading to the width and the thickness of the cloud. The CFD results are in line with the experimental ones both in terms of the overall time evolution and punctual values, proving a good accuracy of the simulation in predicting the rebound/adhered fuel mass split and the local distribution of the fuel after the impingement. Given the reliability of the simulations, insights on the numerical wall film mass and evaporated mass have been provided in order to clarify the effect of increasing pressure, temperature, and distance.

Computational Modeling of Nasal Drug Delivery Using Different Intranasal Corticosteroid Sprays for the Treatment of Eustachian Tube Dysfunction.

Eustachian tube dysfunction (ETD) is a common otolaryngologic condition associated with decreased quality of life. The first-line treatment of ETD is intranasal corticosteroid sprays (INCS). Computational fluid dynamics (CFD) was used to study particle deposition on the Eustachian tube (ET) using two commercial INCS (Flonase and Sensimist). Simulations also considered the effects of nostril side, insertion depth, insertion angle, cone spray angle, inhaling rates, wall impingement treatment, and fluid film. Flonase and Sensimist produced different particle size distributions and sizes. Sensimist droplets are smaller, less sensitive to asymmetry in nostrils anatomy and variation in insertion angle, and therefore can reach the posterior nasopharynx more readily. Flonase produces larger particles with greater inertia. Its particles deposition is more sensitive to intrasubject variation in nasal anatomy and insertion angles. The particle deposition on the ET was sensitive to the wall impingement model. The deposition on the ET was insignificant with adherence only <0.15% but increased up to 1-4% when including additional outcomes rebound and splash effects when droplets impact with the wall. The dose redistribution with the fluid film is significant but plays a secondary effect on the ET deposition. Flonase aligned parallel with the hard palate produced 4% deposition efficiency on the ET, but this decreased <0.14% at the higher insertion angle. INCS with larger droplet sizes with a small insertion angle may be more effective at targeting droplet deposition on the ET opening.

MODELING OF SPRAY WALL IMPINGEMENT AND FUEL FILM FORMATION UNDER THE GASOLINE DIRECT INJECTION CONDITION

Direct-injection spark-ignition (DISI) engines, which have a better fuel economy than conventional gasoline engines, have been widely introduced in the market. However, in these engines, the rich air−fuel mixtures associated with fuel films during cold starts, caused by spray impingement, produce particulate matter. To predict soot formation, it is important to predict the mixture field precisely; thus, accurate spray and film models are prerequisites for creating a soot model. Previous wall impingement models were well matched with low Weber number collision conditions, such as those of diesel engines, which have relatively high ambient pressures and small Sauter mean diameters. In this study, the outliers of the previous model were observed to decrease as the collision distance increased and when a strong droplet dissipation occurred owing to a high ambient pressure. However, the kinetic energy in DISI engines is considerably larger than the dissipation energy calculated using the Weber number and surface tension; thus, the amount of dissipation energy should be determined within a realistic range. To analyze the two-dimensional (2D) spray-wall impingement phenomenon more accurately, a 2D child droplet generation was considered. Finally, the film and spray behaviors were measured to validate the SNU model. The Mie scattering images of the gasoline spray near the wall were captured to measure the rebound spray radius. Then, a laser-induced fluorescence with a total internal reflection was used to determine the film shape and thickness. Compared with existing models, the SNU model exhibits better agreement with the Mie experimental results without requiring case-dependent changes to the model constant. However, the film simulation part needs improvement in future work.

Numerical Simulation of n-Heptane Spray Combustion in a Porous Medium Burner

ABSTRACT A two-dimensional numerical simulation study is conducted to investigate the combustion process of n-heptane spray in a porous medium burner (PMB) based on the previous experimental work performed by this research group. In order to adapt the model for the conditions of different wall temperatures and different splash Mach numbers, the wall-impingement model in this study is based on the model by O’Rourke and Amsden and the interaction mechanism between the spray droplets and the wall is optimized through user-defined functions (UDFs). The effects of air inlet velocity, injected fuel quantity and preheating temperature on spray combustion are analyzed. The results show that the downstream velocity of the combustion flame increases when the inlet air velocity increases or the fuel injection rate decreases or the preheating temperature decreases. Under the same equivalence ratios, the flame propagation velocity increases as the increase of the dimensionless gas-oil joint effect parameter. The flame area also increases with the increase of inlet air velocity, but the rate of increase in the flame area gradually decreases as the reaction proceeds. An initial preheating temperature of 1060 K is conducive to the stable combustion of n-heptane spray for flame lengths less than 0.060 m.

A numerical–experimental assessment of wall impingement models for spark-ignition direct-injection engines

Liquid wall impingement in direct-injection engines can cause soot and hydrocarbon emissions as well as reduced combustion efficiency. This study focuses on detailed evaluations of numerical droplet impingement criteria that govern the onset of splash. The five selected splash criteria, which all extrapolate from single-droplet impacts to full sprays, are representative of those currently in use for spark-ignition direct-injection engines. The computations examined the sensitivity of impinging spray simulations to the splash criteria for a high-pressure, direct-injection swirl spray under atmospheric conditions impinging at a 45° angle onto a flat plate. The numerical results were compared to an unusually extensive set of experimental data: Mie scattering and light transmission imaging, plus quantitative refractive index matching measurements of the fuel film area and thickness, and phase Doppler interferometry measurements of droplet size and velocity near the plate. Good qualitative and at least fair quantitative agreement was obtained for the global spray impingement and wall film formation, especially for single-drop criteria that include the effect of viscosity. The film area and shape were insensitive to the splash criteria, illustrating the importance of film thickness measurements for validating simulations. The results also revealed the sensitivity of impingement calculations to droplet arrival frequency when that is taken into account. In general, the comparisons indicated the need to capture the effect of multiple droplets impinging on the wall at irregular frequencies in the criterion, as well as other important physics of the droplet–wall interaction that may mask the true effect of the impingement criterion.

Dynamic behavior of non-evaporative droplet impact on a solid surface: Comparative study of R113, water, ethanol and acetone

Droplet impact on a solid surface is a common phenomenon observed in industries. Fundamental investigations of droplet impact are helpful in enhancing spray cooling capability and advance spray–wall impingement model. In this work, the effects of droplet diameter, impact velocity, viscosity, and surface tension on droplet impact dynamics were systematically investigated with four liquids, that is, R113, deionized water, ethanol, and acetone. Results illustrated that the initial droplet diameter minimally affects morphology and dynamic spreading factor, whereas large viscosity and surface tension hindered droplet spreading, thereby yielding a small maximum spreading factor and velocity. Low droplet viscosity and surface tension contribute to enhancing spray cooling capability by producing improved atomization, large spreading velocity, and extended contact area. The existing maximum spreading factor correlations failed to predict experimental results accurately. On the basis of experimental data in this work, general maximum spreading factor and splashing threshold correlations are proposed. All the proposed correlations agreed well with the present experimental results and literature data. The maximum spreading factor correlation indicated that large droplet impact velocity, small viscosity, and surface tension will produce a large maximum spreading capability.

An Improved Rate of Heat Release Model for Modern High-Speed Diesel Engines

To meet the increasingly stringent emissions standards, diesel engines need to include more active technologies with their associated control systems. Hardware-in-the-loop (HiL) approaches are becoming popular where the engine system is represented as a real-time capable model to allow development of the controller hardware and software without the need for the real engine system. This paper focusses on the engine model required in such approaches. A number of semi-physical, zero-dimensional combustion modeling techniques are enhanced and combined into a complete model, these include—ignition delay, premixed and diffusion combustion and wall impingement. In addition, a fuel injection model was used to provide fuel injection rate from solenoid energizing signals. The model was parameterized using a small set of experimental data from an engine dynamometer test facility and validated against a complete data set covering the full engine speed and torque range. The model was shown to characterize the rate of heat release (RoHR) well over the engine speed and load range. Critically, the wall impingement model improved R2 value for maximum RoHR from 0.89 to 0.96. This was reflected in the model's ability to match both pilot and main combustion phasing, and peak heat release rates derived from measured data. The model predicted indicated mean effective pressure and maximum pressure with R2 values of 0.99 across the engine map. The worst prediction was for the angle of maximum pressure which had an R2 of 0.74. The results demonstrate the predictive ability of the model, with only a small set of empirical data for training—this is a key advantage over conventional methods. The fuel injection model yielded good results for predicted injection quantity (R2 = 0.99) and enabled the use of the RoHR model without the need for measured rate of injection.

Characterization of soot particle distribution in conventional, non-premixed DI diesel flame using a multi-step phenomenological soot model

Numerical investigation of the soot particle distribution in a conventional, direct-injection (DI) diesel flame was performed. An available experiment from a heavy-duty, DI diesel engine under conventional injection conditions was selected as a benchmark. This experiment reproduced the operating conditions of similar experimental studies performed on an optically accessible engine of same class at the Sandia National Laboratories. The KIVA-3V code was used in the simulation, which features an improved multi-step phenomenological (MSP) soot model, a KH/RT spray breakup model, an extended Zel’dovich NO formation model, a “Shell” ignition model, a laminar-and-turbulent characteristic time combustion (CTC) model, a RNG k- ε turbulence model, a piston-ring crevice model, a droplet wall impingement model, and a wall-temperature function heat transfer model. The prediction reinforces the diesel conceptual model put forth by Dec in many aspects, particularly regarding spatial correlations between the liquid-spray penetration, the fuel–vapor penetration, the flame structure, and the soot concentration distribution. It is observed that, while larger soot particles are located downstream in the fuel-rich “head vortex” zone, a thin layer of larger soot particles at a considerably lower mass concentration exists along the peripheral surfaces of the flame. This thin, soot particle layer might be a result of competition between surface growth and surface oxidation when younger particles flow outwards from the interior zone of combustion to the high-temperature surface of the flame plume. The details of soot-relevant quantities (e.g., particle size, number density, generic precursor, and acetylene concentrations) and reaction rates (e.g., soot inception, particle coagulation, surface growth, and oxidation) provide valuable insights into diesel soot formation and oxidation processes.

Modeling of Gasoline Direct Injection Mixture Formation Using KIVA-3V : Development of Spray Breakup &amp; Wall Impingement Models and Validation with Optical Engine Planar Laser Induced Fluorescence Measurements.(S.I. Engines, G.D.I. Modelling)

Modeling of Gasoline Direct Injection Mixture Formation Using KIVA-3V : Development of Spray Breakup &amp; Wall Impingement Models and Validation with Optical Engine Planar Laser Induced Fluorescence Measurements.(S.I. Engines, G.D.I. Modelling)

Multidimensional engine modeling: NO and soot emissions in a diesel engine with Exhaust Gas Recirculation

The effects of EGR (Exhaust Gas Recirculation) on heavy-duty diesel engine performance, NO and soot emissions were numerically investigated using the modified KIVA-3V code. For the fuel spray, the atomization model based on the linear stability analysis and spray wall impingement model were developed for the KIVA-3V code. The Zeldovich mechanism for the formation of nitric oxide and the soot model suggested by Hiroyasu et al. were used to predict the diesel emissions. In this paper, the computational results of fuel spray, cylinder pressure, and emissions were compared with experimental data, and the optimum EGR rates were sought from the NO and soot emissions trade-off. The results showed that the EGR is effective in suppressing NO but the soot emission was increased considerably by EGR. Using cooled EGR, soot emission could be enhanced without worsening of NO.

Three-dimensional computation of in-cylinder flow and combustion characteristics in diesel engines — Effect of wall impingement models of fuel droplet behavior on combustion characteristics

Abstract A computer code called TurboKIVA was used to perform three-dimensional computations to investigate the effects of fuel spray formation on the combustion and emission characteristics of direct and indirect injection diesel engines. As the first step, the code was modified to facilitate quantitative prediction of soot emissions and to improve prediction accuracy. An investigation was then made of the effects of fuel droplet wall impingement models on combustion characteristics. The results showed that combustion performance was influenced by the models, making it important to select a suitable wall impingement model in predicting NO x and soot emissions based on the operating conditions of IDI diesel engines.

9539185 Three-dimentional computation of in-cylinder flow and combustion characteristics in diesel engines — Effect of wall impingement models of fuel droplets on combustion characteristics Hiroshi Ogawa, Yukio Matsui, Shüji Kimura, Jun-ichi Kawashima (Nissan Motor Co., Ltd.)

9539185 Three-dimentional computation of in-cylinder flow and combustion characteristics in diesel engines — Effect of wall impingement models of fuel droplets on combustion characteristics Hiroshi Ogawa, Yukio Matsui, Shüji Kimura, Jun-ichi Kawashima (Nissan Motor Co., Ltd.)