Gasoline Direct Injection Sprays Research Articles

Atomization characteristics and prediction accuracies of hybrid break-up models for a gasoline direct injection spray

The purpose of this study is to investigate the prediction accuracy of hybrid models on the atomization processes of fuel sprays injected from a gasoline direct injection system. In order to analyze the prediction characteristics of hybrid schemes, various hybrid models for the primary and secondary break-ups of high-pressure gasoline spray are formulated by combining two different models. For the primary break-up, the LISA and WAVE break-up models are used, whereas the TAB, DDB, and RT models are utilized for the secondary break-up, considering the break-up mechanism of each break-up model. Therefore, six hybrid models are applied to the simulation of the atomization process and the prediction accuracies of the break-up processes are evaluated by comparing them with the experimental results. To obtain experimental results for comparison with the predicted ones, the local Sauter mean diameter and axial mean velocity are measured by using a phase Doppler particle analyzer. Also, the spray visualization system is utilized to analyze the process of spray development and spray-tip penetration. It is revealed that all hybrid models show reasonable agreement with the experimental results of spray-tip penetration. On the other hand, different accuracies are shown in the distributions of local SMD and axial mean velocity.

Atomization characteristics and prediction accuracy of LISA-DDB model for gasoline direct injection spray

In this paper, the spray atomization characteristics of a gasoline direct-injection injector were investigated experimentally and numerically. To visualize the developing spray process, a laser sheet method with a Nd :YAG laser was utilized. The microscopic atomization characteristics such as the droplet size and velocity distribution were also obtained by using a phase Doppler particle analyzer system at the 5 MPa of injection pressure. With the experiments, the calculations of spray atomization were conducted by using the KIVA code with the LISA-DDB breakup model. Based on the agreement with the experimental results, the prediction accuracy of LISA-DDB breakup model was investigated in terms of the spray shapes, spray tip penetration, SMD distribution, and axial mean velocity. The results of this study provides the macroscopic and microscopic characteristics of the spray atomization, and prediction accuracy of the LISA-DDB model.

Delphi’s new Flex Metal Catalyst cuts precious metal content while substantially reducing emissions

Performance of internal combustion engines is well known being greatly affected by the air-fuel mixture formation process. In spark ignition engines, in particular, the gasoline direct injection (GDI) technology is currently preferred, as it allows obtaining the desired air-to-fuel ratio distribution at each regime of operation, either by creating stoichiometric mixtures under high power demands, or through charge stratification around the spark plug at intermediate or lower loads. The impact of the gasoline spray on the piston or cylinder walls is a key factor, especially under the so-called wall-guided mixture formation mode. The impact causes droplets rebound and/or the deposition of a liquid film (wallfilm). After being rebounded, droplets undergo what is called secondary atomization. The wallfilm, on the other hand, may remain of no negligible size and evaporate slowly, leading to increased unburned hydrocarbons and particulate matter emissions.Optimization of the heterogeneous mixture behavior in GDI engines is fundamental for guaranteeing high energetic and environmental performance over the whole working map. Computational fluid dynamics (CFD) can be useful in this perspective to effect proper choices of control strategies. Assessment of predictive engine models, able to describe the complex phenomena underlying energy conversion in modern engines, is therefore mandatory to the scope.In the present paper, a basic study is performed on gasoline sprays issuing from high pressure injectors under controlled conditions: the experimental characterization of multi-hole and single-hole GDI sprays in their impact over a plate is carried out with the aim of creating a set of data to be used for the validation of a properly developed simulation model. The multi-hole spray allows accounting for the jet-to-jet interaction and represents a condition closer to the actual gasoline supply mode in present GDI engines. The single-hole injector configuration is instead preferred for a more detailed study, as it allows capturing effects related to the role that diverse parameters characterizing the liquid droplet dynamics play during and after their impingement on heated solid surfaces. The CFD model is conceived with the scope of its future application within numerical calculations of entire engine working cycles. A highly portable free spray sub-model allows correctly reproducing the injection dynamics under different conditions in a confined vessel, while the spray-wall impingement sub-model is shown being able to highlight to an acceptable extent the gasoline splashing and deposition phenomena.

Application technique of particle image velocimetry and entropy analysis toinvestigate spray structure for gasoline direct injection injector

To improve the fuel consumption and exhaust emission for gasoline engines,the GDI (gasoline direct injection) system was spotlighted to meet theserequirements. Many researchers have performed studies to investigate the spraycharacteristics and the mixture formation of the GDI injector. In this work, westudied the spray characteristics of a gasoline direct injector by using entropyanalysis and particle image velocimetry (PIV) methods. The entropy analysis isbased on the concept of statistical entropy, and it identifies the degree ofhomogeneity in the fuel concentration. The PIV algorithm was developed toelucidate the correlation between entropy and vorticity. From the applied resultson a direct injection gasoline spray, we could find that the direct diffusionphenomenon was a dominant factor in the formation of a homogeneous mixturedownstream of the GDI spray, especially under vaporizing ambient conditions,and the mixing phenomenon was also progressed by momentum exchange withinduced air. In addition, these results revealed that entropy analysis and PIV arevery effective methods for the analysis of the mixing process, and the entropyvalues increase with the progress of uniformity in the diffusion process.

엔트로피 해석과 PIV를 이용한 직접 분사식 가솔린의 분무 특성에 관한 연구

To improve the fuel consumption and exhaust emission for gasoline engines, GDI(Gasoline Direct Injection) system was spotlighted to solve above requirements. Thus, many researchers have been studied to investigate the spray characteristics and the mixture formation of GDI injector. In this study, we tried to study the spray characteristics of a gasoline direct injector by using entropy analysis and PlV methods. The entropy analysis is based on the concept of statistical entropy, and it identifies the degree of homogeneity in the fuel concentration. The PlV method was adopted to determine the fluid dynamics information at the spray. From the applied results on a direct injection gasoline spray, we could find that the direct diffusion phenomena was a dominant factor in the formation of a homogeneous mixture at downstream of GDI spray especially under vaporizing ambient conditions, and mixing phenomena was also progressed by momentum exchange with induced air. In addition, the correlation between entropy and vorticity strength enabled to find their relation.

Droplet Size and Velocity Distributions of a Transient Hollow-Cone Spray for GDI Engines

An experimental investigation of a gasoline direct injection (GDI) spray, emerging from an electronically controlled swirl-type injector, was carried out at an injection pressure and duration of 7.0 MPa and 3.0 ms, respectively, in an optically accessible vessel, at atmospheric pressure and ambient temperature. The temporal and spatial spray evolution was investigated in terms of global spray structure, interaction with the external gas, time-resolved droplet size and velocity distribution. The measurements were carried out with an AVL Engine Video System with a CCD camera, a frame grabber and a strobe flash triggered by the injection apparatus. Digital image processing software for the study of the global parameters of the spray was used. A particle Doppler analyzer (PDA) system was used to estimate the local droplet size and velocity as function of the radial coordinate and distance from the nozzle. A laser light extinction technique was applied to investigate the region close to the nozzle up to 5 mm. The spray emerging from the nozzle, at an early time, showed a hollow-cone type of structure because of the swirl motion of the fuel in the orifice that produces a rotational momentum at the nozzle exit. The spray starts with a central pre-injection phase followed, later, by the main body characterized by a large cone angle. The interaction of the fuel with the gas in the spray chamber was evidenced; curls on the external boundary and re-filling of the central part of the cone, during the second part of the injection, were observed. Measurements at different locations within the spray showed high values of the droplet velocity close to the nozzle exit at an early time. These high values were found downstream in the final stage of injection. Radial velocities were present along the entire injection process with an outer direction in the first stage, while an inner direction was observed in the second part. The droplet size distribution showed increasing values along the injector axis and towards the periphery of the spray.

Measurement of Distribution and Concentration of Vapor/Liquid Phases in Gasoline Direct Injection Spray Using Exciplex Fluorescence Method

Measurement of Distribution and Concentration of Vapor/Liquid Phases in Gasoline Direct Injection Spray Using Exciplex Fluorescence Method