Prediction of spray collapse in multi-hole gasoline direct-injection fuel injectors

A detailed prediction of injection and air–fuel mixing is fundamental in modern direct injection, spark-ignition engines to guarantee a stable and efficient combustion process and to minimize pollutant formation. Within this context, computational fluid dynamics simulations nowadays represent a powerful tool to understand the in-cylinder evolution of spray and air–fuel charge. To guarantee the accuracy of the adopted multidimensional spray sub-models, it is mandatory to validate the computed results against available experimental data under well-defined operating conditions. To this end, in this work, the authors proposed the calibration and validation of a comprehensive set of spray sub-models by means of the simulation of the Spray G experiment, available in the context of the engine combustion network. For a suitable validation of the proposed numerical setup in addition to the baseline condition, gasoline direct injection operating points typical of early injection with homogeneous operation, late injection with high ambient density and flash boiling with enhanced fuel evaporation were also simulated. Numerical computations were validated against a wide set of available experimental data by means of an accurate post-processing analysis taking into account axial liquid and vapor penetrations, gas-phase velocity between spray plumes, droplet size, plume liquid velocity, direction and mass distribution. Satisfactory results were achieved with the proposed setup, which is able to predict gasoline spray evolution under different operating conditions.

Section: Late Injection Spray G4 and Spray G7 Conditionsmentioning

confidence: 99%

Validation of a comprehensive computational fluid dynamics methodology to predict the direct injection process of gasoline sprays using Spray G experimental data

Paredi

Lucchini

Onorati

et al. 2019

“…Subsequent expansion of these vapor bubbles due to rapid decompression during the injection process causes catastrophic disintegration of the liquid jet and resulting in finer droplet size distribution. [28][29][30][31][32][33] This unique quality of flash boiling sprays is very important for homogeneous mixture formation. Experimental studies using single hole injector showed that under flash boiling conditions, liquid penetration length reduces compared to normal fuel temperature cases.…”

Section: Introductionmentioning

confidence: 99%

Optical investigation of flash boiling and its effect on in-cylinder combustion for butanol isomers and iso-octane

Kale

Banerjee

2020

Performance of a gasoline direct injection engine significantly depends on the fuel injection phenomenon. It has been shown that variation in the fuel thermo-physical properties and in-cylinder thermodynamic conditions can adversely affect engine performance. Spray collapse due to flash boiling is the consequence of such varying in-cylinder thermodynamics. It has also been observed that gasoline direct injection engines have higher particulate matter emissions compared to port fuel injection engines. One of the possible reasons for this observation may be fuel impingement on the piston head and spray collapse at high fuel injector temperature. In the present work, experiments have been performed to understand spray characteristics under flash boiling conditions and ultimately its effect on in-cylinder combustion quality for the three different fuels: n-butanol, iso-butanol and iso-octane. To mimic in-cylinder conditions, hot fuel was introduced inside an optically accessible engine. It was observed that fuel temperature and their thermo-physical properties have a significant effect on piston head wetting and pool fire on the piston top. Butanol isomers showed significant reduction in sooty combustion with increase in fuel temperature. However, iso-octane showed higher wall wetting at elevated fuel temperature due to spray collapse.

“…The injection pressure is the main driver that initially pushes the spray inside the chamber allowing for the liquid spray to penetrate at early injection timings. Previous analyses of the mixture formation process in the Spray G conditions 13,[32][33][34][35] have shown that during injection, a strong aerodynamic motion is generated by air entrainment which persists after the end of injection. This motion becomes the main driver for the propagation of the vaporized fuel jet.…”

Section: Analysis Of the Aerodynamic Mechanism Leading To The Componementioning

confidence: 99%

Quantitative measurements of preferential evaporation effects of multicomponent gasoline fuel sprays at ECN Spray G conditions

Cordier

Itani

Bruneaux

2019

A two-tracer laser-induced fluorescence technique is used to quantify the effects of preferential evaporation of multicomponent fuels on the fuel component distribution. The technique is based on the simultaneous detection of the fluorescence of two aromatic tracers with complementary evaporation characteristics matched to different components of a multicomponent fuel. Relative variations in the spatial distribution of tracer distribution as a consequence of preferential evaporation are determined from the ratio of laser-induced fluorescence signals measured within two distinct spectral bands. A thermodynamic model is then used to relate the ratio map with the fuel component map. The accuracy and precision of the method are characterized from determining the laser-induced fluorescence signal ratio within two identical spectral bands. Measurements are performed in a high-pressure high-temperature vessel equipped with an eight-hole injector. The Engine Combustion Network Spray G target conditions are chosen as reference conditions at injection. The only difference with these target conditions is the use of a multicomponent surrogate fuel. Parametric variations around these target conditions are also performed in order to investigate their effect on the preferential evaporation effect. The ambient temperature is varied between 525 and 625 K and the injection pressure is reduced from 200 to 100 bar. The impact of ethanol addition is also studied with two different fuel mixtures in addition to the reference surrogate fuel: E20 and E85 which feature 20% and 85% of pure ethanol within surrogate, respectively. A significant preferential evaporation effect is observed in this condition representative of engine applications and results in a spatial segregation between low- and high-volatility fuel components, respectively, at the tail and tip of the plumes. This effect is enhanced by the addition of ethanol and the decrease in ambient temperature and injection pressure.