Numerical Study on the Adaptation of Diesel Wave Breakup Model for Large-Eddy Simulation of Non-Reactive Gasoline Spray

Gasoline direct injection (GDI) is a promising solution to increase engine thermal efficiency and reduce exhaust gas emissions. The GDI operation requires an understanding of fuel penetration and droplet size, which can be investigated numerically. In the numerical simulation, primary and secondary breakup phenomena are studied by the Kelvin-Helmholtz/Rayleigh-Taylor (KH-RT) wave breakup models. The models were initially developed for diesel fuel injection, and in the present work, the models are extended to the GDI application combined using large-eddy simulation (LES). The simulation is conducted using the KIVA4 code. Measured data of experimental spray penetration and Mie-scattering image comparisons are carried out under non-reactive conditions at an ambient temperature of 613K and a density of 4.84 kg/m3. The spray penetration and structures using LES are compared with traditional Reynolds-Averaged Navier-Stokes (RANS). Grid size effects in the simulation using LES and RANS models are also investigated to find a reasonable cell size for future reactive gasoline spray/combustion studies. The fuel spray penetration and droplet size are dependent on specific parameters. Parametric studies on the effects of adjustable constants of the KH-RT models, such as time constants, size constants, and breakup length constant, are discussed. Liquid penetrations from the RANS turbulence model are similar to that of the LES turbulence model’s prediction. However, the RANS model is not able to capture the spray structure well.

A Quasi-Dimensional Fuel Distribution Model for a Radially Stratified Engine

Several combustion strategies leverage radial fuel stratification to adapt combustion performance between the center of the chamber and the outer regions independently. Spark-assisted compression ignition (SACI) relies on careful tuning of this radial stratification to maximize the combined performance of flame propagation and autoignition. Established techniques for determining in-cylinder fuel stratification are computationally intensive, limiting their feasibility for control strategy development and real-time control. A simplified model for radial fuel stratification is developed for control-oriented objectives. The model consists of three submodels: spray penetration, fuel distribution along the spray axis, and post-injection mixing. The spray penetration model is adapted from fuel spray models presented in the literature. The fuel distribution and mixing submodels are validated against injection spray results from an LES 3-D computational fluid dynamics (CFD) reference model for three test points as a function of crank angle. The quasi-one-dimensional model matches the CFD results with a root mean square error (RMSE) for equivalence ratio of 0.08?0.11. This is a 50% reduction from the 0.16?0.20 RMSE for a model that assumes a uniform fuel distribution immediately after injection. The computation time is 230 ms on an Intel Xeon E5-1620 v3 to solve each case without significant optimization for code execution speed.

Investigation of the Spray Development Process of Gasoline-Biodiesel Blended Fuel Sprays in a Constant Volume Chamber

This study investigated gasoline–biodiesel blended fuel (GB) subjected to a fuel spray development process on macroscopic and microscopic scales. The four tested fuels were neat gasoline and gasoline containing biodiesel (5%, 20%, and 40% by volume) at three different ratios. The initial spray near the nozzle revealed that the spray penetration and spray tip velocity both decreased with decreasing biodiesel blending ratio. In addition, the different spray tip velocities at the start of spraying result in different atomization regimes between the fuels. The GB fuels with a low biodiesel blending ratio were disadvantaged in terms of spray atomization due to their lower spray penetration and tip velocity. The macroscopic spray penetration changes were similar to those observed in the microscopic spray. The fuel with the lower biodiesel blending ratio had a larger spray cone angle, indicating increased radial spray dispersion.

Experimental Study on Spray Characteristics of Gasoline/Hydrogenated Catalytic Biodiesel under GCI Conditions

The new blended fuel (gasoline/hydrogenated catalytic biodiesel) is expected to address the cold start problem under low temperature of gasoline compression ignition due to its excellent ignition performance. Additionally, its spray behavior as the combustion boundary condition could have a direct impact on the characteristics of subsequent combustion. Therefore, the objective of this study is to reveal the effects of hydrogenated catalytic biodiesel/gasoline on the spray characteristics under various ambient conditions. As a significant index of spray characteristics, the spray penetration was achieved by applying Mie scattering methods under nonevaporation and evaporation conditions on a constant volume combustion chamber. In addition, the experimental results were compared against the calculated values of the models. As demonstrated by the results, a better spray performance can be achieved by the blended fuel than diesel and hydrogenated catalytic biodiesel. In respect of spray penetration, there is almost no difference among the three fuels under the ambient temperature of 323 K. Nevertheless, the blended fuel is lower than that of hydrogenated catalytic biodiesel and diesel when the ambient temperature is 434 K and 523 K. Moreover, the blended fuel is the first to reach the stable state, and the hydrogenated catalytic biodiesel is earlier than diesel for the spray penetration. Meanwhile, the spray model is identified as suitable for the blended fuel.

A review of phenomenological spray penetration modeling for diesel engines with advanced injection strategy

Driven by the increasingly remarkable problems of environmental pollution and energy crisis, the combustion optimization of diesel engine seems to be more urgent than ever, therefore, advanced injection strategies are gradually proposed and employed in modern diesel engines. Phenomenological model, which serves as an effective tool to conduct the parametric study on the spray penetration, needs to be improved to fit the intensified injection condition. Since that there are no attempts to review the spray penetration model developments, in order to help to build a comprehensive understanding of diesel spray propagation, this article briefly summarized the early history and introduced the widely used classical and improved phenomenological spray penetration models. Besides, to provide a helpful reference for selection of suitable models, the modeling methods were analyzed and features and simulation of various models were discussed and compared. After that, the trend of modeling methods and promising directions for future spray modeling were suggested.