2003-01-0007 Fuel Spray Simulation of High-Pressure Swirl-Injector for DISI Engines and Comparison with Laser Diagnostic Measurements Christos A. Chryssakis, Dennis N. Assanis University of Michigan Jee-Kuen Lee, Keiya Nishida University of Hiroshima Copyright © 2003 Society of Automotive Engineers, Inc. ABSTRACT A comprehensive model for sprays emerging from high- pressure swirl injectors in DISI engines has been developed accounting for both primary and secondary atomization. The model considers the transient behavior of the pre-spray and the steady-state behavior of the main spray. The pre-spray modeling is based on an empirical solid cone approach with varying cone angle. The main spray modeling is based on the Liquid Instability Sheet Atomization (LISA) approach, which is extended here to include the effects of swirl. Mie Scattering, LIF, PIV and Laser Droplet Size Analyzer techniques have been used to produce a set of experimental data for model validation. Both qualitative comparisons of the evolution of the spray structure, as well as quantitative comparisons of spray tip penetration and droplet sizes have been made. It is concluded that the model compares favorably with data under atmospheric conditions. However, discrepancies occur under higher ambient pressures, suggesting that the physics of the breakup mechanism should be further investigated for these conditions. INTRODUCTION The design of more powerful, fuel-efficient, and environmentally friendly gasoline engines is currently one of the main goals of engine researchers and manufacturers worldwide. In this context, the Direct- Injection Spark-Ignition (DISI) engine promises significant advantages, especially in improving fuel economy and reducing CO 2 emissions [1-8]. However, there are challenges associated with the very short amount of time available for the fuel spray to atomize and form an adequate mixture for satisfactory combustion. Consequently, suitable fuel injectors are needed to provide sufficient control on the spray motion and meet the basic requirements for atomization and mixing. Among the various injectors that have been under investigation, the High-Pressure Swirl (HPS) injectors are the most commonly used in commercial applications today. HPS injectors operate at relatively high pressures (4-12 MPa) and their design enhances atomization as well as turbulence levels in the combustion chamber for a more efficient combustion process. Instead of the round jet solid-cone structure common to diesel injectors, the HPS injector produces a hollow-cone spray structure by providing a swirl rotational motion to the fuel inside the injector. The key advantage of hollow cone sprays is the high area to volume ratio, which can lead to the required level of atomization without large penetration lengths. The development of the spray emerging from an HPS injector can be divided into two phases: the transient phase at the beginning of injection and the steady-state phase that corresponds to the largest part of the injection process. Upon the start of injection, due to the lack of high swirl, a solid-cone-like structure appears with narrow cone angle and relatively large droplets. As the fuel velocity inside the nozzle increases, the angular momentum and the centrifugal forces increase too, thus forcing the fuel to form a hollow-cylinder structure, adjacent to the walls of the nozzle. This structure is transformed into a hollow-cone as the fuel emerges in the combustion chamber. It has been found experimentally that the higher the swirl intensity of the emerging fuel, the larger the cone angle of the resulting spray [2,7,8]. The hollow-cone formed is a liquid sheet that penetrates in the high-pressure environment of the cylinder until it disintegrates into circular ligaments that further break up into droplets. A literature review of the most significant approaches towards modeling the liquid sheet shows that the first promising attempt to model a hollow-cone spray has been published in 1995 by Dorfner et al. [9]. In 1997, an improved model has been presented by Han et al. [10],