4. Recent Progress in Primary Atomization Model Development for Diesel Engine Simulations

Predictive engine simulations are key for rapidly exploring and optimizing the design of cleaner burning and more fuel-efficient engines. Injection strategies in advanced engine concepts are resulting in the injection and atomization of fuel under a wide range of operating conditions in order to meet stringent emission regulations. However, the physics governing the breakup of an injected liquid fuel jet into droplets under these conditions have not been well studied or experimentally characterized to date. It is uncertain whether existing atomization and spray breakup models, historically developed to study conventional diesel operation, can be directly applied within engine CFD simulations to study new advanced engine concepts. This chapter summarizes recent progress made in developing an improved physics-based primary atomization model for use in diesel engine simulations across a broad range of in-cylinder conditions. Physical mechanisms that are likely to contribute to the atomization of diesel sprays are first reviewed, with a particular focus on aerodynamic wave growth on the fuel jet surface and turbulence generated in the injector. Then, recent advances in spray diagnostics that have informed characteristic length scales of primary atomization are highlighted. The chapter concludes with the presentation and validation of a newly developed hybrid spray breakup model, the “KH-Faeth” model, capable of representing both aerodynamic and turbulent breakup mechanisms in the atomization of non-cavitating diesel sprays.