Evolving one-dimensional transient jet modeling by integrating jet breakup physics

Abstract

High-speed optical measurements of unsteady liquid fuel jets under engine-like conditions have shown that the initial penetration of the jets does not follow the behavior predicted by previously introduced one-dimensional jet models based on gas-jet principles. The experimental data indicate that the transient jet penetration velocity is initially controlled by the jet exit velocity, transitioning to gas-jet like mixing-dominated penetration further downstream. This behavior is consistent with the common description of high-pressure fuel jets as containing a liquid core surrounded by entrained gas and fuel droplets. In this paper, a new one-dimensional modeling methodology is introduced that couples the transport equations for the evolution of the liquid core of the jet and the surrounding sheath of droplets resulting from breakup. This allows for the penetration of the jet to be initially governed by the liquid core, which is relatively unaffected by the ambient gas, transitioning to spray penetration dominated by the entrained ambient gas. The model also provides a defined jet centerline velocity, which allows for the shape of the radial profiles of fuel velocity and fuel volume fraction to be solved for directly, without the need for a steady-jet assumption, as was used in previous one-dimensional models. This change removes the need for a constant momentum flux assumption, improving the transient nature of the model. The results of the model are validated against the aforementioned optical transient jet measurements. The model and all associated experimental data have been made available for use at rothamer.erc.wisc.edu/dlp.

A Novel One- and Zero-Dimensional Model for Turbulent Jet Ignition

“…This reasoning is further supported by the fact that the model error is mainly concentrated up to Table 4 Operating conditions for the validation of the flow and turbulence jet sub-models a distance x∕d j < 5 , which is approximately the extent of the jet core. Neal and Rothamer (2017) proposed a dynamic equation for the determination of the shape factor, which can potentially offer better agreement with the DNS results in the near nozzle region of the jet. The source term is dependent on the scalar dissipation rate, which is linked to the turbulent mixing frequency computed from Eq.…”

Modeling of diesel spray tip penetration during start-of-injection transients

“…The acceleration behavior of S tip during the SOI transients is believed to be closely related to the needle opening and sac pressurization processes. 19,33 With the development of the advanced optical diagnostics technologies such as the X-ray phase-contrast imaging (XPCI) methods, the in-nozzle needle lift profiles can be measured [41][42][43] and therefore the sac pressurization processes can be simulated, 21 which provides important reference for solving the above two issues. Unfortunately, until now, relevant efforts are still absent.…”

“…In addition to the 0-D models reviewed above, many efforts have been paid on developing 1-D models to predict S tip during the SOI transients. 7,33 Since the sac pressure ramp-up processes have been considered to some extent by coupling the fuel injection rate as boundary condition, these 1-D models can predict the acceleration processes at the injection startup. However, these 1-D models are still computationally expensive for the model-based real-time engine control strategy and will not be discussed in detail in the present study.…”