Note: All transient jet data taken and the full code for the 1-D jet model are detailed in papers [1] and [2] and are available for download and use with citation at the link below.

Click here for link to download portal for experimental data and 1-D model code

The experimental findings have led to the development of an evolved 1-D model that uses the same principle of dividing the jet into a series of axial control volumes representing the cross-sectional average quantities as used in [3] and [4]. In addition, the evolved model integrates jet breakup physics and removes other quasi-steady assumptions. This model displays excellent agreement with the experimental transient data, while not increasing the number of tuning inputs from older 1-D models and maintaining similar computational expense.

modelresults — Results for conditions at 15 (left) and 22 (right) kg/m³ for the following information. Both plots: time at breakup length. (Bottom) Jet penetration versus time for 1-D model from [2] and the 1-D model from [3], and experimental results for 30/52/75 MPa injection pressures. (Top) Model residual penetration (model – data) versus time for the same conditions for the model from [2]. Every other experimental data point is plotted for figure clarity.

Understanding jet behavior for unsteady injections is crucial for the development of improved CFD models of high pressure fuel injection.

This model couples together an internal unbroken liquid segment with a surrounding droplet sheath to simulate jet breakup. Schematics of the conceptual model and the implementation of the model using a discretized control volume approach are shown below.

model graphics — Left: Cross-sectional illustration of model.
Right: Control volumes in breakup region.

By allowing the internal liquid core to maintain its initial momentum until it is shed to the droplet sheath, the early Bernoulli-like penetration characteristics of the experiments are captured, while also correctly modeling the quasi-steady well-mixed behavior downstream.

It is clear that for combustion strategies that utilize short, ramped injections such as multi-injection diesel combustion, GCI, and RCCI, the portion of the jet that is dominated by Bernoulli behavior cannot be treated with quasi-steady scaling laws, especially with the addition of transient rate-of-injection profiles.

References

[1] Neal, N. and Rothamer, D., “Measurement and Characterization of Fully Transient Diesel Fuel Jet Processes in an Optical Engine with Production Injectors,” Experiments in Fluids, Vol. 57, No. 10, pp. 1-19, 2016.

[2] Neal, N. and Rothamer, D., “Evolving One-Dimensional Transient Jet Modeling by Integrating Jet Breakup Physics,” International Journal of Engine Research, doi:10.1177/1468087416688119.

[3] Musculus, M.P.B. and Kattke, K., “Entrainment Waves in Diesel Jets,” SAE Technical Paper, 2009-01-1355, 2009.

[4] Pastor, J.V., Lopez, J.J., Garcia, J.M., and Pastor, J.M., “A 1D Model for the Description of Mixing-Controlled Inert Diesel Sprays,” Fuel, Vol. 87, No. 13-14, pp. 2871-2885, Oct 2008.