Predictions of Transient Flame Lift-off Length With Comparison to Single-Cylinder Optical Engine Experiments

Abstract

A state-of-the-art, grid-convergent simulation methodology was applied to three-dimensional calculations o f a single-cylinder optical engine. A mesh resolution study on a sector-based version o f the engine geometry further verified the RANS-based cell size recommendations previously presented by Senecal et al. ("Grid Convergent Spray Models for Internal Com bustion Engine CFD Simulations," ASME Paper No. ICEF2012-92043). Convergence o f cylinder pressure, flame lift-off length, and emissions was achieved fo r an adaptive mesh refinement cell size o f 0.35 mm. Full geometry simulations, using mesh settings derived from the grid convergence study, resulted in excellent agreement with measurements o f cyl inder pressure, heat release rate, and NOx emissions. On the other hand, the full geometry simulations indicated that the flame lift-off length is not converged at 0.35 mm fo r jets not aligned with the computational mesh. Further simulations suggested that the flame lift-off lengths fo r both the nonaligned and aligned jets appear to be converged at 0.175 mm. With this increased mesh resolution, both the trends and magnitudes inflame lift-off length were well predicted with the current simulation methodology. Good agreement between the over all predicted flame behavior and the available chemiluminescence measurements was also achieved. The present study indicates that cell size requirements fo r accurate prediction o f full geometry flame lift-off lengths may be stricter than those fo r global combustion behav ior. This may be important when accurate soot predictions are required.

A System to Enable Mixing Controlled Combustion With High Octane Fuels Using a Prechamber and High-Pressure Direct Injector

“…These Lagrangian-Drop, Eulerian-Fluid spray and mixing models have been shown by previous researchers to be sensitive to the Eulerian grid resolution (Abani et al, 2008;Wang et al, 2010;Dempsey et al, 2012). Research has shown that using a model setup similar to this one, results in acceptable grid convergence of the lift-off length and reaction zone thickness for a diesel spray with cell sizes of 0.35 mm (Senecal et al, 2013a;Senecal et al, 2013b;Pomraning et al, 2014). Thus, this was used as the minimum cell size in this work.…”

Experimental and computational study comparing conventional diesel injectors and diverging group hole nozzle injectors in a high temperature pressure vessel and a heavy-duty diesel engine

“…These grid settings have been shown to yield good agreement with test data in previous studies performed internally at Caterpillar which have looked at several key outputs including liquid and vapor penetration as well as LOL, fuel and soot distributions. Furthermore, past studies [36][37][38][39] have shown that using a CONVERGE model setup similar to the one described in this work results in acceptable grid convergence of the lift-off length and reaction zone thickness for a diesel spray with cell sizes of 0.35 mm. Accordingly, similar settings resulting in a minimum cell size of 0.35 mm were used for the current study as well.…”

Influence of spray and combustion processes on piston temperatures and engine heat transfer in a high-output diesel engine

“…The fluid computational domain encompassed the full engine geometry including the intake and exhaust manifolds as shown in the Appendix (Figure A2). The mesh details and various simulation parameters, including model specifications for spray atomization and evaporation, were based on the methodology described in Senecal et al 24 Briefly, the spray is initially represented as liquid droplets (blobs) comparable to the orifice diameter, droplet atomization proceeds according to the Kelvin-Helmholtz and Rayleigh-Taylor (KH-RT) instability model, and collisions are predicted by the no-time-counter (NTC) method. 24 Spray parameters for the rate shape, start of injection and injection duration were specified based on the experimental data.…”