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.
An instrumental variable approach to nonlinear model-based adaptive control of engine speed is investigated and implemented on a spark ignition internal combustion engine. A four-step version of the instrumental variable parameter estimation algorithm is used to identify a bias-free and noise tolerant model of the engine dynamics between the by-pass air valve voltage and engine speed. The parametric model representing the engine dynamics is a truncated Volterra series with a time delay. Model-based adaptive control is accomplished through a partitioned inversion of the engine model which is minimum phase and OL stable. The desired closed loop throttle response and disturbance rejection dynamics are introduced via a two-degree-of-freedom feedback control structure. Performance of the nonlinear model-based adaptive control algorithm is verified experimentally.
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