Numerical simulation of the thermodynamics of a nutating engine.

摘要

The purpose of the present work was to investigate the McMaster nutating engine thermodynamic processes by numerical simulation, focusing on combustion. The researched engine was analyzed as a gasoline engine with port injection. The unstructured mesh used to model the combustion chamber has a particularly complicated dynamic, its continuous motion and deformation requiring a sequence of coordinate rotations and transformations. The surfaces were controlled by a set of subroutines implemented into the main codes (CFX or Fluent). The intake process was modeled as a three-dimensional transient process that included turbulent and viscous effects. The valveless version of the engine operating in a range of intake pressures and engine speeds was investigated under dynamic conditions. The computational tools for combustion modeling were first validated for the case of a piston engine. It was shown that the partially premixed combustion model leads to more accurate results. The model considers the combustion process to have a time-history, incorporates typical physical phenomena like flame propagation and includes heat transfer effects. Multidimensional simulation of combustion in McMaster engine was performed, followed by the expansion stroke modeling. A single zone combustion model and three multidimensional models were used with both a stationary and a dynamic mesh, and the results compared. It was concluded that the approximation of the process with the ideal constant-volume combustion model does not provide realistic results in the case of the nutating engine. The flame front propagation could be visualized with the help of contours of temperature and progress variable. A parametrical study of combustion with respect to engine rotational speed, ignition timing, pre-combustion pressure and number of spark plugs was performed. Engine performance was estimated and compared with similar internal combustion engines. Overall, McMaster engine displays operating characteristics typical for small turbocharged spark-ignition engines, some (such as imep) even in the high range of values. A specific trait of the engine is the low RPM for which the torque peaks.