1987-02-01

THREE-DIMENSIONAL COMPUTATIONS OF FLOWS IN A STRATIFIED-CHARGE ROTARY ENGINE 870409

The first three-dimensional rotary-engine computations are reported of exhaust, intake (with side and peripheral ports, and with different intake turbulence intensities and length scales), compression, homogeneous-charge combustion, dual liquid fuel injection, and dual liquid fuel injection and combustion. The model includes a k-ε submodel for turbulence, a stochastic treatment of the fuel drops and a hybrid laminar and mixing-controlled submodel for the conversion of reactant to products. The code is an extensively modified version of KIVA. The latter was developed at the Los Alamos National Laboratory for reciprocating engines. The modifications include: dynamic rezoning of the grid in both the x-y and the x-z planes; adoption of a cartesian coordinate system fixed to the housing with analytical grid generation and grid velocities related to the rotor velocity; inclusion of radial and tangential ports for both intake and exhaust; use of ordinary differential equations in narrow clearances and their coupling to the partial differential equations; and modifications of the finite differencing of viscous and pressure terms to Improve computational accuracy and efficiency. Among the new conclusions for rotary engines are that: near TDC turbulence is always insensitive to the details of the turbulence generated during intake but may depend on the Initial turbulence diffusivity; near TDC the spatial distribution of turbulence is always non-uniform; with preralxed-charges, the degree of mixing of fresh and residual charges and spatial uniformity of turbulence at ignition time are sensitive to the method of introduction of the fresh charge; and means should be considered to produce recirculation in fuel-injected engines. Since no measurements of the flows inside rotary engines exist, the stated conclusions are predictions, not postdictions. An extensive discussion of similarities and differences between flows in reciprocating and rotary engines is included.

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