Calculations and Measurements of the Flow in a Motored Model Engine and Implications for Open-Chamber Direct-Injection Engines

摘要

The purposes of this paper are to present and compare computer calculations and measurements of the velocity characteristics of the flow in axisymmetric, four-stroke model engine and with the consequent knowledge of the precision of the calculation method, to report further predictions which are of relevance to open-chamber, direct-injection engines. The calculations are performed with the rpm multi-dimensional prediction method, which solves the governing equations in a flexible curvilinear coordinate frame with turbulence effects represented by a two-equation (k-epsilon) turbulence model. The results are compared with measurements obtained by laser-Doppler anemometry in a plexiglass cylinder with a flat piston, centrally-located valve with 60 exp 0 seat angle and non-swirling inlet flow, operating at 200 rpm and a compression ratio of 3.5. Moderate overall agreement is obtained between data and predictions, which collectively show that a strong highly-turbulent twin-vortex structure is produced during induction, but commences to decay rapidly around inlet valve closure. The mean motion continues to fall to a low level during compression, but the turbulence intensity attains an approximate constant level of about 0.6 times the mean piston speed, as also observed in other engine configurations. It is concluded that this decay process is one of the motivations for inducing longer-lived swirl motions in direct-injection engines and later augmenting these with squish, and it is suggested that calculation methods can assist in optimizing the fluid dynamics in such engines. (ERA citation 07:059943)