This paper describes the results of a theoretical and experimental study of in-cylinder flow in a reciprocating engine.
The numerical calculations are performed with an implicit, finite-difference computer code developed to solve the compressible Navier-Stokes equations in a three-dimensional, curvilinear coordinate system. The computational domain has the particularity of including a moving valve and the intake port, which consists of a curved duct with circular cross-section. Therefore, the flowfield inside the cylinder is calculated with computed conditions in the port/valve region. Two types of three-dimensional numerical results are given: (a) Compression with a bowl-in-piston arrangement, (b) The non-compressing flow structure for the purpose of testing the computer code against experimental data.
The experimental configuration is an idealized geometry with a fixed piston, a moving valve and an orifice for outflow of air. Laser velocimetry is used to quantify the mean motion and turbulence without compression under both steady (fixed valve) and unsteady conditions. Velocity profiles were investigated in different planes inside the cylinder under and above the valve. Special attention has been paid to the valve periphery. Two complementary laser velocimeter systems were employed for these experimental investigations: a fringe laser velocimeter (LDV) and a laser-two-focus (L2F). Optical access is provided by a transparent piston for a direction parallel to the cylinder axis. Two diametrically opposed small windows allow optical access along a direction normal to the cylinder wall.
The global behaviour of the numerical predictions show satisfactory agreement with steady flow measurements.
Some unsteady velocity measurements and wall pressure fluctuations are reported at the end of the paper.