Measurements in a motored four-stroke reciprocating model engine

Measurements of ensemble-averaged axial velocities and the rms of the corresponding fluctuations obtained by laser Doppler anemometry are reported for the axisymmetric flow in a four-stoke model engine motored at 200 rpm with a compression ratio of 3.5. The flow structure during the intake stroke is dominated by the inlet geometry conditions with small dependence on whether compression is applied and negligible dependence on piston configuration. This structure consists of a system of vortices created by a high-volocity jet associated with high turbulence levels which decay steadily past midstroke. In the early part of the compression stroke the intake-generated flow structure is no longer apparent and the rms values tend to become uniform. In the expansion stroke the flat piston results in the creation of a weak vortex and considerable reduction in the turbulence intensity.