Measurement of Turbulence of Air Swirl in a 4-Stroke Cycle Engine Cylinder

Abstract

The turbulence of air swirl in the cylinder of a motored engine with a shrouded intake valve was measured with a hot-wire anemometer. In order to determine the turbulence characteristics such as turbulence intensity, integral time scale, etc., the flow velocity data were analyzed by the "stationary time average method" during a time interval of compression TDC±Δt/2. By changing the time interval Δt, different values of turbulence characteristics were obtained. It was made clear that the use of a finite time interval Δt meant the use of a high pass filter with a cut-off frequency of about 1/2(2Δt). As the angular speed of swirl, Ω, increased, the turbulence intensity, (u')_v, increased and the integral time scale, (L_t)_v, and the micro time scale, (λ_t)_v, decreased. Here, (u')_v, (L_t)_v and (λ_t)_v are spatial average values in a cylinder. Different correlations between (u')_v and Ω were obtained in different intake valves.