EVALUATION OF THE NONSTEADY FLOW PRODUCED BY INTAKE PORTS OF DIRECT-INJECTION DIESEL-ENGINES

The most usual way to characterize a D.I. Diesel engine cylinder head is based on steady flow tests with fixed pressure drop across the valve and at different valve lifts. A discharge coefficient and a swirl number are defined, which are representative of the breathing capacity and angular velocity generation of the intake system. A question arising is the validity of such parameters in non-steady conditions, with time scales similar to those of the firing engine, where the valve is moving and the pressure drop across the valve is time dependent. Experimental tests were conducted both in steady and non-steady flow test rigs in order to assess the quasi-steady assumption in terms of the mass flow rate across the valve, as well as swirl produced by the intake port. Time resolved laser-Doppler velocimetry was used, together with an extension of a conventional test flow rig to non-steady operation.