Search Results

The paper presents a 1D-3D numerical model to simulate the scavenging and combustion processes in a small-size spark-ignition two-stroke engine. The engine is crankcase scavenged and can be operated with both gasoline and Natural Gas (NG). The analysis is performed with a modified version of the KIVA3V code, coupled to an in-house developed 1D model. A time-step based, two-way coupled procedure is fully described and validated against a reference test. Then, a 1D-3D simulation of the whole two-stroke engine is carried out in different operating conditions, for both gasoline and NG fuelling. Results are compared with experimental data including instantaneous pressure signals in the crankcase, in the cylinder and in the exhaust pipe. The procedure allows to characterize the scavenging process and quantify the fresh mixture short-circuiting, as well as to analyze the development of the NG combustion process for a diluted mixture, typically occurring in a two-stroke engine.

The paper describes preliminary results of a research activity finalized to the development of a new scavenging concept for the reduction of the HC emitted by a small-size two-stroke carbureted crankcase-scavenged SI engine. Further developments of a well-established model (1Dime code) are presented, with particular emphasis on combustion and scavenging processes simulation. The rate of heat release is computed through a two-zone model, based on a “fractal” representation of the turbulent flame front. A CAD procedure evaluating, at each crank-angle and flame radius, the intersections between the flame surface and the actual combustion chamber walls, has been developed. Scavenging is modeled through an original two-zone approach which accounts for mixing and short-circuiting processes. The latter are directly related to the in-cylinder turbulent flow regime, inlet and exhaust flow velocities, and engine speed.