CFD analysis of a two-stroke air cooled engine designed for handheld products

Still today, two-stroke engine layout is characterized by a wide share on the market thanks to its simpler construction that allows to reduce production and maintenance costs respecting the four-stroke engine. Two of the main application areas for the two-stroke engines are on small motorbikes and on handheld machines like chainsaws, brush cutters, and blowers. In both these application areas, two-stroke engines are generally equipped by a carburettor to provide the air/fuel mixture formation while the engine cooling is assured by forcing an air stream all around the engine head and cylinder surfaces. Focusing the attention on the two-stroke air-cooling system, it is not easy to assure its effectiveness all around the cylinder surface because the air flow easily separates from the cylinder walls producing local hot-spots on the cylinder itself. This problem can be bounded only by the optimization of the cylinder fin design placed externally to the cylinder surface. In the present paper the authors present a first analysis of the thermal-flow behaviour of a two stroke engine designed for brush-cutter machine applications. The optimization of the air-cooling system of such a machine is a very challenging task because the machine design is very compact forcing all the engine parts to remain quite close to each other. The proposed analysis is performed by the definition of a specific 3D-CFD simulation methodology based on the Conjugated Heat Transfer approach. The methodology was validated against experimental data.