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A light duty downsized engine, named as “z-engine”, was developed, built and tested on the experimental rig. This engine is a two-stroke diesel with a split compression process and poppet valve for the gas exchange. The split compression process provides sufficient time for the longer exhaust process (over 180 CA degrees). The first stage of fresh air compression takes place in a turbocharger, the second part of the compression takes place in the mechanically driven piston compressor with PR of about 4.5 - 5.5. A very brief induction period, which lasts for about 10-22 CA degrees, is followed by a short final compression in the cylinder in which mixing occurs. The external piston compressor which provides all cylinders with a fresh charge, has relatively cold walls and its outlet is connected to an intercooler, so the total compression work is reduced and the fresh charge has a considerably lower temperature in comparison with a conventional diesel engine.

In this study theoretical investigations were carried out to determine design and working parameters modifications in order to increase by 20% power output and reduce fuel consumption in a marine two stroke medium speed diesel engine with opposite pistons. To achieve the above aim software packages, such as DIESEL-RK, INJECT and ANSYS, were deployed. The phenomenological multi-zone fuel spray combustion model in DIESEL RK software was refined to take into account complex interactions of fuel sprays and the influence of air swirl in the cylinder on evolution of fuel spays. For this purposes a 3D grid was created with regular cubical cells in the combustion chamber of the engine. The density of mesh was 50 cells across the diameter of the cylinder. In contrast to CFD technique, the transfer of liquid fuel and fuel vapour in the computational grid was carried out using empirical equations which had been validated by other researchers.

A previously developed multi-zone direct-injection (DI) diesel combustion model was implemented into a turbocharged diesel engine full cycle simulation tool DIESEL-RK. The combustion model takes into account the following features of the spray dynamics: Detailed evolution process of fuel sprays. Interaction of sprays with the in-cylinder swirl and the walls of the combustion chamber. Evolution of a Near-Wall Flow (NWF) formed as a result of a spray-wall impingement as a function of the impingement angle and the local swirl velocity. Interaction of Near-Wall Flows formed by adjacent sprays. Effect of gas and wall temperatures on the evaporation rate in the spray and NWF zones. In the model each fuel spray is split into a number of specific zones with different evaporation conditions. Zones, formed on the cylinder liner surface and on the cylinder head, are also taken into account. The piston bowl in the modeling process is assumed to have an arbitrary axi-symmetric shape.

A previously developed multi-zone direct-injection (DI) diesel combustion model has been refined for more accurate simulation of a full cycle of a turbocharged diesel engine. The combustion model takes into account the following features of the spray dynamics: Detailed evolution process of fuel sprays; Interaction of sprays with the in-cylinder swirl and the walls of the combustion chamber; Evolution of a Near-Wall Flow (NWF) formed as a result of a spray-wall impingement as a function of the impingement angle and the local swirl velocity; Interaction of Near-Wall Flows formed by adjacent sprays; Effect of gas and wall temperatures on the evaporation rate in the spray and NWF zones. In the model each fuel spray is split into a number of specific zones with different evaporation conditions. Zones, formed on the cylinder liner surface and on the cylinder head, are also taken into account. The piston bowl in the modelling process is assumed to have an arbitrary axi-symmetric shape.