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The objective of this paper is to analyse the flow characteristics inside the cylinder of a DI Diesel engine at variable swirl number. Initially, the cylinder head is characterised by means of three-dimensional calculations of the steady flow through the intake ports. These calculations have been made for several positions of the throttles, from wide open, to closed, using the STAR-CD commercial CFD code. They have been validated with steady flow experimental data measured with torque-meter. Next, 3D calculations of the compression stroke are presented and compared with experimental measurements. The initial conditions inside the cylinder in the TDC have been estimated using the head characterisation tests and a zero-dimensional model. The results obtained are in good agreement with the experiments.

Partially Premixed Combustion (PPC) of fuels in the gasoline octane range has proven its potential to achieve simultaneous reduction in soot and NOX emissions, combined with high indicated efficiencies, while still retaining control over combustion phasing with the injection event. However, the octane range where the ignition properties of a given fuel are optimum depends on the engine running conditions. Thus, low octane fuels present problems for extending the ignition delay at medium to high engine loads; while too high octane fuels have ignition problems at low engine loads. Two-stroke engines arise as a promising solution to extend the load range of the PPC concept, since it intrinsically provides equivalent torque response with only half the IMEP required in a four-stroke engine.