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Among the existing concepts to help improve the efficiency of spark ignition engines on low load operating points, Controlled Auto-Ignition™ (CAI™) is an efficient way to lower both fuel consumption and pollutant emissions at part load without major modifications of the engine design. The CAI™ concept is founded on the auto-ignition of a highly diluted gasoline-based mixture in order to reach high indicated efficiency and low pollutant emissions through a low temperature combustion. The high dilution rates needed to successfully obtain CAI™ combustion imply the use of unconventional valve lift strategies. To correctly control this combustion mode, the rate of dilution has to be precisely known. From a numerical point of view, this induces the need for a CFD tool suited for air path computations, the most relevant one being a 1D simulation approach.

Modern diesel engines operate under injection pressures varying from 30 to 200 MPa and employ combinations of very early and conventional injection timings to achieve partially homogeneous mixtures. The variety of injection and cylinder pressures, as well as injector dynamics, result in different injection rates, depending on the conditions. These variations can be captured by 1-D injection models that take into account the dynamics of the injector, the cylinder and injection pressures, and the internal geometry of the nozzle. The information obtained by these models can be used to provide initial and boundary conditions for the spray modeling in a 3-D combustion code. In this paper, a methodology for coupling a 1-D injection model with a 3-D combustion code for direct-injected diesel engines is presented. A single-cylinder diesel engine has been used to demonstrate the capabilities of the model under varying injection conditions.