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Further Development and Application of a Model for the Calculation of Heat Release in Direct Injection Diesel Engines
Abstract:
A model for the calculation of heat release in direct injection Diesel engines is presented. It needs only one engine-specific experimental parameter. In the form the model is presented here it is limited to the medium and upper load range, where Diesel combustion is mainly mixing controlled. The development of the model is based on data from medium speed engines. The applicability to automotive engines is shown in some examples.
The model is based on the theory of single phase turbulent jets. Starting from the balance of momentum and fuel mass flow the stationary part of the jet can be calculated. The propagation of the front of the unsteady jet is determined from a continuity consideration. Heat release is calculated based on the assumptions of the Simple Chemically Reacting System (SCRS). Fuel that is mixed with air is assumed to be burnt instantaneously.
Adjustment of the model to a good correspondence of measured and calculated heat release results in an experimental parameter which is in the same range as the figures published for turbulent jet flames. With this calibration the model is able to calculate the rate of heat release over a wide load range.
The experimental parameter is engine specific but is a constant except for very short injections. This can be explained by the entrainment wave at the end of injection. Its influence is the larger the shorter the injection is. A correlation is presented to reproduce this effect.
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