Quasi-Dimensional Multi-Zone Combustion Diagnostic Tool for SI Engines with Novel NOx and CO Emissions Models 2020-01-0289
In this work an innovative quasi-dimensional multi-zone combustion diagnostic tool for homogeneous charge spark ignition (SI) engines is developed for the evaluation of heat release, flame propagation parameters, combustion velocities as well as engine-out NOx emissions based on in-cylinder pressure data analysis. The tool can be used to assess the effects of fuel, design and operating parameters on the SI engine combustion and NOx emissions formation processes.
Certain novel features are included in the presently developed combustion diagnostic tool. Firstly, combustion chambers of any shape and spark plug position can be considered due to an advanced model for the calculation of the geometric interaction between a spherically expanding flame and a general combustion chamber geometry. Then, the temperature stratification in the burned gas developed during the combustion phase, which has to be captured for realistic calculations of emissions formation, is taken into account by a multi-zone thermodynamic treatment. According to this, multiple spherically allocated burned zones are sequentially generated at specified (user-defined) crank angle intervals, forming overlapping shells. Also, complex chemical equilibrium compositions are computed, which can include any user-defined mixture of species in the combustion products, using an advanced modular method based on the minimization of Gibbs energy. Furthermore, NOx engine-out emissions are calculated by a novel global algebraic NOx emissions formation model presented by the authors in the past. This model accounts for both thermal and N2O pathway NO formation, based on the calculation of the characteristic timescales of the relevant NO formation mechanisms.
The combustion diagnostic tool is applied to a lean burn gas engine at various engine speeds under full load conditions and constant lambda value. Various combustion and NOx emissions related results are presented and discussed to illustrate the capabilities of the tool for combustion diagnosis, while at the same time calculated engine-out NOx emissions are found to be in good agreement with measured ones.