The present engine development pathway for increased specific power and efficiency is moving Spark-Ignition engines towards unprecedented levels of mean thermo-mechanical loading. This in turn promotes undesired abnormal combustion events in the unburnt mixture (also called “engine knock”), leading to solid parts failure and constituting a severe upper constraint to engine efficiency. In this context, CFD simulations are regularly used to investigate the fluid-dynamic reasons for engine knock and to address knock suppression strategies, using dedicated models to simulate the chemical reaction rate of the fuel/air/residual mixture at the same thermodynamics states as those encountered in engines. In this paper three different approaches are coherently compared to simulate knock occurrence on a turbocharged GDI engine, representing some of the most popular choices for modelers in the RANS framework. The first one considers the on-the-fly solution of chemical reactions, which represents the state-of-the-art knock modelling approach albeit its problematic computational cost for industrial turnaround times. The other two methods consider pre-calculated libraries of ignition delay times (calculated at constant pressure and volume, respectively) for the same fuel model, and knock timing is predicted using a classical Livengood-Wu approach coupled to the same main combustion model. All the analyzed models for the end-gas reaction rate are coupled with a dedicated combustion model for propagating flame (G-equation). A comprehensive analysis of computational cost and of knock prediction accuracy is carried out for library-based methods against the detailed chemistry model. Finally, results are critically discussed and explained using combined ignition delay time maps and traces for thermodynamic in-cylinder states, and guidelines for the a priori choice for constant pressure- or volume-generated libraries are provided. In this context, the use of a synthetic knock model combined with libraries of ignition delays calculated at constant volume emerges as an accurate and efficient modelling strategy. The study outlines a method for the well-supported use of simplified CPU-efficient models, with a promoted confidence in simulation results from the comparison with detailed chemistry.
Comparison of library-based and detailed chemistry models for knock prediction in spark-ignition engines / CICCI, FRANCESCO; D'ADAMO, Alessandro; BARBATO, ALESSIO; BREDA, SEBASTIANO. - (2019). ((Intervento presentato al convegno 74th ATI National Congress tenutosi a Modena nel 11-13/9/2019 [10.1063/1.5138779].
|Data di pubblicazione:||2019|
|Data di prima pubblicazione:||17-dic-2019|
|Titolo:||Comparison of library-based and detailed chemistry models for knock prediction in spark-ignition engines|
|Autore/i:||CICCI, FRANCESCO; D'ADAMO, Alessandro; BARBATO, ALESSIO; BREDA, SEBASTIANO|
|Digital Object Identifier (DOI):||http://dx.doi.org/10.1063/1.5138779|
|Codice identificativo Scopus:||2-s2.0-85077878294|
|Codice identificativo ISI:||WOS:000552623000046|
|Nome del convegno:||74th ATI National Congress|
|Luogo del convegno:||Modena|
|Data del convegno:||11-13/9/2019|
|Citazione:||Comparison of library-based and detailed chemistry models for knock prediction in spark-ignition engines / CICCI, FRANCESCO; D'ADAMO, Alessandro; BARBATO, ALESSIO; BREDA, SEBASTIANO. - (2019). ((Intervento presentato al convegno 74th ATI National Congress tenutosi a Modena nel 11-13/9/2019 [10.1063/1.5138779].|
|Tipologia||Relazione in Atti di Convegno|
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