*Article* **Computational Methodology for Knocking Combustion Analysis in Compression-Ignited Advanced Concepts**

## **José Ramón Serrano, Ricardo Novella \*, Josep Gomez-Soriano and Pablo José Martinez-Hernandiz**

CMT-Motores Térmicos, Universitat Politècnica de València, Camino de Vera s/n, 46022 Valencia, Spain; jrserran@mot.upv.es (J.R.S.); jogoso1@mot.upv.es (J.G.-S.); pabmarh2@mot.upv.es (P.J.M.-H.) **\***Correspondence:rinoro@mot.upv.es;Tel.:+34-96-387-9650

 Received: 5 September 2018; Accepted: 17 September 2018; Published: 20 September 2018

**Abstract:** In the present work, a numerical methodology based on three-dimensional (3D) computational fluid dynamics (CFD) was developed to predict knock in a 2-Stroke engine operating with gasoline Partially Premixed Combustion (PPC) concept. Single-cycle Unsteady Reynolds-Averaged Navier Stokes (URANS) simulations using the renormalization group (RNG) *k* − *ε* model were performed in parallel while the initial conditions are accordingly perturbed in order to imitate the variability in the in-cylinder conditions due to engine operation. Results showed a good agreemen<sup>t</sup> between experiment and CFD simulation with respect to cycle-averaged and deviation of the ignition timing, combustion phasing, peak pressure magnitude and location. Moreover, the numerical method was also demonstrated to be capable of predicting knock features, such as maximum pressure rise rate and knock intensity, with good accuracy. Finally, the CFD solution allowed to give more insight about in-cylinder processes that lead to the knocking combustion and its subsequent effects.

**Keywords:** gasoline PPC concept; 2-stroke engine; knocking combustion; CFD modelling; cycle-to-cycle variation
