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 agreement 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.
Highlights
The automotive industry is currently confronted with the hard challenge of achieving a compromise between performance and sustainability [1]
The use of more complex turbulence approaches (LES) and the simulation of several consecutive cycles is currently the standard approach to reproduce the cycle pressure variations (CCV) in spark-ignited (SI) engines [31,32] in which the combustion variability due to the larger turbulent scales is traditionally considered as the main cause of the cycle-to-cycle variation [33]
It is not clear that pure stochastic fluctuations could explain the whole variation of flow conditions among consecutive cycles in gasoline Partially Premixed Combustion (PPC) mode
Summary
The automotive industry is currently confronted with the hard challenge of achieving a compromise between performance and sustainability [1]. Most research efforts are focused on further developing spark-ignited (SI) engines and the exploration of new advanced combustion modes due to their advantages in terms of pollutant emissions [2]. In both concepts, knocking combustion is a major drawback to achieving higher thermal efficiency. The overall tendency to knock is highly dependent on engine operating conditions as well as other aspects such as fuel anti-knock properties or combustion chamber design It is, critical to gain a better understanding of knock generation mechanisms in order to develop robust knock mitigation strategies.
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