Experimental Analysis of Cyclical Dispersion in Compression-Ignited Versus Spark-Ignited Engines and Its Significance for Combustion Noise Numerical Modeling

Abstract

As noise pollution remains one of the biggest hurdles posed by thermal engines, increasing efforts are made to alleviate the generation of combustion noise from the early design stage of the chamber. Since the complexity of both modern chamber geometries and the combustion process itself precludes robust analytic solutions, and since the resonant, highly three-dimensional pressure field is difficult to be measured experimentally, focus is put on the numerical modeling of the process. However, in order to optimize the resources devoted to this simulation, an informed decision must be made on which formulations are followed. In this work, the experimental cyclic dispersion of the in-cylinder pressure is analyzed in two typical compression-ignited (CI) and spark-ignited (SI) engines. Acoustic signatures and pressure rise rates (PRRs) are derived from these data, showing how while the preponderance of flame front propagation and dependency of previous cycle in SI engine noise usually calls for multicycle, more complex turbulence modeling such as large Eddy simulation (LES), simpler unsteady Reynolds-averaged Navier-Stokes (URANS) formulations can accurately characterize the more consistent pressure spectra of CI thermal engines, which feature sudden autoignition as the main noise source.

Understanding the unsteady pressure field inside combustion chambers of compression-ignited engines using a computational fluid dynamics approach

“…Traditionally, the engine spectrum is divided into three regions of interest. 49 The low-frequency range, commonly ranged between 0 and 400 Hz, is exclusively caused by the compression-expansion process itself without any contribution of combustion. Within the rest of the spectrum, there are two different regions in which the pressure waves behaviour can be considered distinct.…”

Experimental Investigation on the High-frequency Pressure Oscillation Characteristics of a Combustion Process in a DI Diesel Engine

“…In addition, the intensity of the pressure oscillation is relative to the pressure rise rate in the preliminary stage of combustion. In fact, the pressure rise rate is related to combustion calibration parameters such as main injection timing, pilot injection interval, and pilot injection quantity [15]. Pressure oscillations have a significant impact on the NVH performance, and polluted emissions of the diesel engine [16].…”

“…Kyrtatos et al [21][22][23] found the in-cylinder pressure fluctuations and its effects on emission trends (Soot and NO x ), in the research of pressure resonance and cycle-to-cycle variation in a diesel engine. At the same time, Alberto Broatch et al [15] and Luján et al [17] used the signal of cylinder pressure oscillation to estimate the trapped mass of the cylinder. Chiatti Giancarlo et al [24] indicated that there are high values of correlation coefficients exist between the indices for combustion development and injection process characterization.…”

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

“…), turbulence field (flow velocity and at the spark plug) and species distribution (EGR, fuel injection, etc.) is determinant for the knock [9] and CCV prediction.Misdariis et al[23] has proven the suitability of multi-cycle LES and dual heat transfer to reproduce the cycle-to-cycle pressure variations (CCV) under knocking-like conditions [24]. However, requirements in terms of mesh resolution and runtime are prohibitive for practical applications.…”

“…[23] has proven the suitability of multi-cycle LES and dual heat transfer to reproduce the cycle-to-cycle pressure variations (CCV) under knocking-like conditions [24]. However, requirements in terms of mesh resolution and runtime are prohibitive for practical applications.…”