An Experimental and Simulation Study of Early Flame Development in a Homogeneous-charge Spark-Ignition Engine

Abstract

An integrated experimental and Large-Eddy Simulation (LES) study is presented for homogeneous premixed combustion in a spark-ignition engine. The engine is a single-cylinder two-valve optical research engine with transparent liner and piston: the Transparent Combustion Chamber (TCC) engine. This is a relatively simple, open engine configuration that can be used for LES model development and validation by other research groups. Pressure-based combustion analysis, optical diagnostics and LES have been combined to generate new physical insight into the early stages of combustion. The emphasis has been on developing strategies for making quantitative comparisons between high-speed/high-resolution optical diagnostics and LES using common metrics for both the experiments and the simulations, and focusing on the important early flame development period. Results from two different LES turbulent combustion models are presented, using the same numerical methods and computational mesh. Both models yield Cycle-to-Cycle Variations (CCV) in combustion that are higher than what is observed in the experiments. The results reveal strengths and limitations of the experimental diagnostics and the LES models, and suggest directions for future diagnostic and simulation efforts. In particular, it has been observed that flame development between the times corresponding to the laminar-to-turbulent transition and 1% mass-burned fraction are especially important in establishing the subsequent combustion event for each cycle. This suggests a range of temporal and spatial scales over which future experimental and simulation efforts should focus.

Understanding the Origin of Cycle-to-Cycle Variation Using Large-Eddy Simulation: Similarities and Differences between a Homogeneous Low-Revving Speed Research Engine and a Production DI Turbocharged Engine

“…The operating condition analyzed in this study is a 1300 rpm premixed stoichiometric propane-air operation, with MAP (Manifold Absolute Pressure) equal to 40 kPa and SA=18 CA bTDC. For such operating condition, a first simulation study in [34] showed the relevance for MFB1 duration for this engine/operation. The second unit (Engine 2) is a 4-valve production turbocharged GDI engine, whose analyzed condition is the peak-power 7000 rpm one.…”

“…The quality of the filtered flow fields was assessed by Ko et al in [63] for Engine 1 under motored conditions: as for fired operations, analogous considerations can be undertaken as shown in [34,38], where the average flow fields were obtained in PIV and LES on two cutting planes both under motored and fired conditions. A similar analysis based on the kinetic energy fraction modelled at subgrid-scale was carried out in [31,32], confirming the adequacy of the grid used for Engine 2 simulations.…”

“…In [31][32][33] d'Adamo et al showed the early application of ISSIM-LES in the STAR-CD CFD code. In [34] the TCC engine was first studied under fired conditions, comparing two combustion models (ECFM-LES [35,36] and Thickened Flame Model [37,38]) and using optical diagnostics to correlate flow variability at spark with combustion CCV. The relevance of the early 1% of Mass Fraction Burnt (MFB) duration was found to be a leading parameter for the entire combustion event, and flame visualizations allowed to compensate the poorresolution of pressure-based analysis at the very initial stage.…”

Preliminary study on the influence of Octane Sensitivity on knock statistics in a GDI engine

“…Kalghatgi [3,4] synthesized all of these contributions using the Octane Index to express the link between engine-related and fuel-related parameters. Following previous studies [5,6,7,8,9,10], in the present paper the authors run virtual experiments of a GDI engine operated at 2000 RPM fuelled with five surrogates, purposely built [11,12] to span a wide range of anti-knock characteristics using a state-of-the-art gasoline chemical kinetics model [13]. In particular, an original statical knock model is here adopted and it is briefly recalled.…”

A Preliminary 1D-3D Analysis of the Darmstadt Research Engine Under Motored Condition

“…Focusing on gasoline engines, specific consumption reduction is mainly obtained promoting knock mitigation by means of different techniques, such as improved cooling [3], variable compression ratio [4], bore reduction [5], alternative valve strategies [6,7], cooled EGR, water or water/methanol injection [8][9], split injections [10] and increased injection pressures (up to several hundred bar to promote evaporation and mixing) [11]. In this panorama, a key-role is played by CFD simulations whose capabilities to predict knock onset, to understand its origin and to investigate other in-cylinder process (such as complex turbulent flow [12][13][14][15][16], injection [17,19], flame kernel development [20] and combustion [21]) are fundamental to guide design, thus saving costs and time [22][23][24]. Focusing on the field of internal combustion engine research, numerical investigations under motored conditions represent a common practice in order to evaluate the agreement between 1D/3D models and experiments [25].…”