Research on the Measures for Improving Cycle-to-Cycle Variations under High Tumble Combustion

In the spark-ignition engine development and optimization process, the cyclic variability of combustion is an essential and current issue. Cycle-to-cycle variations are extensively investigated by means of quasi-dimensional (zero-dimensional/ one-dimensional) simulation modeling. To date, these model approaches have been limited either because they neglected particularly significant physical causes and factors influencing cyclic combustion variations or because of their solely empirical combustion modeling basis. However, in order to ensure the high validity of simulation results, quasidimensional model approaches have to accurately describe the physical background of engine combustion. Therefore, a new cyclic combustion variation model is introduced in this study. This cycle-to-cycle variation model is based on previously developed, highly sophisticated physical turbulence, ignition and combustion models, thus for the first time enabling the physical description of cycle-to-cycle variation. The model integrates the most significant physical causes of combustion variations and the factors which influence them, obtained from a literature study. Hence, the derived cycle-to-cycle variation model can physically react to changes in engine parameters such as the engine speed, load, spark timing, valve lift and timing as well as the air-fuel equivalence ratio l. For validation, the new cycle-to-cycle variation model is compared to a state-of-the-art cycle-to-cycle variation model and analyzed by means of engines with different combustion processes. This new cycle-to-cycle variation model uniquely features the physical background of the underlying combustion model and the integration of more influencing factors than in previous approaches. Another unique feature is its basis on extensive experimental data, gained by changing various engine parameters for homogeneous charge sparkignition engines with different combustion/engine concepts. These include engines with high turbulence generation or a long expansion stroke via crank and valve train.

Section: Model Design Calibration and Validationsupporting

confidence: 93%

Section: Physical Background Of CCVmentioning

confidence: 99%

A physical-based approach for modeling cycle-to-cycle variations within a zero-dimensional/one-dimensional simulation environment

Krost

Hübner

Hasse

2017

“…Both the vortex intensity and its proper location greatly affect both the speed and preferential direction of the early flame propagation in SI engines. 51,52 Graftieaux et al 53 developed an algorithm for the tracking of a vortex core using equation (11). For any given position P, eight surrounding vectors in a square region S are picked on the 2D discretized section, as shown in Figure 5.…”

Section: Tumble Ratio and Tumble Center Positionmentioning

confidence: 99%

Methodology for the large-eddy simulation and particle image velocimetry analysis of large-scale flow structures on TCC-III engine under motored condition

Rulli

Fontanesi

et al. 2020

Large-eddy simulation has been increasingly applied to internal combustion engine flows because of their improved potential to capture the spatial and temporal evolution of turbulent flow structures compared with Reynolds-averaged Navier Stokes simulation. Furthermore, large-eddy simulation is universally recognized as capable of simulating highly unsteady and random phenomena, which drive cycle-to-cycle variability and cycle-resolved events such as knocks and misfires. To identify large-scale structure fluctuations, many methods have been proposed in the literature. This article describes the application of several analysis methods for the comparison between different datasets (experimental or numerical) and the identification of large-structure fluctuations. The reference engine is the well-known TCC-III single-cylinder optical unit from the University of Michigan and GM Global R&D center; the analyses were carried out under motored engine conditions. A deep analysis of in-cylinder gas dynamics and flow structure evolution was performed by comparing the experimental results (particle image velocimetry of the velocity fields) with a dataset of consecutive large-eddy simulation cycles on four different cutting planes at engine-relevant crank angle positions. Phase-dependent proper orthogonal decomposition was used to obtain further conclusions regarding the accuracy of the simulation results and to apply conditional averaging methods. A two-point correlation and an analysis of the tumble center are proposed. Finally, conclusions are drawn to be used as guidelines in future large-eddy simulation analyses of internal combustion engines.

“…SI engines demand ignition systems that can reliably ignite an air-fuel mixture with minimal energy consumption, despite being required to ignite a rapidly moving flow of a highly diluted mixture. [1][2][3][4][5][6][7] To realize this, an ignition system must be highly efficient.…”

Section: Introductionmentioning

confidence: 99%

“…The heat of combustion falls as the air-fuel mixture is diluted, causing the temperature of the flame and its surrounding mixture to fall. In such an environment, the development of the initial flame slows down, leading to fluctuations in the combustion 2,7 and even misfires. If the thermal energy of the spark discharge could be used to efficiently heat the air-fuel mixture, it would be possible to accelerate the initial flame development.…”

Section: Introductionmentioning

confidence: 99%

Measurement of vibrational and rotational temperature in spark-discharge plasma by optical emission spectroscopy: Change in thermal equilibrium characteristics of plasma under air flow

Kinoshita

Fuyuto

Akatsuka

2018

The vibrational and rotational temperatures in a spark-discharge plasma were measured using optical emission spectroscopy, and the influence of the air flow velocity and ambient pressure on these temperatures was investigated. The optical emissions from the plasma were led to an imaging spectroscope through an optical fiber. The temperature was estimated by fitting a theoretically calculated spectrum to that which had been acquired experimentally, formed by nitrogen molecule emission from 372 to 382 nm. The spark-discharge plasma was examined with a flow of ambient air at a discharge energy of 80 mJ. The air flow caused the spark-discharge channel to elongate downstream. At the center of the spark plug gap, the vibrational temperature in the plasma was 4000 K, whereas the rotational temperature was 2000 K. This plasma can be regarded as being in non-thermal equilibrium because the vibrational temperature was higher than the rotational temperature. At a position approximately 3 mm downstream from the spark plug gap, the vibrational and rotational temperatures increased to 4500 and 4000 K, respectively, while approaching each other. Both temperatures reached a maximum value. These results show that the plasma transitions from non-thermal equilibrium to thermal equilibrium as it is elongated by the air flow. Ignition efficiency improvements can be expected if the time required to transition from non-thermal to thermal equilibrium can be shortened.