In this paper, a generalized description of the complex topology of turbulent premixed flames stabilized in a model gas turbine combustor is obtained using network analysis. Networks are created using the visibility algorithm applied to points on the flame edge obtained from Hydroxyl radical (OH)-Planar Laser Induced Fluorescence images of turbulent premixed flames. The network structure thus obtained showed the emergence of a few massively connected nodes which were found to represent the folded regions of the flame front. These nodes, which are called the hubs of the network, are vital for determining the overall structure of the flame front. Degree distribution of the formulated networks is used to characterize the flame-turbulence interaction inherent in the system. Turbulent flame front networks were found to be rigid enough to be unaffected by random perturbations but highly vulnerable towards coordinated removal of hubs or folds. These findings could serve as the first network-analytic approach to characterize turbulence-flame interaction dynamics with the use of a flourishing network theory, which enhances ongoing works based on vortex dynamics, hydrodynamic stability, and thermo-acoustic instability.
Ion current has been the subject of extensive research in gasoline engines for in-cylinder combustion sensing and as a feedback signal for closed-loop engine control. The sources of the ion current in gasoline engines have been identified. Such identification is not the case in diesel engines. This paper presents experimental data and analysis of the ion current produced in a single-cylinder diesel engine equipped with an electronically controlled common-rail-injection system using an accessible engine control unit. The experiments cover a wide range of engine speeds, loads, injection pressures, and injection timings. The effect of each operating parameter on the shape of the ion current signal, as well as its amplitude, timing, and phase shift relative to the rate of heat release, are determined.
The low temperature combustion regime (LTC) has been known to simultaneously reduce both NOx and smoke emissions. The concept is to burn the fuel vapor-air charge, low in oxygen concentration, at low temperatures to reduce the formation of both NOx and smoke emissions. The paper investigates two combustion concepts in the LTC regime, the MK (modulated kinetics) and the smokeless locally rich diesel combustion and proposes a new strategy for a further reduction in emissions with minimum penalty in fuel economy. Tests were carried out under simulated turbo charged conditions on a single cylinder, small bore HSDI diesel engine with a re-entrant bowl combustion chamber. The engine is equipped with a common rail fuel injection system. Tests covered a wide range of injection pressures, EGR rates, injection timings and swirl ratios to determine their individual and collective contributions in engine-out emissions and fuel economy within this combustion regime. The proposed strategy is based on the results of this experimental investigation.
This paper introduces a phenomenological model for the fuel distribution, combustion, and emissions formation in the small bore, high speed direct injection diesel engine. A differentiation is made between the conditions in large bore and small bore diesel engines, particularly regarding the fuel impingement on the walls and the swirl and squish gas flow components. The model considers the fuel injected prior to the development of the flame, fuel injected in the flame, fuel deposited on the walls and the last part of the fuel delivered at the end of the injection process. The model is based on experimental results obtained in a single-cylinder, 4-valve, direct-injection, four-stroke-cycle, water-cooled, diesel engine equipped with a common rail fuel injection system. The engine is supercharged with heated shop air, and the exhaust back pressure is adjusted to simulate actual turbo-charged diesel engine conditions. The experiments covered a wide range of injection pressures, EGR rates, injection timings and swirl ratios. Correlations and 2-D maps are developed to show the effect of combinations of the above parameters on engine out emissions. Emphasis is made on the nitric oxide and soot measured in Bosch Smoke Units (BSU).
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