Statistical Behaviour and Modelling of Fuel Mass Fraction Dissipation Rate Transport in Turbulent Flame-Droplet Interaction: A Direct Numerical Simulation study

This experimental study investigates the flame-initiation period variability in the spark-ignited homogeneous charge third-generation transparent combustion chamber optical engine. The engine was operated with lean, rich, and stoichiometric, propane and methane, with and without nitrogen dilution. These operating conditions were chosen to systematically change the unstretched laminar flame velocity and the Markstein number. Traditional pressure measures, apparent heat release analysis, particle image velocimetry, and OH* flame imaging were used to generate over 400 metrics for 750 cycles at each of the 34 tests at 11 operating conditions. A multivariate statistical analysis was used to identify the parameters important to the variability of the crank angle at 10% fuel mass fraction burned but could not reveal physical mechanisms or cause and effect. The analysis here revealed that the combustion-phasing cycle-to-cycle variability is established by the time of the notional laminar-to-turbulent flame transition that occurs by 1% mass burn fraction, measured here from the flame image growth. Both the Markstein number and stretched laminar flame speed were found to be important. The velocity magnitude and direction were found to correlate with fast and slow 10% fuel mass fraction burned as found in early literature. It was also revealed that the shear strength, a property of the strain rate tensor at the scales resolved here (1 mm), deserves further investigation as a possible effect on 10% fuel mass fraction burned.

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Reduction of NOx Emission of Heavy Duty Gas Turbines by Improving Mixing Quality Using CFD Tools

Energy Conversion and Resources: Fuels and Combustion Technology, Energy, Nuclear Engineering, and Solar Engineering ◽

10.1115/imece2003-41268 ◽

2003 ◽

Author(s):

Weiqun Geng ◽

Douglas Pennell ◽

Stefano Bernero ◽

Peter Flohr

Keyword(s):

Gas Turbines ◽

Mass Fraction ◽

Cross Flow ◽

Nox Emission ◽

Injection System ◽

Water Tunnel ◽

Injection Hole ◽

Fuel Mass ◽

Mixing Quality ◽

Fuel Mass Fraction

Jets in cross flow are one of the fundamental issues for mixing studies. As a first step in this paper, a generic geometry of a jet in cross flow was simulated to validate the CFD (Computational Fluid Dynamics) tool. Instead of resolving the whole injection system, the effective cross-sectional area of the injection hole was modeled as an inlet surface directly. This significantly improved the agreement between the CFD and experimental results. In a second step, the calculated mixing in an ALSTOM EV burner is shown for varying injection hole patterns and momentum flux ratios of the jet. Evaluation of the mixing quality was facilitated by defining unmixedness as a global non-dimensional parameter. A comparison of ten cases was made at the burner exit and on the flame front. Measures increasing jet penetration improved the mixing. In the water tunnel the fuel mass fraction within the burner and in the combustor was measured across five axial planes using LIF (Laser Induced Fluorescence). The promising hole patterns chosen from the CFD computations also showed a better mixing in the water tunnel than the other. Distribution of fuel mass fraction and unmixedness were compared between the CFD and LIF results. A good agreement was achieved. In a final step the best configuration in terms of mixing was checked with combustion. In an atmospheric test rig measured NOx emissions confirmed the CFD prediction as well. The most promising case has about 40% less NOx emission than the base case.

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