The effect on the dynamic stability of combustors with and without flame holders were investigated experimentally and computationally with thermal loads of 3, 5, and 9 kW. Three different cases were studied, large flame holder (LFH), small flame holder (SFH) and no flame holder (NO_ FH). Flame topology was investigated in these three cases. Moreover, lean propane-air premixed combustion were also considered for two models, turbulent flame speed closure (TFC) and coherent flame (CFM). These models were investigated using different turbulent kinetic energies and turbulence dissipation rates. Experiments were performed with mean inlet velocities of 16.5, 17, 29.2, 30.8, and 52.6 cm/s, excess air ratios (λ) of 1.6, 1.65, 1.7, and 1.8. The results showed that the flame topology and location are more sensitive to the increase in the excess air ratios and thermal loads in the large flame holder than in the small flame holder. Heat transfers and species distributions caused by combustion are also investigated for the large and small flame holders; in both cases, flame stability was sustained, and the flame front position moved upward regarding to the flame holder region.
The turbulent lean premixed combustion simulation is implemented in 4- stroke spark ignition (SI) engine. The Turbulent Flame speed Closure model (TFC) is used in different turbulent flow conditions. The model is tested for a variety of flame configurations such as turbulent flame speed, the heat release from the combustion and turbulent kinetic energy in the radial direction of the cylinder at 15.5 mm below the top dead center TDC point. The simulation performs in the three cases of the (intake / exhaust) valve timing. The exhaust valve case is an essential leverage on the turbulent flame specification. The combustion period is very important factor in SI engine which is controlled especially by the turbulent flame speed. The turbulent flame speed and heat transfer is ascendant less than 10 % and 3% in case of intake and exhaust valves are closed respectively. Moreover, the results show that the brake power enhances less than 4% and more than 40% with increase fuel temperature 60 K and engine speed 3000 rpm respectively.
The behaviour of a premixed propane flame in three dimensions was studied numerically and experimentally in a jet flow combustor at different equivalence ratio, Reynolds numbers and turbulent intensity. The detailed attract here has come up with data of propane -air mixtures flame propagation over a range of equivalence ratios (e) between 0.6 lean flame to 1.3 rich flame on environmental conditions of temperature and atmospheric pressure. The instantaneous flame was visualized using a high-speed camera on the domain of the burner of 100 mm diameter. From 174 to 472 images were recorded for each experimental test. Flame surface density was obtained from the instantaneous image of the flame. The influence of the flame area density in the evaluation of the flame propagation will be discussed. The study shows that the increase in turbulent intensity leads to increase the turbulent flame propagation speed subsequently increase in flame area density at a constant an equivalence ratio value. Also, it was shown that the wrinkling flame shape is the dominant characteristic leading to the increased turbulence intensity. The research results are expected to be used for developing jet flow combustor burners.
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