Showing papers by "RV Ravikrishna published in 2013"

Mixing Enhancement in a Compact Trapped Vortex Combustor

Abstract: Previous studies on a single-cavity, compact trapped vortex combustor concept showed good flame stability for a wide range of flow conditions. However, achieving good mixing between cavity products and mainstream flow was still a major challenge. In the present study, a passive mixing enhancement strategy of using inclined struts along with a flow guide vane is presented and experimentally tested at atmospheric pressure conditions. Results show excellent mixing and consequently low values of the combustor exit pattern factor in the range of 0.1 and small flame lengths (57 times the main-duct depth). The pressure drop is small in the range of 0.35%, and NOx levels of the order of 12ppm are achieved. The flame stability is excellent, and combustion efficiency is reasonable in the range of 96%. The effectiveness of the proposed strategy is explained on the basis of in-situ OH chemiluminescence images and prior numerical simulations of the resulting complex flow field. The flow guide vane is observed to lead to a counterclockwise cavity vortex, which is conducive to the rise of cavity combustion products along the inclined struts and subsequent mixing with the mainstream flow.

A Review on Atomization and Sprays of Biofuels for IC Engine Applications

Abstract: Ever increasing energy requirements, environmental concerns and energy security needs are strongly influencing engine researchers to consider renewable biofuels as alternatives to fossil fuels. Spray process being important in IC engine combustion, existing literature on various biofuel sprays is reviewed and summarized. Both experimental and computational research findings are reviewed in a detailed manner for compression ignition (CI) engine sprays and briefly for spark ignition (SI) engine sprays. The physics of basic atomization process of sprays from various injectors is included to highlight the most recent research findings followed by discussion highlighting the effect of physico-chemical properties on spray atomization for both biofuels and fossil fuels. Biodiesel sprays are found to penetrate faster and have narrow spray plume angle and larger droplet sizes compared to diesel. Results of analytical and computational models are shown to be useful in shedding light on the actual process of atomiza...

Full Chemical Kinetic Simulation of Biogas Early Phase Combustion in SI Engines

Abstract: This paper presents computational work on the biogas early phase combustion in spark ignition (SI) engines using detailed chemical kinetics. Specifically, the early phase combustion is studied to assess the effect of various ignition parameters such as spark plug location, spark energy, and number of spark plugs. An integrated version of the KIVA-3V and CHEMKIN codes was developed and used for the simulations utilizing detailed kinetics involving 325 reactions and 53 species The results show that location of the spark plug and local flow field play an important role. A central plug configuration, which is associated with higher local flow velocities in the vicinity of the spark plug, showed faster initial combustion. Although a dual plug configuration shows the highest rate of fuel consumption, it is comparable to the rate exhibited by the central plug case. The radical species important in the initiation of combustion are identified, and their concentrations are monitored during the early phase of combustion. The concentration of these radicals is also observed to correlate very well with the above-mentioned trend.Thus, the role of these radicals in promoting faster combustion has been clearly established. It is also observed that the minimum ignition energy required to initiate a self-sustained flame depends on the flow field condition in the vicinity of the spark plug.Increasing the methane content in the biogas has shown improved combustion.

Experiments on Stability of Syngas Combustion in a Trapped Vortex Combustor

Abstract: Syngas is being studied extensively as an effective alternate fuel for various applications in recent times. Syngas combustion offers significant challenges because of varying compositions and considerably low calorific values. Trapped vortex combustor (TVC) is an established design in gas turbine engine combustors utilizing the RQL (rich-burn quickquench lean-burn) strategy for achieving stable combustion under various operating conditions and meeting stringent pollution norms at the same time. TVC design consists of a cavity in which a vortex is established where rich combustion takes place. The products then mix quickly with the main flow and then the ultra lean mixture undergoes combustion. Previous studies on methane combustion in TVC have shown that this concept helps to achieve a very wide operating range of equivalence ratios with low NOx and particulate emissions. A single cavity TVC rig is used to study the combustion and mixing phenomena. Preliminary experiments on syngas combustion in TVC have shown stable combustion even for very lean equivalence ratios (Φ~0.1). However, the dynamics in the cavity seem to differ considerably from previous methane combustion studies. The flame is characterised by equivalence ratio which might mean that mixing in the cavity is minimal. To understand the cavity mixing, acetone PLIF has been employed. These results show that the fuel jet momentum plays a very important role in determining the mixing within the cavity. Fuel mixing increases with the increase in fuel jet momentum as also with the guide vane air momentum. Flame luminosity images do not show a flame at the center of the cavity possibly indicating a lack of cavity recirculation vortex. Further comparison between methane and syngas can be carried out by employing parameters like jet momentum ratio.

Effect of pressure on NO kinetics in Syngas Combustion

Abstract: In the present work, an attempt has been made to understand the kinetics of NO formation in low calorific value syngas combustion. Specifically, counterflow diffusion flames of syngas have been modeled using the OPPDIF code. Three different chemical kinetic mechanisms from the literature which can model H2/CO oxidation have been evaluated. A comparison of NO predictions by these mechanisms has been done at pressures varying from 1 bar to 20 bar and a significant disagreement has been found among the predictions. Upon further analysis, different kinetic mechanisms have shown different pathways dominating the NO formation in these flames highlighting the need for further detailed studies.

Studies on Spray in Crossflow for a Cavity Combustor

Abstract: The present work focuses on studies involving spray in a cross flow with potential applications in a cavity combustor. Three commercially-available airblast atomizers are characterized in terms of spray structure and droplet size measurements using Shadowgraphy and the PDIA technique, respectively. One of the atomizers exhibiting a small cone angle (around 20°) and low SMD (∼20 μm) is used for crossflow studies. An experimental set up is designed and fabricated to study spray injection in transverse direction to the air flow. The effect of Weber number and momentum ratio is assessed on spray penetration and dispersion. Under certain conditions, it is found that the penetration decreases with increase in momentum ratio which is caused by the higher GLR leading to formation of smaller droplets.