Browsing by Author "Kumar, G. N."

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Heat Transfer Distribution of Impinging Methane-Air Premixed Flame Jets
(National Institute of Technology Karnataka, Surathkal, 2019) Ramkishanrao, Kadam Anil.; Kumar, G. N.
Flame jets find importance in industrial and household applications like metal and glass melting/forming and cook stoves respectively. Heat transfer distribution of impinging flame jet was compared with that of the impinging air jet based on the experimental data reported in literature for methane-air flame jet and air jet impingement for Reynolds number, Re = 600 to 1400 and the non-dimensional nozzle tip to impingement plate distance, Z/d = 2 to 6. The comparative data based on mapping experimental data reported in literature suggested that there is a good agreement between the Nusselt numbers for higher Z/d near stagnation region. However, away from the stagnation region, the Nusselt number for flame jet is higher than that of air jet for similar operating conditions of Re and Z/d. A CFD simulation for impinging air jet and impinging flame jet was carried out using FLUENT software to explain the physics and reason for the deviations observed in experimental data. A scale analysis was carried out to identify the dominant forces and their influence on the heat transfer distribution on the impingement plate. Heat transfer from impinging flame jets to a flat plate has been assumed to be onedimensional in most of the investigations and without radiation loss treatment. In the present work, the exact nature of diffusion of heat in the plate is investigated via solution to multidimensional heat conduction problem. Two procedures have been employed – Duhamel theorem and three dimensional transient analytical inverse heat conduction problem (IHCP). The Duhamel theorem which is analytical model for transient one dimensional heat conduction was applied and its application failed the check of linearity requirement of the convection rate equation. From the solution by analytical IHCP for transient three dimensional heat conduction, the distribution of wall heat flux and the wall temperature was perfectly linear. This check confirmed that three dimensional approach has to be used. Experimental data is then analyzed by the three dimensional analytical IHCP for short and larger time intervals. It was found that for short time data, heat transfer coefficient and the reference temperature have oscillatory distribution along the radial direction on the impingement plate and for larger time data the oscillations die out. However, at larger time, radiation loss from the impingement plate becomes significant. The effect of variation in thermal conductivity of the impingement plate with the temperature on heat transfer coefficient and reference temperature is discussed. Anovel method was developed to correct the heat transfer coefficient and reference temperature to incorporate radiation losses. The deviation in heat transfer coefficient and reference temperature estimated without considering variable thermal conductivity and radiation loss for large time interval was upto 50%. The scope of the present technique is examined through its application to impinging jets with various configurations. The present study covers the applications of hot jet, cold jet and multiple jets with distinct Reynolds numbers and the nozzle-to-plate spacing and results confirms the validity of technique to impinging jets as well. Effect of plate thickness on the accuracy of the present technique is also studied. Upto 5 mm thick plates can be used in impinging jet applications without compromising much on accuracy. Use of present technique significantly reduces the experimental cost and time since it works on transient data of just few seconds Experiments were carried out on ribbed plates with three different geometrical shaped rib elements i.e. circular, rectangular and triangular. In addition, numerical simulations were performed to study flow field on and around ribs. During the experiments, Reynolds numbers varied from 600 to 1800 and burner tip to target plate distance from 2 to 4. Heat transfer coefficients were found lower whereas reference temperatures were observed higher on ribbed surfaces than smooth surfaces. Obstruction to the flow, flow separation and decrease in momentum are the reasons attributed for lower heat transfer rate to the ribbed surfaces.
Heat Transfer Studies on Gas Turbine Combustor Liner Cooling
(National Institute of Technology Karnataka, Surathkal, 2019) Felix, J.; Kumar, G. N.; Rajendran, R.
This study deals with the combination of film cooling techniques in an effusion cooled test plate. Geometrical parameters of the effusion cooling test plate have holes of diameter 1 mm, hole angle of 27° and 7.2 mm pitch in both streamwise and spanwise directions. Effusion holes are placed in a staggered manner with 9 holes per row, and there are 13 rows in total. Experimental and numerical investigation of adiabatic cooling effectiveness and convective heat transfer coefficient on an effusion cooled test plate is carried out with and without machined ring geometries upstream. For these tests, the effusion cooling geometrical parameters are scaled up by 3 times. Tests are carried out at blowing ratio ranging from 0.5 to 2.5, coolant to mainstream density ratio of 1.3 and at a mainstream velocity of 20 m/s. The convective heat transfer coefficient investigations are carried out using a constant heat flux surface with coolant and mainstream at the same temperature. Test plate surface temperature measurements are recorded by an infrared camera. Effusion cooling along with machined ring geometries upstream shows higher adiabatic film cooling effectiveness and higher film heat transfer coefficients than effusion cooling alone at all the blowing ratios. Measurements of overall film cooling effectiveness are also carried out in stainless steel effusion cooling test plate of 2 mm thickness with and without machined ring geometries. This comparison result also shows that the overall cooling effectiveness increases significantly before the effusion cooling holes with the presence of machined ring geometries. Another combination of impingement with effusion cooling is studied for an effusion test plate having a 5.4 mm pitch in both the spanwise and streamwise directions. An impingement plate is kept backside of the effusion plate at a distance of 6 mm. The holes in the impingement plate are arranged in a staggered manner such that each effusion hole is surrounded by four impingement holes. The result shows that the effusion cooling with impingement gives higher overall cooling effectiveness than effusion cooling alone. The comparison is made between effusion cooling with impingement and effusion with machined ring geometries. The result shows that the effusion with machined ring geometries has higher overall cooling effectiveness than effusion cooling with impingement. Numerical analysis is performed using ANSYS workbench, and the methodology is validated against the experimental results. The numerical results are matching with the experimental results and the temperature contours obtained are compared with infrared camera images. A MATLAB program isiii used to obtain the effectiveness contours for both the experimental and numerical results.
Performance and Emission Characteristics of Vateria Indica Oil as Alternative Fuel for Petrodiesel in CI Engine
(National Institute of Technology Karnataka, Surathkal, 2019) Rao, Gangadhara.; Kumar, G. N.; Herbert, Mervin A.
Vateria Indica Linn seeds contain nearly 19% oil/fat which can be converted into biodiesel by normal method of esterification followed by transesterification generally adopted for high FFA oils. Biodiesel is a promising alternative fuel for CI engines. In the present work, study of the combustion, performance and emission characteristics of a CI engine fuelled with Vateria Indica biodiesel blends at 180 bar, 200 bar and 220 bar injection pressures (IP) and injection timings at 19obTDC, 23obTDC and 27obTDC (before TDC) is carried out. Blending is done in volumetric ratios of 10%, 15%, 20%, 25% of biodiesel with diesel which are called as B10, B15, B20, B25. Increasing fuel injection pressure promotes atomization, and full penetration into the combustion chamber leading to better combustion. Blend B25 showed better thermal efficiency of the order of 33.03% and minimum NOX emission of 1047ppm at 220 bar injection pressure and 75% Load. Advancing the injection is proved to be advantageous because of longer residence time and complete combustion with thermal efficiency of the order of 37%, but it also causes higher NOX and soot emissions. Blend is restricted to 25% due to low cetane number of biodiesel which causes severe knocking problem at higher blends. Due to high NOX emission with the blend (B25), NOX mitigation technique like hot EGR is adopted to the extents of 5% and 10%.Finally, it is concluded that blending up to25% can be adopted with 10% EGR at 220 bar injection pressure with 27obTDCinjection timing for better performance, combustion and emission characteristics.
Suitability of Biofuels and Plastic Oil Blended With Diesel in CRDI Engine
(National Institute of Technology Karnataka, Surathkal, 2017) Lamani, Venkatesh T.; Yadav, Ajay Kumar; Kumar, G. N.
Nitrogen oxides and smoke are the substantial emissions for the diesel engines. Fuels comprising high-level oxygen content can have low smoke emission and higher efficiency due to better combustion. The objective of this research is to assess the potential to employ oxygenated fuels such as dimethyl ether, ethanol and butanol, and waste plastic oil in direct injection engine as alternative fuels for diesel. To reduce NOX, exhaust gas recirculation technology for various fuels is studied. Computational fluid dynamics (CFD) studies on combustion and emission characteristics of common rail direct injection (CRDI) engines using oxygenated fuel-diesel blends are less developed and still under intense study. In view of that detailed CFD simulation is carried out in present study and also validated with experimental results. Ethers are favourable alternative for diesel engine due to their chemical structure. Presence of more oxygen, absence of carbon-carbon (C-C) bond in chemical structure, and high cetane number of dimethyl ether (DME), cause less pollution in DME operated engine compared to diesel engine. Study emphasizes the effect of various EGR rates (0-20%) and DME-diesel blends (0-20%) on combustion characteristics and exhaust emissions of CRDI engine using CFD simulation. Results show that, due to better combustion characteristics of DME, indicated thermal efficiency (ITE) increases with the increase in DME- diesel blends. Ethanol is an attractive alternative fuel because it is oxygenated, renewable and bio-based resource; thereby it has potential to reduce smoke emissions in compression-ignition engines. CFD simulation is carried out to study the effect of EGR and injection timing on the performance, combustion and exhaust emission characteristics of CRDI engine fuelled with bioethanol-diesel blends. The results indicate that the mean CO formation and ignition delay increase whereas mean NOX formation and in-cylinder temperature decrease with increase in the EGR rate. Further, CFD simulation is carried out to find optimum injection timing for bioethanol-diesel blends (0-30% ethanol). Optimum injection timing is obtained for maximum ITE. Obtained CFD results are validated with experimental data available in literature and found good agreements.Several second generation biofuels (e.g., n-butanol) are also promising alternative to diesel fuel. The experimental and CFD simulation is carried out to estimate the performance, combustion and exhaust emission characteristics of n-butanol-diesel blends (0 to 30%) for various injection timings and various EGR rates using modern twin-cylinder, four-stroke, CRDI engine. Experimental results reveal the increase in brake thermal efficiency (BTE) for n-butanol-diesel blends. Attention is also focused to counter plastic waste disposal problem and to find alternate fuel to diesel by waste to energy retrieval. Present range of investigation evaluates the prospective use of waste plastic oil (WPO) as an alternative fuel for diesel engine. Experiments are conducted for various injection timings and for different EGR rates. Combustion, performance and tail pipe emissions of CRDI engine are studied. The NOx, CO and soot emissions for waste plastic oil-diesel blends are found more than neat diesel. To reduce NOx, EGR is employed which results in reduction of NOx considerably. Brake thermal efficiency (BTE) of blends is found to be higher compared to diesel. The higher NOx emitted by engine operated with WPO-Diesel blends are treated by multiple injection strategies. Experiments are carried out for various pilot injection timings and different main injection timings. The remarkable reduction in nitrogen oxide is observed by retarding main injection timing and injecting more fuel in pilot injection compared to single injection.