Ramkumar N. Parthasarathy

Concentration measurements of CH and OH radicals in laminar biofuel flames.

An investigation to determine the dominant route of NOx formation in biofuel flames and to confirm the relationship of the NOx increase with iodine numbers in fuels has been presented. This is done through the measurement of the concentration of OH and CH radicals, indicators of the formation of NOx through the Zeldovich and Fenimore mechanisms. A laminar partially pre-mixed flame at an initial fuel equivalence ratio (φ) = 7 was used to minimize the effects of fluid mechanics and isolate the effects of fuel chemistry. Three biofuels, with different iodine numbers, were studied: soy methyl ester (SME), canola methyl ester (CME) and methyl stearate (MS). Planar Laser-Induced Fluorescence (PLIF) images of hydroxyl radicals (OH) and CH radicals were captured with a diagnostic system consisting of a pulsed Nd:YAG laser and an Optical Parametric Oscillator (OPO) with frequency doubler option (FDO) using proper wavelengths. It was found that the population of OH radicals was low in the flames of all fuels, but significant CH radical concentrations were detected in all the flames, with the maximum population occurring in the SME fuel flame. The presence of high concentrations of CH measured in the regions of peak NOx indicate that NOx formation is primarily through the Fenimore mechanism, rather than the thermal mechanism, at this fuel-rich condition. Moreover, the fuel with highest iodine number, SME, produced significantly more NOx because of its tendency to facilitate the production of more soot, C, and CH radicals.

Experimental Characterization of Limit Cycle Oscillations in Membrane Wing Micro Air Vehicles

The idea of using small-scale vehicles, often termed micro air vehicles, for various surveillance applications has become increasingly popular in recent years. A micro air vehicle design of particular interest is the membrane wing micro air vehicles, in which the structural skeleton is covered with a thin membrane instead of conventional wing skin materials, developed in particular for its lightweight nature, static stability, and passive gust rejection. In the current work, membrane wing micro air vehicles are developed and tested experimentally in order to determine the structural response of batten-reinforced membrane wing micro air vehicles to varying conditions: small angles of attack, number of battens, and membrane pretension. A self-excited instability (flutter) was noted for each model with limit cycle oscillations occurring at postflutter flow velocities. Small angles of attack had little effect on the flutter velocity, frequency, and mode for a given configuration, while increasing the membrane pretension delayed flutter and reduced the magnitude of limit cycle oscillation experienced by the model at a given flow velocity. Increasing the number of structural battens for the membrane wing micro air vehicle models also delayed the flutter velocity and reduced the magnitude of limit cycle oscillation at a given flow velocity while altering the flutter mode.

Effect of Iodine Number on NOx Formation in Laminar Flames of Oxygenated Biofuels

The present study employed a recently developed experimental technique to investigate the effect of iodine number on NOx formation in laminar partially premixed flames of three vaporized biofuels: canola methyl ester, soy methyl ester, and methyl stearate. The iodine numbers for the selected fuels varied over a wide range from 0.5 to 141. Key measurements included NOx concentration and temperature fields. The peak NOx concentration occurred in the near-burner region for all biofuels: 1166 ppm for soy, 1067 ppm for canola, and 414 ppm for the methyl stearate. We observed that the peak NOx concentration significantly increased with the iodine number, indicating a strong correlation between the chemical structure of the fuel and NOx emission.

Effects of Fuel Injection Timing in the Combustion of Biofuels in a Diesel Engine at Partial Loads

Methyl and ethyl esters of vegetable oils have become an important source of renewable energy with convenient applications in compression-ignition (CI) engines. While the use of biofuels results in a reduction of CO, particulate matter, and unburned hydrocarbons in the emissions, the main disadvantage is the increase of nitrogen oxides (NOx ) emissions. The increase in NOx emissions is attributed to differences in chemical composition and physical properties of the biofuel, which in turn affect engine operational parameters such as injection delay and ignition characteristics. The effects of fuel injection timing, which can compensate for these changes, on the performance and emissions in a single cylinder air-cooled diesel engine at partial loads using canola methyl ester and its blends with diesel are presented in this study. The engine is a single cylinder, four stroke, naturally aspirated, CI engine with a displacement volume of 280 cm3 rated at 5 HP at 3600 rpm under a dynamometer load. It was equipped with a pressure sensor in the combustion chamber, a needle lift sensor in the fuel injector, and a crank angle sensor attached to the crankshaft. Additionally, the temperature of the exhaust gases was monitored using a thermocouple inside the exhaust pipe. Pollutant emissions were measured using an automotive exhaust gas analyzer. Advanced, manufacturer-specified standard, and delayed injection settings were applied by placing shims of different thicknesses under the injection pump, thus, altering the time at which the high-pressure fuel reached the combustion chamber. The start of injection was found to be insensitive to the use of biofuels in the engine. The late injection timing of the engine provided advantages in the CO and NO emissions with a small penalty in fuel consumption and thermal efficiency.

Effects of Slip on the Flow Characteristics of Laminar Flat Plate Boundary-Layer

A uniform stream of viscous fluid flowing past a flat plate with slip at the fluid-plate interface is considered. The aim of this investigation is to examine the effects of slip at the wall on the laminar boundary-layer flow characteristics. For this purpose, an analytical and a computational study were conducted. The analytical study is based on the Blasius similarity solution for laminar boundary-layer flow past a flat plate. In the computational study, the flow over a flat plate is modeled and solved (using FLUENT) by dividing the computational domain into small control volumes and discretizing and solving the governing equations around these control volumes. The slip at the fluid-solid interface is accounted for by the Navier boundary condition (NBC). Three cases are considered, wherein the slip boundary condition is incorporated in three different ways, i.e., by specifying the slip length, or the slip velocity, or by assuming the slip length to be a function of shear rate. The flow characteristics are evaluated for different amounts of slip. The wall shear stress, the skin-friction coefficient, and the drag coefficient decrease by about 38% when the nondimensional slip length is increased from zero (noslip) to 2. The boundary-layer thickness, the displacement thickness, and the momentum thickness also decrease with increase in slip. The reduction in displacement thickness is much greater (about 68%) than the boundary-layer thickness or the momentum thickness. An excellent agreement between the analytical and computational results is noticed.© 2006 ASME

Pool Fires Of Biofuels And Their Blends With Petroleum Diesel

The combustion characteristics of pool fires of biofuels, canola methyl ester (CME), soy methyl ester (SME), and their blends with a petroleum fuel (No. 2 diesel) were studied. The fuels were burned in cups of two sizes (0.042 m and 0.057 m in diameter and 0.038 m height) that simulated convection-dominated small pool fires of liquids. Blends of CME and SME with diesel fuel were tested with biofuel concentrations of 25, 50, and 75% by volume. The mass burn rate, the fuel surface regression rate, the radiation emission from the flames, the flame temperature field, and the emission indices of CO and NOx were recorded. The fuel surface regression rate in both containers was comparable. Both the fuel mass burning rate and surface regression rate varied non-monotonically with the volume concentration of biofuel in the blend. The radiation fraction of heat release and the temperature profiles were similar for all the flames. The CO emission index decreased with the biofuel content in the fuel. The NOx emission index did not show a systematic and significant dependence on the fuel blend; however, it was smaller than that measured in the turbulent gas jet and liquid spray flames of the corresponding fuels.

Experimental Characterization of Aerodynamic Behavior of Membrane Wings in Low-Reynolds-Number Flow

An experimental study of the aerodynamic characteristics of a flat-plate membrane wing was conducted. Three different values of membrane prestrain (5, 7, and 10%) were investigated, along with a rigid flat plate, at Reynolds numbers of 13,700, 22,600 and 36,300 and angles of attack up to 27 deg. It was found that 1) the dependence of the prestall mean lift on model prestrain is negligible, 2) prestall mean lift at a given level of prestrain is a strong function of Reynolds number, and 3) the mean drag increased with a decrease in model prestrain. In addition, the stall angle of attack is weakly dependent on prestrain and increases with increasing Reynolds number. With the exception of the highest Reynolds number, the flexible-model stall angles were found to be similar to the rigid flat-plate results. At the largest Reynolds number, dynamic results for the flexible models revealed large rms values of lift and drag, which generally decrease with increasing angle of attack. In comparison to the flexible models, the rms values for the rigid flat plate were insignificant. An aeroelastic flutter instability is postulated to be the cause of the large dynamic response for the flexible models. This hypothesis is supported by results that were generated using a potential flow- based computational aeroelastic model. These aeroelastic instability-induced vibrations are also proposed as the mechanism by which the flexible models showed better stall characteristics at the highest-tested Reynolds number.

Phase behaviors, fuel properties, and combustion characteristics of alcohol-vegetable oil-diesel microemulsion fuels

ABSTRACT Biofuels are being considered as alternatives to fossil-based fuels due to depletion of petroleum-based reserves and pollutant emission concerns. Vegetable oils and bioalcohols have proven to be viable alternative fuels both with and without engine modification. However, high viscosity and low energy content are long-term operational problems with vegetable oils and bioalcohols, respectively. Therefore, vegetable oil-based microemulsification is being evaluated as a method to reduce the high viscosity of vegetable oils and enhance the miscibility of alcohol and oil phases. Studies have shown that microemulsification with different alcohols lead to varying fuel properties depending on their structure. The overall goal of this study was to formulate microemulsion fuels with single and mixed alcohol systems by determining the effects of water content, alcohol branching structure and carbon chain length on phase behaviors, fuel properties, and emission characteristics. It was found that microemulsion fuels using certain alcohols displayed favorable stability, properties, and emission characteristics. Flames of fuels with linear short-chain-length alcohols had larger near-burner blue regions and lower CO and soot emissions indicating the occurrence of more complete combustion. In addition to alcohol effects, the effect of vegetable oils, surfactants, and additives on emission characteristics were insightful in pursuit of appropriate microemulsion fuels as cleaner burning alternatives to both No.2 diesel and canola biodiesel.

Effects of Biofuel on the Performance and Emissions Characteristics of a Small Scale Gas Turbine

A 30 kW gas turbine was used to characterize the performance and exhaust emissions of Jet A, soy methyl ester, canola methyl ester, and their blends in Jet A (50% by volume). Measurements included static thrust, thrust-specific fuel consumption, and thermal efficiency over a range of throttle settings. The exhaust concentrations of CO and NO produced by the combustion of these fuels were measured. Results indicated that the addition of biofuel to the Jet A fuel reduced the static thrust and the thrust-specific fuel consumption, and increased the thermal efficiency of the gas turbine. An increase in the biofuel content of a fuel blend also reduced the CO and NO emissions. The performances of biofuel-Jet A blends suggest that an optimum mixture can be used to reduce the pollutant concentrations while still producing the desired thrust. This study demonstrates that biofuels can become viable alternatives or supplements to petroleum-based fuels currently used in gas turbine engines.

Combustion Characteristics of Partially Premixed Prevaporized Palm Methyl Ester and Jet A Fuel Blends

Palm methyl ester (PME) is an attractive alternate biofuel produced by the transesterification of palm oil with methanol. This paper is a sequel to our earlier papers on the comparison of the flame structure and emission characteristics of neat PME with those of petroleum-derived fuels (No. 2 diesel and neat Jet A). Blends of prevaporized Jet A fuel and PME (25%, 50%, and 75% by volume) were studied in a laminar flame environment at burner-exit equivalence ratios of 2, 3, and 7. The global combustion characteristics including flame length, CO and NO emission indices, radiative heat fraction, and in-flame profiles of species concentration (CO, CO2, NO, and O2), temperature, and soot volume concentration were measured. The global CO emission index decreased significantly with the PME content in the blend at an equivalence ratio of 7; a 30% reduction was observed with the addition of 25% PME by volume, and a further reduction of 25% was observed with the addition of another 25% PME. The global NO emission index of the neat PME flame was 35% lower than that of the Jet A flame at an equivalence ratio of 2. The near-burner homogeneous gas-phase reaction zone increased in length with the addition of PME at all equivalence ratios. The concentration measurements highlighted the nonmonotonic variation of properties with the volume concentration of PME in the fuel blend. The fuel-bound oxygen and hydrogen of PME affected the combustion properties significantly.