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, CO 2 , NO, and O 2 ), 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.

Biofuels, such as canola methyl ester (CME), continue to receive considerable attention for their potential use as alternatives to petroleum diesel fuel. The studies on the application of biofuels in internal combustion engines, in general, have shown a considerable reduction in carbon monoxide (CO), soot, and radiative heat emissions, and a small increase in NO x emissions. Radiative heat transfer from flames, which is important in applications such as gas turbines and glass-manufacturing furnaces, has received little attention. The objective of this investigation was to document radiative heat transfer and radical and gas concentration measurements to understand the dominant mechanism of heat transfer in CME/diesel blend flames. In order to isolate the fuel chemical effects on the combustion characteristics of fuels, laminar flames of prevaporized liquid fuels were studied at injector-exit equivalence ratios of 1.2, 2, 3, and 7. Measurements of radiative heat transfer and flame structure including OH and CH radical concentration field were completed. While the peak temperatures in the various blend flames were comparable at the same equivalence ratio, the total flame radiation decreased with the increase in CME concentration in the fuel. Estimates of radiation from gaseous species and soot indicated that about 27–30% of the radiation was from gases, and the rest from soot. The gaseous species contribution to the flame radiation increased slightly with the biofuel content in the blend.

Palm methyl ester (PME) is a renewable biofuel that is produced by the transesterification of palm oil and is a popular alternative fuel used in the transportation sector, particularly in Asia. The objective of this investigation was to study the combustion characteristics of flames of prevaporized number 2 diesel and PME in a laminar flame environment at initial equivalence ratios of 2, 3, and 7 and to isolate the factors attributable to chemical structure of the fuel. The equivalence ratio was changed by altering the fuel flow rate, while maintaining the air flow rate constant. The global CO emission index of the PME flames was significantly lower than that of the diesel flames; however, the global NO emission index was comparable. The radiative fraction of heat release and the soot volume fraction were lower for the PME flames compared to those in the diesel flames. The peak temperatures were comparable in both flames at an equivalence ratio of 2, but at higher equivalence ratios, the peak temperatures in the PME flames were higher. The measurements highlight the differences in the combustion properties of biofuels and petroleum fuels and the coupling effects of equivalence ratio.

Biofuels, such as canola methyl ester (CME) and soy-methyl ester (SME) derived from vegetable oil, are alternative sources of energy that have been developed to reduce the dependence on petroleum-based fuels. In the present study, CME, SME, and commercial Jet-A fuel were tested in a porous-media burner at an equivalence ratio of 0.8 at the burner entrance. The measured combustion characteristics included NOx and CO emission indices, radiative fraction of heat release, and axial temperature profile in the surface stabilized and extended flame. The effects of fuel on the injector and porous-media durability were also documented. The NOx emission index was higher for the SME and CME flames than that of the Jet-A flame. Furthermore, the axial temperature profiles were similar for all the flames. The prolonged use of CME and SME resulted in more solid-particle deposition on the interior walls of the injector and within the structure of the porous medium than for Jet-A fuel, thereby increasing the restriction to the fuel/air flow and pressure drop across the burner.

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 (NO x ) emissions. The increase in NO x 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 cm 3 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.

As a result of decreasing petroleum supplies, new fuel sources, such as transesterified biofeedstock based oils and their blends with petroleum diesel fuels, have emerged with potential to partially replace conventional diesel and gasoline fuels. Although these fuels have shown some promising results in engine studies, their basic combustion properties have not been well documented. Also, research is underway to develop new fuels from other sources or by altering their molecular structure to be fungible with conventional fuels. Thus, there is a need for tests to characterize the combustion and emission properties of these new liquids, which are available only in small quantities at the research and development stage. This paper deals with a technique that meets those goals. The fuel was prevaporized and mixed with air and burnt in a tubular burner (9.5 mm inner diameter) at atmospheric pressure under laminar conditions. A pilot methane/air flame was used as the ignition source. The test conditions were so chosen that the measured properties could be attributed primarily to the fuel chemical structure. Several liquid fuels were tested, including commercially available petroleum-based No. 2 diesel fuel, canola methyl ester (CME B100) biodiesel, kerosene, methanol, toluene, and selected alkanes. The radiative heat flux from the flames was measured using a wide-angle pyrheliometer; the emissions from the flames were sampled to measure the concentration of CO, CO 2 , and NO. The measured radiant heat fraction values and the emission indices of NO and CO of both petroleum-derived and biofuels agreed well with those found in literature; thus, the feasibility of this method to rapidly characterize the combustion and emission properties of new liquids, such as biofuels, is demonstrated.

A study of the breakup of planar viscous liquid sheets subjected to gas flow on both sides was conducted. A linear spatial stability analysis was used to determine the instability wave characteristics. The analysis included the effects of liquid properties such as viscosity, density, and surface tension; the gas was treated as inviscid. Dispersion relations were obtained relating the wave growth rates to the frequency and other flow variables. The wave characteristics were determined by numerical solution of the governing dispersion relations for a wide range of operating conditions. In all cases, the gas velocity was found to be destabilizing; increases in the liquid density, viscosity, and surface tension were all found to have stabilizing effects. When the liquid sheet was exposed to unequal gas velocities, the wave propagation characteristics were found to be altered from the case of equal gas velocities.

The flow around a half-ellipsoid with axes ratio 12:6:1 mounted on a plane wall at an angle of attack of 25° and at a Reynolds number of 47,000 (based on the maximum chord) was studied using a three-dimensional LDV system. In this paper the mean velocity distributions in a volume enclosing the separated region and the near wake are described. The flow is shown to be consistent with the findings of Johnson (1991) based on flow visualization and related topological analysis. The flow on most of the pressure side was attached and laminar, while that on the suction side and in the wake was separated and turbulent. The region of separation had mean negative streamwise velocities as large as 25 percent of the freestream velocity, and the reversed-flow region extended up to one chord length behind the body. The measurements clearly reveal the complex vortex structure that arises from the three-dimensional separation.

A theoretical and experimental study of turbulent bubbly condensing jets is reported. Tests involved initially monodisperse carbon dioxide bubbles in water (∼ 1 mm diameter bubbles with initial gas volume fractions of 2.4 and 4.8 percent) injected vertically upward in still water. Measurements were made of mean and fluctuating phase velocities, mean bubble diameters, mean bubble number intensities, and mean concentrations of dissolved carbon dioxide. Three theoretical methods were used to interpret the measurements: (1) locally homogeneous flow analysis, assuming infinitely fast interphase transport rates; (2) deterministic separated flow analysis, where finite interphase transport rates are considered but bubble/turbulence interactions are ignored; and (3) stochastic separated-flow analysis where both finite interphase transport rates and bubble/turbulence interactions are considered using random-walk methods. Both finite interphase transport rates and the turbulent dispersion of bubbles were important for present test conditions; therefore, only the stochastic separated flow analysis provided reasonable agreement with measurements.