Methodology.6 Report Examples

Abstract

Three tests were made on the kerosene sample: (a) determining hydrogen content by Nuclear Magnetic Resonance [NMR], (b) determination of viscosity by U-tube viscometer, and (c) flash point determination by Pensky-Marten closed-cup tester. Results suggest that the kerosene sample has 13.73% hydrogen content, 7.706 mm2/s kinematic viscosity at -20°C (extrapolated using Sutherland Viscosity Law), and 52-53°C flash point. These parameters characterized the kerosene sample as aviation fuel in terms of heating value, degree of saturation, pressure drop in fuel lines, pumping characteristics and safe handling. All parameters passed the standards derived from aviation literature. These parameters could be used by the engineer to design better turbine engine in aircrafts in the future.

Abstract.2

Introduction...4
Literature Review..5

Results8
Discussion of Results9
Conclusion12

References13

List of Figures and Tables:
Figure 1: U-tube Viscometer.7
Figure 2: Plot of Viscosity versus Temperature9

Fuel is a nonrenewable energy source. It powers growth of industries particularly in manufacturing, agriculture, and transportation sectors. The consumption is dictated by fossil fuel reserves even with ongoing trends in utilization of nonrewable energy sources. To maximize the use of fuels, their properties have to be studied. This characterization of fuels is needed to use them efficiently and with less emission of pollution. In this experiment, characterization of aviation kerosene is done. Aviation kerosene is a type of commercial grade turbine fuel. Three types of test are done on the samples: (a) determining hydrogen content by Nuclear Magnetic Resonance [NMR], (b) determination of viscosity by U-tube viscometer, and (c) flash point determination by Pensky-Marten closed-cup tester.
First, hydrogen content is determined by using a Newport Analyser. It is a low-resolution continuous-wave instrument capable of measuring the nuclear magnetic resonance of hydrogen atoms. The overall hydrogen content of turbine fuels is a quality indicator of performance in jet turbines. Hydrogen content indicates degree of hydrogen saturation in the hydrocarbon. High hydrogen content indicates high calorific value in most cases. Calorific value refers to the amount of heat obtained from a specific mass of fuel. Also, low degree of saturation implies double bonds in the structure which polymerizes to produce tar and soot. Thus, minimum hydrogen content is established by the aviation industry to improve burning efficiency and cleaner emissions.
Next, the kinematic viscosity is measured based on IP 71/ ASTM D445. The kinematic viscosity (measured in centistokes) indicates the resistance of a fluid to gravity flow. The U-tube viscometer is used by which a constant has already been measured by principle of related rates with water as reference standard.
Lastly, flash point of the fuel is determined by heating the sample in a closed cup at a slow steady rate with continuous stirring. A small flame is directed to the cup to ignite the vapor periodically. The temperature at which the vapor of the sample first ignites is the flash point. The flash point is particularly important as aircrafts operate at times in the lower-temperature regions of the atmosphere.
Literature Review
Characterization of liquid fuels involve determination of specific properties that describe their behavior during combustion. One fuel property is the hydrogen content which measures the degree of hydrogen saturation by the hydrocarbon mixture. In ASTM D7171-05, nuclear magnetic resonance is used (Oxford Instruments 2012). The hydrogen protons in the sample resonate due to two factors: (a) the magnetic field and (b) radio waves of correct frequency. The protons absorb the energy of the radio waves and re-emitting it. The intensity of the emitted energy corresponds to the number of resonating hydrogen protons in the fuel being tested.
Another parameter is viscosity which is the resistance of fluid to flow. Kinematic viscosity, in particular, is a measure of the time for a fixed volume of liquid to flow by gravity through a capillary. It measured in centistokes or (mm2/s). Viscosity of fuels affect the fuel line pressure drop and pumping charcateristics (Lawicki 2002). Furthermore, low temperatures increase viscosity. IP 71/ ASTM D445 is a standard method covering the determination of kinematic viscosity for liquid petroleum products (American Society for Testing and Materials 1964). It is intended for Newtonian fluids where the rate of shear is directly proportional to the shearing stress. The time is measured for a fixed volume of the sample liquid to flow through the capillary of the viscometer. The time is then multiplied with the calibration constant of the viscometer to obtain the kinematic viscosity. This is done in a controlled-temperature environment for accurate results.
ASTM D93 is a standard method for flash-point determination using Pensky-Marten closed-cup tester. The flash point temperature is a measure of the tendency of a fuel to form a flammable mixture with air at controlled laboratory conditions (American Society for Testing and Materials 2002). It helps one assess the flammability hazard of a given fuel. A brass test cup is filled with the fuel sample and covered (closed cup). The test cup is heated at a slow steady rate with continuous stirring. An ignition source is directed to the test cup at regular intervals, until a flash is observed. The temperature at which this flash is observed is the flash point.
Methodology
TEST 1: Hydrogen Content by NMR
The test includes: (1) sample and standard preparation, (2) the actual test procedures, and (3) the computation. First, the gate width, radio frequency level, audio frequency level, and integration time is set-up as prescribed by the manual. Then, 30±1 mL of the reference standard (cyclohexane) is placed in the test cell. The PTFE plug is inserted into the test cell, just above the surface of the cyclohexane. Then, the test cell is placed in a sample conditioning block. The procedures are repeated for the fuel sample. Conditioning takes at least 30 minutes. The reference standard is then placed in the analyser magnet unit. The tuning is adjsuted so that the peaks on the oscilloscope coincide. After 3s, the reset button is pushed for full polarization of the hydrogen nuclei. After 128s, the digital display measures the integrator count. The steps are repeated for the second reading, and the fuel sample to be tested. The final weight of the standard and sample are also recorded to compute for the hydrogen content.
TEST 3: Determination of Viscosity by U-tube Viscometer
The test started with clean and dry U-tube viscometer (See Figure 1). They are assembled in holder with the bottom U part submerged in a water bath (at 25 deg. Celsius) and for the second set-up, in a mineral oil bath (at 45 deg. Celsius). Using a pippete, sufficient sample is introduced to the viscometer until the large bulb is around ¾ full. The sample is added gradually to fill the second bulb at the other end of the viscometer (mark A), and to equilbriate the sample to the temperature of the bath. Using a pippete pump, the sample is sucked upward to above the large bulb (mark B). The pump is released and sufficient time is allowed until the sample is below the large bulb (mark C). The time is recorded and multiplied by the viscometer constant to compute for the kinematic viscosity.
Figure 1: U-tube Viscometer (http://www.paragon-sci.com)
TEST 4: Flash Point Determination by Pensky-Marten Closed-Cup Tester
The cup is filled with sample and closed with a lock. The stirrer is switched on with the heater at a heating rate of 5-6 degrees per minute. The manual adviced a setting of 4. As the sample increases by each degree interval, flame is tested correspondingly. This is done by turning off the stirrer, and lowering the test flame. When a distinct flash is observed, the temperature is recorded as the flash point.
Results
TEST 1: Hydrogen Content by NMR
Hydrogen Content of Sample = STSR×WRWT×HR%
Where ST = mean of integrator counts on sample under test
SR = mean of integrator counts on reference standard
WR = weight of reference compound
WT = weight of sample under test
HR = hydrogen content of reference compound = 14.29% cyclohexane
Thus,
Hydrogen Content of Sample = 153.1153.8×22.879923.6991×14.29 % = 13.73 %
TEST 3: Determination of Viscosity by U-tube Viscometer

There are two types of common aviation fuels used at present. One is the kerosene type or Jet-A1 and the other is the wide-cut type or the Jet-B specification. The sample used in the experiment is of the kerosene-type. Kerosene is a flammable pale yellow or colorless oily liquid with a characteristic odor intermediate in volatility between gasoline and gas/diesel oil that distills between 125°C and 260°C. Typical applications of kerosene is primarily in aviation, heating, and illumination.
TEST 1: Hydrogen Content by NMR
For the hydrogen content determination using nuclear magnetic resonance (NMR), the hydrogen content obtained from the calculations is 13.73% m/m. The minimum prescribed for kerosene type turbine fuels is 13.4% m/m for the JP-8 (NATO F-34), NATO F-35, and JP-8+100 (NATO F-37) used in military aircrafts (United States Department of Defense). Therefore, the kerosene sample passes the hydrogen content test according to this standard. Hydrogen content describes the burning quality of the fuel. A high hydrogen content signifies high degree of saturation. This means there are less carbon-carbon double bonds inherent in the hydrocarbon mixture. Double bonds polymerizes at high temperatures and produces unwanted combustion products such as soot and tar. Thus, fuels with high hydrogen content burn more completely. However, aside from hydrogen, there are sulfur, oxygen, and nitrogen groups attached to hydrocarbons. Although they occur in trace quantities, these functional groups also contribute to burning quality of fuels and this burning quality is especially important in aviation applications.
The principle involved in hydrogen content determination is brough about by advances in the NMR technology. The hydrogen protons in the fuel sample responds to the induced magnetic field and the radio waves transmitted to it. The energy emitted by the protons is reflected in the integrator count. The larger the number, the higher is the amount of hydrogen in the sample being tested.
TEST 3: Determination of Viscosity by U-tube Viscometer
For the kinematic viscosity, it is observed that as temperature increases, viscosity increases. At 25 degree Celsius, the kinematic viscosity of kerosene is 1.531 mm2/s while at 45 degree Celsius, the kinematic viscosity of kerosene is 1.227 mm2/s. The 25°C data was observed in water bath while the 45°C data was observed in mineral oil bath. At higher temperatures, the kerosene molecules have faster molecular speeds. Thus, the time of interaction between molecules also decrease. This results in less cohesive forces, allowing the sample fluid to flow more easily. With respect to aviation use, kerosene as jet fuel is injected at high pressure into the combustion chamber of the turbine engine. The injection method is through a nozzle which produces a fine spray (Lawicki 2002) of fuel droplets that vaporizes rapidly as combined with air to produce thermal energy. Also, the pumping characteristics are aslof affected by viscosity. Too high viscosity results in more work on the art of the pump just to control a steady flow of fuel. That is why the aviation industry puts an upper limit to viscosity. Current standard is at 8 mm2/s at -20 degree Celsius (Hemmighaus et al 2006). To compare the experimental results with that of tabulated data, the Sutherland Viscosity Law using two coefficients (Fleunt, Inc. 2006). Sutherland Viscosity Law can be explained by the equation: μ=C1T1.5 T+C2 where µ is the visocsity in kg/m.s, T is absolute temperature in K, and C1 and C2 are constant coefficients. From the two data points: C1 = 1.5843 x 10-8 and C2 = -244.87. Substituting these coefficients to temperature = -20°C. The viscosity obtained is 7.706 mm2/s. This is lower compared to the upper limit standard of aviation industry at 8 mm2/s at -20 degree Celsius. Thus, the kerosene sample passed the viscosity test. Generally, kinematic viscosity decreases with increase in temperature as shown in Figure 2. However, the relationship is not linear but follows the Sutherland Viscosity Law.
For the experiment, good timing is key, as well as, the careful set-up of the viscometer with respect to the individual water baths. The viscometer are immersed in their respective baths, and temperature has to be maintained to get accurate results. Viscometers are calibrated glasswares similar to burettes and pipettes, and can cost much. Care during handling needs to be done to avoid breakages.
TEST 4: Flash Point Determination by Pensky-Marten Closed-Cup Tester
The flash point obtained for kerosene is 52-53 degree Celsius. The flash point is the lowest temperature at which vapors above a flammabe liquid will ignite on application of flame.
The minimum flash point of Jet A and Jet A-1 kerosene-type jet fuel is 38 degree Celsius. Thus, the kerosene sample pass the test since it is higher than the minimum flash point. This is based on safe handling practices since the flash point determines the flammability hazard of a fuel. The Pensky-Marten Closed Cup, as an apparatus, contributes to the equal distribution of heat gradients in the liquid-vapor mixture due to the stirring mechanism. It is the vapor here (resulting from the vapor-liquid equilibrium) that is being ignited.
Conclusion
In the experiment, three properties of kerosene as aviation fuel were determined (See Table 3 for Summary of Findings). Compared to standard values prescribed in the literature, all parameters passed. The results for viscosity, however, needed additional processing of data using Sutherland Viscosity Law. Kerosene-type turbine fuels are used extensively in the aviation industry. Their properties affect certain systems such as fuel line pressure drop and fuel pumping capacity. Thus, they have to be consiedered during the design of the modern turbine engine in aircraft. The obtained values are close to standard values. Some errors might have been incurred due to sampling procedures, timing, and parallax errors during observations.

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