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Different Tests Of Liquid Fuels @ Www.07 Met.Tk
 

Different Tests Of Liquid Fuels @ Www.07 Met.Tk

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    Different Tests Of Liquid Fuels @ Www.07 Met.Tk Different Tests Of Liquid Fuels @ Www.07 Met.Tk Document Transcript

    • WWW.07MET.TK Assignment (1) Fuel & Furnaces “Different Tests of Liquid Fuels” Submitted by: Muhammad Arslan Afzal 2007-MET-14 Submitted to: Mr. Abdul Khaliq Sb.
    • WWW.07MET.TK Date: 25-10-08 LIQUID FUEL TESTS Viscosity Test Viscosity is a measure of the resistance of a fluid which is being deformed by either shear stress or extensional stress. In general terms it is the resistance of a liquid to flow, or its "thickness". Viscosity describes a fluid's internal resistance to flow and may be thought of as a measure of fluid friction. The word "viscosity" derives from the Latin word "viscum" for mistletoe. A viscous glue was made from mistletoe berries and used for lime-twigs to catch birds. Viscosity coefficients When looking at a value for viscosity, the number that one most often sees is the coefficient of viscosity. There are several different viscosity coefficients depending on the nature of applied stress and nature of the fluid. They are introduced in the main books on hydrodynamics and rheology • Dynamic viscosity determines the dynamics of an incompressible Newtonian fluid; • Kinematic viscosity is the dynamic viscosity divided by the density for a Newtonian fluid; • Volume viscosity (or bulk viscosity) determines the dynamics of a compressible Newtonian fluid; • Shear viscosity is the viscosity coefficient when the applied stress is a shear stress (valid for non-Newtonian fluids); • Extensional viscosity is the viscosity coefficient when the applied stress is an extensional stress (valid for non-Newtonian fluids). Shear viscosity and dynamic viscosity are much better known than the others. Viscosity measurement Dynamic viscosity is measured with various types of rheometer. Close temperature control of the fluid is essential to accurate measurements, particularly in materials like lubricants, whose viscosity can double with
    • WWW.07MET.TK a change of only 5 °C. For some fluids, it is a constant over a wide range of shear rates. These are Newtonian fluids. The fluids without a constant viscosity are called Non-Newtonian fluids. Their viscosity cannot be described by a single number. Non-Newtonian fluids exhibit a variety of different correlations between shear stress and shear rate. One of the most common instruments for measuring kinematic viscosity is the glass capillary viscometer. Viscosity is also measured by three makes of commercial viscometers 1. The Red Wood Viscometer 2. Saybolt Viscometer 3. Engler Viscometer. In case of viscometers, a fixed volume of a liquid at a fixed temperature is allowed to flow through a standard capillary tube and the time of flow is noted. The result is sometimes described in terms of time taken by oil to flow through a particular instrument. Vibrating viscometers can also be used to measure viscosity. These models such as the Dynatrol use vibration rather than rotation to measure viscosity. Extensional viscosity can be measured with various viscometers that apply extensional stress.Volume viscosity can be measured with acoustic rheometer. Ignition Temperature The ignition or autoignition temperature or kindling point of a substance is the lowest temperature at which it will spontaneously ignite in a normal atmosphere without an external source of ignition, such as a flame or spark. This temperature is required to supply the activation energy needed for combustion Measurement of ignition temperature: Autoignition temperatures of liquid chemicals are typically measured using a 500 mL flask placed in a temperature controlled oven in accordance with the procedure described in ASTM. The ignition temperature of distillate fuel is measured by apparatus which includes a block having an ignition cavity. The block is heated to an elevated temperature above the ignition temperature of the fuel and then allowed to cool slowly. As it cools, samples of fuel are injected into the ignition cavity at times which are controlled by a digital computer. A pressure transducer and a thermocouple measure the pressure and temperature, respectively, in the cavity. For each injected sample, the digital computer measures ignition delay as the time between injection of a sample and ignition as indicated by a peak in measured cavity pressure or cavity temperature. The ignition delay is recorded as a function of the cavity temperature prior to fuel injection.
    • WWW.07MET.TK Using the temperature required for a given ignition delay, the octane rating of distillate fuels may be estimated from a calibration curve established by comparing unit data with results from the ASTM octane number test. It has been found that the ignition temperatures of the tested distillate fuels fall on a smooth correlation curve which can be used to provide octane number estimates for unknown fuels. These are in excellent agreement with observed ASTM values. Viscometers for Oil Viscosity Measurement Viscosity measures a lubricant's resistance to flow (fluid thickness) at temperature and is considered oil’s most important physical property. Depending on lube grade, viscosity is tested at 40 and/or 100° Celsius. Viscosity Measurement is extremely important for hydraulic oils, diesel engine oils, Enclosed gears & fuel oils. Kittiwake supply a range of Viscometers varying in price & sophisticated from the Heated Viscometer & Unheated Viscometer, which form part of the Fuel & Lube Oil Laboratory equipment, to the more simple Viscometers in the Oil Test Kit range, listed below. DIGI Viscometer - Viscotube FG-K14828-KW The Kittiwake DIGI Viscometer (or Viscotube) uses a falling ball technique to measure the viscosity of oil in centistokes. Three sizes of ball are included in the kit. Supplied complete with viscosity calculation The Kittiwake DIGI Viscometer uses a falling ball technique for software. viscosity measurement. Kit also includes DIGI thermometer. Range: 20-600 cSt @ 40°C using 3 sizes of ball. Lubricating oils, hydraulic oil, warm fuel oil
    • WWW.07MET.TK Flash Point The flash point of a flammable liquid is the lowest temperature at which it can form an ignitable mixture in air. At this temperature the vapor may cease to burn when the source of ignition is removed. A slightly higher temperature, the fire point, is defined as the temperature at which the vapor continues to burn after being ignited. Neither of these parameters is related to the temperatures of the ignition source or of the burning liquid, which are much higher. The flash point is often used as one descriptive characteristic of liquid fuel, but it is also used to describe liquids that are not used intentionally as fuels. Mechanism Every flammable liquid has a vapor pressure, which is a function of that liquid's temperature. As the temperature increases, the vapor pressure increases. As the vapor pressure increases, the concentration of evaporated flammable liquid in the air increases. Hence, temperature determines the concentration of evaporated flammable liquid in the air under equilibrium conditions. Different flammable liquids require different concentrations in air to sustain combustion. The flash point is that minimum temperature at which there is a sufficient concentration of evaporated fuel in the air for combustion to propagate after an ignition source has been introduced. Flash point is basically the lowest temperature at which there is enough fuel vapour to ignite. Measuring flash point There are two basic types of flash point measurement: a) Cleveland Open Cup - ASTM D92 b) Pensky-Martens Closed Cup - ASTM D93 These two methods introduced by ASTM are known as Standard Measuring Methods. Cleveland Open Cup - ASTM D92 In open cup testers the sample is contained in an open cup which is heated, and at intervals a flame is brought over the surface. The measured flash point will actually vary with the height of the flame above the liquid surface, and at sufficient height the measured flash point temperature will coincide with the fire point. Pensky-Martens Closed Cup - ASTM D93 Closed cup testers, of which the Pensky-Martens closed cup is one example, are sealed with a lid through which the ignition source can be introduced periodically. The vapour above the liquid is assumed to be in reasonable equilibrium with the liquid. Closed cup
    • WWW.07MET.TK testers give lower values for the flash point (typically 5-10 K) and are a better approximation to the temperature at which the vapour pressure reaches the Lower Flammable Limit (LFL). The flash point is an empirical measurement rather than a fundamental physical parameter. The measured value will vary with equipment and test protocol variations, including temperature ramp rate (in automated testers), time allowed for the sample to equilibrate, sample volume and whether the sample is stirred. Methods for determining the flash point of a liquid are specified in many standards. For example, testing by the Pensky-Martens closed cup method is detailed in ASTM D93, IP34, ISO 2719, DIN 51758, JIS K2265 and AFNOR M07-019. Determination of flash point by the Closed Cup Equilibrium method is specified in ISO 1523:2002. Specific Gravity Specific gravity is defined as the ratio of the density of a given solid or liquid substance to the density of water at a specific temperature and pressure, typically at 4°C (39°F) and 1 atm (14.7 psi) , making it a dimensionless quantity. Specific gravity measurement: Hydrometer is used for determination of specific gravity upto 0.001.for higher values, specific gravity bottle is used and for the semi solid fuel like tar, indirect mathod is used.
    • WWW.07MET.TK The operation of the hydrometer is based on the Archimedes principle that a solid suspended in a liquid will be buoyed up by a force equal to the weight of the liquid displaced. Thus, the lower the density of the substance, the lower the hydrometer will sink.