The flash point and ignition point measurement experiment of flammable liquid

The purpose of the experiment 　　1. To grasp the definition of the flash point and ignition point of flammable liquids and the reasons for the flashover phenomenon of the liquid; 　　2. To master the method of measuring the flash point and ignition point of flammable liquids with an open cup and closed cup flash point tester. Experimental principle When the liquid temperature is relatively low, due to the low evaporation temperature and slow evaporation rate, the concentration of vapor molecules formed above the liquid surface is relatively small, which may be less than the lower explosion limit. At this time, the mixed gas formed by vapor molecules and air cannot meet the fire source. Ignited. As the temperature continues to rise, the concentration of vapor molecules increases. When the concentration of vapor molecules increases to the lower explosive limit, the mixed gas formed by the saturated vapor of the combustible liquid and the air will flash and extinguish when it encounters a fire source. This kind of flash-out instantaneous combustion phenomenon is called flashover. Under the specified experimental conditions, the lowest temperature corresponding to the flashover of the liquid surface is called the flash point of the liquid. At the flash point temperature, the liquid can only flash but not continue to burn. This is because at the flash point temperature, the evaporation rate of the combustible liquid is lower than its burning rate. After the vapor above the liquid surface burns out, the vapor is too late to replenish, causing the flame to extinguish itself. Continue to increase the temperature, and the vapor concentration above the liquid surface will increase. When the mixture of vapor molecules and air meets the fire source and can burn for no less than 5 seconds, the liquid is ignited at this time, and its corresponding temperature is called the The ignition point of the liquid.　　From the firefighting point of view, flashover is a warning of fire danger and a prelude to fire. Mastering the burning phenomenon of flashover can prevent fire from occurring or reduce the damage caused by fire. The basic parts of the experimental instrument: oil sample container, heating and heating device, temperature control circuit, temperature measuring device, ignition source 1. Manual open cup flash point and ignition point tester: inner crucible, outer crucible, gas conduit, thermometer, electric furnace, Electrical equipment, windshield, etc., the structure diagram is shown in Figure 1. (1) The material of the inner crucible is 0.3 high-quality carbon structural steel, the inner diameter of the upper mouth is 64±1mm, the inner diameter of the bottom is 38±1mm, and the total height is 47±1mm. There is a line at the inner wall of 12mm and 18mm from the edge of the upper mouth. Engraved lines, the surface is black-plated.　　 (2) The material of the outer crucible is the same as that of the inner crucible. The inner diameter of the upper mouth is 100±5mm, the inner diameter of the bottom is 56±2mm, the total height is 50±5mm, and the surface is black-plated.　　(3) The diameter of the nozzle of the gas pipe is 0.8～1.0mm, and the surface of the inner hole is smooth, which can adjust the flame to a spherical flame with a diameter of 3～4mm, and the total height is 50±5mm. (4) The bracket is composed of a base, a pole, an electric stove holder, and a thermometer clip. The electric stove holder, thermometer clip and fastening screws are fixed on the pillar, and the height can be adjusted up and down. The thermometer clip should ensure that the thermometer is located in the center of the inner hole of the electric stove. .　　 (5) The electric furnace part is composed of a silicon carbide electric stove plate, a silicon carbide gasket, and a 220V/800W electric heating wire. The heating power is controlled by an electric device according to the requirements of use.　　 (6) The electrical device is composed of a set of electronic voltage regulating circuit, indicator light, toggle switch, transformer, precision multi-turn wire wound resistor and AC ammeter.　　2. Manual closed cup flash point and ignition point tester: oil cup, stirrer and oil cup lid, electric stove, sliding plate, flame lighter, electrical device, thermometer, wind shield, etc. The structure is shown in Figure 2.　　 (1) The inner diameter of the standard oil cup is 50.8mm, the depth is 56mm, the oil test capacity is about 70mm, and the depth of the oil test capacity is 34.2mm.　　 (2) The aperture of the igniter is 0.8mm.　　(3) The electric heating device is composed of a voltage-regulating silicon controlled rectifier and a 600W electric heating wire. The heating rate of the oil test is within the range of 1-12°C/min.　　(4) The electric stirring device is composed of a constant speed motor and a stirring blade. The size of the stirring blade is 8×40mm. The transmission mode is soft shaft transmission, and the stirring speed is 105r/min.　　3. Semi-automatic open cup flash point and ignition point tester: Cleveland oil cup, igniter, electric stove, thermometer, temperature sensor, microcomputer control panel, control keyboard, display, wind shield, etc. Experimental drugs 1. Kerosene 2. Diesel oil experiment content and method Basic steps: install sample → place on electric furnace → install thermometer → heat up (according to regulations) → ignition test → record data 1. Manual open cup flash point tester (1 ) Put the inner crucible into the outer crucible containing the spun yarn, make the surface of the spun yarn about 12mm from the edge of the mouth of the inner crucible, and keep a 5-8mm sand layer between the bottom of the inner crucible and the bottom of the outer crucible. (2) Inject the sample into the inner crucible. For samples with flash points below 210°C and 210°C, the liquid level is 12mm away from the edge of the crucible mouth (that is, the upper scale line in the inner crucible). For samples above 210°C, the liquid level is 18mm from the edge of the crucible mouth (that is, the lower scale mark in the inner crucible). Note: First put the crucible flat on the experiment table, then pour the medicine into the small beaker, and then add the small beaker to the crucible. When it is almost flush with the scale line, use a dropper instead. Note that the sample should not be splashed, and the crucible wall above the liquid level should not be stained with the sample.　　

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