Flash and Fire Points PDF

## 2. Flash and Fire Points (80 points for the report and 20 points for the preparation) ### A. Objectives 1. Comprehend the difference between the flash point (open and closed), the fire point and the self-ignition point. 2. Measure the open flash point using the open cup method. 3. Measure the...

## 2. Flash and Fire Points (80 points for the report and 20 points for the preparation) ### A. Objectives 1. Comprehend the difference between the flash point (open and closed), the fire point and the self-ignition point. 2. Measure the open flash point using the open cup method. 3. Measure the closed flash point using the closed cup point. 4. Measure the fire point. ### B. Background 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 the temperature of the burning liquid, which are much higher. These temperatures are not to be confused with the self-ignition temperature, which is the lowest temperature at which a substance will spontaneously ignite in a normal atmosphere without an ignition source. 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. 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 vapor to ignite. An example of the use of these different points appears in spark ignition engines. These engines use gasoline fuel. The fuel is premixed with air within its flammable limits and heated above its flash point, then ignited by the spark plug. The fuel should not pre-ignite in the hot engine. Therefore, gasoline is required to have a low flash point and a high self-ignition temperature. Diesel fuel is designed for use in a compression ignition engines. Air is compressed until it has been heated above the self-ignition temperature of diesel engine; then the fuel is injected as a high-pressure spray, keeping the fuel-air mix within the flammable limits of diesel. There is no ignition source. Therefore, diesel is required to have a high flash point and a low self-ignition temperature. ### C. Experimental Setup The Pensky-Martin apparatus is used for all petroleum products having a flash point above 50°C. It consists of a cup with a circumscribed filling mark, fitted with a lid which carries the thermometer. There are three ports cut in the lid; one for admittance of the test flame, which is usually about 3mm long: and two for the observation of the flash. The shutters for the ports and the mechanism for depressing the test flame are operated by a spring loaded handle. The cup is fitted with a stirrer which should not be operated whilst applying the test flame. ### D. Experimental Procedure 1. Fill the cup to the circumscribed mark with fresh oil. 2. Place the oil cup in the flash-point apparatus bath. 3. Place the top onto cup and lock. The top houses an electrically driven paddle, a thermometer and an ignition/pilot burner. 4. Place the thermometer into the cup via the port hole and clamp into position 5. Heat the sample with the electric heater. 6. Rotate the stirrer at a uniform rate. 7. At 15 °C below the estimated flash point the test flame is applied at intervals of 1 °C. 8. As the flash point is approached an enlargement of the test flame, due to enrichment of the oil vapor, will be noticed 9. Recorded the temperature at which a distinct flash is noted as a closed flash point. 10. Open the cup and recorded the temperature at which a distinct flash is noted as an open flash point at this case. 11. Record the fire point at which the oil is firing and still firing for a 5 sec. at minimum. ### E. Required Work **Activity #1:** Define the open and closed flash points. Explain the difference between them. Which one is higher and why? (20 points) **Activity #2:** Define the fire point. What is the difference between the fire point and the self-ignition point? (20 points) **Activity #3:** State the values of the flash (open and closed) and fire points of the oil used. (20 points) **Activity #4:** Using textbooks or the internet, find the range of flash, fire and self-ignition points for different fuels. (20 points) ### F. Suggested Reading 1. https://beeindia.gov.in/sites/default/files/2Ch1.pdf 2. http://en.wikipedia.org/wiki/Fire_point 3. http://en.wikipedia.org/wiki/Flash_point ## 3. Volatility And Distillation of Gasoline (80 points for the report and 20 points for the preparation) ### A. Objectives 1. Comprehend the concept of volatility and its relationship to the distillation of crude oil. 2. Generate the gasoline distillation curve for the sample provided and to estimate the percent of residuals (heavy hydrocarbons) that are not distillable in the temperature range of the test. 3. Comprehend the effects of volatility on the spark ignition engine performance in summer and in winter. 4. Differentiate between evaporation and vaporization. ### B. Background Volatility is a measure of the tendency of a substance to evaporate. Evaporation is totally different from vaporization. Evaporation is the escape of the molecules from the liquid surface even if there is no heat transfer. Evaporation occurs on the microscopic level (only the molecules on the surface escape) and therefore requires more time than vaporization. Evaporation occurs for many reasons, including mass transfer due to the concentration gradient. i.e., the liquid molecules escape from high concentration (liquid surface) to low concentration (air). During evaporation, the liquid molecules absorb their latent heat from the liquid surface or from the air itself before escaping as vapor. Substances of high molecular weights (heavy hydrocarbons) are less volatile than substances of low molecular weights (light hydrocarbons). Also, the heavy hydrocarbons have more calorific value than the light hydrocarbons. **Vaporization (boiling)** requires a heat source and is a full macroscopic phase change from liquid to vapor at the saturation conditions. It requires less time than evaporation and occurs on the macroscopic scale (i.e., the whole liquid vaporizes, not just the layer on the surface) As the temperature increases, the liquid molecules at the surface gain more kinetic energy, which enhances their escape to the air. This means that as the temperature increases the evaporation process is enhanced causing higher volatility. When the temperature reaches the boiling point, the whole liquid starts to vaporize on full scale. Note that pure water will vaporize at one temperature. However, a mixture of different substances (like gazoline) will evaporate in a range of temperatures. Because of the strong relation between volatility and boiling points the method used to measure the volatility of gasoline is the distillation test. **Distillation test** is the heating of a chemical mixture of liquids to a set of given temperatures. At each temperature, a percentage of the liquid volume evaporates (boils) and is then cooled to condensation. The result of this test is a curve showing the temperature on the vertical axis and the percentage of the volume evaporated on the horizontal axis. **Commercial gasoline fuel** is obtained from crude oil and it is a mixture of several hydrocarbons. Therefore, its properties are not as those of a pure substance. Gasoline is used in spark ignition engines (SIE) in a vaporized phase mixed with air, and this makes the volatility of the gasoline a very important property for smooth ignition in spark ignition engines. Volatility affects the fuel mixing with air and subsequently affects engine performance. Many engine parameters are strongly affected by the volatility of the fuel. ### C. Requirements in the Fuels 1. **Cold engine starting:** Because the gasoline must evaporate at low temperatures, the engine will need a more volatile fuel to make cold starting easier. Therefore, gasoline should contain highly volatile hydrocarbons to ensure easy starting even at low temperatures in winter. 2. **Short warm-up time:** The more the volatility of the used gasoline, the shorter the warm-up period of the engine. This will reduce emissions and will conserve engine life. The crank case dilution will be minimized if the warm-up period is as short as possible. 3. **Crankcase dilution:** As the fuel enters the cold cylinder at starting, it condenses and falls into droplets which go down through piston rings and mix with lubricating oil spoiling it. A more volatile fuel will reduce this problem even at low temperatures. 4. **Vapor lock:** This phenomenon happens when the temperature increases. The fuel in the fuel pump or the fuel line evaporates too much forming bubbles. The bubbles prevent the fuel from reaching the engine. In old engine designs, where a mechanical fuel pump was used (which contains a rubber diaphragm), this was a common fault that occurred especially in hot climates. For modern fuel injection, this fault has been seldom detected. 5. **Fuel economy:** A fuel with low volatility reduces the amount of vapor escaping from the fuel tank. Also, the low volatile elements (i.e., heavy hydrocarbons) have more calorific value thus improving fuel economy which gives another reason to lower the volatility. Usually, gasoline contains a mixture of light and heavy hydrocarbons; the more the percentage of the heavy compounds the better is the fuel economy. 6. **Smooth acceleration:** At sudden acceleration an extra amount of fuel is sprayed into the intake manifold to compensate for the rapid air rush. If the fuel is highly volatile, then it will evaporate immediately and the engine will accelerate smoothly. Usually, the more volatile elements tend to do this job, but unfortunately, they have low calorific values. Thus for smooth and sudden acceleration, an extra amount of gasoline is required to be sprayed into the intake manifold. 7. **Carburetor icing:** In spark ignition engines, fuel is sprayed in the entering air stream in an adjusted amount in the carburetor. In order for the fuel to evaporate in this mixture it absorbs its latent heat from the air stream. The air stream, however, has some water vapor in it. As the fuel absorbs its latent heat, the temperature of the air stream decreases causing the water vapor in it to freeze. Therefore, in cold climates, ice may form on the walls of the carburetor plugging it. A more volatile fuel will make the evaporation easier, and the temperature will not be lowered to the freezing point of water. For carbureted engines this problem occurs for high altitudes (helicopters or mountains) and for moderately cold climates (very cold climates has no water vapor in the air). Engines with injection systems do not suffer from such a problem 8. **Mixture distribution problems on cylinders:** after completing the carburetion or injection process some droplets of fuel are not evaporated yet. These droplets are distributed on the cylinders among the flow but due to inertia effects they are not evenly distributed causing different A/F ratios inside cylinders and different cycle efficiencies for each cylinder. A more volatile fuel is easier to evaporate and will not suffer from such a problem. A famous phenomenon in SIE is the knock which is a noisy sound resulting from violent variations in pressure inside cylinders damaging the cylinders and reducing the engine lifetime. Some additives are added to solve this problem, but they are heavy hydrocarbons, and they are not easily evaporated and so they cause distribution problems causing knocking to occur in some cylinders and not to occur in others. 9. **Spark plug fouling:** Due to mixture distribution problems, some liquid droplets enter the cylinders as liquids. Therefore, they do not react properly and they form soot particles on the spark plug affecting spark timing and causing problems in combustion and even damaging the spark plug with time. More volatile fuel will not suffer from this problem. ### D. Gasoline Distillation Curve Gasoline is a mixture of several hydrocarbons, and each constituent has its own boiling temperature, thus gasoline does not have a single boiling temperature like pure water but rather has a range of evaporation that may extend from 25°C to 220°C for different types and additives. Usually, three temperatures give an indication of the volatility of gasoline, the first at which 10% of the condensed volume is received (10% point), the second at which 50% of the condensed volume is received (50% point) and the third at which 90% of the condensed volume is received (90% point). A small percentage of components that vaporize (boil) at low temperature is needed to ensure smooth cold engine starting, short warm up time, minimum crank case dilution and no vapor lock. These components are called front-end volatility components. Their percentage in the fuel controls the 10% point to match the need at summers and another match is for winters. Also, components of high temperature vaporization are present in the gasoline mixture by a certain percent that controls the 90% point to have enough heavy hydrocarbons for a high calorific value, on the other hand heavy hydrocarbons shouldn't give liquid droplets that cause mixture distribution problems on cylinders or spark plug fouling. These components are called high-end volatility components. The 50% point is also controlled by the ratio between front- and high-end components in the mixture. 50% point also, governs the behavior of the engine regarding carburetor icing and sudden acceleration. The 50% and 90% points are adjusted with different values in summers and winters. An example of the Gasoline Distillation Curve is shown in Figure #1. An example of the seasonal variation of volatility from summer-grade gasoline to winter-grade gasoline is shown in Figure 2. ### E. Experimental Setup Figure 3 shows the simple standard distillation apparatus used in this experiment. The facility consists of: 1. Heating source (burner) 2. Fuel flask 3. Thermometer 4. Condenser (ice bath) 5. Graduated receiver A known amount of fuel is placed in the fuel flask. The fuel is then heated using the burner causing the fuel to evaporate gradually as the temperature increases. The vapor is then condensed in the condenser and received in the graduated receiver. ### F. Experimental Procedure 1. Fill the fuel flask with 100 milliliters of commercial gasoline then mount it on its position and make sure that the apparatus is completely sealed from outside air (safety precaution for no fires or explosions). 2. Light on the burner to start heating. 3. Start observing the receiver as the fuel evaporates into the condenser and condense back in the receiver. 4. Record the temperature as the first droplet falls into the receiver which presents this mixture's initial boiling point (IBP). 5. Record temperature each 10 ml volume condensation on the receiver until you reach the 90 ml volume (100 ml will not be reached as some residuals exist in the fuel which have high molecular weight making its boiling point very high and can't be reached on the test range). 6. Observe the temperature until it reaches a maximum value and starts to decrease (the flask contains air only as all distillable gasoline is vaporized and due to low heat transfer coefficient of air lower heat is transferred and temperature is decreasing) then record the final distillated volume with maximum temperature and switch of the burner. 7. Fill in the following table: T(°C) | % vol. | Evap. --- | --- | --- 0 | 10 | 20 | 30 | 40 | 50 | 60 | 70 | 80 | 90 | 8. Measure the volume of residuals in the flask using another receiver. You will find that summation of volumes is still not 100 ml. The rest of losses have escaped to the atmosphere. Now calculate their volume. 9. Plot the distillation curve and determine the key points on this curve. ### G. Required Work. **Activity #1:** Make a table that summarizes the advantages and disadvantages of high and low volatile fuel components in spark ignition engines (10 points) **Activity #2:** Clearly define volatility, evaporation, boiling and distillation (10 points) **Activity #3:** Fill-in Table 1 above (10 points) **Activity #4:** Plot the distillation curve of the sample tested (20 points) **Activity #5:** Show the IBP, 10%, 50% and 90% points on the curve and state their values (10 points) **Activity #6:** Using reference books or the internet, find and print the distillation curve of any crude oil. State your references. (10 points) **Activity #7:** Sketch the distillation curve of pure water (10 points) ### H. Suggested Reading 1. http://en.wikipedia.org/wiki/Volatility_(chemistry) ## 4. Measurements of Calorific Value (80 points for the report + 20 points for the preparation) ### A. Objectives 1. Comprehend the difference between the lower and higher calorific values for a given sample of a fuel 2. Measure the lower and higher calorific values for a given sample of a fuel 3. Comprehend the effects of the fuel chemical composition on the combustion efficiency ### B. Background The heating value (calorific value) for a certain fuel is the amount of energy released when a unit of mass (or unit volume) of fuel is burned completely in a steady flow process and the product are returned to the state of the reaction. There are two types of heating values: The higher heating value (HHV), which occurs when H₂O in the products is in the liquid form; and the lower heating value (LHV) which occurs when H₂O in the products is in the vapor form. ### C. Experimental Setup In this experiment, the Junker calorimeter will be used. In this device, a certain mass flow rate of fuel is burnt. Water, with a known flow rate, is cooling the inside of the device. The inlet and outlet temperatures of the water are measured. Part of the water condenses and is also measured. The products of combustion leave the device and their temperature is measured. ### D. Experimental Procedure 1. Fill the calorimeter with water which passes inside the tubes. 2. Light on the burner to start heating. The fuel used is liquefied petroleum gas (LPG)- assume its composition as 50% propane (C3H8) and 50% butane (C4H10). 3. Record the water inlet temperature 4. Record the water exit temperature and the exhaust temperature 5. Measure the water mass flow rate mow by measuring the time needed to fill a certain volume of water. 6. Similarly, measure the condensed water mass flow rate mow cond. 7. Fill your measurements in the following tables: twi | two | texh | Vw | Vw. condensed | time | time | time ---| --- | --- | ---| ---| ---| ---| --- 8. Measure mor using a rotameter. The rotameter was initially calibrated for air, not for LPG. You can still use it for LPG by correcting its reading as follows: m°= m √pf pa ### E. Required Work **Activity #1:** Fill-in all the tables above (10 points) **Activity #2:** Calculate the higher heating value (HHV) from an energy balance: the energy released by the fuel is equal to the increase in the water's energy: mw*Cp.w* (two-twn) = m°f *HHV (10 points) **Activity #3:** Calculate the lower heating value (LHV) by accounting for the latent heat of the condensed water: m°* HHV = m° *LHV + m°w.cond *hfg (10 points) **Activity #4;** Compare the calculated HHV and LHV of LPG to the published values for propone and butane. Comment. (10 points) **Activity #5:** The more hydrogen in the fuel, the more water vapor forms and more is the difference between the HHV and the LHV. Fill-in the table below and then plot the carbon-to-hydrogen ratio on the horizontal axis and the (HHV-LHV)/HHV on the vertical axis. Comment. (15 points) | Fuel | Chemical Formula | Carbon-to-hydrogen ratio | HHV | LHV | (HHV-LHV)/HHV | |---|---|---|---|---|---| | Hydrogen | H₂ | =0/2 | | | | | Methane | CH4 | -1/4 | | | | | Propane | C3H8 | -3/8 | | | | | Butane | C4H10 | -4/10 | | | | **Activity #6:** What do you think is the difference between the HHV and the LHV for carbon? Why? Would the combustion efficiency be higher for a fuel made of only carbon or for fuel made of only hydrogen? Why? (15 points) **Activity #7:** One of the methods of waste management is to actually burn the waste in a controlled manner inside an incinerator. Can we also generate electricity while getting rid of the waste? Why yes or why no? (10 points) ### F. Suggested Reading 1. http://en.wikipedia.org/wiki/Heat_of_combustion 2. http://www.engineeringtoolbox.com/fuels-higher-calorific-values-d_169.html