Heres some additional excerpts that might be helpful for ethanol & Biodiesel included correlation between Cloud/Pour Points & BD Cetane **
"Alternatives to Traditional Transportation Fuels: An Overview" June 1994 149 page, 1239K PDF > http://tonto.eia.doe.gov/FTPROOT/alternativefuels/0585o.pdf Cetane The combustion and ignition characteristics of diesel engine fuels are expressed in the cetane number. Fuels with high cetane numbers have low autoignition temperatures and short ignition delay times. Since a high octane number means a low cetane number (see Chapter 7), Cetane Number The most important engine performance property of diesel is the cetane number, which is a measure of the ease with which fuel will self-ignite under compression. The delay between the time the fuel hits the hot compressed air and when it ignites depends to a large extent on hydrocarbon composition. The higher the cetane number, the shorter the ignition delay and the better the engine performance. Cetane number is highest for linear paraffins, and lowest for aromatics as shown below: Fuel Component Contribution to Cetane Number Aro- Naph- Branched Linear Branched Linear matics thenes Olefins Olefins Paraffins Paraffins -----------------Increasing Cetane Number----------------> <-----------------Increasing Octane Number---------------- A high octane number, desirable for gasoline, means high aromatics and low linear paraffins, whereas the opposite is true for cetane numbers. Higher aromatic content means a lower cetane number and poorer diesel engine performance, as well as increased particulate formation. In spark-ignition engines, aromatics are good for engine performance but bad for emissions. In compression-ignition engines, aromatics are bad for both performance and emissions. Thus, in the case of diesel, there is no tradeoff between performance and emissions regarding aromatics. Low cetane number and associated long ignition delay cause rough engine operation, misfiring, and incomplete combustion in a cold engine at low temperatures, resulting in power loss and exhaust smoke. Vehicle/Engine Systems Alcohol-Fueled Vehicles [Such as methanol & ethanol] AFVs, including near-neat alcohol vehicles, are being used to gain environmental benefits and enhance energy security by using a nonpetroleum-based fuel. However, these vehicles have some disadvantages which offset some of the benefits. Engine Systems. Since alcohol fuels are high-octane fuels, flexible-fueled engines are optimized with a somewhat advanced ignition timing and an adjusted air/fuel ratio. An optimized ethanol engine could exhibit a theoretical efficiency gain of 15 percent over an optimized gasoline engine. But theoretical efficiencies usually are not fully realized. For example, one test using E-95 showed efficiency improvements of 8 percent when increasing the compression ratio from 8 to 12, while 12- percent improvement was expected from theoretical considerations. [MH: A report done by the SAE (Society of Automotive Engineers) has similar comments issued March 1993. ] Autoignition Temperature Autoignition temperature is a measure of when a fuel will selfignite. Self-ignition is a concern in environments where the fuel might escape and come into contact with hot engine parts. As a safety feature, high autoignition temperatures are desirable. Hydrogen has the highest autoignition temperature at about 1,065 degrees Fahrenheit, followed by natural gas, propane, methanol, and ethanol. Gasoline and diesel have the lowest autoignition temperatures at 495 and 600 degrees Fahrenheit, respectively. Based on this measure, all the alternative fuels have an advantage over gasoline. While both natural gas and hydrogen have high autoignition temperatures, they require very different amounts of energy to ignite mixtures of fuel and air. Since natural gas fuel/air mixtures are difficult to ignite, natural-gas-fueled engines must use high-energy spark plugs. Hydrogen fuel/air mixtures, on the other hand, need very little energy to ignite. For stoichiometric fuel/air ratios, hydrogen requires about one-tenth the energy to ignite that hydrocarbon fuels require. Flashpoint The flashpoint is the lowest temperature at which combustible mixtures of fuel vapor and air form above the fuel. In the presence of a spark, such mixtures will ignite. A high flashpoint is desirable from a safety standpoint, but none of the alternative fuels has an advantage in this area. All fuels but diesel have flashpoints at ambient or lower than ambient temperatures; however, the alcohol fuels have higher flashpoints than gasoline. Heat of Vaporization Heat of vaporization affects engine power and efficiency. It is the amount of heat absorbed by a fuel as it evaporates from a liquid state, which occurs when the fuel is mixed with air prior to combustion. Higher heat of vaporization leads to improved cooling ability. Higher cooling during the intake stroke of a spark-ignition engine results in a denser air/fuel mixture. A denser mixture has two effects: (1) it allows for greater power, and (2) it permits a greater compression ratio, which improves power and efficiency. However, although a high heat of vaporization improves power and efficiency, it also adds to coldstart problems when there is little heat in the air or in the engine to vaporize the fuel prior to spark ignition. The alcohol fuels have much higher heats of vaporization than gasoline or diesel. Flame Speed The speed at which a flame front propagates through a fuel/air mixture can affect engine performance and emissions. High flame speeds allow for more complete combustion and potentially leaner fuel mixtures. While the liquid fuels have similar flame speeds, methanol is thought to have a higher flame speed than gasoline. Natural gas, however, has a slower flame speed than the other fuels, which impairs spark-engine efficiency unless the spark timing is advanced to compensate. The need for advanced timing can be offset by use of high compression ratios and compact, turbulent compression chambers that decrease the distance the flame must travel. Hydrogen has the highest flame speed of the alternative fuels, which reduces burning time and thus heat losses from the cylinder,, improving thermal efficiency over fuels with lower flame speeds. Flame Temperature and Luminosity The alcohol fuels distinguish themselves in this area. For alcohol fuels, the flame temperature is lower than that of gasoline, and luminosity is so low that less thermal energy is lost through conduction or radiation. Low flame temperature also helps reduce nitrogen oxide formation. Low luminosity, however, is a safety issue, because the flame is essentially invisible. When gasoline is is the added to the neat alcohol fuels as in M-85 or E-85, it increases the luminosity. Hydrogen also is virtually invisible when burning. Flammability Flammability limits measure the range of fuel/air mixtures that will ignite. From a safety perspective, a wide range is less desirable than a narrow range. Of the hydrocarbon fuels, methanol has the widest flammability limits (7.3 percent to 36 percent) followed by ethanol. In partially filled or empty storage tanks, the alcohol fuels are more likely to produce a combustible mixture above the fuel than the other alternative hydrocarbon fuels. Gasoline tank vapors are too rich in fuel to ignite, and the addition of gasoline to the alcohol fuels reduces the flammability limits of M-85 and E-85 compared to M-100 and E-95, respectively. Relative to gasoline, the safety concerns associated with the wide flammability limits of alcohols are offset by the safety advantages of alcohol fuels' relatively high lower flammability limits, higher flashpoint temperatures, higher autoignition temperatures, and lower vapor pressures than gasoline.156 For example, the high lower-flammability limit of methanol keeps it from igniting in air at concentrations below about 6 percent, while gasoline will ignite at concentrations as low as 1.4 percent. Hydrogen has the widest flammability limits of all of the alternative fuels, ranging from 4.1 percent to 74 percent. When coupled with the small amount of energy needed to ignite fuel-air mixtures, the wide flammability limits present a safety concern for hydrogen relative to the other fuels. ** Cloud/Pour Points. These are low-temperature performance measures. The pour point is the temperature at which fuel ceases to flow. As the temperature nears the pour point, fuel becomes more difficult to pump. Pour point is a function of the molecular structure of the fuel components. Naphthenes tend to have low pour points, while paraffins (high cetane) have high ones. The cloud point is somewhat above the pour point (usually 5-10 degrees Fahrenheit above). At this temperature, the fuel becomes cloudy because wax crystals form that can block fuel filters. ------------------ ** "Better Cold-Weather Starts for Biodiesel Fuel" [Some excerpts] When overnight temperatures fall near or below freezing, biodiesel fuels form small, solid, waxy crystals that stick together to form bigger ones. These larger crystals block fuel filters and plug fuel lines. Winterizing causes changes in the makeup of biodiesel fuels that lead to a lower cetane number--as well as a decreased stability during long-term storage that the scientists are also trying to improve. "Unfortunately, harmful exhaust emissions, especially nitrogen oxides, may be expected with a lower cetane number," Read more > http://www.ars.usda.gov/is/AR/archive/apr98/cold0498.htm Would this contribute to worn injector pumps besides solvent characteristics in diesel fuels? ` Biofuel at Journey to Forever: http://journeytoforever.org/biofuel.html Biofuels list archives: http://archive.nnytech.net/ Please do NOT send "unsubscribe" messages to the list address. To unsubscribe, send an email to: [EMAIL PROTECTED] Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
