Excellent references for both gasoline and diesel fuel can be found at www.chevron.com/prodserv/fuels . Click on the Motor Gasoline Technical Review and the Diesel Fuel Technical Review for in depth information about each type of fuel and the refining process. Both documents can be downloaded as a pdf file.
Crude oil is found throughout the world and, thus, varies widely in its characteristics and properties. Some crude oils are light with the consistency of water, and others are heavy with the consistency of molasses. Color, too, varies from a resemblance of weak iced tea to black paint. Generally speaking, light crude oils yield more gasoline than heavier crude oils, which yield more distillate products and asphalt. Two key properties of crude oil are density and sulfur content. The price of crude oil is based largely on these two properties. Heavy crude oils have a high density and are “sour” (have a high sulfur content), require more complex and expensive processing steps than light, sweet crude oils, and are less desirable. Thus, light, sweet crude oils are priced higher. Crude oil consists primarily of carbon and hydrogen along with minor amounts of sulfur. Nitrogen and metals are present in very low quantities. Crude oil is a mixture of about 1000 different molecules. Because of this complexity, the molecules are generally characterized by bulk properties such as gravity and boiling point ranges rather than by discrete molecular structures.
Crude oil flows from less to more developed countries. For the U.S., three out of the top five sources of crude oil (the Persian Gulf, Venezuela, and Nigeria) are considered unstable.
Refineries are complex plants that are capable of producing finished fuels and other hydrocarbon-based products. Refineries utilize crude oil as their primary raw material to produce these products through a series of separation, conversion, purification, and blending processes. As of January 1, 2006, there were 142 refineries in the US with a total capacity of 16.4 million barrels per day. No two refineries are alike in their processing capabilities, nor do any two make products with the exact same composition. Refinery processes can be divided into three basic types: separation, conversion, and upgrading. The most common separation process is distillation. This process separates hydrocarbons based on boiling point but does not change their structure. Conversion processes change the molecular structure of hydrocarbons. Catalytic cracking takes big molecules and “cracks” them into compounds in the gasoline boiling range using heat and a zeolite catalyst. Alkylation combines two gases to make high octane gasoline using an acid catalyst. In reforming, a metal catalyst rearranges the structure of molecules to make high octane gasoline. Upgrading processes improve the quality of hydrocarbons. Hydrotreating removes sulfur and nitrogen compounds using high pressure hydrogen in the presence of a catalyst. Sweetening converts foul smelling mercaptans to disulfides using a catalyst.
The graph shows that U.S. product consumption, and, therefore, refinery production, is geared toward gasoline while European consumption is geared toward diesel fuel. Currently, about 50% of new cars sold in Europe are diesel-powered compared to about 1% in the US.
Fuel coming from the refinery must first be transported to a supply terminal before it can be moved to the retail station. The vast majority of fuel (>70%) moves by pipeline to supply terminals. Other important means of transportation, in order of decreasing importance, are barge (for areas near the coast or on major rivers), railcar, and truck. The supply terminal serves as the bulk storage area for fuel. Trucks transport fuel from the terminal to the retail station. It is at the supply terminal that ethanol and biodiesel are added to the base fuel to make biofuel blends.
“Conventional” refers to standard gasoline that is used in areas not exceeding mandated levels of atmospheric pollutants such as ozone in summer or carbon monoxide in winter . “RFG” (reformulated gasoline) refers to specially formulated federal low emissions gasoline for use in ozone non-attainment areas during the summer. It typically contains 10% ethanol. “California gasoline” refers to low emissions gasoline specifically for use in California. It currently contains 5.5% ethanol but will contain 10% beginning in 2010. State governments have developed low emission gasoline blends tailored to meet their particular emission reduction targets. Collectively, these gasolines are called “boutique fuels”. Examples are “low RVP gasoline” and “clean burning gasoline”. Generally, these fuels are summer gasoline blends with reduced vapor pressure (volatility) for use in areas that nearly exceed the ozone limit but do not require reformulated gasoline. Starting with model year 2007, diesel vehicles have particulate filters that require ultra low sulfur fuel (maximum 15 ppm sulfur) for proper operation. ULSD also can be used in older diesel vehicles and engines. Low sulfur diesel fuel (maximum 500 ppm sulfur) can be used in older engines without particulate filters, and it will be available until June 1, 2010. High sulfur diesel fuel contains over 500 ppm sulfur and is intended for use in older off-road diesel engines. It should never be used in an on-road vehicle. All diesel fuel will become ULSD in 2014.
A map of US gasoline requirements as of June 2006 (courtesy ExxonMobil Corp.). The number of different types of gasoline presents a logistics challenge to the refining industry. The Energy Policy Act of 2005 limits the number of these so-called “boutique fuels” to no more than what were in place in 2005.
The map shows the extensive pipeline system used to distribute fuels. Not only do refiners need to produce gasoline and diesel fuel, but they also must ensure that consumers in all regions are adequately supplied with fuel. In addition to gasoline, pipelines also move diesel fuel and jet fuel. To ensure adequate supply, all fuels are considered to be “fungible”, that is, a gallon from one refinery can be replaced with a gallon from another refinery as long as it meets ASTM specifications. As an example, several oil companies put gasoline produced at their respective refineries in the Houston, TX, area into a common pipeline. The gasoline moves up through the southeastern states all the way to New York City. Along the way, terminals siphon off a portion of the product to supply their respective areas. The gasoline that oil company (refiner) A puts into the pipeline is mixed with gasoline from oil companies B and C. The product company A pulls off the pipeline at a terminal and sells as brand A has not necessarily come from its own refinery. However, the company is still responsible for the quality of the fuel. Fungibility allows for efficient distribution of petroleum products but makes it harder for the oil company to differentiate its product.
The vast majority of transportation fuels, such as gasoline, diesel fuel, and jet fuel, flow through to their destinations via pipeline. The products are segregated by batches and move through the pipeline abutting each other. As the products flow through the pipeline, there will be some mixing of the abutting batches. The region where the batches touch is called the interface, and the mixed product is called “transmix”. In some cases, the mixed region can be put into a storage tank without adversely affecting product quality, while in other cases, the transmix must be segregated into a separate tank. The batches of various products are ordered in such a way as to minimize the volume of transmix. The disposition of each interface must be evaluated on a case by case basis. For example, putting a small amount of RFG premium gasoline into a RFG regular tank would be acceptable, but putting conventional premium into RFG premium would not be acceptable because RFG gasoline must be certified for certain properties above those required for conventional gasoline. In another example, putting a small amount of diesel fuel into conventional gasoline is acceptable (as long as the distillation is not affected) while putting gasoline into diesel fuel is not acceptable because it would cause the flash point to go below the minimum limit (safety concern). In short, transporting fuels via pipeline is a complicated business.
The definition of gasoline is taken from ASTM D 4814, “Specification for Automotive Spark-Ignition Engine Fuel.” The definition notes a number of important points. First, gasoline is very volatile. Although it is mostly a liquid at normal ambient temperatures, it can easily vaporize. This property is necessary for good atomization, vaporization, and subsequent combustion in an engine. Second, gasoline is not a single, pure component such as water or propane. It is a complex mixture of about 200 hydrocarbon molecules, ranging from 4 to 12 carbon atoms, each with its own set of chemical and physical properties. Third, gasoline may contain different additives to enhance performance or to avoid problems. The common additives include detergents, corrosion inhibitors, and antioxidants. Some of these additives are available as aftermarket products, which the consumer can purchase and add directly to the fuel. Third, gasoline is for use in spark-ignition engines. Air and gasoline are mixed in the intake manifold before they enter the combustion chamber. In the chamber, the mixture is ignited by a spark plug. Gasoline is the predominant fuel for spark-ignited engines.
Gasoline must be a vapor in order to burn. Thus, a gasoline’s ability to vaporize is a key property that affects vehicle performance. Gasoline volatility is measured primarily by three tests: vapor pressure at 100 ° F (ASTM D 5191); distillation (ASTM D 86), and temperature at which the vapor to liquid ratio equals 20 (ASTM D 5188). Gasoline volatility increases as: vapor pressure increases, distillation temperature decreases, and temperature for the vapor-liquid ratio of 20 decreases. Gasoline volatility is adjusted seasonally to provide proper vehicle performance. During winter, the emphasis is on providing sufficient volatility to start an engine at low temperature. Vapor pressure is increased during winter by the addition of butane to gasoline, and the distillation profile is altered to produce a more volatile fuel throughout the boiling range. Typical wintertime vapor pressure ranges from 13.5 – 15.0 psi, maximum, depending on location. During summer, vapor pressure of gasoline is reduced by removing butane, and the distillation profile is altered to produce a less volatile fuel throughout the boiling range. The emphasis is on providing lower volatility so that hot restart problems do not occur and evaporative emissions are minimized. Typical summertime vapor pressure ranges from 7.0 – 10.0 psi, maximum, depending on location.
Driveability is defined as the response of a vehicle to throttle position. Good driveability is manifested by ease of starting, smooth idle, smooth acceleration, and the absence of hesitation or surging while cruising. Trained raters are used to evaluate vehicle driveability using a set driving cycle. Parameters measured include start time, idle quality, and smoothness of operation during acceleration and cruise conditions. Malfunctions are rated by severity, and the total number are tallied to obtain a total weighted demerit value. Good driveability fuels have low demerit values.
Antiknock quality, measured by octane number, is the most recognized gasoline property. Normal combustion is initiated by the spark plug. The flame front moves smoothly to the end of the combustion chamber, consuming unburned fuel. Knocking or pinging is the sound produced by abnormal combustion. It occurs when part of the fuel mixture ignites separately from the flame front, causing a rise in cylinder pressure, which results in engine noise we call knock. Knock occurs when the gasoline’s antiknock quality (octane number) is below the engine’s requirement at that moment. Generally, the situation occurs during high load conditions such as hard acceleration or climbing a grade. A gasoline’s antiknock quality is given by octane number. An octane number measurement is based on comparing the test gasoline to reference fuels in standardized, single cylinder, variable compression laboratory engines. There are two types of octane engines: research and motor. Each engine measures the antiknock quality of gasoline under different operating conditions. Reference fuels are mixtures of the pure chemicals isooctane and heptane. The octane numbers of isooctane and heptane have been defined as 100 and 0, respectively. Reference fuel blends are made using the two chemicals to provide a range of octane numbers. For instance, a blend of 90% isooctane and 10% heptane makes a fuel with an octane number of 90. To determine octane number, a technician first runs the test gasoline and adjusts the compression ratio of the engine to produce a knock of standardized intensity. Then the technician runs reference fuels until he finds one whose knock intensity matches that of the test fuel at the set compression ratio. The octane number of the matched reference fuel is the measured octane number for the test fuel.
There are two types of octane engines that measure octane at different engine operation conditions. Consequently, two separate octane measurements are made on different engines to determine a gasoline’s antiknock index. Research octane number (RON) correlates with low speed, mild-knocking conditions. Motor octane (MON) correlates with high speed, high temperature knocking conditions and with part-throttle operation. For a given gasoline, RON is always higher than MON. The antiknock index is posted on gasoline pumps by law and is the average of the RON and MON values. It is typically shown as (R+M)/2. The ASTM test method numbers are D 2699 for research octane and D 2700 for motor octane.
The vast majority of vehicles are designed for unleaded regular gasoline. Some high performance vehicles either recommend or require premium octane fuel. But for vehicles that recommend 87 octane, buying a higher octane gasoline will not improve vehicle performance. Current vehicles have knock sensors that retard the spark advance if knock is detected. Engine noise will be avoided, but a consequence will be a loss of power because spark timing is no longer optimized.
Oxygenates were originally added to gasoline to increase octane. Today they are added largely as a result of federal regulations. The oxygenates allowed in gasoline belong to two classes: alcohols and ethers. Gasoline is limited to 2.7 mass percent oxygen, except when ethanol is used, in which case the limit is 3.5 mass percent. Oxygenates have a lower energy content than hydrocarbons. As a rule of thumb, fuel economy decreases 1% for every 1 mass percent oxygen in the fuel. Ethanol is an alcohol and is now the only oxygenate used in gasoline. Pipelines prohibit shipment of gasoline containing ethanol because of its hydroscopic nature. Thus, ethanol must be blended into gasoline at the terminal. On a volume basis, ethanol can be used up to 10 percent. Ethanol is produced by fermentation of biomass (mostly corn in the US) and is more expensive than gasoline and other oxygenates such as ethers. The Renewable Fuels Standard as part of the Energy Policy Act of 2005 requires that a certain volume of renewable fuel be used every year starting in 2006 and increasing through 2012. Also, ethanol receives favorable federal and state excise tax exemptions. A fuel blender that uses ethanol receives a $0.51/gal tax credit. MTBE (methyl tertiary butyl ether) up to about 2005 was the predominant oxygenate used in gasoline because it is more hydrocarbon-like than ethanol, and gasoline containing it could be shipped by pipeline. On a volume basis, MTBE can be used up to 15 percent. MTBE is slightly soluble in water and not very biodegradable. Controversy over leaking underground gasoline tanks and ground water contamination by MTBE has caused many states to ban its use in gasoline. Liability concerns finally caused some pipelines to ban shipment of gasoline containing MTBE. As a consequence, its presence in US gasoline has disappeared.
A distillation test (ASTM D 86) has been used to measure the boiling range of a petroleum product since the oil industry began. The distillation test is very simple and results in a gross separation of components by boiling point. The distillation graph plots temperature as a function of percent evaporated. For road fuels, the test is done at atmospheric pressure using a specified heating rate. For petroleum fractions with very high boiling points, the distillation is performed at reduced pressure. The graph above shows the distillation range of two gasolines: a blend without ethanol (E0) and a blend with 10% ethanol (E10). Note that 10% ethanol distorts the distillation curve somewhat, creating a plateau between the 30 and 50% evaporated temperatures.
Ten percent ethanol blends are approved by all auto companies and can be used even in most 1980s vintage vehicles. Only flex-fuel vehicles (FFVs) can use blends containing more than 10% ethanol. Methanol is a very corrosive alcohol. Many auto companies in their owner’s manuals prohibit the use of any fuels containing methanol, even in FFVs. Care should be taken not to use aftermarket deicers containing methanol. If gas line freeze-up has occurred, use a product containing isopropanol. Do not use solvent-type chemicals touted as fuel economy improvers. Acetone is currently popular, but it can attack certain elastomers, even some fluorocarbons. Also, the data used to substantiate claims is anecdotal. The U.S. EPA evaluates submitted aftermarket devices and additives free of charge and posts results on its website. A link can also be found on the Federal Trade Commission’s website. To date, no device or additive has shown a statistically significant improvement in fuel economy.
The fuel system components and the engine management system are integrated to deliver a precisely metered quantity of fuel through the fuel injectors. Therefore, deposits on fuel injectors can have a significant detrimental effect on a vehicle’s driveability and emissions. Deposits on intake valves can affect fuel mixture flow into the combustion chamber. They can either impede flow or they can act as a sponge that absorbs fuel during cold start, causing either no start or poor driveability during engine warm-up. Deposits normally form in the combustion chamber. They result in increased NOx emissions and an increase in the engine’s octane appetite. In extreme cases, deposits can cause the piston top to hit the cylinder head, resulting in an annoying noise. Since 1995, EPA has required the use of deposit control additives in all gasoline. Unfortunately, the performance standards set by EPA are minimal and, in many cases, do not provide adequate protection against deposit formation. Deposit control additives are polymeric surfactants, which at low levels act to keep the intake system clean and at higher levels act to clean up existing deposits. TOP TIER Detergent Gasoline is a new class of gasoline with enhanced detergency. It meets new, voluntary deposit control standards developed by four automotive companies (Audi, BMW, GM, Honda, Toyota, and Volkswagen) that exceed the detergent requirements imposed by the EPA. TOP TIER Detergent Gasoline will help keep engines cleaner than gasoline containing the “Lowest Additive Concentration” set by the EPA. Clean engines provide optimal fuel economy and performance and reduced emissions. Also, use of TOP TIER Detergent Gasoline will help reduce deposit related concerns.
In order to meet the TOP TIER standard, more deposit control additive is needed than what is required by EPA – about 2.5 times more. The intake valves photos show the benefit of using higher levels of additive in the same base gasoline in a test run according to ASTM D 6201. This test uses a Ford 2.3 L engine run for 100 hours under specified conditions, approximating 5,000 miles.
Diesel fuel is unique in that upon compression the material will auto-ignite. In a diesel engine, un-throttled air is forced into the combustion chamber. As the air is being compressed by the piston and heated to high temperature, diesel fuel is injected into the chamber at about 20,000-25,000 psi, where it ignites without the aid of a spark plug. Diesel fuel is a refinery product with a higher distillation range than gasoline. It is comprised of molecules ranging from 10-22 carbon atoms. Because diesel fuel is heavier and is more dense that gasoline, it contains more energy per gallon (130,000 vs. 114,000 BTU/gal net heating value). Kerosene, grade 1-D, can also be used in compression-ignition engines. It boils between gasoline and diesel fuel. Thus, it has less heating value than grade 2-D but has better flow properties at very cold temperatures. ASTM D 975 specifies the properties of diesel fuel.
The graph above shows the distillation range of gasoline and diesel fuel. A more volatile product, such as gasoline, appears at the lower portion of the graph whereas diesel fuel, which is much less volatile, appears at the upper portion of the graph. Petroleum products encompass a wide range of distillation temperatures, resulting in overlap between products. For instance, the tail end of gasoline is in the distillation range of the front end of diesel fuel.
Diesel fuel typically contains up to 3% wax. These molecules represent the tail-end of the distillation curve. They are in solution at room temperature, but as the fuel cools, they first cause an increase in fuel viscosity, and finally, they precipitate from solution. Solid wax particles coat the fuel filter, preventing fuel flow, causing the engine to starve for fuel. A typical remedy in wintertime in the U.S. is to blend up to 50% kerosene (1-D) into diesel fuel to make it less viscous and to dilute the wax molecules. In Arctic regions, straight kerosene is used year round. Unfortunately, kerosene provides less heating value than diesel fuel, which results in poorer fuel economy. This becomes a big concern for the trucking industry, and, therefore, they use winter-blended diesel fuel for as short a time a practicable. Additives are often added to diesel fuel instead of kerosene to improve cold flow properties. They do not prevent wax crystals from forming but rather act to provide many nucleation sites so that the agglomerated crystals on the filter are small enough to allow fuel to pass through. Additives, however, tend to be expensive, and their performance may not be consistent in different base fuels. The fuel purchaser must decide whether kerosene blending, additives, or a combination of both are the most cost effective remedy.
Cetane number is a measure of the ability of the fuel to ignite on compression. The shorter the ignition delay after fuel is injected into the chamber, the higher the cetane number of the fuel. Cetane number is important in diesel startup performance, especially at low temperature. Inadequate cetane results in hard starting, rough operation, noise and white smoke from unburned fuel. These symptoms disappear once the vehicle warms up. Cetane number and octane number are inversely related: as cetane goes up, octane goes down. The cetane number is measured by a rating procedure using a standardized laboratory test engine (ASTM D 613). ASTM D 975 specifies a minimum cetane number of 40; the minimum in Europe is 51. The average cetane number of U.S. diesel fuel is about 44, compared to European diesel fuel which averages about 53. Refiners can increase cetane number through process and blending variations or through cetane improver additives. Actual cetane number of diesel fuel is rarely measured by the refiner. Instead, a predictive number called cetane index has been developed to approximate cetane number based on a fuel’s density and distillation properties. Cetane index is preferred by the refiner because it is much simpler and less expensive to run than cetane number. Both ASTM D 4737 and D 976 are use to calculate cetane index. The minimum cetane index value by both methods is 40. EPA requires reporting cetane index using D 976 while ASTM regards D 4737 as the official substitute for cetane number. In reality, refiners are required to calculate cetane index using both methods. Note if additives are used, the increase in cetane number can only be measured using a cetane engine; the cetane index calculation cannot comprehend the effect of additives.
“Alternative fuels” have been defined by federal legislation as any non-petroleum based fuel. Alternative fuels include: Methanol (M85) consists of nominally 85% methanol and 15% gasoline. Neat Methanol (M100) is 100% methanol. Methanol has a much lower energy density than gasoline and is corrosive. Ethanol (E85) consists nominally of 85% ethanol and 15% gasoline. Neat ethanol (E100) is 100% ethanol. The current manufacturing process, fermentation followed by distillation of corn and sugar, is costly. Ethanol, or grain alcohol, has less energy density than gasoline. Liquefied natural gas or compressed natural gas (LNG or CNG) must be kept under high pressure in large heavy tanks to provide sufficient range, but is inexpensive and abundant. Liquefied petroleum gas (LPG or Propane). Propane provides only marginally better emissions performance, and the propane distribution/supply infrastructure is limited.
A good reference for E85, Handbook for Handling, Storing, and Dispensing E85 , can be found at www. eere.energy.gov/afdc/ . E85 is a blend of 70-83 volume percent ethanol and hydrocarbons in the gasoline boiling range. The percent ethanol depends on the desired vapor pressure. Ethanol itself has a low vapor pressure (~2 psi). To increase the ease of starting in cold months, more hydrocarbons are added to increase the vapor pressure of the blend. Since ethanol contains an oxygen atom, the air/fuel ratio is lower than for gasoline. As a consequence, injectors must be larger and able to flow more fuel to compensate for the increased oxygen content of the fuel. E85 has a high octane value (~96-98) and could provide a 3-5% power increase if the engine was optimized for it. Unfortunately, flex-fueled vehicles must be able to run on both gasoline and E85 and cannot take advantage of E85’s higher octane value. The presence of oxygen in ethanol results in a lower net heating value for E85 compared to gasoline (12,500 vs. 18,500 BTU/lb).
E85 vehicles have been around since the early 2000’s. The recent interest in E85 stems primarily from the sharp increase in gasoline prices and the desire to wean the U.S. from foreign oil. E85 is attractive because it is a home-grown fuel that can reduce dependence on petroleum, it is renewable, and it can significantly reduce CO 2 emissions.
The information indicates that one vehicle produces a significant amount of CO 2 . The assumptions are the vehicle is driven 15,000 miles per year and achieves 25 mpg.
The pictorials represents a wells-to-pump analysis generated by Argonne National Laboratory on the fossil energy needed to produce 1 million BTU’s of energy from ethanol and gasoline. ANL considered all the energy inputs required in each step to make the fuels, such as procuring raw material, processing raw material into the final product, and transporting the fuel to the retail pump. The results show that producing ethanol requires less energy than it ultimately provides while producing gasoline requires more energy than it ultimately provides.
Data from Argonne National Laboratory show the percent reduction in CO 2 emissions from various ethanol blends. An explanation of the x-axis labels is as follows: E10 – ethanol derived from a dry mill process run in a gasoline vehicle as a 10% blend. E10 cell – ethanol derived from cellulose run in a gasoline vehicle as a 10% blend. E85 – ethanol derived from a dry mill process run in a flex-fuel vehicle as an 85% blend. E85 cell. – ethanol derived from cellulose run in a flex-fuel vehicle as an 85% blend. The reduction in greenhouse gas emissions is modest with E10 but significant with E85. Cellulosic ethanol has the potential to dramatically decrease CO 2 emissions if the technology proves efficient and scalable.
The biggest disadvantage of E85 is its lack of availability. The number of stations offering it amounts to less than 1% of the total number of gasoline stations in the U.S., and most of those are concentrated in the Midwest. Also, some stations that offer E85 sell only to commercial or government fleets. E85 has a lower energy content than gasoline, and according to EPA figures, offers about 25% less fuel economy than gasoline. Thus, E85 needs to be priced accordingly to account for this loss. Unfortunately, this is typically not the case, the exception being pricing found in farming communities. Even if the price is right, the question becomes whether the consumer will accept more frequent fill-ups. Finally, while the federal government and some states are setting policy to force more ethanol usage, there is a concern that increased use of ethanol may divert crops from food to fuel. Early studies on the food versus fuel controversy have tended to only reinforce the positions of the respective parties funding them, and the true impact won’t be known until ethanol has saturated the gasoline market, which will be in 2010 – 2015.
A good reference, Biodiesel Handling and Use Guidelines , can be found at: www.nrel.gov/vehiclesandfuels/. Oils and fats are triglycerides that contain three long chain fatty acids connected to the glycerin backbone. The fatty acids are typically 16-20 carbons in length. Biodiesel is made by reacting vegetable oils, used cooking oils, or fats with caustic in the presence of an alcohol, typically methanol. When methanol is used, the finished product is a fatty acid methyl ester (FAME). A by-product is glycerin, which must be removed.
Pure biodiesel is designated as B100. Blends with diesel fuel have the designation BX, where X represents the percent biodiesel in the blend. Soy beans are the primary feedstock in the U.S. followed by yellow grease (recycled cooking oil) from restaurants. In Europe, rapeseed is the primary feedstock followed by sunflower. Asia-Pacific uses mainly palm oil. In the U.S. there is an ASTM specification for B100 (D 6751) but currently none for biodiesel blends. In Europe, B5 is considered the same as standard diesel fuel. Because biodiesel tends to pick up water much more readily than diesel fuel, biodiesel blends cannot be transported by pipeline and, therefore, must be made at a supply terminal. All vehicle manufacturers allow the use of up to B5, and some allow higher blends.
Biodiesel has the advantage of being a renewable energy source that has much lower life-cycle CO 2 emissions than diesel fuel. Biodiesel also has higher cetane and better lubricity than diesel fuel and lower HC, CO, and particulate emissions. However, there is some evidence that biodiesel may increase NO x emissions, especially in older engines. The U.S. EPA and the California Air Resources Board will be investigating the effect of biodiesel on NO x emissions in newer engines shortly.
The biggest disadvantage of biodiesel is its propensity to oxidize rapidly and form deposits. Oxidation can be controlled by additives, but unfortunately the biodiesel industry does not typically use them. Biodiesel has a cloud point that is 10 °F or more higher than diesel fuel. Thus, winter operation with biodiesel blends must be done cautiously. The higher cloud point can be overcome by using additives or by making blends with kerosene instead of standard diesel fuel. The polar nature of biodiesel make it more prone to entrain water, which can lead to engine corrosion. There is a slight loss in fuel economy with biodiesel blend. With B5, the difference is not noticeable, and even with B20, the loss is small. Without government financial support, biodiesel would not have a future. Currently, biodiesel blenders receive a federal excise tax credit of a penny per percent biodiesel derived from vegetable oil and half a penny per percent for biodiesel derived from recycled oil (yellow grease).
Oils and fats can be reacted with hydrogen to form hydrocarbons that fall in the diesel fuel boiling range. The glycerin from the triglyceride backbone is converted to propane and oxygen is converted to water. The final product has been designated as ‘renewable diesel’ or ‘green diesel’. Its main advantage is the fuel is more like standard diesel fuel than biodiesel. It also has a higher cetane value than biodiesel. The disadvantages are that this fuel requires more capital investment because of the necessity to use high pressure hydrogen. Thus, this process is relegated to a refinery setting. Renewable diesel also has poorer lubricity than biodiesel, and the cloud point tends to be higher than for diesel fuel. Like biodiesel, renewable diesel should be thought of as a way to extend the supply of diesel fuel, not as a stand alone fuel.
(11/29) Road Vehicle Fuels
Michigan State University College of Engineering Fall 2007 – ME 444 Andrew Buczynsky Fuels and Lubricants Department General Motors Powertrain Fuels for Road Vehicles Basics of Gasoline, Diesel Fuel, E85, and Biodiesel
Petroleum <ul><li>Source of fuels </li></ul><ul><ul><li>Petroleum-based fuels come from crude oil </li></ul></ul><ul><ul><li>Crude oil varies depending where in the world it comes from </li></ul></ul>
Flow of Crude Oil Map: API, Understanding Today’s Energy Needs. Crude oil import data: EIA Three-quarters of U.S. crude oil imports come from 5 locations: Persian Gulf (21%), Canada (17%), Mexico (16%), Venezuela (11%), Nigeria (10%).
Regional Consumption by Fuel Type Source: BP Statistical Review of World Energy June 2007 Lt dist = Aviation and motor gasoline. Mid dist = jet fuel, kerosene, and diesel fuel. Hvy dist = Marine bunker fuel and crude oil used as fuel. Other = refinery gas, LPG, coke, lubricants, solvents, bitumen, wax.
Flow From Refinery to Pump Pipeline, barge railcar, truck Supply terminal Retail station Truck Ethanol Biodiesel
States Have Developed “Boutique” Fuel Recipes to Avoid RFG
U.S. Pipeline Distribution System Gasoline, diesel fuel and jet fuel move in the same pipelines Fuels are fungible (interchangeable) products
Pipeline Primer <ul><li>Different product batches are “pushed” through the system abutting each other. The mixing zones between batches are called interfaces. </li></ul>RFG reg. ULSD Jet fuel HSD Conv. ULR RFG prem. RFG reg. Product flow Interfaces
Gasoline <ul><li>Defined by ASTM D 4814 </li></ul><ul><ul><li>“ a volatile mixture of liquid hydrocarbons, generally containing small amounts of additives, suitable for use as a fuel in spark-ignition, internal combustion engines.” </li></ul></ul>
Volatility <ul><li>The tendency of a fuel to vaporize </li></ul><ul><ul><li>Measured by </li></ul></ul><ul><ul><ul><li>Vapor pressure </li></ul></ul></ul><ul><ul><ul><li>Distillation </li></ul></ul></ul><ul><ul><ul><li>Vapor-liquid ratio </li></ul></ul></ul><ul><li>Gasoline volatility is adjusted seasonally </li></ul><ul><ul><li>Winter: cold start </li></ul></ul><ul><ul><li>Summer: hot restart, evaporative emissions </li></ul></ul>
Driveability <ul><li>Volatility affects driveability </li></ul><ul><ul><li>Driveability: the ability of a vehicle to operate satisfactorily under normal driving conditions: </li></ul></ul><ul><ul><ul><li>Ease of starting </li></ul></ul></ul><ul><ul><ul><li>Smooth idle </li></ul></ul></ul><ul><ul><ul><li>Smooth acceleration and cruise </li></ul></ul></ul><ul><ul><li>Driveability is quantified by trained raters using a set driving protocol </li></ul></ul><ul><ul><ul><li>Lower demerits mean better driveability </li></ul></ul></ul>
Antiknock Quality <ul><li>Ability of a gasoline to resist knocking </li></ul><ul><ul><li>Knock – engine noise produced by rapid pressure rise as a result of abnormal combustion </li></ul></ul><ul><li>Expressed as octane number </li></ul><ul><ul><li>Two laboratory test methods measure octane number </li></ul></ul><ul><ul><ul><li>Both use single cylinder, variable compression engines </li></ul></ul></ul><ul><ul><ul><li>Each uses different operation conditions </li></ul></ul></ul>
Octane Number <ul><li>RON (R): Research Octane Number </li></ul><ul><li>MON (M): Motor Octane Number </li></ul><ul><li>Antiknock Index: (R+M)/2 </li></ul>87 MINIMUM OCTANE RATING (R+M)/2 METHOD
Octane Grades <ul><li>Current offerings </li></ul><ul><ul><li>Regular 87 (R+M)/2: sufficient for >90+% of vehicles </li></ul></ul><ul><ul><li>Midgrade 89 (R+M)/2: for vehicles with a higher octane requirement </li></ul></ul><ul><ul><li>Premium 91 (R+M)/2: for performance vehicles </li></ul></ul><ul><li>Regular versus premium </li></ul><ul><ul><li>Octane higher than required to prevent audible knock or knock sensor activity is a waste of money </li></ul></ul>
Oxygenates <ul><li>Oxygenates are fuel molecules that contain oxygen </li></ul><ul><ul><li>Ethanol (EtOH) is the only oxygenate now used in gasoline </li></ul></ul><ul><ul><ul><li>Limited to 10 volume % in gasoline </li></ul></ul></ul><ul><ul><ul><li>About 50% of U.S. gasoline contains 10% ethanol </li></ul></ul></ul><ul><ul><li>Ethers were formerly used but have been banned by many states </li></ul></ul><ul><ul><li>Biodiesel is used in diesel fuel </li></ul></ul><ul><li>Renewable Fuels Standard (RFS) </li></ul><ul><ul><li>Requires a certain volume of renewable fuel be used </li></ul></ul><ul><ul><li>By about 2010-2015, all U.S. gasoline will contain 10% ethanol </li></ul></ul>
Oxygenate Use in Vehicles <ul><li>10% ethanol blends </li></ul><ul><ul><li>Compatible with all vehicles </li></ul></ul><ul><li>Flex-fuel vehicles </li></ul><ul><ul><li>Can run on up to 85% ethanol </li></ul></ul><ul><ul><li>Check your owners’ manual to know if you have a FFV </li></ul></ul><ul><ul><li>Do not use more than 10% ethanol in a standard vehicle </li></ul></ul><ul><li>Never put methanol into your vehicle </li></ul><ul><ul><li>That includes de-icers in the winter </li></ul></ul><ul><ul><li>That includes FFVs </li></ul></ul><ul><li>Solvent chemicals touted to improve fuel economy </li></ul><ul><ul><li>Can be aggressive toward elastomers plastics </li></ul></ul>
Comparison of TOP TIER and EPA Additive Concentrations Base Fuel + EPA detergent concentration Base fuel + TOP TIER detergent concentration After 100-hrs in Ford 2.3 L engine
Diesel Fuel <ul><li>A liquid hydrocarbon mixture, for use in compression-ignition engines </li></ul><ul><ul><li>ASTM D 975 </li></ul></ul><ul><ul><li>Types of compression-ignition fuels </li></ul></ul><ul><ul><ul><li>Diesel fuel – grade 2-D </li></ul></ul></ul><ul><ul><ul><li>Kerosene – grade 1-D </li></ul></ul></ul>
Distillation Comparison of Gasoline and Diesel Fuel
Cold Flow Properties <ul><li>Diesel fuel can gel at low temperatures </li></ul><ul><ul><li>Diesel fuel contains wax molecules </li></ul></ul><ul><ul><li>Wax causes the fuel to become more viscous as temperature drops </li></ul></ul><ul><ul><li>Wax also will precipitate from the fuel at low temperatures and plug fuel filters </li></ul></ul><ul><ul><li>Remedy is to blend kerosene to improve cold handling properties or use additives </li></ul></ul><ul><ul><ul><li>Kerosene results in a fuel economy debit </li></ul></ul></ul><ul><ul><ul><li>Additives are expensive and their performance depends on the base fuel </li></ul></ul></ul>
Cetane Number <ul><li>A measure of how readily a fuel auto-ignites </li></ul><ul><ul><li>A high cetane number is desirable </li></ul></ul><ul><ul><ul><li>Indicates short ignition delay after injection </li></ul></ul></ul><ul><ul><ul><li>Makes starting easier, reduces white smoke and engine noise </li></ul></ul></ul><ul><ul><li>Cetane number of diesel fuel in the U.S. is poor compared to the rest of the world </li></ul></ul><ul><ul><ul><li>ASTM 975 specifies a minimum of 40 </li></ul></ul></ul><ul><ul><ul><li>Europe specifies a minimum of 51 </li></ul></ul></ul><ul><ul><li>Cetane index is a calculated value used to approximate cetane number </li></ul></ul><ul><ul><ul><li>Based on density and distillation temperatures </li></ul></ul></ul>
Alternative Fuels <ul><li>Any non-petroleum based fuel by legislative definition . </li></ul><ul><ul><li>Alternative fuels currently of primary interest </li></ul></ul><ul><ul><ul><li>Ethanol (E85) </li></ul></ul></ul><ul><ul><ul><li>Biodiesel </li></ul></ul></ul><ul><ul><li>Others alternative fuels </li></ul></ul><ul><ul><ul><li>M85 </li></ul></ul></ul><ul><ul><ul><li>M100 </li></ul></ul></ul><ul><ul><ul><li>E100 </li></ul></ul></ul><ul><ul><ul><li>LPG </li></ul></ul></ul><ul><ul><ul><li>CNG </li></ul></ul></ul>
E85 <ul><li>70-83 volume % denatured ethanol blended with hydrocarbons </li></ul><ul><ul><li>Controlling specification is ASTM D 5798 </li></ul></ul><ul><ul><ul><li>Based on early 1990s vintage vehicles </li></ul></ul></ul><ul><ul><ul><li>Currently undergoing extensive review </li></ul></ul></ul><ul><ul><li>Ethanol content controlled by desired volatility </li></ul></ul><ul><ul><ul><li>Ethanol has a low vapor pressure </li></ul></ul></ul><ul><ul><ul><li>Less ethanol in winter to ensure good start-up </li></ul></ul></ul><ul><ul><li>Stoichiometric air/fuel ratio is 10 compared to 14.7 for gasoline </li></ul></ul><ul><ul><li>E85 has (R+M)/2 octane value of about 96-98 </li></ul></ul><ul><ul><li>Lower heating value than gasoline (12,500 BTU/lb vs. 18,500 BTU/lb) </li></ul></ul>
Benefits of E85 <ul><li>Reduces dependence on foreign oil </li></ul><ul><li>Renewable fuel </li></ul><ul><li>Reduces CO 2 (greenhouse gas) emissions </li></ul>
Carbon Dioxide in Perspective 600 gallons gasoline per year Creates ~12,000 lbs CO 2 Requires 240 trees to extract the CO 2 Source: Automotive News
Energy to Produce Ethanol vs. Gasoline Source: Argonne National Laboratory
Disadvantage of E85 <ul><li>Only 1,252 E85 stations exist nationwide as of August 1, 2007 (some stations are for private fleet vehicles only) </li></ul><ul><ul><li>Compared to more than 150,000 for gasoline* </li></ul></ul><ul><ul><ul><li>317 in Minnesota </li></ul></ul></ul><ul><ul><ul><li>151 in Illinois </li></ul></ul></ul><ul><ul><ul><li>49 in Michigan </li></ul></ul></ul><ul><ul><ul><li>5 in California </li></ul></ul></ul><ul><li>Price is still not competitive in many areas </li></ul><ul><li>Lower fuel economy </li></ul><ul><li>Food versus fuel controversy </li></ul>
Biodiesel Oil or Fat Soybean Corn Canola Cottonseed Sunflower Beef tallow Pork lard Recycled cooking oils Catalyst Sodium hydroxide Potassium hydroxide Fatty acid methyl ester (FAME or biodiesel) + Glycerin (removed) <ul><ul><li>Made by a chemical process using vegetable or used cooking oils, animal fat, or grease as starting material. Oils or fats that have not undergone the chemical process are not biodiesel. </li></ul></ul>+ Alcohol Methanol
Biodiesel <ul><li>Biodiesel blends are designated B___ </li></ul><ul><ul><li>5% biodiesel is B5 </li></ul></ul><ul><ul><li>20% biodiesel is B20 </li></ul></ul><ul><ul><li>100% biodiesel is B100 </li></ul></ul><ul><li>B100 in U.S. comes primarily from soy beans </li></ul><ul><ul><li>Yellow grease is a secondary source </li></ul></ul><ul><li>B100 in Europe comes primarily from rape seed </li></ul><ul><ul><li>B5 is considered standard diesel fuel </li></ul></ul><ul><li>Biodiesel blends are made at a supply terminal, not at a refinery </li></ul>
Advantages of Biodiesel <ul><li>Renewable energy source </li></ul><ul><li>Reduces CO 2 life-cycle emissions by 78% compared to diesel fuel </li></ul><ul><li>Improves cetane and lubricity of diesel fuel </li></ul><ul><li>Improves most regulated emissions </li></ul>
Disadvantages of Biodiesel <ul><li>Can oxidize (become rancid) </li></ul><ul><ul><li>Results in gums, deposits, and acids </li></ul></ul><ul><li>Has poor cold temperature properties </li></ul><ul><li>Entrains more water than diesel fuel </li></ul><ul><li>May increase NOx emissions </li></ul><ul><li>Heating value about ~10% lower compared to 2-D </li></ul><ul><ul><li>B20 users experience a 1-2% loss in fuel economy </li></ul></ul><ul><li>Requires tax incentives to be competitive </li></ul>
Hydrogenated Biodiesel <ul><li>Also called ‘renewable diesel’ or ‘green diesel’ </li></ul><ul><li>Hydrogen is used to convert fats and oils to hydrocarbons </li></ul><ul><li>Advantage is a product more like standard diesel fuel </li></ul><ul><li>Disadvantages are high capital requirement and poor lubricity </li></ul>Source: OMV Refining and Marketing CH 3 (CH 2 ) 16 COO CH 2 CH 3 (CH 2 ) 16 COO CH CH 3 (CH 2 ) 16 COO CH 2 3 n-C 18 + 1 C 3 H 8 + 6 H 2 0 + H 2