Diesel Fuels - Goodheart
Contents
1. fuel can affect the operation of the engine If an engine is not developing the proper horsepower an improper grade of diesel fuel could be the cause An easy way to confirm this is to use a diesel fuel quality tester such as shown in Figure 14 3 Diesel Fuel Properties In a diesel engine fuel system the fuel itself performs three functions It supplies chemical energy to be trans formed into mechanical energy lubricates precision parts in the fuel system components and cools metal surfaces operating in conditions of friction The properties or characteristics of diesel fuel must meet these three if the engine is to perform with reliability This sample chapter is for review purposes only Copyright The Goodheart Willcox Co Inc All rights reserved Chapter 14 Figure 14 3 A typical diesel fuel quality tester Kent Moore Tools Fuel processors as well as engine manufacturers run lab oratory tests on all fuel used in diesel engines These mea sured properties give a good indication of the way the fuel will perform however there is no real substitute for an actual engine test The major diesel fuel properties affecting engine performance are Heat value Specific gravity Flash point Volatility Cetane number rating Pour point Cloud point Viscosity Carbon residue Sulfur content Fungus and bacterial contaminants Oxidation and water OUUUUUUUOOUOUDU Heat Value The heat v2. will need to meet a limit of 15 ppm sulfur and in 2012 locomotive and marine LM diesel fuel will also be regu lated at 15 ppm Fungus and Bacterial Contaminants Fungus and bacteria are the most common contami nants found in diesel fuels Fungus and bacteria live in the 308 water and feed on the hydrocarbons found in diesel fuel These contaminants are called hydrocarbon utilizing microorganisms HUM HUM will soread through a fuel system where moisture or trace amounts of water are pre sent The resulting bacterial problems can shorten engine filter life Draining the fuel system will reduce HUM activity but will not eliminate it The only way to eliminate HUM growth entirely is to treat the fuel system with a biocide Oxidation and Water Precipitants and particulates are noncombustible materials formed when either two incompatible fuels are mixed or when a fuel oxidizes Oxidation can occur when an unstable fuel circulates through a diesel engine Precipitants and particulates will normally settle out in low or slow flow areas of the fuel system or become part of the tank s bottom sludge Both can get mixed into the fuel system during fuel delivery and can plug fuel filters Water causes the greatest concem because it is the most common form of diesel fuel contaminant Water is found in the fuel system in two forms free and dissolved Most diesel fuels contain some dissolved moisture Diesel fuel has a saturation level of
3. of low sulfur diesel fuel as well as refor mulation procedures diesel engines will be performing well into the 21st century Total monoxide hydrocarbons grams bhp hr grams bhp hr 1 Diesel 20 Biodiesel 20 Biodiesel and catalytic converter Figure 14 12 In the future biodiesel fuels can play a role in reducing exhaust emissions National Soy Diesel Development Board This sample chapter is for review purposes only Copyright The Goodheart Willcox Co Inc All rights reserved Chapter 14 Diese Fuels Summary Only two recommended grades of diesel fuel are con sidered acceptable for use in high speed trucks and buses in North America These are the number 1D and number 2D classifications Grade 1D is generally the most refined and volatile diesel fuel available It is a premium quality fuel used in high rom engines requiring frequent changes in load and speed Grade 2D is more widely used in truck fleets due to its greater heat value per gallon particularly in warm to moderate climates Diesel fuels are blended on a seasonal and geo graphical basis to satisfy anticipated temperature condi tions In a diesel engine fuel system the fuel supplied chemical energy is transformed into mechanical energy Diesel fuel also cools and lubricates precision parts in the fuel system The heat value of fuel is a general indication of how heat energy is supplied to an engine and thus how well the en
4. STM Each individual refiner and supplier attempts to pro duce diesel fuels that meet as closely as possible with ASTM and American Petroleum Institute API standards Figure 14 2 Depending on the crude oil source the diesel fuel end product may be on either the high or low end of the prescribed heat energy scale in Btus per gallon This is why individual diesel fuels grades may vary slightly from one supplier to another Grade 1D is generally the most refined and volatile diesel fuel available It is a premium fuel used in high rom engines requiring frequent changes in load and speed Grade 2D is more widely used in truck fleets due to its greater heat value per gallon particularly in warm to moderate climates Although Grade 1D fuel has better properties for cold 303 Condenser a Reflux Crude oil heater lt Steam lt Steam N Heat exchanger JH a gt as YY Reboiler heater Gases Gasoline Kerosene Cooler Diesel fuel Diesel Technology Long residue lube oil feedstock Crude oil Figure 14 1 A fractionating column is used to separate crude oil into the various hydrocarbon products As the vaporized products rise in the tower they settle onto trays at different levels and are then piped out to other equipment for further refining Allis Chalmers Engine Div General Fuel Classification BTU Gal average Gravity API Flash point minimum F C Viscosity kine
5. This sample chapter is for review purposes only Copyright The Goodheart Willcox Co Inc All rights reserved After studying this chapter you will be able to Explain diesel fuel grades Discuss fuel properties and characteristics Explain the reason for the use of fuel additives Describe the proper procedures for handling and storage of diesel fuel Name the various alternative fuels and their properties All engines have a few things in common One of them is that they all need fuel in order to operate Most mobile and stationary engines use fuels derived from crude oil Diesel engines use several variations of diesel fuel depending on their application In this chapter you will learn about the dif ferent types of diesel fuel used in diesel engines Hydrocarbon Fuels The liquid fuel used to operate diesel engines is obtained from crude oil Crude oil consists of a mixture of hydrocarbons hydrogen and carbon and compounds such as benzene petane hexane heptane toluene propane and butane These compounds have different relative volatility points because they will vaporize or flash at different temperatures Hydrocarbon fuels are sep arated in a fractionating column As crude oil is heated these hydrocarbons are given off as a vapor Figure 14 1 After the natural gas is vapor ized from the crude oil the applied temperature is raised and the hydrocarbon with the next highest vapor point is obtained The
6. acteristics Therefore viscosity is a very important consideration when selecting a diesel fuel Carbon Residue Ash or carbon residue is the deposit left in the com bustion chamber due to incomplete combustion or the use of fuels made from residual blends It can be measured in the laboratory by heating a measured fuel sample in a closed container in the absence of air Carbon residue is the final product that remains in the container after heating This product is then expressed as a percentage by weight of the original sample The amount of carbon residue considered acceptable in diesel fuel oil varies depending on the combustion chamber design the injector adjustments and the general condition of the engine This amountis generally more critical in small high speed engines than in large Sow speed industrial engines Soot ash which originates from either additives or the crude oil itself also causes wear of fuel injection compo nents the pistons and the piston rings Standard require ments allow for a maximum of 001 soot ash content Due to air quality concerns future legislation may further limit the amount of soot ash a diesel engine can produce Sulfur Content The wear of pistons rings and cylinders in a diesel engine generally increases when there is an excessive amount of sulfur in the fuel Excess sulfur content also Good Poor spray pattern spray pattern Figure 14 5 Proper fuel viscosity results in a g
7. alue of fuel is a general indication of how heat energy is supplied to an engine and how well the engine converts heat energy into work The heat value can be found by testing with a calorimeter With this test a pre measured amount of fuel is burned and the amount of heat emitted is carefully measured in Btus per pound of fuel A British thermal unit Btu is the amount of heat required to raise the temperature of one pound of water one degree Fahrenheit The metric equivalent of this unit is Known as a joule To convert Btus into joules multiply by 1054 8 Specific Gravity The specific gravity of fuel is a ratio of the fuel den sity to the density of water It is measured using a hydrom eter Specific gravity affects the fuel s spray penetration as it is injected into the combustion chamber Because water is the standard it has a specific gravity of one Since oil floats on water a diesel fuel s specific gravity is always less than one Diesel fuel s specific gravity ranges from 0 8 to 0 94 Specific gravity is also a factor in measuring the heat value of the fuel In general heavier fuels usually have a greater heat value per gallon Btus than lighter fuels Thus specific gravity is a good indicator of the amount of heat Btus available in a given amount of fuel The American Petroleum Institute API employs another scale to determine specific gravity Water has a specific gravity of 20 on the API gravity scale Ten is the lo
8. blending 2 diesel fuel with kerosene Fuel suppliers will often do this themselves and market it as winter fuel Although this fuel will be more viscous at lower temperatures its performance will stll vary depending on where it was purchased A 40 60 blend in one area may have a higher cloud point that a 40 60 blend in another A fuel additive with a cloud point depressant will have limited effect At most it will lower the cloud point by 3 4 Pour Point Pour point is another common way of measuring a diesel fuel s performance in cold weather It is the min imum temperature at which fuel can flow and is expressed as the temperature 5 F 8 8 C above the level at which the oil becomes solid or refuses to flow The pour point aver ages about 10 lower than the cloud point Fuel treated with special additives called flow improvers or wax modi fiers keep the wax crystals from forming clumps and choking fuel lines They will generally give satisfactory per formance at 9 lower than untreated fuel However fuel improvers do not have any impact on the fuel s cloud point since they do not prevent the formation of wax or paraffin crystals themselves Viscosity Viscosity or stiffness is the property of a diesel fuel that resists the force which causes the fluid to flow It is related closely to specific gravity and pour point Two common methods of measuring viscosity are the Saybolt test and the kinematic centistokes test Bot
9. cetane number required by most on highway vehicles cetane improvers are added to the blends The lower cetane compounds are less responsive to these improvers than the higher cetane pareffin fuels Octane 100 90 80 Slow burning 70 Fast burning 30 40 50 Cetane Figure 14 4 Comparison of the relationship between octane and cetane Note that as the cetane number increases the burn rate increases The improvers promote early uniform ignition of fuel and prevent high pressure increases in the combustion cycle Depending on the amount of cetane components in the base fuel typical alkyl nitrate additive treatment can increase cetane by three to five numbers 1 1000 ratio With high natural cetane premium base fuels containing a high percentage of paraffins and a 1 500 alkyl nitrate treatment ration cetane may increase as much as seven numbers Most improvers contain alkyl nitrates which break down readily to provide extra oxygen for combustion They also break down and oxidize fuel in storage However they also generate organic particulates water and sludge all of which degrade fuel quality Recently several new cetane improvers or reformulaters without alkyl nitrates have been used and properly blended will improve oxidation stability while providing a cetane increase of two to five increments It is only recently that engineers have learned how important the cetane level is in meeting the emissions equat
10. eakage problem O The visible leakage of fuel from a line during operation and shutdown O The opening in a suction line or fiting which pulls foreign material into the system during operation and may or may not present a visible leak during shut down Visible leakage should be stopped as soon as it is dis covered Loss of flow volume generally means a loss of pressure The leak which allows fuel contamination by pulling in air water or dirt is more difficult to locate and can be more damaging Foreign materials such as air sed iment dirt and water present problems and can enter the fuel system in various ways Air Air drawn into the fuel system may make pick up of fuel much more difficult or prevent it entirely In addition it may show up as Q Low power QO Gear pump wear OQ Rough operation OQO Soft or non responsive throttle Air enters the fuel in any one or more of the following ways O Suction leaks lines fittings filters or tank Q Fuel turbulence especially when coupled with poor tank venting Q Fuel pick up point near retum O Combustion gases entering injector This sample chapter is for review purposes only Copyright The Goodheart Willcox Co Inc All rights reserved Chapter 14 Diesel Fuels Dirt Dirt is as damaging to moving parts in the fuel system as itis in any other part of the engine Dirt can Q Clog filters Q Abrade metal surfaces Q Increase combustion chamber dep
11. etermine the ignition quality of the fuel oil Diesel fuel oil is injected into the combustion chamber in liquid form The fuel must then be able to vaporize quickly and ignite without a flame or spark This ability to vaporize and ignite easily is called ignition quality The ignition quality of a diesel fuel is determined by its cetane number rating or cetane value The cetane rating or value of a diesel fuel is based on the ability of the fuel to ignite The cetane rating of a fuel is determined by comparing it with pure cetane which is a test fuel and is identified by a cetane number Figure 14 4 This cetane number represents the percentage of pure cetane in a ref erence fuel which will exactly match the ignition quality of the fuel being tested The cetane rating scale ranges from O to 100 with 100 being the highest ignition quality In general the higher a fuel s cetane rating the lower the emissions Currently a 40 cetane or above rating is standard for all on highway diesel engines In some areas 50 cetane and higher are current standards Newer diesel engines may require higher cetane fuel The diesel engine service manual will specify what cetane number to use Improving Ignition Quality Fuels with poor ignition qualities can be improved or reformulated by blending them with fuels that have good ignition properties The cetane number of such blends are an average of the cetane numbers of the individual fuels To meet the
12. first hydrocarbon engine fuel obtained is high octane aviation gasoline If everything is working properly and you continue to raise the temperature other hydrocarbon fuels such as commercial gasoline kerosene diesel fuel domestic heating fuel industrial fuel oil Chapter 1 4 Diesel Fuels lubricating oil and paraffin are obtained Finally only coke and asphalt remain The type of hydrocarbons obtained will vary depending on the original geographic location of the crude oil This heating of crude oil to obtain various hydrocarbons is known as distillation It is a highly complicated process and precision control of pressure and temperature is required Diesel Fuel Grades While the American Society of Testing Materials ASTM has divided diesel fuels into three classifications only two recommended grades are considered acceptable for use in high speed trucks and buses in North America These are the number 1D and number 2D classifica tions Grade number 4D the heaviest diesel fuel is used in large stationary constant speed engines or in some marine applications Number 4 and bunker fuels are not used in high speed mobile diesel engines which are continually accelerating and changing speed Grade number 3D was discontinued a number of years ago and is obsolete The Canadian govemment 3 GP 6D diesel fuel has its own fuel specifications recognizing five categories of diesel fuels with even more restrictive standards set by A
13. found above ground Tanks are made of steel fiberglass or steel clad with fiberglass Galvanized copper tanks are not used to store diesel fuel There is a chemical reaction between the fuel and copper that produces a residue which will quickly clog fuel filters The term tank systems includes the piping connected to the tank s In some large industrial operations diesel fuel is fed from the main supply tank located above or in the ground outside of the building to a one day tank in the engine room Figure 14 7 This tank has a sufficient capacity to provide fuel for one day of operation The main storage normally stores only a one week supply of fuel Fuel stored for longer periods of time can form gum which along with corrosive com pounds causes deterioration Many refineries are also using additives that help stabilize the fuel in order to reduce gum for mation Moisture condensation inside a fuel storage tank increases as the tank size increases Condensation in a large tank can be reduced by using a series of smaller tanks and con necting them into the line as needed The size of tanks is gen erally controlled by the Bureau of Fire Underwriters and local regulations Alternative Fuels The Clean Air Act of 1990 requires that all centrally fueled on highway transportation operations of 10 or more vehicles in certain high emission areas are to phase in alternative fuel vehicles beginning in 1998 The act does not mandate an
14. g oils in addition to soybean and processed animal fats can be used in the making of biodiesel fuels Industry interest is high in biodiesel since it is nota stand alone fuel like the other alternative fuels but rather a blend with existing diesel fuels This means little or no alter ations to the fuel injection system are necessary nor is any special training of service personnel needed The two most popular blends today are 20 30 soybean oil to 80 70 diesel oil In physical properties biodiesel has almost the same btu gallon ratio as number 1 diesel Further it has slightly better lubricating qualities than number 1 diesel can handle winterizers and has a gel point slightly Particulate matter grams bhp hr higher than number 2 It has very low toxicity if ingested and is actually biodegradable by some standards The main drawback to biodiesel is its relative high cost in comparison to regular diesel fuel Biodiesel is now being tested in some city buses and is seeing increased popularity for use in marine diesel engines In the near future biodiesel fuels may play a major role in the future in reducing engine exhaust emissions Figure 14 12 More money and time must be spent on alternative fuel engine development on board fuel storage and fueling facilities before they can become a reality At the present diesel fueled engines are still cheaper and more efficient than any of the proposed altematives With the federal mandate
15. gine converts heat energy into work Specific gravity is a ratio of the density of fuel to the density of water The cetane rating or value of a diesel fuel is based on the ability of the fuel to ignite There is currently no common method of removing dissolved water from diesel fuel Free or nondissolved water in the fuel tank usually comes from bulk storage tanks from condensation or from dissolved water Free water gets into the fuel as storage tank bottoms become agitated while dispersing or receiving fuel Fuel additives are commonly used to improve diesel fuel flow properties under cold or winter like conditions Additives can also help eliminate fuel contaminants The importance of clean fuel in the operation of a diesel engine cannot be overemphasized Foreign mate rials such as air sediment dirt and water presents various problems and can enter the fuel system in various ways such as suction leaks careless filling and handling and dirty fittings and lines It is important to periodically per form inspection cleaning and maintenance checks on all fuel handling and filtering equipment The method of storing the fuel depends on the size of storage tanks or drums the frequency and method of fuel delivery climatic conditions and local regulations Fuel stored above ground will deteriorate more quickly than fuel stored underground due to the greater temperature ranges found above ground Underground storage tanks as well as abo
16. h tests involve heating the oil to an exact temperature and measuring its flow rate through a standard sized orifice The viscosity of diesel fuel is generally specified at 100 F 38 C Viscosity of fuels for medium speed and high speed engines normally ranges from 2 4 to 4 1 centistokes cSt or about 39 seconds Saybolt Universal SSU In gen eral any fuel with a viscosity lower that 2 4 cSt or 34 SSU when measured at 100 F 38 C will be too thin and could damage injectors as well as other parts of the fuel system Diesel fuel also has a low viscosity index meaning that itis thin when hot but gets thick when cold A diesel fuel that can go through an injection system easily in warm weather may get too thick to flow propery in cold weather As men tioned previously diesel fuel is supplied in several grades Grade 1D is a winterized diesel fuel It is thinner or less This sample chapter is for review purposes only Copyright The Goodheart Willcox Co Inc All rights reserved Chapter 14 Diesel Fuels viscous than grade 2D which is the fuel used at normal oper ating temperatures Diesel fuel viscosity also affects the spray pattern in the combustion chamber Figure 14 5 Low vis cosity creates a fine mist while high viscosity results in coarse or heavy atomization In other words viscosity affects Q Lubrication capability at various temperatures Q Atomization or spray capability Q Ignition and buming char
17. ike ethanol methyl alcohol is a colorless odorous flammable liquid Methanol is currently being used in several urban diesel powered bus fleets with some success It is one of the major contenders as a feasible alter native fuel for heavy duty high speed diesel engines Biodiesel Fuels Biodiesel is a comparative latecomer to the alternative fuels scene but as on highway off highway stationary and even marine engine manufacturers continue to investigate any and all alternative sources of fuel biodiesel is quickly 312 Second stage regulators ise aa Fm Solenoid shutoff vaive ignition switch activated First stage ean Shutoff valve Refueling receptacle Refueling line Protection ring operating pressure OS Engine A 125 psig nominal pressure coe Solenoid shutoff valve low oil pressure activated we i a a CY Check valve Fuel manifold tube Diesel Technology Manual shutoff valve typical each cylinder Composite cylinder fuel storage 6 cylinders Ze Gey D Fuel pressure gauge SaS Figure 14 11 Schematic showing typical CNG tank arrangement under a bus Diesel amp Gas Turbine Publications gaining support in the transportation industry At present the most popular is a biodiesel blend of number 1 diesel fuel and soybean oils There is also especially strong interest in biodiesel from the agricultural community because used cookin
18. introduce a biocide to the fuel to prevent fungi and bacteria from growing in the diesel fuel There are a number of commercially available fuel additives that will reduce smoke and corrosion of vital Diesel Technology parts and others that are oxidation inhibitors In addition remember that geographical locations operating condi tions type of fuel storage handling methods and mainte nance procedures are all factors that can determine whether or not a fuel additive might help a diesel fuel In most cases the fuel supplier or marketer will select and add the additive they believe will best improve the quality of their fuels Fuels containing special additives may be more expensive than those without additives Fuel Handling and Storage The importance of clean fuel in the operation of a diesel engine cannot be overemphasized Diesel fuel is generally delivered clean and free of impurities However every time it is transferred or handled the risk of contami nation increases While fuel storage and its handling are not normally within the engine technician s job classifica tion the results of improper storage and handling certainly are A problem often found by the engine technician when troubleshooting a diesel engine is dirty fuel One of the major problems either in storage or in the engine s fuel system is leakage Each connection or fitting in either system is a potential source of leakage There are two phases to the l
19. ion The airfuel mixing time in a direct injected diesel is about one tenth the time of a carbureted gasoline engine Early ignition promotes smooth and complete combustion leading to reduced emissions Excessive delay can produce very high peak cylinder pressures which make for rough and noisy engine operations The higher the cetane number the shorter the ignition delay which is the time between the start of fuel injection into the cylinder and the actual start of combustion Cloud Point Diesel fuel contains paraffin and in cold temperatures wax crystals can start to form accumulate and clog engine filters The temperature at which this happens is referred to as the cloud point or wax appearance point WAP Generally if the fuel s cloud point is at least 10 below the Diesel Technology ambient temperature engine performance will be satisfac tory The most commonly available and recommended fuel oil grade 2D has a cloud point or WAP of 10 F 12 C while the thinner grade 1D has a cloud point of 20 F 28 8 C In extremely cold areas engine clogging can be minimized by using only grade 1D in winter In most places mixing a base of grade 2D with grade 1D or other special additives will work well in colder weather As a rule grade 2D s cloud point drops two degrees for every 10 of grade 1D that is added up to a ratio of 50 50 One of the most effective chemical means for low ering the fuel s cloud point is by
20. lfur diesel fuel ULSD ULSD has a dramatically lower sulfur content than previous on highway grade diesel fuels The sulfur content of ULSD cannot exceed 15 parts per million 0015 by weight Using ultra low sulfur diesel dramatically reduces diesel exhaust emissions The lower sulfur content of ULSD produces fewer sulfate emissions It also enables use of emissions reduction equipment such as particulate traps and catalytic converters that lowers emissions of particles and nitrogen oxides NO When these systems are used with ULSD emissions of fine particulates can be reduced by more than 90 and emissions of hydrocarbons can be reduced to nearly undetectable levels Even without special emission reduction equipment using ULSD reduces sulfate pollutants ULSD fuel provides significant clean air benefits while ensuring the same energy and performance standards as regular highway diesel Ultra low sulfur low aromatic and high cetane number diesel fuels enhance engine performance because improved engine combustion results in easier starting smoother running less noise and less smoking during start up Only off highway non road diesel engines can cur rently use higher sulfur content fuels These include farm tractors boats locomotives and stationary engines The 2007 sulfur content standard for non road locomotive and marine fuel NRLM is 500 parts per million ppm In 2010 all on and off highway non road NR diesel fuel
21. matic at 100 F 40 C cSt Cloud point F Sulfur content maximum wt Carbon residue on 10 maximum wt Accelerated stability total insolubles maximum mg 100 ml Ash maximum wt Cetane number minimum Distillation temperature F C Initial boiling point typical 10 typical 50 typical 90 Endpoint Water and sediment maximum Figure 14 2 General classification chart for diesel fuel Detroit Diesel No 1 ASTM 1D 137 000 40 44 100 38 1 3 2 4 10 F 0 5 0 15 1 5 0 01 45 350 177 385 196 425 218 500 260 maximum 550 288 maximum 0 05 No 2 ASTM 2D 141 800 33 37 125 52 1 9 4 1 10 F 1 0 0 35 1 5 0 02 40 375 191 430 221 510 256 625 329 maximum 675 357 maximum 0 05 weather operation many fleets still use Grade 2D in the winter Other cold weather aids include a fuel heater water separator for easier starting as well as fuel additive condi tioners that can be added directly to the fuel tank Like gasoline diesel fuels are blended on a seasonal and geographical basis to satisfy anticipated temperature conditions It is usually best and cheapest to bum the heav iest fuel that will work under given circumstances Heavier grades of diesel can usually produce more energy than light grades just so long as the increased viscosity does not make the fuel too thick to flow and inject properly Itis important to remember that the wrong grade of diesel
22. nt of heat emitted is called A British thermal unit Btu B joule C flash point D Both A amp B 314 10 Volatility of diesel fuel is indicated when or the fuel is distilled off A 75 B 90 C 50 D 100 Sulfur is removed from diesel fuel by A distillation B hydrotreating C filtering D None of the above Which of the following types of tanks should not be used to store diesel fuel A Steel B Fiberglass C Copper D Steel clad with fiberglass Fuel stored above ground will deteriorate than fuel stored underground due to the greater tem perature ranges found above ground Name three ways air commonly enters diesel fuel True or False Flow improvers help redissolve paraffin crystals that have formed in the diesel fuel A Type Questions Technician A says that grade 1D diesel fuel is gener ally the most refined and volatile diesel fuel available Technician B says that grade 2D is more widely used in truck fleets due to its greater heat value per gallon particularly in warm to moderate climates Who is right A A only B B only C Both A amp B D Neither A nor B The of fuel is a general indication of how heat energy is supplied to an engine and how well the engine converts heat energy into work A heat value B viscosity C flash point D cetane number rating All of the following are contaminants
23. of diesel fuel EXCEPT A water B dirt C cetane D air 10 Diesel Technology All of the following are diesel fuel properties EXCEPT A heat value B pour point C specific gravity D octane rating The temperature at which wax crystals begin to form in diesel fuel is Known as the A cloud point B pour point C viscosity point D specific gravity level The viscosity of diesel fuel affects all of the following EXCEPT A the lubrication capability of the fuel at different temperatures B the cloud point C the burn capability D the atomization capability The of diesel fuel is based on the ability of the fuel to ignite A volatility B specific gravity C cetane number D viscosity Technician A says that fungus and bacterial growth in diesel fuel can be eliminated by draining setted water out of the fuel tanks at regular intervals Technician B says that the only way to eliminate bacterial growth entirely is to treat the fuel system with a biocide Who is right A Aonly B B only C Both A amp B D Neither A nor B Diesel fuel tanks can be made from A galvanized copper B aluminum C steel clad with neoprene D fiberglass Technician A says that as the temperature of diesel fuel goes down it will hold less dissolved water Technician B says that there is no common method now available for removing dissolved water from die
24. ood spray pattern However improper viscosity will give a poor spray pattern 307 causes varnish to form on the piston skirt and creates oil sludge in the engine crankcase Sulfur also combines with water to form corrosives as a result of the combustion process These corrosives can etch finished surfaces accel erate engine wear attack softer metals Such as bearings and deteriorate engine oil Similar corrosion damage from sulfur is frequently found in the engine s exhaust system Sulfur and aromatic content of diesel fuel are most respon sible for harmful exhaust emissions Sulfur dioxide emissions are reduced when sulfur content is reduced The reduction of aromatics will reduce carbonaceous particle emissions Sulfur is removed from diesel fuel in a process called hydrotreating Hydrogen is used with a catalyst at temper atures between 500 and 800 F 260 and 430 C to react with the sulfur compounds present The reaction forms hydrogen sulfide which is separated from the hydrocarbon and sent to a sulfur plant to be converted to elemental sulfur The sulfur content can only be determined by chem ical analysis of the fuel EPA regulations mandate the sulfur content in diesel fuel The 2004 standards called for a sulfur content of no greater than 500 parts per million 05 by weight and a maximum aromatic content of 35 in all on highway diesel fuels EPA regulations for 2007 on highway engines require the use of ultra low su
25. ose as possible to that of a diesel without making major component changes Figure 14 8 Compressed and Liquefied Natural Gas Natural gas has been used for 60 years to power industrial intemal combustion engines Natural gas is one of the lightest fractions parts of crude oil Chemically it is very similar to gasoline Unlike gasoline natural gas contains several light gases heavy gases and other impurities For natural gas to be used as an altemative fuel for on highway vehicles it must be refined into either compressed natural gas or liquefied Compressed natural gas CNG is composed primarily of methane and hydrocarbons that have a high carbon to hydrogen ratio Hydrogen is an ideal fuel that bums well while producing litte pollution It is the main reason CNG is a very desirable fuel It produces good power economy and low exhaust pollution levels On board fuel tanks for the storage of CNG while the vehicle is on the road is a problem that needs to be addressed For example experimental taxi cab operations using two or three tanks placed in the trunk had a range of only 120 160 miles 192 256 km Liquefied petroleum gas LPG is mainly propane and butane along with small amounts of other gases It has combustion qualities equal to or better than high grade diesel LPG is a vapor or gas at normal room temperature and atmospheric pressure This presents some design prob lems In fact since LPG is not a liquid the entire f
26. osits Dirt enters the fuel when Q A suction leak is in an exposed area QO Dirt collection in the tank allows it to be picked up with the fuel O Careless filling and handling permits mud dust or grime to enter tank or lines The technician may unintentionally add dirt to the fuel system by O Using containers and tools exposed to dirt O Using lines and fittings that have accumulated dirt or dust without cleaning them out O Allowing dirt to enter a line while it is removed for repair This is especially critical between filter and pump Water Water in the fuel may show up as low power also but it is even more damaging as already stated when it simply contributes to corrosion on fuel system components Water enters the fuel system through OQ A suction leak in an exposed location QO As condensation due to warm fuel O Careless storage and handling Careless storage and handling of diesel fuels can be a major concem in the engine s operation Figure 14 6 It is important to periodically perform inspection cleaning and maintenance checks on all fuel handling and filtering equipment Many state and local regulations include record keeping and periodic inspections Storage Tanks Diesel fuel tanks may be underground storage tanks UST or above ground storage tanks AGST systems Fuel stored in AGSTs will deteriorate more quickly than the fuel stored in USTs due to sunlight exposure and the greater temperatures
27. quate clearance underneath the bus Figure 14 11 to allow for several tanks In addition most city buses do not accu mulate as many miles in a day as would a long haul tractor trailer Buses can also be fueled up locally at their Figure 14 10 Buses in some major cities are now able to operate on compressed natural gas CNG Pierce Transit Inc depot by a fast charge facility which takes about the same length of time as it would to fuel up a diesel powered bus Alcohol Based Fuels Alcohol based fuels are being studied as an altemative fuel for the transportation industry The two types used to power intemal combustion engines are ethyl alcohol ethanol and methyl alcohol methanol Alcohols are especially desir able as an automotive fuel because they can be manufactured from sources other than crude oil Alcohol intended as an automotive fuel must be almost pure Quite often several refining steps are needed to approach this purity Denatured ethanol or grain alcohol is colorless harsh tasting and highly flammable It can be made from numerous farm crops such as wheat corn Sugar cane potatoes fruit oats soy beans or any material rich in car bohydrates Crop wastes are also a source One of the major drawbacks of using ethanol clean buming as it is is that it does emit carbon dioxide CO 5 Methanol or wood alcohol can be made from wood chips coal oil shale tar sands comstalks garbage or even manure L
28. sel fuel Who is right A A only B B only C Both A amp B D Neither A nor B
29. uel system must be redesigned to handle it Figure 14 9 Figure 14 8 Natural gas engines are used in place of basic diesel engines in some mobile and stationary applications Diesel amp Gas Turbine Publications This sample chapter is for review purposes only Copyright The Goodheart Willcox Co Inc All rights reserved Chapter 14 Diese Fuels 311 Control switch Relief lhe Special LPG valve L carburetor mixer Converter changes d LPG from liquid to a gas eE Fuel strainer fuel lock High pressure EE eee To engine cooling system _ LPG tank Toported E wesectan Ce ad y NS vacuum source Figure 14 9 Simple schematic for a liquefied petroleum gas LPG fuel system LPG has operating characteristics almost identical to those of gasoline and diesel However because it is already a gas the problem of breaking up liquid fuel is eliminated Since the fuel enters the intake manifold and combustion chamber as a vapor combustion is much more efficient For this reason LPG is generally an excellent alternative fuel Liquefied natural gas LNG has the same characteristics as LPG A heavy duty truck would need too many fuel storage tanks to make it a feasible concept at this time Conversions on city buses however are presently being done in several big cities since fuel tank storage is not as great a problem Figure 14 10 In most cases there is ade
30. ve ground storage tank systems must meet rigid safety and environmental regulations Storage tanks should be made of either steel fiber glass or steel clad with fiberglass Galvanized and copper tanks should not be used to store diesel fuel The most promising alternative fuels are compressed natural gas liquefied petroleum gas liquefied natural gas methanol and ethanol 313 Important Terms Hydrocarbons Fungus Relative volatility Bacteria Distillation Leakage Heat valve Foreign materials British thermal unit BTU Air Joule Dirt Specific gravity Water Flash point Underground storage tank Volatility UST Ignition quality Above ground storage tank AGST Cetane number rating Altemative fuel vehicles Ignition delay Cloud point ka AAE P int Our poin Liquefied petroleum gas Viscosity LPG Carbon residue Liquefied natural gas LNG Soot ash Ethyl alcohol Sulfur Methyl alcohol Hydrotreating Biodiesel Review Questions Chapter 14 Do not write in this text Place your answers on a sep arate sheet of paper 1 Which of the following grades of diesel fuel are rec ommended for use in high speed trucks and buses A number 1D B number 2D C number 4D D Both A amp B 2 Like gasoline diesel fuels are blended on a and basis to satisfy anticipated temperature conditions 3 Heavier grades of diesel fuel usually produce energy than lighter grades 4 The value s used to measure the amou
31. water at any given tempera ture As the temperature goes down the fuel will hold less dissolved moisture There is currently no common method of removing dissolved water from diesel fuel Free or nondissolved water in the fuel tank usually comes from bulk storage tanks from condensation or from dissolved water Free water mixes with the fuel as storage tank bottoms become agitated while dispersing or receiving fuel When water in vapor form is present in air itis called humidity As air replaces fuel in storage tanks or vehicle tanks when the tanks disperse or receive fuel mois ture in the form of humidity finds its way into the fuel system From there moisture may condense as hot fuel returning from the injectors flows back into the cooler fuel tank Free water in liquid form is heavier than diesel fuel and settles on the low flow or slow flow areas of the fuel system The reverse is tue when water freezes Ice is lighter than diesel fuel and floats in the system to create plugs in fuel separators filters even going as far as the fuel pump injectors Fuel Additives Generally no fuel additives are necessary when a good quality clean and properly selected fuel is used Certain fuel characteristics however can be improved by treatment with a fuel additive or conditioner As already mentioned additives are used to improve fuel flow prop erties under cold or winter like conditions increase the cetane number of the fuel and to
32. west value on this scale the reverse of the system just described Diesel fuels generally range from 20 to 45 on the API gravity scale with most ranging between 34 to 36 at 60 F 15 5 C Hash Point A fuel s flash point is the lowest temperature at which it will give off flammable vapors in sufficient quantity to flash or momentarily ignite when brought into contact with an open flame The flash point has no effect on engine per formance or on its ignition qualities It is specified simply as an index of fire hazard a fuel oil with an extremely low flash point is dangerous to store and handle Diesel fuel flash points are not an indication of how they will ignite in an engine cylinder however This depends on the ignition quality of the fuel For example gasoline which has a very low flash point would be a very poor diesel fuel due to its ignition quality Volatility Volatility is a fuel s ability to change to a vapor It is indi cated by the air vapor ratio that is formed at a specific tem perature Diesel fuel volatility is indicated by a 90 distillation temperature the temperature at which 90 of the fuel is distilled off As volatility decreases carbon deposits and engine wear increase Depending on such factors as the combustion chamber condition more smoke will also affect power output performance starting and warnrup Cetane Number Rating The ease of diesel fuel oil ignition and the manner in which it bums d
33. y specific alternative fuels such as gasoline Figure 14 6 Care must be taken whenever filling a storage tank A Below ground tanks can present as much danger as above ground tanks B Always take care when filling any vehicle s tank Heavy Duty Trucking and Andrew Ryder 310 Pr Final as Ls stage Secondary L filter filter Diesel Technology Injector return Vent Primary filter Figure 14 7 Schematic of a stationary fuel system with day tank and storage tank Waukesha Engine Div or diesel The altemative fuels now being considered for use with compressed diesel type engines are compressed natural gas CNG liquefied petroleum gas LPG liquefied natural gas LNG and alcohol based products such as methanol and ethanol The Clean Air Act regulations are closely tied to clean fuel vehicle programs in each state s air quality implemen tation plan Since the supply of certain fuels varies across the county not all states favor the same fuel Southem states are a big supporter of natural gas while some western states favor liquid petroleum gas and a number of midwestem states actively tout ethanol Some engine companies are devoting research and testing to natural gas Many of their initial products are being offered for urban buses which are on a stricter emis sions schedule than medium and heavy duty trucks Engine makers face the challenge of designing new engines with efficiency as cl
Download Pdf Manuals
Related Search