Alternative fuel sources are used as a way of reducing the operating cost of vehicles, or to reduce pollution from vehicle emissions, or both.
Some alternative fuels can be mixed with gasoline as a fuel additive to reduce the total amount of gasoline used, others are a complete fuel alternative which may require some modifications to the vehicle.
Ethanol is usually derived from an organic process such as the fermentation of sugar cane, and is therefore referred to as a bio-fuel. It is normally used in the ratio of 9:1 or 9 parts gasoline to 1 part ethanol and is primarily used to reduce the negative emission effects of gasoline.
Methanol is produced from wood or other organic materials. Its calorific value, or burn rate, is not as high as that of gasoline fuel and cannot be used in conventional vehicles without significant modifications.
Liquefied Petroleum Gas or LPG is a petroleum derived colorless gas, and has been used for many years to power specially modified gasoline engine vehicles. It is the third most common fuel and emits much fewer harmful emissions than gasoline. It is generally cheaper than gasoline and is non-toxic and non-poisonous with a very small flammability range. It is popular with high-mileage applications such as taxis, where the cost of vehicle modification can be recouped over time more easily through lower fuel costs.
Compressed Natural Gas or CNG is being used as an alternative fuel in vehicles such as light-duty passenger vehicles, delivery trucks and buses. CNG powered vehicles use natural gas stored in cylinders at pressures of 2,000 to 3,500 pounds per square inch or 140 to 240 Bar.
Liquefied Natural Gas or LNG is being used in heavy-duty diesel powered vehicles such as long-haul trucks, delivery trucks and buses. LNG is almost pure methane and has an energy storage density much closer to gasolinethan CNG, but for the gas to become a more compact and easily stored liquid it has to be cooled to an extremely low temperature, minus 263.2 degrees Fahrenheit, or minus 164 degrees Celsius. The need to keep the liquid very cold at all times limits the more widespread use of LNG.
Natural gas, whether liquified or compressed, is less expensive than diesel and natural gas vehicles are substantially cleaner than comparable diesel vehicles.
Fuel cell technology has been used for a number of years in the space industry. Recent improvements in technology and the need to seek alternative fuel technologies for the automotive industry have seen a number of manufacturers develop fuel cell technology for use in automobiles. In a vehicle powered by a fuel cell, the electrical motor is powered by electricity generated by the fuel cell.
A fuel cell is an electro chemical device that combines hydrogen and oxygen to produce water and in the process it produces electricity and heat. Fuel cells operate without combustion so they are virtually pollution free.
Another electrochemical device you are already familiar with is the vehicle battery. In a battery all the chemicals are stored inside, and it converts those chemical into electricity. This means the battery eventually becomes discharged until you recharge it.
In a fuel cell, the chemicals oxygen and hydrogen constantly flow through the cell, like fuel through an engine, so it continues to produce electricity as long as fuel is available.
There are four basic elements to a fuel cell, the anode, the cathode, the electrolyte and the catalyst.
Pressurized hydrogen flows into the fuel cell anode. The platinum coating on the anode helps to separate the gas into protons (hydrogen ions) and electrons. The electrolyte in the center allows only the protons to pass through to the cathode side of the fuel cell. The electrons cannot pass through this electrolyte and flow through an external circuit in the form of electric current.
At the same time, oxygen flows into the fuel cell cathode where another platinum coating helps the oxygen, protons, and electrons combine to produce pure water and heat.
A fuel cell only produces a voltage of about 0.7 volts. To get the required voltage for automotive applications a fuel cell stack is created. The number of fuel cells in the stack determines the total voltage, and the surface area of the cells determines the total current.
Fuel cells use hydrogen and oxygen to produce electricity. The oxygen can come from the air, however hydrogen it is not readily available. Hydrogen is difficult to store and distribute. To address this problem in automotive applications, an additional device called a reformer is used.
The reformer turns hydrocarbon or alcohol fuels into hydrogen. So to make fuel cells practical for automotive applications car manufacturers are developing better fuel cell systems and technology to improve the efficiency of the system while using readily obtainable fuels.
Ethanol and methanol
As responsible professionals working in the automotive service industry, we owe it to ourselves and our customers to be informed about ethanol, methanol, and the unique vehicles which burn these alcohol fuels.
They’re part of the growing fleet of alternative fuel vehicles (AFVs) on the road today, and from the outside, they look pretty much like any other you’ve seen; you may have already had one in your service bay without realizing it. But once you know the differences in the fuels and the vehicles, you’ll be more confident and better prepared to answer customers’ questions, and to service their alcohol-fueled cars.
Both ethanol and methanol fuels are important alternatives to petroleum.
They offer specific advantages for use in today’s alternative fuel vehicles, and are just two of a variety of domestically supplied “renewable” alternatives to gasoline for internal combustion engines. As the name implies, renewable fuels can be “replenished.” By contrast, traditional fossil fuels like gasoline or diesel were formed over millions of years: once they’re gone, they’re gone!
You may already be familiar with ethanol and methanol. Ethanol was commonly blended with gasoline as a fuel extender during the gas shortage in the ’70s when a 10% ethanol blend known as gasohol was sold.
Since the phase-out of lead, refiners sometimes blend high-octane ethanol with gasoline as an octane improver. Sometimes ethanol serves as an oxygenate in reformulated g asoline (RFG) to lower CO emissions. Methanol on the other hand is probably best known as the racing fuel for Indy cars and as a de-icer.
Both ethanol and methanol are alcohol based, but they should not be confused with one another. They come from different feedstocks and thus have somewhat different properties which affect engine operation.
Ethanol is often called grain alcohol and is principally made from fermented corn, but it is denatured to prevent human consumption. Methanol is known as wood alcohol and is principally made from natural gas, but feedstocks like forest residues and municipal waste can also be used to produce methanol.
Ethanol and methanol engine/system requirements
Some in the aftermarket may claim to have burned ethanol fuel successfully without modifying engine parts or engine re-tuning.
For safety and vehicle performance reasons, however, OEs go to great lengths to optimize the vehicle for ethanol and methanol’s unique properties.
For example, the manufacturer may modify compression ratio, cam profile, piston and head design, cooling system, and spark plug heat range.
Additionally, injectors, AIR systems, and catalytic converters are likely to be redesigned and calibrated for alcohol fuel.
Without advancing the ignition timing, gasoline-dedicated engines cannot take advantage of the higher octane ratings of ethanol or methanol. Because alcohol fuels provide less lubricity than gasoline, valves and/or seats, pistons, and other parts may be hardened, and special lubricants may be specified along with more frequent service intervals. Recalibration of the power-train control module (PCM) is required for optimum management of fuel, OBD-II and emission systems.
Chemical attack is another concern for engineers who design alcohol-fueled vehicles. Gasoline fuel system components—injectors, Orings, fuel lines, hoses and tanks—could possibly be ruined if exposed to high concentrations of alcohol.
Methanol especially will attack certain metals; both fuels will possibly soften or dry elastomers, polymers and coatings leading to the possibility of contaminated fuel and fuel system component failures, or worse yet: hazardous fuel leaks. It is imperative, despite their similar appearance, that you use only replacement parts designed and intended for alcohol fueled vehicles.
Vehicles in the marketplace
In some countries, neat (100%) ethanol/methanol is widely used in dedicated E100/M100 vehicles. Here in the U.S. you’ll see flexible fueled vehicles or FFVs (see FFV chart). These look like dedicated gasoline vehicles, but can burn a mixture of up to 85% ethanol (E85), or methanol (M85) with gasoline. Unlike dedicated-gasoline vehicles, an FFV’s fuel management system must constantly adjust for varying fuel viscosity, energy content, octane and other factors. For example, Chrysler’s FFV mini-van (with the 3.3 liter engine) relies on the O2 sensor to provide input to the PCM for fuel trim and timing adjustments. Ford uses a separate “fuel sensor” to determine alcohol content and fuel temperature for making PCM calculations. (See Ford schematic below.)
Fuel handling
Alcohol fuels (unlike gasoline) easily absorb water. Extra care should be taken to prevent snow or rain from dropping into fuel tanks where water in the fuel will cause gasoline-alcohol blend phase separation, leading to “water bottoms” in the tank and subsequent driveability problems. Unlike gasoline, alcohol is easily absorbed into the human body; thus ingestion, inhalation and exposure of the skin to alcohol fuels should be avoided. Neat (100%) alcohol fuel burns cooler than gasoline and with very low luminosity (difficult to see in sunlight), so a fire would be difficult to spot. But the gasoline-alcohol blend, i.e. E85 & M85, makes flames more visible. Because alcohol fuels are water soluble, a small fire may be doused with water; a larger fire is extinguished with dry chemical or with foam.
Fuel properties
Alcohol fuels offer both advantages and disadvantages to vehicle performance.
Ethanol, and especially methanol, fall short on Btu energy content compared to gasoline. This translates to an estimated 27% to 30% loss of vehicle miles-per-gallon traveled compared to gasoline; it’s even worse for methanol. On the positive side, with ethanol and especially methanol’s higher octane ratings, vehicle operators are impressed with improved torque and horsepower over much of the engine speed range. Extreme cold-weather starting is difficult with alcohol fuel due to its lower RVP, so OEs may recommend using a winter blend of up to 30% gasoline, for colder climates. At least one OE equips its FFVs with block heaters and programs the PCM for increased fuel injector pulse width during cold weather alcohol startups. On the other hand, during hot weather, alcohol’s higher latent heat of vaporization means increased demands on the EVAP system. On a hot day an FFV’s engine may be running mostly on fuel tank vapors. You’ll find a much larger EVAP canister on-board an alcohol vehicle.
The real world
Ethanol is sold mostly in the cornbelt sta tes - that’s where the present feedstock is. Methanol is more difficult to find. Locating either an ethanol or methanol filling station can be a challenge, but if you or your customer needs to find one, check the web for AFDC’s refueling site map, the alcohol fuel associations’ websites, or with your alcohol fuel producers. Obviously, as more FFVs are purchased and driven, more refueling sites will appear. Federal and state fleets, fuel providers and utilities, are now mandated to use alternative fuel vehicles which include alcohol-burning FFVs. Numerous financial incentives exist to promote such purchases, and cost/payback models are available “on-line” for fleet owners, managers and operators wishing to explore the alternative fuel choices; go to the [www.ccities. doe.gov] website for more information.
The increased use of alternate fuels will help America to achieve energy independence and reduce fossil fuel defense spending. As an automotive service professional, you may not see many AFVs just yet, but they are finding their way into the marketplace. In the meantime, you may wish to learn all you can about alternate fuels, and flexible fuel vehicles using ethanol or methanol. In so doing, you’ll be able to explain their environmental and economic advantages to your customers, and you’ll enhance your image as an informed professional in the business. Most of all, you’ll be better prepared to diagnose, service and repair this unique breed of alternative fuel vehicles.
Starting in 1998 all 3.3 liter equipped Chrysler Town & Country, Dodge Caravan and Plymouth Voyager mini-vans are FFVs. Note the FFV logo on the door.
Environmental and feedstock considerations
As a technician you are concerned about tailpipe emissions: 5-gas readings will verify that both ethanol and methanol burn relatively clean compared to gasoline: HC and CO emissions are lower for both fuels, and NOx emissions are lower due to cooler burning of alcohol, yet a problem of aldehyde emissions remains a challenge. From a global perspective, alcohol fuels reduce greenhouse gas emissions. According to the DOE, substituting ethanol for gasoline would reduce the production of greenhouses by 35-46%, and according to the American Methanol Institute, substituting methanol for gasoline would cut greenhouse gas emissions by 50%.
Ethanol may soon be economically produced from waste feedstock like corn stover, normally left in the field after corn is harvested, or waste sugar (bagasse) which is normally landfilled or burned. Yard clippings and tree and pulp mill wastes are other possible ethanol feedstocks. Agricultural and forestry “energy crops” like rice straw, wheat, milo, hay, and straw may be grown specifically for ethanol production.
The Coors Brewery in Golden, Colorado has partnered with two other companies to recycle its 22 million gallons per y ear of “beer spillover”— otherwise wasted 7% alcohol condensate—into a pure ethanol gasoline additive.
Methanol is principally produced from natural gas, or from coal or residual oil. Future sources include energy crops like grasses and trees. Industrial and municipal waste may also be used to produce methanol.
| FFVs Currently Available |
If you want to see an E85 flexible fuel vehicle close-up, watch for these.
Note:FFVs look like any other vehicle, and OEs may not aggressively advertise them as FFVs—check the fill cap or the owner’s manual to be sure. |
| OE | Year | Model | Engine |
| Chrysler | 1998 and newer | T & C, Caravan, Voyager | 3.3 liter |
| Ford | 1996 and newer | Taurus | 3.0 liter |
| Ford | 1999 and newer | Ranger | 3.0 liter |
| Chevrolet | 2000 | S-10, Sonoma | 2.2 liter |
| Mazda | 2000 | B 3000 | 3.0 liter |
| Source: U.S. DOE’s Alternative Fuels Data Center |
| Ethanol (C2H5OH) & Methanol (CH3OH): Pros & Cons |
| Pros | Cons |
| Higher octane than gasoline (R+M)/2=100 | Degrades zinc, brass, lead, alum. etc. |
| Increase of HP & torque (~5% or more) | Lower energy ratio (E=93%; M=66%) |
| Fewer VOC compounds | Lower RVP; difficult cold starting1 |
| Cleaner burning/less deposits | May require special motor oil & service |
| Lower tailpipe emissions of HC & CO | Toxic, aldehyde emissions, low flame luminosity |
| Dries water in gas line and tank | Water soluble2 |
| Reneweable | Limited availability/distribution |
| 1 Cold starting—At least one OE recommended that fuel providers supply a higher gasoline blend with ethanol (E70) during the winter, and equipped its FFV vehicles with engine block heaters. |
| 2 Absorbs water—a blend of 10% ethanol in gasoline can hold almost 4 teaspoons of water per gallon in solution. That can be good news for preventing gas line freeze up, but bad news if the station operator hasn’t kept his tanks free of moisture. |
Natural gas
If you’re a technician and haven’t yet seen a natural gas powered vehicle (or NGV), you soon will... especially if you work in a fleet environment. Being familiar with NGVs—what they look like, and how they work—
before they show up at your shop, could make a difference in whether you confidently and successfully service them, or turn them away. Here we’ll explain the basics of natural gas (NG) and NGVs to help you feel confident enough to look under a few hoods and attend some classes. Having done so, you’re sure to appreciate the safety and clean performance of natural gas motorfuel over liquid gasoline.
Overview
Natural gas vehicles have filled a “niche” in the marketplace for many years; until recently, most NGVs were converted from dedicated-gasoline to bi-fuel vehicles so the driver could select either fuel. Conversion system suppliers still sell quality products to the marketplace, but with tighter EPA standards and OBD-II, the buying trend has shifted towards OE designed and built NGVs.
Vehicle Applications
According to the DOE, there are an estimated 102,000 compressed natural gas (CNG) vehicles in the U.S. Common on-road applications include taxicabs, vans, school buses, coaches, refuse & delivery trucks, police & municipal vehicles. Non-road applications include material and baggage handling vehicles. The obvious reason: fleet vehicles can be centrally NG refueled at lower cost, there’s reduced fuel pilferage, and extended vehicle range is not a requirement.
Why Switch?
Admittedly, EPACT mandates that federal, state and municipal (and certain private) fleets use alternative fuel vehicles. Yet, financial incentives do help make AFV purchases attractive, with natural gas vehicles (NGVs) being one such option. The fuel is generally less expensive and considered by many as safer than gasoline. It burns clean, is domestically sourced, abundant, and often locally available.
Whether converted or OE, dedicated or bi-fuel, NGVs serve a variety of needs in the marketplace. The
AFDC website (
www.eere.energy.gov/afdc) lists NGV models from manufacturers like Honda, DaimlerChrysler, Ford, GM, and Toyota.
Fuel Definitions and Characteristics
In the utility industry, natural gas is sold in standard cubic feet, or SCF. In the automotive industry, gaseous CNG is sold in gasolinegallon-equivalents, or GGE. The DOE states that “The GGE of CNG is 123 CF …(based on 929 Btu/CF of CNG and 114,264 Btu/Gallon of gasoline).” By mass, a GGE of NG has been defined as 5.66 pounds.
Pipeline NG is typically 95-96% methane(>88% is required for motorfuel); LNG (see below) is about 99% methane. NG’s simple chemical makeup (CH4) is easily broken down during combustion, thus it’s very clean burning for domestic or vehicle use. While NG is piped into the home at <1 psi, the same gas is either compressed to 3000-3600 psi for on-board storage, or chilled to
minus 260 degrees Fahrenheit to become a clear cryogenic liquid (LNG) at 1/600th its gaseous volume. While LNG saves space, it requires doublewalled insulated tanks to keep it cryogenic; if not, it boils off. LNG is considered impractical for passenger cars because of tank size, but an attractive alternative for truck and bus use.
Compared to gasoline, NG contains considerably less thermal energy. At 29,000 Btu per gallon; a bi-fueled vehicle running on CNG has somewhat limited range. A dedicated NGV with cranked up compression ratios, however, can take advantage of NG’s 120–130 (R+M)/2 octane rating for a considerable improvement. Natural gas is not visible, so suppliers add Mercaptan (with its familiar rotten-egg scent) to NG so it can be detected; building codes may require methane detectors if NGVs are to be stored indoors.
Infrastructure
Stationary and mobile vehicle “fast-fill” compressor stations can be set up wherever NG is available. These tend to be expensive, but overnight “timed-filling” offers a less expensive option. Only a small compressor is required for timed-filling; “at-home” filling is not uncommon. Because natural gas temperature and pressure are inter-related, fast-filling raises tank temperature and pressure, thus affecting fill capacity. By contrast, timed-filling keeps tank temperatures down so more NG can be compressed and stored for greater vehicle range. For refueling of line-haul trucks and buses, both CNG and LNG fill-sites are being established at strategic locations on certain interstate highways forming a system of “Clean Corridors.”
Want to Learn More about NGVs?
For in-depth information, search the
EERE, visit a dealer selling NGVs, or attend an NGV or Clean Cities Conference- you’ll quickly learn about NGVs and perhaps drive a few during a “ride ‘n’ drive.”
Ask lots of questions to learn about natural gas vehicles: you’ll be better prepared for them when they show up in your service bay… if they’re not there already!
The Nuts and Bolts of CNG Vehicles
The outstanding difference between a dedicated gasoline auto and an NGV is the pressure at which CNG is stored on board—typically 3000 to 3600 psi. The robust cylindrical tanks required to contain such pressures take up space, add weight, and affect handling. The two or more tanks needed for gasoline-comparable range may be located between the frame rails and/or behind the rear axle. Light-duty CNG vehicles often have tanks behind the back seat or in the trunk/pickup bed. Some low-ride buses have CNG tanks on the roof. CNG tanks may be constructed of steel or aluminum and/or composite materials. Tanks are manifolded together and safety valves, regulators and other unique components ensure safety and reliable operation of the NG fuel system. On bi-fuel vehicles, the NG components parallel the normal gasoline delivery system. If the vehicle is aftermarket converted to natural gas, NFPA-52 regulations determine how, and often where, CNG components are to be installed.
A Word on Tank Safety
Some people have anxieties over servicing (or driving) an NGV, usually over possible tank rupture and fire. These fears are understandable, but extensive tests show NGV fuel systems to be safer than gasoline systems.
Very few tank-related incidents have occurred. Just like SCUBA tanks, however, CNG tanks must be handled properly and be periodically inspected, tested and replaced. Tanks are robust and are rated well above working pressures, are equipped with pressure relief devices (PRDs), and are vented to the outside.
The NG Fuel System
On-board CNG tanks are filled from a fast-fill, or a time-fill compressor station. A standardized quick-connect fill-valve (with breakaway provision) is located at the normal gasoline cap location (or possibly in the grill or under the hood), and feeds CNG to the on-board tanks. Each tank has its own pressure relief device and shutoff valve. From the tanks, CNG is routed through hefty stainless steel lines to an externally accessible quarter-turn manual shutoff valve, then to the engine compartment.
All NGVs use pressure-reducing regulators to drop and stabilize fuel pressure to workable levels (typically ~100 psi). A primary or multistage regulator, located along the frame rail and/or under the hood, is usually warmed with engine “coolant” to prevent freeze-up. On naturally aspirated NGVs, a secondary regulator drops pressure to near atmospheric.
A vacuum or ignition controlled valve serves as a fuel “lockoff” to shutoff the fuel supply to the engine. Fuel is delivered to the intake system via either a fuel mixer, a “throttle body” injector assembly, or port injectors. Naturally aspirated bi-fuel vehicles often feed NG into the intake system via a variable venturi “mixer,” which sits above the gasoline system’s throttle body or carburetor. Sometimes gaseous fuel is released to the intake air stream using a fixed venturi “spray bar” or a “fuel ring,” which resembles a stovetop burner.
Electronically controlled systems may use a bank of EFI gaseous injectors (similar to gasoline port-injectors) for metering the fuel to the intake. Some engine families use port NG injection systems. Because NG is gaseous, it displaces incoming air. Thus, bi-fuel vehicles tend to lose power (~10%) on NG because of lost volumetric efficiency. Only dedicated NGVs can make up for this loss with raised compression ratios. Dedicated NGVs may also use a unique catalytic converter, but no EGR or knock sensor.
Combustion and Emissions
Ignition demands are higher for NG: it’s harder to ignite, and the timing curve must be adapted (advanced) for the slower and longer burntime. NG’s higher stoichiometric ratio (17.2:1) requires closed-loop bifuel adaptation via added electronics for HO2S, knock sensor, and EGR functions. OBD-II systems must remain intact, and engines must be certified under EPA regulations. Natural gas vehicle (NGV) pre-cat HC and CO emissions are inherently low. Dedicated NGV tailpipes easily pass a “white glove” inspection; in fact, Honda calls their dedicated Civic GX the “cleanest on earth.”
From the exterior, most CNG and LNG vehicles look similar to gasoline or diesel vehicles, minus the pollution and the noise. All can be identified by a diamond-shaped label on the rear of the vehicle.
ASE F-1 Compressed Natural Gas Vehicle Exam
ASE’s “F-1” Light Vehicle Compressed Natural Gas technician exam is crafted by NGV industry experts. The exam focuses on knowledge of NGV conversions; engine performance, diagnosis and repair; and NGV safety (see test specs below). Those interested in taking the F-1 exam may obtain more test information from ASE’s Official ASE Preparation Guide available at
www.asecert.org. Subject matter expertise can be obtained from many sources, including the
National Alternative Fuel Training Consortium; and the
National Fire Protection Assn (ask for publication
NFPA-52).
ASE “F-1”(CNG Technician) Test Specifications
|
| Content Area | No. of Q’s | % of test |
| a. Vehicle Conversion Compatibility Analysis | 4 | 7% |
| b. Conversion Parts Fabrication | 3 | 5% |
| c. Conversion Equipment Installation | 9 | 16% |
| d. Leak Testing and Repairs | 7 | 13% |
| e. Conversion Initial Adjustments and Performance Verification | 8 | 15% |
| f. In-service system Diagnosis and Repair | 17 | 31% |
| g. Cylinder Safety | 7 | 13% |
| Total | 551 | 100% |
| 1 Does not include up to 10 questions used for statistical research. |
