Agricultural Mechanics 8208-C Operation & Service of LP & Natural Gas PDF

# AGRICULTURAL MECHANICS 8208-C ## OPERATION AND SERVICE OF LP AND NATURAL GAS FUEL SYSTEMS ### IMPACT OF NATURAL GAS AND ALTERNATIVE FUELS In recent years, there has been increased concern about the environmental effects of exhaust gasses produced by internal combustion engines. Over the same peri...

# AGRICULTURAL MECHANICS 8208-C ## OPERATION AND SERVICE OF LP AND NATURAL GAS FUEL SYSTEMS ### IMPACT OF NATURAL GAS AND ALTERNATIVE FUELS In recent years, there has been increased concern about the environmental effects of exhaust gasses produced by internal combustion engines. Over the same period, there has been a resurgence of interest in alternative energy sources. There is continuing pressure for legislation requiring equipment manufacturers to develop engines that are more fuel-efficient and produce fewer harmful exhaust gasses. Implementation of the Clean Air Act of 1990 eliminated the production of gasoline blends containing tetra-ethyl lead (TEL) to control pre-ignition. U.S. automobile manufacturers no longer make cars that run on leaded gasoline, and petroleum refiners have almost completely stopped producing leaded gasoline. Small gasoline engines also run on unleaded fuel. Environmental and economic concerns have shifted public attention to alternative fuels such as compressed gasses and biofuels. Two common compressed-gas fuels are liquefied petroleum gas (LPG) and compressed natural gas (CNG). These fuels can be used in conventional spark-ignition engines after modifications have been made. Some equipment manufacturers have designed engines specifically to run on CNG or LP gas. Alternative fuels, especially LPG and CNG fuels, produce fewer emissions, are generally less expensive than gasoline, have higher octane ratings, increase the intervals between oil changes, prolong engine life, and meet or exceed clean air standards. In an example that we all understand, forklifts can run in closed warehouses year round because they are fueled by economical, clean-burning LP-gas and natural gas engines. ### Characteristics of Selected Alternative Fuels | Fuel | Chemical Formula | Components | Source | Energy per gallon | Power Factor** | Form | |---|---|---|---|---|---|---| | Compressed Natural Gas (CNG) | CH4 | 90% Methane | Underground reserves | 114,000 BTU | 1.00 | Vapor | | 15% Ethanol, 85% Gasoline (E85) | CH3CH2OH | Denatured alcohol & gasoline | Corn, other grains, agricultural waste | 80,000 BTU | N/A | Liquid | | Liquefied Petroleum Gas (LPG) | C3H8 | Propane - butane mixture | Refining or natural gas processing byproduct | 84,000-91,000 BTU | 1.38 | Liquid | | 15% Methanol, 85% Gasoline (M85) | CH3OH | Methanol (methane) & gasoline | Natural gas, coal, or woody biomass | 65,000 BTU | 1.74 | Liquid | **Gallon gasoline equivalent (GGE) - amount of product to generate same amount of energy as one gallon of gasoline (114,000 BTU) * Underlined words are defined in the Glossary of Terms. ### ADVANTAGES TO USING LP-GAS AND CNGAS FUELS Spark ignition engines can use these fuels after a few modifications, although some equipment manufacturers produce engines specially designed to burn LP or natural gas. In some regions and some years, LP and CNG are less expensive than gasoline. Both of these fuels have higher octane ratings than gasoline, reduce harmful exhaust gases, burn cleanly and more completely, may increase the interval between oil changes, and may increase engine life. The interval between oil changes increases because these "dry" gases do not dilute engine oil. Dry gases may increase engine life because carbon deposits are not created in engines, and maintenance and replacement of internal parts is decreased. In some comparison tests, fleet fuel costs using LP or CNG used are 60% lower, carbon monoxide emissions have decreased about 80%, and hydrocarbon emissions have dropped almost 70%. In addition to environmental concerns, this trend is of major economic importance to gas-producing states. About one-third of America's natural gas reserves are in Texas. Kansas and New Mexico also have plentiful natural gas reserves. | Fuel | Octane Rating | |---|---| | Gasoline | 87-95 | | LP-Gas | 104-110 | | Natural Gas | 125-130 | There are two basic types of fuel delivery systems in compressed-gas engines, carburetor air-fuel mixer systems and electronic fuel injection (EFI) systems. ### Components of EFI Compressed Gas Fuel systems EFI systems are used in applications that require variable engine speeds such as trucks and tractors. These systems minimize the amount of fuel consumed by using electronic technology to carefully monitor and adjust the air-fuel ratios. This process optimizes the power available through the use of compressed gas. Spark-ignition engines can be set up to run strictly on compressed gas, or they can incorporate a bi-fuel system. Bi-fuel systems use two solenoid valves to switch between gasoline and compressed gas. Each fuel line is equipped with a solenoid valve. A switch connected to the solenoid valves allows the operator to select either gasoline or compressed gas as the fuel. Bi-fuel engines have the air-fuel mixer mounted between the carburetor and air cleaner.  ### NATURAL GAS FUEL SYSTEM  The engine control unit (ECU) is an on-board computer responsible for monitoring EFI engine performance. The ECU receives inputs from various sensors and translates those signals into digital information for the CPU. The CPU then diagnoses the information and adjusts engine performance. The three subsystems that make up the ECU are: * a converter to change analog signals from sensors into digital signals for the CPU; * a CPU to perform the mathematical calculations that adjust airflow, fuel delivery, and engine timing; and, * memory chips for RAM, ROM, and PROM (programmable read-only memory). The ECU of a CNG engine uses three major types of sensors to monitor operation. These sensors are pressure sensors, temperature sensors, and position sensors. Pressure sensors use low-voltage loops to monitor resistance changes in components such as fuel tanks, fuel lines, and manifolds. Temperature sensors use a low-voltage loop to monitor temperature changes in the engine coolant and manifold. Low-voltage position sensors are used on throttles and foot pedals. These sensors transmit information to the ECU, which uses the information to modify the pulse width, or amount of fuel, the injector releases.  A major difference between gasoline and compressed gas engines is that, in compressed-gas engines, the fuel is a vapor before reaching the carburetor. In gasoline engines, the fuel is a liquid, and must be vaporized in the carburetor. Compressed-gas systems do not require a fuel pump, since the fuel is under constant pressure. These systems must have a fuel lockoff valve that allows fuel flow only when starting or running the engine. Fuel locks can be combined with filters to remove rust flakes and sediment from the fuel tank. These filters also remove minute amounts of oil that enter through the gas pressurization process.  The lines that connect these fuel systems must be approved for use with propane or natural gas. Use only specifically manufactured flexible reinforced stainless steel wire braid hoses with a rated working pressure of 350 psi and minimum bursting pressure of 1750 psi on propane systems. Stainless steel CNG fuel lines must have a rated bursting pressure of 4 times the maximum working pressure, or at least 14400 psi. ### Components of Carburetor Air-Fuel Mixer Systems Carburetor air-fuel mixer systems use a mixer and throttle body arrangement in place of fuel injectors. The mixer and pressure regulator work together to proportion fuel flowing through the mixer. This type of system is common in stationary engine applications such as irrigation engines. Air-fuel mixer systems also work well on machines such as forklifts, which do not require a wide range of engine speeds. The components of a typical air-fuel mixer system are 1) a carburetor-mixer; 2) the air intake; 3) a throttle body; and 4) an intake manifold.  The air-fuel mixer performs the same duties as a gasoline carburetor, except that the fuel is already a vapor when it reaches the mixer. Many systems combine the air-fuel mixer with the throttle body.  ### LPG FUEL SYSTEM SPECIFICS The LPG used in spark ignition engines is a combination of propane and butane. Propane has an octane rating of 110 to 125, while butane has a rating of about 95. Propane vaporizes easier, but butane is more stable in warm weather, and does not produce as much pressure when it vaporizes. In most cases, LP-gas ranges from 90 to 100 percent propane, with a minimum octane rating of approximately 104. For information on the specific contents of LPG, check with your local supplier. Vapor fuels provide a more complete combustion with fewer exhaust emissions and fewer contaminants in the lubricating oil. LPG is stored in a steel tank capable of containing a maximum pressure of 250 PSI, the pressure required to keep the gas in a liquid state. LPG fuel tanks must never be filled completely; space must be left at the top of the tank in order to compensate for increases in pressure changes caused by vapor that is formed as the temperature of the LPG changes. LPG fuel systems use either liquid withdrawal or vapor withdrawal to pull fuel from the tank. Most systems use the liquid withdrawal method to supply the engine with fuel during normal operation; however, the vapor withdrawal method can be used to help start the engine in very cold weather. Before the engine can mix the fuel with air, a converter must vaporize the liquid fuel. LPG tanks are equipped with a pressure relief (pop-off) valve, which momentarily opens to release some of the vapor if the pressure rises above safe limits. In addition to the pop-off valve, tanks fittings also include: 1. Manual shutoff valve -- equipped with excess flow check valve 2. Liquid withdrawal valve and high-pressure fuel line – draws fuel from the fuel tank 3. Liquid level gauge - shows when the tank is 80 percent full. Tanks should never be filled to more than 80 percent of their capacity to allow for expansion of the liquid. 4. Filler valve - used to fill the tank with fuel. It will have a double check valve to prevent fuel from flowing back when the filler hose is disconnected.  Replace worn or damaged gauges or valves as soon as possible. However, the tank itself should not be serviced in any way. Fuel tanks should be serviced only when empty. Exhaust the fuel supply by running the engine, and contact your local LP-gas distributor. Do not attempt to weld on LP-gas tanks. ### Converters and Fuel Pressure Regulators The converter vaporizes and expands LPG by warming it and reducing its pressure. The liquid fuel warms while moving through a spiral chamber that circulates engine coolant in an adjacent spiral chamber. These two spirals make up the heat exchanger chamber. The low-pressure chamber reduces the pressure of the vaporized gas and passes it on to the carburetor. This chamber connects to the heat exchanger through a low-pressure valve, operated by a lever actuated by a flexible diaphragm.  When the engine withdraws some vaporized fuel from the low-pressure chamber, the pressure inside the diaphragm reduces. This change in pressure causes the diaphragm to depress the lever and open the low-pressure valve to allow the intake of vaporized fuel from the heat exchanger. As the pressure inside of the low-pressure chamber increases, the diaphragm moves back to its normal position, and a spring moves the lever to close the valve. Converters seldom need servicing as long as the fuel and coolant are clean. Freezing of the engine coolant is the main cause of damage to converters. To avoid this problem, use an adequate antifreeze mixture, or drain the converter and disconnect the coolant lines when storing an engine for the winter. Converters also have a flexible gasket, which allows for expansion of the coolant if it should accidentally freeze.  Converters are similar to the fuel pressure regulator in an EFI system. Pressure changes activate diaphragms that monitor fuel flow rates. Engine coolant circulating though the regulator prevents the fuel from returning to a liquid state. ### NATURAL GAS FUEL SYSTEM SPECIFICS Compressed natural gas (CNG) is a good alternative fuel since it burns cleanly and is less expensive in some regions than gasoline or diesel. However, unlike propane and butane, which are produced from petroleum, natural gas is a naturally occurring fuel that is removed from the earth, stored, and transferred in a gas state. Natural gas is mostly methane (CH4), which has a molecular weight of 16. This makes natural gas lighter than air (molecular weight 29), and causes CNG to dissipate if a leak occurs. A chemical odorant is added to natural gas to alert users to leaks. LPG has a molecular weight of 44, so leaks tend to settle into low areas and form explosive pools. Natural gas fuels have ignition temperatures in the range of 1300°F, higher than gasoline. Liquefied natural gas (LNG) is natural gas cooled to -259°F (-126°C) to form a liquid. For LNG to remain in a liquid state, temperature, as well as pressure must be maintained. LNG is not generally used for transportation purposes. The fuel system required to deliver CNG to the engine is similar to the LPG system. The National Fire Protection Association (NFPA) specifies that a CNG fuel system consist of: 1. fuel storage cylinders, 2. pressure relief valves, 3. manual shut-off valves, 4. a filling connection with a check valve, 5. a manual valve downstream from the container valves, 6. a pressure regulator capable of reducing the fuel supply pressure to the lower engine service pressure, 7. an automatic shut-off valve (in the event of engine stall), 8. a carburetor or gas-air mixer, and 9. a pressure gauge. CNG is stored in cylinders under pressure of approximately 2,000 to 3,000 PSI. The cylinders can be made of aluminum or steel, and may be coated with a layer of composite fiberglass to provide additional strength and insulation. The cylinder size ranges from 5 to 12 gallons, and the size and number of cylinders determines the maximum amount of fuel that can be stored on the vehicle. Natural gas travels from the fuel storage cylinders throughout the system in stainless steel fuel lines. These lines must be of high quality to withstand pressure and corrosion. A fuel pressure regulator receives the gas from the fuel storage cylinders and reduces the pressure. The gas enters the regulator at approximately 2,000 to 3,000 PSI, where the first stage of the regulator reduces its pressure to about 300 PSI. The second stage of the regulator further reduces the pressure of the gas to approximately 2.5 ounces PSI. Fuel injected engines are designed to handle high pressures, and only require one electronically - controlled regulator to reduce the pressure of the gas to around 130 PSI before entering the fuel metering block. In a fuel-air mixer system, the gas enters the mixer after the pressure is reduced. Because CNG has a higher octane rating than gasoline, the timing must be advanced significantly to allow for complete combustion and avoid pre-ignition. CNG fuel systems should only be installed, serviced, or repaired by service technicians who have been specially trained to work on them. ### SAFETY PRACTICES FOR HANDLING AND STORING LPG OR CNG Most accidents involving LPG or CNG are due to unsafe handling procedures or ignorance of safety procedures related to the handling and storage of these fuels. Neither LPG or CNG is dangerous if the recommended safety and operating procedures outlined by the National Fire Protection Agency (NFPA), Texas Railroad Commission (RRC), Department of Transportation (DOT), and the owner's or operator's manual for each type of system are followed. The most important factor to remember about LPG or CNG fuel systems is that the fuel is always under pressure. Although the pressures will vary from component to component according to the type of system, the entire system is under pressure and the recommended safety precautions should be followed at all times. Some of the general safety guidelines for handling and storing LPG and CNG are listed below. 1. Stay outdoors when filling storage tanks and equipment fuel tanks. 2. Never smoke or use an open flame when filling or servicing the fuel system. 3. Never fill an LPG fuel tank more than 80% (allow for fuel expansion). 4. Always use a vapor return line when filling a fuel tank. 5. Close both the vapor and liquid valves on the fuel tank when storing equipment. 6. If the equipment is to be operated indoors, be certain that the building is well ventilated. 7. Before servicing fuel system, evacuate lines by closing the tank shutoff valve and running the engine out of fuel. Repairs should only be performed by trained service technicians. It is important to remember that LPG vapors are heavier than air and will settle in low areas to create a "pocket" that can explode if exposed to a spark or flame. Extra precaution should be taken when filling the fuel tank, since some gas will escape from the system during the filling process. If the filling area is not properly ventilated, pockets can form and explode when the engine is started. This is a concern with LPG. It is also important to remember, CNG vapors are lighter than air and will normally dissipate into the atmosphere. CNG vapors can gather in a confined space. CNG is stored under higher pressures than LPG. Test CNG storage tanks for corrosion and cracks every three to five years, depending upon the material used to construct them. However, the newer NGV-II tanks offer a 15-year life with periodic visual inspections. There is not a required inspection interval for LPG tanks, but they should be checked periodically for corrosion or damage. Fuel storage tanks should be painted to prevent rust. The biggest challenge in dealing with LPG and CNG fuel systems is dealing with the pressures involved. Specialized training is required for technicians to be able to safely work with compressed gas fuels. Currently, there is a shortage of both training and qualified personnel to deal with compressed gas fuels. Pressurized equipment to store the gas and refuel equipment is expensive as well. For these reasons, the use of alternative fuels such as CNG and LPG has great implications for use in fleet applications such as materials handling, transportation, and warehousing. CNG and LPG technologies are also very well suited for use with irrigation wells, portable welders, generators, and similar situations. ### Careers The National Propane Gas Association operates a Certified Employee Training Program (CETP). This program involves eight different functions of the LP-gas industry. The introductory-level course in basic principles and practices serves as a prerequisite to all other levels. This level involves 3 to 5 hours of objective instruction. The CETP dual-certification process involves both written assessment and skills performance. The NPGA has also developed a training program and materials for propane carburetion installation and service personnel. A significant portion of this training is dedicated to understanding the operation of the electronic fuel injection system. The National Institute for Automotive Service Excellence (ASE) certifies programs to train technicians for servicing CNG and LPG systems on light and medium-duty trucks. This certification program is supervised by the National Automotive Technicians Education Foundation (NATEF). Training programs may be certified in several areas: 1. Electrical/Electronic Systems 2. Engine Performance 3. LPG Diagnosis & Repair 4. LPG Maintenance 5. LPG Conversion/Installation 6. CNG Diagnosis & Repair 7. CNG Maintenance 8. CNG Conversion/Installation Programs may certify in LPG, CNG, or both. Conversion/Installation is an optional course of study for minimum certification in either area. In Texas, LPG/CNG technician certification and instruction is offered through the Railroad Commission's Alternative Fuels Research and Education Division (AFRED). **(For further information about careers dealing with alternative fuels, refer to IMS video #96809 Career Encounters: Alternative Fuels Vehicle Technician.)** **(After completing an SAEP activity related to alternative fuels, be sure to record the entry in the journal page of your web-based record book, and click on 421-I or 422-G for the Course and Unit of Instruction.)** ### GLOSSARY OF TERMS * **Alternative fuel** - A fuel that is substantially non-petroleum, and yields energy security as well as environmental benefits. * **Bi-fuel** - An engine power system capable of operating on either gasoline or compressed gas. * **(BTU)** - Amount of heat needed to raise the temperature of one pound of water at approximately 60ºF by one degree F. A therm is equal to 100,000 BTU's, while a kilowatt-hour (kWh) is equal to 3413 BTU's. * **Converter** - Reduces pressure and vaporizes fuel to a dry gas before entering the carburetor. * **Lean-burn** - A system that uses more air than is theoretically needed to burn all the fuel. * **Lock-off valve** - Controls the flow of fuel in a compressed-gas system. * **Mixer** - The engine component that combines fuel with air to form a combustible mixture. * **Octane** - The measure of resistance of a fuel to detonation or pre-ignition. * **Solenoid** - An electromechanical device that, when connected to an electrical source, produces mechanical movement such as opening or closing a valve. * **Throttle body** - The engine component that uses a butterfly valve to control the fuel-air mixture entering the intake manifold. ### REFERENCES * Fuels and Lubricants. Athens, GA: American Association for Vocational Instructional Materials. * Fundamentals of Machine Operation: Tractors. Moline, IL: Deere and Company. * Fundamentals of Service: Fuels, Lubricants, and Coolants. Moline, IL: Deere and Company. * Fundamentals of Service: Engines. Moline, IL: Deere and Company. * Natural Gas Vehicle Quick Reference Guide. Natural Fuels Company LLC. (2000) [On-line]. Available: http://naturalfuels.com * NFPA 52: Compressed Natural Gas (CNG) Vehicular Fuel Systems Code. Quincy, MA: National Fire Protection Association, 1998. * NFPA 58: Liquefied Petroleum Gas Code. Quincy, MA: National Fire Protection Association, 2001. * Training Manual for Propane Carburetion Installation and Service Personnel. Skokie, IL: National Propane Gas Association, 1995. ### RELATED WEB SITES * General Land Office: http://www.glo.state.tx.us * Impco Technologies, Inc.: http://www.impco.ws * Railroad Commission of Texas: http://www.rrc.state.tx.us * National Automotive Technicians Educational Foundation: http://www.natef.org * National Fire Protection Association: http://www.nfpa.org * National Propane Gas Association: http://www.npga.org * Natural Gas Vehicle Coalition: http://www.ngvc.org * US Department of Energy, Alternative Fuels Data Center: http://www.afdc.nrel.gov * National Research Center for Coal & Energy: http://www.nrcce.wvu.edu * American Gas Association: http://www.aga.org