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This is the second of two articles about the future of alternative energy for off-highway products. Read the first article here.
The use of alternative fuels requires several changes to the vehicle structure, some of which may affect the safe, efficient operation and maintenance of the vehicle.
Over the next decade, as the construction and agricultural industries move towards alternative energy sources, now is a good time to become familiar with these changes.
CNG (compressed natural gas) is usually stored at a pressure of approximately 3600 psi. Well-built tanks can usually last 15 to 25 years. In other words, regular tank inspections are essential. Unlike liquid fuels (such as gasoline or diesel), CNG leaks are not easily detected by puddles on the ground.
LNG (liquefied natural gas) must be stored at -260°F. LNG storage tanks must include methane detectors to monitor leaks.
The storage pressure of propane or LPG (liquefied petroleum gas) is 150 psi. Its energy density is 270 times greater than that of the gas form. Cummins Technology Project Leader David Langenderfer said: “When propane leaks, once exposed to ambient temperature, the fuel will expand rapidly.” He talked with virtual participants at the AEM product safety and compliance seminar. “For safety, the puncture resistance of the fuel tank must be 20 times higher than that of gasoline or diesel fuel tanks. The propane tank also has a quick-release K15 dispenser connector.”
Hydrogen fuel cells have extremely high pressures-rated pressures of 5,000 to 10,000 psi. Sensors are also needed to detect leaks.
Diesel remains the universal energy source for agriculture and construction. Its energy content is 130,500 btu per gallon. Natural gas has a higher energy content at 140,000 btu. Propane is a very fast burning fuel with an energy content of approximately 90,000 btu per gallon.
Hydrogen began to become interesting. If it is slightly pressurized at a concentration of 7 to 50%, the hydrogen will automatically ignite. Unfortunately, hydrogen fuel cell manufacturers cannot add odorants to help detect leaks. Doing so will damage the fuel cell. Hydrogen is also 57 times lighter than gasoline vapor and 14 times lighter than air, so it is immediately released into the atmosphere.
Langenderfer pointed out: “The biggest problem with hydrogen is people’s ability to see flames.” Hydrogen burns very cleanly and is difficult to see during the day. If the vehicle leaks and catches fire, specific safety sensors and protocols are required. For example, exhaust chimneys should be installed in storage facilities along with alarm flame detectors in storage facilities and gas stations.
Langdefer said that current hydrogen fuel tanks include a plastic lining, a carbon fiber reinforced plastic layer to ensure pressure resistance, and a glass fiber reinforced plastic layer to protect the outer surface. ISO/TS 15869 is an important standard for testing tank durability.
From the perspective of alternative energy sources, the full electrification of off-road buildings and agricultural machinery is imminent. Langenderfer said it’s a good idea to be one step ahead and start learning battery characteristics and key terms.
First, the battery system is usually assembled from multiple modules. According to the energy demand of the vehicle, from two to eight.
A diode refers to an electrical connector at both ends that allows current to flow in only one direction.
HVIL stands for dangerous voltage interlock circuit. This is a security feature designed to protect the end user. HVIL is a low-voltage circuit that runs parallel to the high-voltage circuit and is used to monitor the connection of components and cables to ensure the safety of all high-voltage connections. Langenderfer pointed out: “HVIL is connected to all equipment that runs high voltage.” If HVIL is disconnected, the entire battery system will open the contactor for safe maintenance.
MSD stands for manually operated main service disconnect switch. MSD is just a switch you use to disable the high voltage system.
In addition to the above functions, the high-voltage battery system also has other safety elements built in.
For example, orange cables are used to signal high-voltage lines. The battery has a battery discharge hole or a tearable lug, which can be properly discharged when the battery is overcharged. Langenderfer said: “Many battery architectures also have current-breaking devices and current-limiting fuses.”
Many safety standards are being developed for battery systems, including SAE J2910, which discusses basic PPE, the need for properly insulated repair tools, and the requirements for power outage after disconnection.
The main safety hazards of electrification include overcharging, internal/external short circuit and thermal runaway. “The best and most effective operating temperature of the battery system is 20 to 30°C,” Langenderfer said. “These systems can be air-cooled, but many systems are liquid-cooled with chillers.”
Another security consideration is related to connections. Langenderfer said: “When measuring the terminal, you need to make sure that it is connected to the right side of the battery.” “There is a lot of energy there. If it is not done correctly, the connector may eventually melt. This is why safety glasses and high-voltage protective gloves are used. The reason why PPE is so important.”
What is easily available is called a rescue stick or steering stick. Langenderfer explained: “A joystick that complies with ASTM F711 will help you move the shocked person without being shocked.”
It is also necessary to prepare for battery fire. Langenderfer said that because the metal casing surrounds the battery, it is difficult to obtain enough water from the fire. However, if you do not cool the area sufficiently, the fire threat may last for more than 20 hours. In addition, the effectiveness of the fire extinguisher depends on the chemical nature of the battery.
“High ambient temperature is not your friend,” Langenderfer added. “This will extend the aging time of the battery and put a greater burden on battery cooling. It is important to understand your high ambient temperature capabilities in order to appropriately adjust the size of the battery thermal management system to provide the necessary cooling.”
The lower ambient temperature is not a good friend either. As the temperature decreases, the battery’s reaction speed becomes slower. Therefore, you may have to heat the battery to a temperature range of 20 to 30°C for it to operate efficiently. “Manufacturers need to consider this when determining the battery size,” Langenderfer said. “You still have to provide electric heating for the cab heater. But you must also provide enough energy to heat the large battery pack.”
OEMs must also consider other accessories in the entire battery system. These include heat management pumps and fans, hydraulic pumps, air compressors, inverters and converters. Where will these items go, how will they function, and how will they affect the end user’s vehicle maintenance and maintenance capabilities?
Langenderfer said that some propane and natural gas engines require unique spark plugs. In other words, a lower amount of carbon burn will result in a longer engine life. Since the fuel is gaseous, the cold start should also be improved, thereby eliminating the need for grid heaters, as required by diesel engine powertrains operating in very cold conditions.
Regarding hydrogen, it is important to ensure the durability of the balancer equipment. The end user must also stay in the cooling system and fuel filter maintenance.
For battery systems, major preventive maintenance needs have emerged around coolants, lubricants and related filters, religious inspections of HVIL and wiring, and continuous monitoring of battery health.
Langenderfer said: “Sometimes, the battery system is located in the location where the vehicle is usually lifted in the store.” “When designing the battery system, the OEM really needs to consider how the end user will repair the battery.”
Similarly, the size of the fuel tank should also be considered. Propane, natural gas and hydrogen tanks are usually larger than gasoline or diesel tanks. In addition, because these fuels are gaseous, regular inspections are essential to monitor for emerging defects and leaks. Therefore, it is important for OEMs to ensure that the fuel tank is easy to overhaul and repair.
The routing of the exhaust system has also become more important. Langenderfer said: “You don’t want to put anything next to the fuel tank, battery or cable, because you don’t want to damage or melt anything.”
As mentioned in the first article, the benefits of using alternative energy sources to refuel off-road machinery are obvious. It is also clear that the alternative fuel vehicle architecture has many similarities with conventional powertrains. There are also many differences. Understanding these differences helps manufacturers design products to make the construction and agricultural industries more energy-efficient and environmentally friendly, while still meeting the end-user productivity, safety and maintainability needs.
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