DRIVETRAIN SYSTEM
PROPANE AUTOGAS Vs. Battery Electric Drivetrains
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Propane and electric vehicle drivetrains are different in design, but offer their own set of benefits when used in the appropriate duty cycles. Contributed by Adam Wilkum, Director of eMobility, ROUSH CleanTech
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e hear a lot about various alternative fuel vehicles. Just how different are vehicles fueled by propane autogas and those charged by electricity? We get into the details and explain the benefits of each. From a drivetrain perspective, propane and electric vehicles are very different; however, each have their own benefits when used in ideal duty cycles. Propane-powered vehicles use an internal combustion engine, but since the combustion of the fuel does not produce the same level of harmful chemicals as diesel or gasoline, they do not require the complex engine aftertreatment to meet tailpipe emission standards. Electric vehicles use a high voltage motor and battery for propulsion; there is no engine required.
How the drivetrains operate A battery-electric vehicle operates when energy is stored in the form of direct current within hundreds of individual battery cells wired together in series within a large battery pack. Some trucks may operate with a single battery pack, however, most use multiple battery packs to provide enough
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power for a usable vehicle range. When the operator uses the accelerator pedal, the high-voltage direct-current electric motor takes energy from the battery packs and transfers it into mechanical torque to move the vehicle forward. When the accelerator pedal is released or the service brakes are applied, the electric motor then reverses to act like a generator, which provides a source to recharge the high voltage battery packs. While the regen created by capturing this kinetic energy isn’t enough to fully recharge the batteries, it can provide for higher vehicle efficiency, increasing total vehicle range. A propane-powered vehicle operates with liquid propane that is kept under relatively low pressure in a fuel tank and pumped to the engine via a fuel pump. While most of us generally think of propane as a gas, it is a liquid at -44 F (-42.2 C) or at pressures over 100 psi (6.9 bar). A liquid fuel system is much more reliable than a gaseous vapor system, because fuel pressure can be kept more constant and environmental factors like temperature and humidity have less of an effect on vehicle reliability. Once the liquid propane is pumped to the engine, it is
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injected into the combustion cylinder and fueled much like gasoline. This combustion creates force to turn the engine crankshaft, which is transferred to the vehicle transmission, then finally to the driveshaft and rear axle to propel the vehicle forward.
Fueling and charging Propane vehicles are fueled in a traditional sense, meaning the vehicle operator connects a fueling nozzle to the vehicle, which is connected to a pump that transfers propane from a large stationary tank into the vehicle fuel tank. At a rate of 8-10 gpm (30.337.9 lpm), fueling a propane vehicle takes about the same time as refilling a gasoline vehicle. Obtaining and dispensing fuel is one of the major operational benefits of propane as a vehicle fuel, as it is easily transported from refineries to end user locations, it is non-toxic and non-carcinogenic, and it can be obtained for a relatively low cost — less than any other transportation fuel
