Powering the U.S. Army of the Future (2021) / Chapter Skim
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6 Vehicle Power and Large Weapon Systems
6 Vehicle Power and Large Weapon Systems
Pages 73-91
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From page 73... ...
On COTS engines, emission-related hardware is typically removed due to lower emissive requirements. Unique military-specific power packs provide higher performance, but are typically higher cost due to lower production volumes.
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From page 74... ...
Cummins, Daimler, Navistar, and Volvo have all demonstrated a capability to provide more than 50 percent brake thermal efficiency on their Department of Energy (DOE) -sponsored SuperTruck projects.1,2 Weichai, a Chinese engine manufacturer, also recently announced that it has introduced into production a 13 L, 417 kW truck engine that has achieved 50.26 percent brake thermal efficiency.3 They noted that this was 1 D
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From page 75... ...
Each of these programs will enhance the power density, fuel efficiency, and/or thermal signature of military power packs. Additional information regarding the content and functional benefits of each of the above programs is contained in Chapter 8, "Fuel Conversion Efficiency and Other Material Driven Opportunities." Recommendation: The Army has undertaken a number of internal vehicle power plant programs (Advanced Powertrain Demonstra tor, Projected Propulsion System, Advanced Mobility Experimental Prototype, and Platform Electrification Mobility)
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From page 76... ...
vehicle power bus. The system is expected to provide approximately 3 miles of silent mobility, 40 percent improved acceleration, 30–35 percent reduced fuel use, and 15 percent improved speed on grade.4 JP8/DIESEL FLEX FUEL CAPABILITY (AN OPPORTUNITY TO SHORTEN THE FUEL SUPPLY LINE)
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From page 77... ...
As another, Germany's IWIS Group has a simpler "bang/bang" compression ratio system going into production in 2023.9 Another approach that might enable use of gasoline in a diesel engine without modifying the compression ratio is to use spark plug assistance. Mazda's Skyactive-X spark-assisted gasoline compression ignition engine provides such an example, with its 16.3:1 compression ratio.
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From page 78... ...
Combustion is initiated either with a spark plug (or possibly two) in the combustion chamber combined with a high-energy ignition system or with a diesel pilot injection.
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From page 79... ...
FREE-PISTON ENGINES A free-piston engine is a linear internal combustion engine in which the piston motion is not controlled by a crankshaft but instead determined by the interaction of forces from combustion chamber gases, an oscillator or rebound device (e.g., a gas spring chamber) , and a linear alternator (see Figure 6.2)
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From page 80... ...
TURBINE ENGINES Within the Army, turbines are the clear power plant of choice for helicopters used in Combat Aviation Brigades because of their superior power-to-weight and power-to-volume ratios. The M1 Abrams Battle Tank is unique in the world's fleet of ground combat vehicles in its use of a gas turbine.
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From page 81... ...
It is anticipated that these engines will continue to be much more advantageous on a power-to-weight basis but less fuel efficient than diesel engines sized for combat vehicles.20,21 Conclusion: Gas turbines continue to be the power pack of choice for most Army helicopters due to their power-to-weight advantages. On the other hand, diesel engines will continue to be the power pack of choice for most ground combat and tactical vehicles due to their fuel efficiency advantages.
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From page 82... ...
The analysis in Figure 6.3 shows that the problems with an electric tank are fundamental due to the significantly reduced energy density of batteries, both on a volumetric and gravimetric basis, versus JP8. However, up to 90 percent of the time, a ground combat vehicle is idling, therefore running a large kilowatt internal combustion engine (such as the Abrams' 1100 kW)
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From page 83... ...
Internal Army studies at the Ground Vehicle Systems Center based on a more detailed analysis of a much lighter tank with anticipated vehicle improvements show similar results. Note that they are projecting that the battery pack for an all-electric tank using batteries with the same energy density as a Tesla Model S would weigh 60,100 lb and require a space claim of 605 ft3.
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From page 84... ...
, a 95 MW power source connection of the right voltage and current would be required.24 BATTERY ELECTRIC TACTICAL VEHICLES Similar to the above conclusions for armored vehicles, all-electric tactical vehicles have limited practicality on the battlefield, given their recharging requirements. For example, as shown below, the committee's analysis showed that each Joint Light Tactical Vehicle (JLTV)
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From page 85... ...
demonstrator, which is intended to leverage learning from present and planned battery electric vehicles, such as the Tesla Class 8 truck and the AMEP program mentioned earlier. Projected 6.2/6.3 funding in fiscal years 2023–2027 is $74 million.26 Conclusion: The power requirements to recharge the batteries of an all-electric armored ground combat vehicle make an all-electric design impractical.
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From page 86... ...
(Tier 2, Lead) HYBRID COMBAT VEHICLES As shown in Figure 6.7, the Army is studying a number of hybrid combat vehicles consisting of internal combustion engines, battery packs, motor/generators, and electronic controls.
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From page 87... ...
It is a constraint due to the enormous power required to transfer massive amounts of energy in a short time period. IMPORTANCE OF RUNNING AT BSFC "SWEET SPOT" Figure 6.8 is a brake-specific fuel consumption (BSFC)
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From page 88... ...
Although this braking energy recovery should be possible in a wheeled vehicle, such as Stryker, it is unlikely in a tracked vehicle due to the enormous friction within the tracks. In a series hybrid configuration, only under high torque demand is electrical power provided by both the internal combustion engine generator and the battery energy storage.
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From page 89... ...
Recommendation: The Army should conduct a modeling and simula tion analysis of different battlefield scenarios to define the optimal silent mobility range that is required for ground combat vehicles. The results will influence the size of the battery storage required and inform the optimum mix of research and development for parallel and series hybrid configurations.
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From page 90... ...
3. Hybrid configurations (using internal combustion engines)
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From page 91... ...
Potentially, future ground combat vehicles could be designed with multiple "plug and play" power packs (electric/ICE hybrid, fuel cell, battery electric) that could be substituted for one another, thereby enabling the same ground combat vehicle to provide different performance attributes dependent on the specific battlefield mission profile.
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