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MIT Says We're Overlooking a Near-Term Solution To Diesel Trucking Emissions (arstechnica.com)
An anonymous reader shares a report: Trucking in the US is still driven by diesel-fueled, compression-ignition (CI), internal combustion engines. Daniel Cohn and Leslie Bromberg, a pair of researchers from the Massachusetts Institute of Technology (MIT), published a paper with the Society of Automotive Engineers, suggesting that the best way forward is not to wait for all-electric or hydrogen-powered semis, but to build a plug-in hybrid electric (PHEV) truck with an internal combustion engine/generator that can burn either gasoline or renewable ethanol or methanol. Such a setup preserves the range and affordability that's expected of diesel long-haul trucks while significantly reducing the emissions associated with diesel. To boot, it's a near-term solution; no waiting for battery weight to fall or hydrogen refueling stations to be installed.
A hybrid heavy-duty system isn't a completely novel idea, though a PHEV system has yet to be widely applied and tested in long-haul heavy-duty trucking. A company called Hyliion introduced a hybrid electric-diesel truck in 2017, and San Diego uses a hybrid electric-compressed natural gas bus on its transit system, though the former still grapples with diesel emissions and the latter is not for long-haul use. But there are some distinct problems with all-electric and all-diesel trucks that a hybrid flex-fuel truck could solve. First, freight companies are looking for the cheapest way to transport goods from point A to point B, so expensive electric vehicles don't make short-term economic sense, especially if you're competing with other freight companies using cheaper diesel engines.
A hybrid heavy-duty system isn't a completely novel idea, though a PHEV system has yet to be widely applied and tested in long-haul heavy-duty trucking. A company called Hyliion introduced a hybrid electric-diesel truck in 2017, and San Diego uses a hybrid electric-compressed natural gas bus on its transit system, though the former still grapples with diesel emissions and the latter is not for long-haul use. But there are some distinct problems with all-electric and all-diesel trucks that a hybrid flex-fuel truck could solve. First, freight companies are looking for the cheapest way to transport goods from point A to point B, so expensive electric vehicles don't make short-term economic sense, especially if you're competing with other freight companies using cheaper diesel engines.
They're not hybrid in the same sense as hybrid cars.
In fact, IMHO wouldn't call them a hybrid at all: The diesel never turns the wheel directly, the electrics motors never work without the diesel engine generating electricity, there are no batteries involved in the powertrain. Power always comes from the diesel engine.
It's a diesel engine with an electric transmission.
The electric part of a diesel-electric locomotive just replaces what would be the gear box & clutch / torque converter in a car/truck.
The diesel engines generates electricity which is fed directly to electric motors that drive the wheels because no clutch or torque converter as found on trucks and cars could survive launching an entire cargo train, they'd almost instantly disintegrate/melt/explode, and the gearbox would be impractically enormous to not wear down in seconds under the torque required.
They vary the "gear ratio" (if you will) by increasing or reducing the magnetic field on the electric generator to keep the diesel engine at the same ideal RPM range while changing the effective torque/power output.
And when diesel-electric locomotive brake using the electric motors they send all that energy to huge resistor banks, not batteries, just spewing out the energy as heat.
They don't stock and reuse the braking energy like an hybrid car because no batteries could handle the amount power being dumped when braking a freight train to be even worth trying to recuperate that energy.