One notes that operating a compression-ignition engine at constant speed near the peak of a correctly-engineered torque curve would give reasonably full combustion without the various transients. Likewise, accelerating the engine where necessary while decreasing excitation or other load, or even providing ‘motorization’ both at the crank and on any forced induction, will reduce the particulates. And increasing combustion ratio will help assure complete carbon burn during the duration of combustion in the power strokes.
One operating mode for a hybrid commuter locomotive or DMU is to run the prime mover at a constant speed or a slowly varying speed and let the battery take care of supplying power for acceleration and absorb the regenerate braking energy. This would have a number of advantages: cleaner exhaust; less fuel consumption; potentially faster schedules from quicker loading and higher peak power; for DMU a dramatic reduction in brake wear and brake dust.
The main reason why such a hybrid locomotive hasn’t been built is that suitable batteries have only recently come into existence. To make the technology viable, the batteries would a cycle lifetime in the tens of thousands. One of the first that I’ve run across are the sodium ion batteries being made by Natron, which is claiming 50,000 cycles and has a high specific power (watts/lb, not watt-hr/lb).
What is the advantage? Previous hybrid locomotives use a diesel engine or fuel cell to charge batteries, which then power the electric motor. This simplifies the drive train.
Regards, Volker
My impression is that most of the hybrid locomotives in the US have been used as switchers. My idea for a hybrid commuter locomotive would require a battery system capable of sourcing 4MW and sinking 6MW to allow for adhesion limited tractive effort at 60 to 70mph and also to recover much of the kinetic energy with regenerative braking.
CN has bought a Progress Rail SD70H dieselbattery hybrid locomotive that is said to be comparable to the SD70ACe-T4. I haven’t found specifics.
Metro North RR has bought Siemens Charger B+AC locomotives that can run under catenary or on batteries. They can power trains at speeds up to 125 mph under catenary and on battery power for up to 100 miles, depending on train configuration and route characteristics.
One could exchange the AC equipment with a small diesel generator, but what for?
I think for commuter line multiple unit trains are better especially if you look for short travel times.
The Hitachi HTR412 of Trenitalia can run on diesel, catenary and on batteries but only for a few miles within city limits.
The Stadler Class 756 for Transport of Wales is similar with a 480 kW diesel generator, 560 kWH battery capacity and overhead catenary capability.
For locally emmission free service there are alternatives using Hydrogen fuel cells instead of the diesel.
So if you want a hybrid why not go the next step and use fuel cells? You get mor range than with batteries alone.
Regards, Volker
You need the whole hydrogen-carrier distribution architecture, which is already being deprecated (I believe in favor of better distributed charging) on some of the European ‘hydrogen’ battery trains.
I happen to like combination fuel-cell/battery locomotives – they are actually a workable solution, as opposed to pure battery locomotives or pure fuel-cell locomotives. But the critical thing is having the distribution and the fuel supply assured at a cost that makes sense. I am in favor of blue hydrogen with sequestration, not ‘green’ electrolysis kludge, as the source.
Erik talked about commuter trains so the hydrogen infrastructure seems manageable and can be limited to tank trucks if necessary.
In Germany, there were problems with hydrogen supply and interrupted supply chains at Alstom. I see no reason why things should not work better in the US.
In Germany, pure BEMUs, which are charged either via plug-in or short stretches of overhead lines, are usually sufficient for distances of less than 100 miles.
This is by far the more energy-efficient option, as it saves the electricity required for the production, liquefaction, etc. of hydrogen.
Each country has its own specific constraints.
Regards, Volker
Hydrogen has a very low energy density requiring significant energy input to compress or liquefy. The major use is rocket fuel where the high Isp justifies the expense and the hassle of using a cryogenic propellant.
Hybrid with diesel engines and fuel has the potential of being much cleaner than non-hybrid along with significant reductions in fuel consumption. Having on board generation also avoids depending on the grid.
Battery hybrid make more sense than diesel or hydrogen IMO. Hydrogen is not readily available in most major US cities and diesel is a pollutant. Electric buses are already in use on buses, as are LNG and CNG.
The Stadler class 756, a Flirt tri-mode model, can provide 1300 kW at the wheels in diesel-battery mode. In this hybrid mode the train can save about 50% fuel and emissions compared to a diesel train.
I know too little about American commuter railways to be able to judge whether pure battery-powered trains would suffice.
Regards, Volker
IIRC, going from 100% to 30% charge and back wile losing 20% of battery capacity. IIRC, LFP batteries are good for maybe 5,000 similar cycles. Cycle life will likely be much higher with a narrower range of charge/discharge. I would size the battery so that the normal start/stop cycle would use no more than 30% of battery capacity.
Also IIRC, the Natron batteries were good for several hundred watts per pound.
Battery cycles mean full discharge and recharge. So if one recharge per day that’s 137 year life. Outlast the train. Even if it recharges say every round trip than means a couple decades.
We used RP-1, which is just fancy kerosene, for the big Saturn 5 first stage.
And the LH SSMEs would never get anywhere near orbit without the very large solid-fuel boosters that failed (unnecessarily, in my opinion) in the Challenger explosion.
I have long been a proponent of cryomethane as a high-speed vehicle propellant; LNG is a tad cheaper and more readily available.
And the most practical approach to ‘distributed charging’ at stops vastly extends the ‘cycle time’ from 80% down to 20%, if not almost act as float charging.
The far more important criterion, so painfully recognized by the Green GOAT people, is the peak discharge rate at high acceleration, something touted as an important advantage of ‘electric’ equipment (cf. the MARC Penn Line vs. the various ex-B&O runs). It is possible that some kind of KERS might be used in such trains as an analogue of spinning wayside-power installations on electrified lines, to augment battery power and to limit peak regenerative-brake charging rate.
I checked the Natron Energy website for the discharge rate, thinking it was somehwere above 10C. Turns out it is 40C, so that would work very well for a hybrid commuter locomotive or DMU. “Supercaps” have an even higher charge/discharge capability, but the specific energy (w-hrs/lb) is not high enough. The voltage of capacitors droops during discharge, but the voltage on the Natron sodium batteries is relatively flat.
NB: I would want to see data on how the batteries handle high vibration and shock before saying that this is the best choice for commuter hybrids, but the technology looks very promising.
Explanation of “C” for those who are wondering: 1C means charging or discharging at a rate that would go from fully discharged to fully charged or vice versa in 1 hour. Supercaps can do about 1000C.