I realize this was designed to be suitable for retrofits, but why choose a serial over a parallel hybrid for this type of application (short, lightweight passenger trains plying non-electrified corridors)? With particulate filters and SCR, a parallel hybrid drivetrain would be clean enough while providing more peak power and better fuel economy.

Either type could be modified by adding a pantograph or third rail pickup to take advantage of grid connectivity where available on partially electrified lines.

Note also that the rated power of 400kW (535bhp) is modest compared to US train propulsion systems for two reasons:

1) The FRA (Federal Rail Administration) is focused primarily on passive safety, i.e. surviving crashes. This suits private freight operators but burdens passenger services with high train weight and fuel costs.

The rest of the world is focused primarily on active safety, i.e. avoiding crashes through advanced signaling, positive train control, track surveillance etc. (as appropriate). This suits state-owned railroads that must prioritize passenger service.

2) DMU (diesel multiple unit) designs eliminate the traditional locomotive in favor of self-propelled cars with coordinated traction management. The ones at the ends feature a driver cab to facilitate direction reversal at the end points of single-track lines. A typical DMU train would therefore feature at least two small diesel engines.

This unit could be used today to completely redesign tractor-trailer truck morphology. There are two components:

1) serial diesel hybrid mounted underfloor; no mechanical transmission; hubmotors in every axle, tractor and trailer, making every axle a driver.

2) reduce total frontal area by lowering the height of the whole rig through taking advantage of the box beam nature of a shipping container, eliminating the need for a separate I-beam trailer frame, and placing the trailer wheels in a trailing position rather than underneath the trailer.

This allows for diesel-electric drive advantages of high electric motor torque and dynamic braking (no need for jake brakes), and the reduction of frontal area by about 25 square feet, greatly improving aerodynamics. The trailer would run less than a foot off the pavement and would be raised to dock height with hydraulics. There are issues dealing with bridge loadings that would need to be resolved.

Such a redesigned tractor trailer should be able to see a doubling in fuel economy.

@ yaross -

I don't see a driveshaft or transmission anywhere. A serial hybrid system can use the final drive motors as generators when braking.

But yes, the press release isn't really all that clear on what type of hybrid architecture this is.

@ Henry Gibson -

diesel efficiency: up to 45%
microturbine efficiency: around 25%

Gas turbines have many advantages once you get to the multi-megawatt scale. For small powerplants, they are suboptimal unless you have a very low cost source of hydrocarbon fuel.

@Rafael-
I'm not sure why, but heavy diesel-electric trains are, and have always been, series electric drive. The diesel engine turns a generator, and the wheels are driven by electric motors. They are more like axle motors than hub motors, though, since trains don't have differentials or steering. I'd guess that there were difficulties in achieving direct mechanical power transmission and gearing across all the drive axles in the locomotive. Since the wheels are steel, you need all all the wheels to be driven so you can get some traction. As it is, they still have systems to spray sand on the track for extra traction when they are climbing mountain grades.

Something tells me that even if they could achieve power transmission, gear reduction, and a suitable range of gear ratios in order to make it a parallel hybrid, the power transmission equipment would take up too much space, and have lubrication problems. The gears wouldn't be turning that fast, but the forces put on them would be huge. It would be tough to find a suitable lubricant. Oh, yes, don't forget that all this gearing and drive mechanism would still need reverse gearing too!

Plus when you need to start moving a multi-million-pound load, from a dead stop, the 0-RPM torque of electric motors is unbeatable. Now to translate this to light rail, some of the concerns are different- the weight and traction concerns are reduced- but you still have the issues of needing to achieve direct power drive across several axles. The cost and complexity of power distribution, gear reduction, and the range of gearing needed, would add up in a serious way if you had to put it in every car. (Has direct drive from an ICE ever been attempted in a rail application at all?) And as we always say, series has advantages in applications that do a lot of starting and stopping relative to the amount of high speed cruising.

Interesting thought exercise one way or another.

The best part of this is passenger comfort !
When was in Scotland last year, most of the trains had diesel motors under each car that rattled even when stopped at stations. For someone who grew up with smooth electric trains, this ruins the train experience.

Hybrids rule! (at least until we go to all electric)