It was over 100 years ago that the railroads discovered the most efficient way to use diesel engines.
What was it? Bolt them up to a DC generator and use the electricity to turn DC electric motors which, in turn, provide the motive force to turn the wheels of the locomotive.
Diesel electric was/is attractive for locomotives for a number of reasons, but efficiency isn't one of them. They are about the only way to deliver a few thousand HP from zero to maybe a hundred rpm. And dynamic braking (using the motor as a generator with a huge load bank) is about the only way to control speed down a long grade. But those critical features come at the expense of efficiency, not with the benefit of efficiency.
Let's just be clear about one basic thing. A gear drive for any particular load with ALWAYS be more efficiency than a motor/generator/motor. It's basic physics. Power loss in a gear drive is about 3%. Power loss in a modern m/g/m is about 10% for the generator, 10% for the switch gear, and 10% for the motor.
So with a m/g/m you are starting out at a 27% deficit, so the other benefits need to be pretty compelling, or you need some clever way to make up the energy loss. On a locomotive, it's worth it for the transmission and braking characteristics. On a hybrid car, the deficit is reduced because much of the propulsion is via gear, not m/g/m. And the big win is taking the locomotive dynamic braking idea and storing that energy for re-use rather than dumping it as heat as conventional car brakes do.
And this is why a hybrid boat is just a plain silly idea. You incur the losses of a m/g/m, and don't have any regenerative braking to make up for it. The only benefit once again comes back to it's characteristics as a transmission, allowing you, within limits, to more optimally set the engine's operating point for improved bsfc. But that can much more easily and efficiently be accomplished by a two speed transmission - something that actually already exits for marine applications. In short's a losing proposition before you even start the engine.
Oh, people typically cite diesel electric tugs and cruise ships as success examples. However in both cases, it's all about maneuverability and flexibility. A cruise ship that can enter a port and dock itself every day or two is a huge savings over hiring a couple of tugs each time. They accomplish that with pod drives and a multitude of thrusters, all electrically driven for speed control, much like a locomotive. It's about the transmission, baby.
Best of all worlds.
We all know that any diesel engine is most efficient AND most reliable when it runs in squarely the 'sweet spot', where HP and torque curves intersect with the demand curve, where exhaust tempertures and combustion chamber temperatures are optimized. Where the intake and exhaust systems can be tuned exactly to the HP/cu-in ratio.
Sort of. The HP, torque, and demand will always intersect at any operating point, But it think I understand what you are saying, which is that diesels typically have an rpm/torque region where bsfc is lowest (best). If you plot it like a terrain map, there is a sink hole where bsfc is lowest. But important to note - lowest bsfc comes in a specific load zone, and load is a combination of rpm and torque, not just rpm, and not just torque. Just spinning an engine at a particular rpm doesn't create efficiency.
Surprise surprise!!! This is also where diesel engines produce the least soot and pollutants! Surprise surprise!!! The 'demand curve' of a generator back-end is the only load that allows 100% perfectly managed loading of a diesel engine.
That's really no the case at all. A truck running at the same load would be the same. And a boat operating at the right speed would be the same. Boat propulsion is ideal for this since it is such a constant load, and this is the basis for the whole over-prop you boat approach to engine loading.
Regardless of whether its a diesel-electric locomotive or a trawler, the one technology that is utterly ignored in this debate is diesel-electric.
Hardly ignored. It has been optimized to create hybrid cars.
If I were designing the 'greenest' possible trawler, it NOT have $150,000 worth of chinese lithium batteries. It would have:
1) a relatively small, naturally aspirated, diesel engine spinning happily away in it's sweet spot, turning...
2) an ultra-efficient American-made (i.e Polar Power of CA) DC generator, feeding...
3) an American made electric motor propulsion system (i.e. Electric Yacht in MN), AND...
4) ...just enough chinese-made battery capacity to keep the diesel generator duty-cycle under 90% in the worst case scenarios.
Nigel Calder tried very hard to show how this might be an efficiency improvement in a series of articles in Passagemaker magazine. I think he found one very narrow scenario where it was equivalent or perhaps a tiny bit better, but in all other cases it was worse. And certainly not worth the added cost and complexity.
A more efficient approach would be a UN built Cummins or Deere engine, and a US built Twin Disc gear
Now...those of you who have been paying attention to electro-motive engineering during the last 100 years will recognize thiis as a natural evolution of the diesel-electric locomotive. You might slap palm to forehead and exclaim "D'oh! of course this is the answer!"
I would invite anyone to do the end-to-end energy chain math, including the impact on diesel engine reliability, and present any other solution that even gets close.
For cars, I would agree that a diesel hybrid would be better than a gas hybrid. But hardly a break through.
Question: Barring maintenance failures, anybody here ever seen a diesel-powered generator with a naturally aspirated engine fail at less than 10K-20K hours? When run in their 'sweet spot', diesel engines used solely to generate electricity last for a VERY long time...
So...why no 'hype-cycle" for diesel-electric?
Well, now you know why there is no "hype-cycle". And now you know why there are no performance tests showing a hybrid out performing non-hybrid under the same conditions. The "same conditions" part if critical. Most performance data shows reduced speed, which of course reduces power demand.
