Developing dieselelectric concepts.

[Powerconversion]

How much would be acceptable price versus an conventional system and how much should savings on fuel consumption be before it's considered a option?

Don't have any new and radical idea, but rather a better integration and implementation that could reduce consumption by 2-20% depending on engine configuration and actual loading of diesels.

 

[DCockey]

Depends on who the customer is.

If it's a commercial customer who does good financial analysis it would depend on the added cost, efficiency differences, maintenance cost differences, reliability differences, noise and vibration differences, durability differences, space requirement differences, any added flexibility in configuration (prime mover does not need to be mechanically connected to the shaft?); the customer's use profile, expected length of service, and access to capital; and some other factors I didn't think of. "Green" image may also be a consideration for some customer.

 

[Powerconversion]

"Green" image may also be a consideration for some customer.

Green image is a sad thing. Lots of systems are marketed great, but are less fuel efficient than traditional propulsion both because of configuration and user-profile. Sadly few firms advice the customers correctly, but prefers to sell what give most profit.
I been involved with diesel-electric systems for 10 years and I see lots of concepts, but most of them are too complicated and mostly been made for green profile and not actual savings. I think better integration between systems can reduce fuel much more without added complexity.

 

[gonzo]

Diesel electric may be more efficient on some applications. For example, I used to work on a 185' (57m) tug with diesel electric. We run eight (8) generators. Depending on the load we would fire from three to all. With a single generator your consumption will be much higher. Also, the reason we had diesel electric was for precise speed control. Unless you need to be within 1/10 of a knot at all times, it doesn't make much sense.

 

[Powerconversion]

Diesel electric may be more efficient on some applications. For example, I used to work on a 185' (57m) tug with diesel electric. We run eight (8) generators. Depending on the load we would fire from three to all. With a single generator your consumption will be much higher. Also, the reason we had diesel electric was for precise speed control. Unless you need to be within 1/10 of a knot at all times, it doesn't make much sense.

The reason consumption was higher on one generator should be power oscillations or load higher than the single diesels optimum load.
An correctly set up system according to fuel consumption would have several DG's with different nominal set-point so that the one or the combination of those achieving best fuel efficiency would run at any time.
Diesel electric also have the benefit of saving maintenance since engines can go on fixed load even at heavy seas unlike conventional where load will vary.

 

[gonzo]

Read carefully. We run the amount of generators necessary for the required power. That is no feasible in a smaller boat.

 

[Powerconversion]

Depending on the load we would fire from three to all. With a single generator your consumption will be much higher.

This is what I read and this is the theory I argue. 1 generator running 80% will have a better consumption than 3 running at 25% load. it will be obvious from datasheet on any diesel on the market. Running more than 1 is in lot of applications required in order to maintain redundancy or to maintain enough reserved power for variable consumers.

 

[gonzo]

Ok, I see what you mean. We run the generators as close to optimum as possible. However, we didn't have diesel/electric for economy, but for accuracy and quick response. It is appropriate for tugs.

 

[Powerconversion]

Ok, However, we didn't have diesel/electric for economy, but for accuracy and quick response. It is appropriate for tugs.

Depends the power requirement, the real large ones with 40 000kW I struggle to see a pure diesel-electric system working out since the machinery would take up a lot of space(size of generators and propulsion motors). One advantage is as u say the response since you have the same torque at all RPM and therefore a linear power-curve.
Was wondering a few years ago why tugs could not have a ecofriendly diesel supplying "normal" consumption for hotel consumers and transit and gasturbines for serious work. Would downsize the machinery spaces and make the vessel a few tonn's lighter with few disadvantages except the efficiency.

 

[gonzo]

I think that buzz words like "ecofriendly" should be left to politicians. As an engineering problem we can discuss efficiency, type and amount of emissions, noise production, etc. What do you mean by "hotel consumers" as it applies to a tug?

 

[Powerconversion]

What do you mean by "hotel consumers" as it applies to a tug?

Anything used in the accommodation, frying-pan, microwave, lights, heat and ventilation.

 

[gonzo]

Gas turbines are good for high power to weight ratio. They are high maintenance and have low efficiency. I have only seen them in high speed craft. In the USA the most common ones are surplus from Apache helicopters.

 

[Powerconversion]

They are high maintenance and have low efficiency.

Only one of those statements are true.
They have quite low maintenance since they have few moving parts.
You can't compare a air grade turbine with the aviation industry's standards of maintenance with marine. Turbochargers are also gas-turbines and they are not known for be high maintenance.
The efficiency is crap, but that would not be a problem if they where in paralell operation with diesels who could operate during low powerdemands and transit.

 

[philSweet]

I would say that the idea of diesel + turbine has been fully developed since 1950 or so. There are people here much better qualified than me to talk about them, but a couple points are worth mentioning.

Jet engines began as piston engine bolt-on gadgets to improve fuel economy and power-to-weight around 1930. A basic arrangement circa WWII would have a blowdown turbine running off exhaust which would drive a supercharger plus pump a good bit of extra power to the crankshaft. Development happened very quickly and they soon realized they didn't need the piston engine anymore, it was just in the way. There were many engines left on the drawing board when jets got rid of the piston block. The term for these units is turbo compounded.

The Russians made a big, badass 42 cylinder turbocompound radial diesel for missile boats. Detroit Diesel and Scania still make them. You can combine the two in nearly any power proportion you like. I know Cat also made at least one of them because I saw it at a demo. The turboshaft was used as the starter motor for a massive genset that could pick up load in 12 seconds. Basically a jet engine pony starter that also worked as part of the runtime turbo system when you turned the burner off.

Napier Nomad 1949

 

[philSweet]

The next option, that actually has something to do with the thread, is a direct electric takeoff from the turboshaft. Again, this can be scaled up to a significant portion of the total rated power of the unit.

Here's an example from Cat, but all the other Turbo Mfgs have these on the test pads. They are about 2 generations out for over-the-road trucks. But as a shaft generator for marine use, they could be engineered today.

One of the drivers for this was to get rid of VGT designs and switch to cheaper turbos, using the electrics to do what the variable geometry did. But if you want a genset, keep the VGT and use it to supply whatever the electrical demand is via the turbo.

http://energy.gov/sites/prod/files/2014/03/f9/2004_deer_hopmann.pdf