[markus_GE]

As for Diesel-mechanic-electrics, maybe there´s some sort of gearing done between the diesel engine and the Generator / alternator? That way, higher Generator / alternator RPM could be achieved, using less diesel RPM. Just a Logical thought, no Research done yet, but it all sounds interesting.

Cheers, Markus

[Lindsayts]

Matej Pacha, on 16 August 2013 - 02:38 AM, said:

Yes - since a diesel engine cannot run at lower RPM than the idle is and still produce some power (but yes, there is some range the engine will make it)

Just a small comment, diesels produce good torque from __VERY__ low revs (unlike a petrol engine) one has no difficulty in starting a diesel car even a Landcruiser in 1st gear without using the clutch. The only requirement being one is on a flat or down hill as the starter will not normally drive such a vehicle up a hill.

Quote

Actually, I didn't make any difference between mechanic and hydraulic setting, because I don't know how to handle the hydraulic one correctly. Let's say that this is a part of my main tasks for v1.0.

If required I can send some information on the performance of hydraulic couplings including torque convertors which should help with the mathematical modelling. The torque handling ability of such couplings is proportional to the square of the rpm. The items are from "Marks Standard Handbook for Mechanical Engineers" one of THE best books on how machinery operates, although VERY expensive. Also there is an item (a graph) from Voith.

One of the major reasons for the wide use of such couplings in industry both straight and torque convertors is reduced maintence and a great improvement reliabilty. Torque amounts in the 1000's of ft pounds and higher range being VERY difficult to control.

Lindsay

[Lindsayts]

markus_GE, on 16 August 2013 - 11:29 AM, said:

As for Diesel-mechanic-electrics, maybe there´s some sort of gearing done between the diesel engine and the Generator / alternator? That way, higher Generator / alternator RPM could be achieved, using less diesel RPM. Just a Logical thought, no Research done yet, but it all sounds interesting.

Cheers, Markus

This has been done is some cars using an electric transmission, including a gas turbine car in the Le man's 24 hour (from memory it was a Chrysler, Note 1). This was/is done to reduced the size and weight of the transmission.
This is not usually an issue though with rail vehicles, the weight of the altenator being small compared with the overall weight of the vehicle.

Note 1, It has a 500 bhp gas turbine, the transmission both altenator, energy storage unit and motors weighed less than 100 kgs. The total power to the wheels was around 700 bhp, being 500 from the main engine and 200 from the energy storage unit. There was an article in the "New Scientist" about it sometime late 1980's I think.

Lindsay

[markus_GE]

I guess, less weight would be a DISadvantage on a loco indeed (reduced friction - think of 25% of the weight of a modern diesel loco being balast!), but there would be the Advantage that the diesel engine can be run at lower RPM in what we know as run 8 / notch 8 thereby still feeding higher RPM to the alternator. Would mean fuel savings altogether: Lower revs = less cyles = less injections of fuel = less fuel burnt = fuel saved. *I hate Long equations :) *

Cheers, Markus

[copperpen]

In a vehicle that uses a fluid coupling between engine and gearbox, the rpm would only be controlled by the throttle, not the speed of the vehicle. This applies to both automatic and manual gearboxes. Far as I am aware there are no DMU classes that have a manual clutch although there may well be some small locomotives that do have one, and there are some that have direct drive. Therefore all diesel mechanical DMU classes in OR should operate with throttle determining RPM, not unit speed.

[Lindsayts]

markus_GE, on 16 August 2013 - 12:52 PM, said:

I guess, less weight would be a DISadvantage on a loco indeed (reduced friction - think of 25% of the weight of a modern diesel loco being balast!), but there would be the Advantage that the diesel engine can be run at lower RPM in what we know as run 8 / notch 8 thereby still feeding higher RPM to the alternator. Would mean fuel savings altogether: Lower revs = less cyles = less injections of fuel = less fuel burnt = fuel saved. *I hate Long equations :) *

Cheers, Markus

There would unlikely be a fuel saving, the engines in both EMD and GE are pushed quite hard for a continous duty engine, ie the power/litre/100's rpm is quite high and dropping the revs would mean the engines would have to be bigger to get the same power.
Also these loco's are already quite fuel economic, the actual fuel used per hour being quite low for the power produced. Note this is common in engines with high volume cylinders as its easier to get a better burn of the fuel in a large cylinder.

Have a look at a cross section of a DE loco, one finds the main altenator is quite small compared to the size of the engine.

Lindsay

[Lindsayts]

Below is the Tractive effort charteristics for a Voith T312, these use a torque conveter for 1st speed and fluid couplings for 2nd and 3rd speed, Note the engine speed is nearly constent for 1st gear but varies with velocity for 2nd and 3 rd gears.



Image is from the Voith publication "T312 br turbo transmission" page 4. From Voith's web site.

Lindsay

[Lindsayts]

Note on the above,
Gear change points are just over 80kph and around 130kph, transmission efficiency in the cruising gears is stated as 94 to 95%.

Lindsay

[markus_GE]

I don´t know any numbers of how much fuel a modern diesel uses at full Speed / power (or whatever - not really any clue), yet, as I observed on my car yesterday, it´s right that too low RPM (for the power wanted / needed) also increase fuel consumption. So you´re right, Lindsay, according to how modern Diesel locos are used, this probably would be no real Advantage at all. But for DMU´s, I think it would be interesting.

As for how big the alternator, I guess, the smaller it is, the "easier" it might be moveable (less weight in Motion = less Initial inertia), but again, a lack of knowledge on my side.

Cheers, Markus

[copperpen]

Lindsayts, on 16 August 2013 - 07:18 PM, said:

Note on the above,
Gear change points are just over 80kph and around 130kph, transmission efficiency in the cruising gears is stated as 94 to 95%.

Lindsay

Very nice lines in the previous post of yours. However, because the fluid coupling is there, if the throttle is closed RPM will decay regardless of vehicle speed because the engine is no longer providing the required force to drive the coupling.