Diesel Electric?

[John Candy]

ADMIN NOTE : This thread is a continuation of http://lakes-pages.com/gauge3.co.uk/G3Forum/index.php?topic=125.msg5286#msg5286



Quote:

Starting and cooling are not big problems

Unquote:

Errmmm I beg to differ.... I did the maths (and actually they did turn out to quite nasty). The amount of cooling required for a small G1 model can be coped with a simple fan and provided the model is not supposed to run for more than about 10-15 minutes -then an 8cm @240 Litres per minute fan can (just) keep a finned 3.5cc aero engine within bounds, (i.e. below 60C). The amount of waste heat that my engine has to dissipate is 300 Watts. This is a rate of flow of 1.2 Litres per minute with a drop of 15C across the radiator.

I don't think that anybody, (without green skin), could flick over the 7.5cc engine that I use. The starter motor is 7cm diameter and 17cm long with Car Battery croc clips....

As to sound -that is a physical and mathematical no-go area. It is impossible to produce a note of the depth required to emulate a true exhaust system tone within the confines of the G3 loading gauge. I have no problems with sound cards and the like -but I accept what is possible.

My locos have chassis made of 3mm thick metal and are very heavy compared to a G1 model(!)

regards

ralph

[Peaky 556]

Put like that Ralph, 300W is a large amount of heat to dissipate.  I'd like to see your calcs for this if poss?  Are you assuming about 65% comes out as heat, 35% mechanical power? 
I could estimate we don't need more than about 30-35W mechanical power at the wheels for a loco in G3, but I have no experience.  It's estimated like this:
Assuming a pretty poor efficiency of 50% for the final drive electrical to mechanical conversion at the bogies, gives electrical power consumption of ~65 W to drive our train at scale speed with a rake of coaches.  This is 5A drawn by a 12V electric set up.  Does that sound reasonable to the battery-electric guys?
Taking this one step further and assuming our D/E has a fairly inefficient generator and driveline/gearbox of about 40% efficiency, we need about 75-90W of mechanical power from the engine. 
This could give about double this as waste heat output, ie 150 - 180W needs to be dissipated by a fan blowing cold air over the fins, or one of Ralph's liquid cooled radiators.  This seems more likely to be achievable without the engine cooking.
However for a much less efficient transmission......such as could might be achievable in a diesel-mechanical, then engine power requirements and waste heat are going to rise badly!
Any thoughts?
Regards,
Tim

[Moonraker]

There is a lot of information on live diesels on the continental garden railway forum at http://www.cgtrains.com. The guy who runs it, Carl Hibbs, has built four live diesels so far and has a lot of knowledge to pass on.

Regards
Peter

[cabbage]

Having unearthed the notebook and deciphered the LSD doped spiders death convulsions that seems to be my natural handwriting style…

Engine: ASP 0.46m

Fuel: Methanol 70% Nitro Methane 5% Oil 25% SG=1.1

LHC Methanol:  726kJ Mole

Air/ Fuel Ratio: 7 to 1 Air to Methanol =  4.9 to 1 (call it 5:1) Air to Fuel

Idle 2,000RPWM Peak 4,500RPM Use 4,000RPM

Energy = (4,000 x 7.5 / 5) x (0.7 x 726) / 60  = 6,000 x 508.2 / 60 = 50,820

Assume 9% Thermal = 0.09 x 50,820 =  4,573.8

Usable power 25% = 1143.45 Watts (manu specs say 1.2kW!!!)

spent through exhaust 50% = 571.7W
spent as cooling 25% = 285.8W
tractive power 25% = 285.8W

Torque convertor ratio 4.2 : 1 therefore tractive power to gearbox = 68Watts

Tim, most of my electric locos use 12 Volts at 5 Amperes, (the NER EE-1 uses 20A -but then it has 6 Motors). If you like I can do the calculations for you based on the dynamo design that I used for the Heiilmann Steam Electric loco.

regards

ralph

[454]

OK I was a sceptic but now I am convinced.
Just been checking out some you tubes.

http://www.youtube.com/watch?v=gSwha_Ug7sk

Try this one

Come on Tim Peaky squeeze that little lot into a class 45 or a 40. 

Cheers
Dave
454

[Moonraker]

Rather than just re-inventing what many others have done, with mediocre results, how about taking a new direction? Last weekend, a friend demonstrated a Maier Mechanic gas engine which he purchased on Ebay. It uses butane gas fuel, runs at 200-1500rpm and makes a much more appropriate sound than a model aircraft engine. Could it be the basis for a live diesel loco? Google "Maier Mechanic " for details.

Regards
Peter

[cabbage]

I have to admit that they are incredibly pretty.... But as a source of power I don't think they are robust enough. There are no details as to the torque curve or power output of the devices. If it was to be used for a torque source for a dynamo then Rho the Voltage Generation Loss factor (here I am guessing) would have to be something colossal like 9 or 10!!!

The rating of the a dynamo is the number of lines of flux cut per second X diameter of rotor X 1/Rho

Rho you look up on the tables but it is a function of the thickness of the wire and the number of winding on the rotor. A 3 phase alternator could be made by rewiring a 3 phase brushless outside runner aero engine with a 3 phase bridge,  a "dustbin" of a capacitor and a HUGELY over rated Voltage regulator to provide a 12 Volt source.

regards

ralph

[andrewfoster]

spent through exhaust 50% = 571.7W
spent as cooling 25% = 285.8W
tractive power 25% = 285.8W

Torque convertor ratio 4.2 : 1 therefore tractive power to gearbox = 68Watts

Tim, most of my electric locos use 12 Volts at 5 Amperes, (the NER EE-1 uses 20A -but then it has 6 Motors). If you like I can do the calculations for you based on the dynamo design that I used for the Heiilmann Steam Electric loco.

regards

ralph

Ralph - you've lost me in the calculations. Is there a typo in the units? The power (torque x speed) delivered by a torque convertor is reduced only by its efficiency, not the torque ratio, so it looks as though the figure should be rather higher than that. Apologies if I am misreading you!

Andrew

[cabbage]

Quite right! Last line should read

Torque convertor rotation reduction 4.2 : 1

output RPM 952.3 @ 0.6Nm = 58Watts

I think I can get a higher rating but the problem is with pumping the fluid in and out of the torque convertor chamber -it is made of layers of 6mm thick polycarb....

regards

ralph

[Peaky 556]

Peter - thanks for the CGTrains link, am awaiting approval to get on the site.  The gas engine has a Victorian beauty, but is probably just a display piece that will not produce useful power.  Look at the weight and size too!  There is a lot more power density in an aeromodellers glo-engine, but it only achieves it by running much faster.  My approach is to run such an engine more slowly to get the right pitch and only demand about 20% of its peak power (which may be plenty)!

Dave - I'm trying, really!  But I need to match powers and speeds and atune my ear to distant memories of Sulzers, before ordering gears or cutting metal!  It might happen, with the encouragement of this forum! 

Ralph - thanks very much for going to that trouble.  Not quite what I was expecting - a 1st principles approach.  There must be a fuel flowrate term in there somewhere, but difficult to pick out factors and units.  No matter, I am heartened that we are talking similar orders of magnitude of waste heat to dissipate.  Are you saying that the 300W of your 7.5cc engine is a losing battle and it cooks up after 10 mins or can you keep it steady-state?  Will I have a big problem with a PC fan or two trying to blow away 180W of heat do you think?

Regards, Tim

[cabbage]

Tim -Sorry!!!  Being a Chemist I tend to think of things in MOLES....

1 Mole of methanol is 32Grammes. Call it an Ounce of Fuel!!!

The fuel tank is a 6oz one and it keeps the loco in grumble for at least 20 minutes -the longest operational run has been in the 40 minutes mark. The constant coolant temperature from my AMD XP1700 CPU cooler and 43 Litres per minute 80mm fan is 36C with a nominal air temperature of 20C the volume of the coolant is 0.6 litres. I chose the XP on the grounds that it had a nice thick base that I could drill and tap into! The radiator element is a 1mm thick sheet of ABS cut into a folded pathway and epoxied to the base. This is then covered with a gasket and a plate of 6mm polycarb which is tapped and has the brass "hose fittings"... The Lucas style windscreen washer pump flows the coolant (50/50 water and fernox) at a rate of 1.2 litres per minute.

regards

ralph

[Peaky 556]

Tim -Sorry!!!  Being a Chemist I tend to think of things in MOLES....

The constant coolant temperature from my AMD XP1700 CPU cooler and 43 Litres per minute 80mm fan is 36C with a nominal air temperature of 20C the volume of the coolant is 0.6 litres. I  The Lucas style windscreen washer pump flows the coolant (50/50 water and fernox) at a rate of 1.2 litres per minute.

Ralph -
1. I won't hold that against you!
2. Looking only at the water side of your heat balance I calculate 595W is being added to the water. 
I am encouraged that you can take away this much heat.  My coolant fan is rated at 31.5 CFM (892 litres/m) and to carry away my estimated 180W only raises the bulk air temp by 10 deg C.  Check your air flow rate, it seems far too small. 
All very manageable I'm thinking.  Very good....
Tim

[cabbage]

Yes you are right! It should read 43 Cu ft per minute(!)

regards

ralph

[andrewfoster]

Quite right! Last line should read

Torque convertor rotation reduction 4.2 : 1

output RPM 952.3 @ 0.6Nm = 58Watts

I think I can get a higher rating but the problem is with pumping the fluid in and out of the torque convertor chamber -it is made of layers of 6mm thick polycarb....

regards

ralph

I'm still not quite with you, but it may just be my reading of it.  With 286W going into the torque convertor and 68W emerging, then its efficiency is about 24% - probably quite good for a very small unit, though now you also have to dissipate the lost 218W.  But your torque ratio appears to be the inverse number (4.2:1) if I am reading this correctly, which seems more than coincidence. Presumably that's a steady state when running, as the ratio will vary with speed and load?

Andrew

PS Remember the complaint of the sick D800 Warship? "I can't torque - I've lost my Voith!"

[Peaky 556]

Ralph - back to cooling, I had assumed your coolant temperature varied between 20C after cooling and 36C after heating.  A bit presumptious that your radiator is so efficient!  If the cold leg was say 28C then the heat dissipated is more like the 300W of your calcs. 
I'm also impressed by a 43 CFM fan at 80mm diameter - I want to get one!
Regards, Tim