Can a Computerized System Improve Performance of Miniature Steam Locomotives?

[jim hardy]

With most "equivalent circuits," you can simply apply Kirchoff's laws and have the describing equations.

I've always said we EE's have it easy - our stuff is well behaved. No mass, no entropy, no pv^γ .

Ohm's law for mechanical engineers is Bernoulli's equation and it's intimidating with all those ρ, ν², 2g, C_D terms.
But they have one huge advantage - they can see their stuff move.
Maybe that's why i so enjoyed electric machinery class.

old jim

 

[Keggyleg]

Hi Jim
I think your idea is sound' the only reason why diesel engines are efficient is because they use the heat of the engine to vapourise the fuel. Applying the same idea to steam engines we come up with the flash boiler or hot top engine. Off course its a hell of a control problem but that's what computers do best.

 

[anorlunda]

Hi Jim
I think your idea is sound' the only reason why diesel engines are efficient is because they use the heat of the engine to vapourise the fuel. Applying the same idea to steam engines we come up with the flash boiler or hot top engine. Off course its a hell of a control problem but that's what computers do best.

Look up "feedwater heater", it is a feature of almost all steam systems.

 

[Keggyleg]

Consider the phut-phut model boat which draws water onto its hot parts then shoots it out as steam then the steam condenses drawing in more water to its hot parts thus repeating. The technology must be in its infancy.

 

[Baluncore]

I think your idea is sound' the only reason why diesel engines are efficient is because they use the heat of the engine to vapourise the fuel.

Not quite. The fuel is atomised at the injectors. The energy to atomise the fuel comes from the fuel injection pump, either a common rail or a “jerk” pump that is driven by the engine crankshaft.

The diesel efficiency comes from the higher compression ratio possible since ignition cannot occur until the fuel is injected. Pre-ignition in gasoline engines typically limits compression ratio to between 8 and 10. Diesel has a compression ratio between 16 and 21.

 

[Keggyleg]

HI
Efficiency is a difficult subject maybe diesel has more calories for your buck but I do know that the engines sometimes need glow plug just until they are hot and sometimes the cylider heads have metal plates which retain the heat of combustion. See this link for old timers flash boilers.

http://www.onthewire.co.uk/flash.htm

 

[Baluncore]

Efficiency is a difficult subject maybe diesel has more calories for your buck but I do know that the engines sometimes need glow plug just until they are hot and sometimes the cylider heads have metal plates which retain the heat of combustion.

You are clearly quite new to diesel engines. This is a bit off topic so I will keep it short.
IC engine efficiency is not a difficult subject at all. The buck is irrelevant. Even running on the same gasoline there is still 50% more energy from the same fuel by burning it in a high compression ratio diesel engine, but when cold it makes more diesel knocking noise because of the delayed combustion. External combustion engines are less efficient than IC engines.

A high speed indirect injection diesel employs glowplugs to start because it has precombustion chambers in the cylinder head. Those precombustion chambers when starting from cold result in immediate condensation of the fuel. The glowplugs are in those chambers only to assist starting from cold. Once hot, the precombustion chambers throw the partially burned fuel out into the cylinder which improves mixing and so speeds up completion of combustion cycle. It produces a cleaner exhaust.

A direct injection, (DI), diesel engine injects the atomised fuel directly into the cylinder. The DI engine runs slower because mixing is poor and combustion takes longer to produce a clean exhaust. To start a very cold DI diesel requires an explosive cartridge, the addition of ether or the burning of a small amount of diesel fuel in the air intake manifold.

 

[Keggyleg]

The jist of the story so far is that modern diesel engines are more efficient than old" iron horses " whether or not you factor in that diesel has a higher calorific value than gasoline. But old" iron horses " have not been developed and don't have micro-processors. Flash boilers might be the way to go from the old timers link I posted before. I note that different regions of a flame have different temperatures that would be the way to go. I did some programming in assembly for pics a while back but have many other projects. It would be better to use C and I am licsenced as a Agilent VEE developer which is useful.

Cheers and beers

 

[Baluncore]

whether or not you factor in that diesel has a higher calorific value than gasoline.

Get your facts straight. You need to stop making false statements about subjects you know nothing about.
1kg of diesel has a lower calorific value than 1kg of gasoline.
http://www.acea.be/news/article/differences-between-diesel-and-petrol says;
“The calorific value of diesel fuel is roughly 45.5 MJ/kg (megajoules per kilogram), slightly lower than petrol which is 45.8 MJ/kg.

Diesel engines are efficient because the compression ratio of the engine can be greater. That is independent of the fuel calorific value.

 

[cjl]

Get your facts straight. You need to stop making false statements about subjects you know nothing about.
1kg of diesel has a lower calorific value than 1kg of gasoline.
http://www.acea.be/news/article/differences-between-diesel-and-petrol says;
“The calorific value of diesel fuel is roughly 45.5 MJ/kg (megajoules per kilogram), slightly lower than petrol which is 45.8 MJ/kg.

Diesel engines are efficient because the compression ratio of the engine can be greater. That is independent of the fuel calorific value.

Yes, but fuel efficiency of vehicles is often expressed per volume of fuel, not per mass of fuel, and diesel is significantly denser than gasoline. As a result, diesel has substantially more energy per liter than gasoline, which is clearly what was intended. Your reference even states this quite clearly.

 

[Baluncore]

Yes, but fuel efficiency of vehicles is often expressed per volume of fuel, not per mass of fuel,

But not for the comparison between fuels, except by the uneducated public. That is because liquid hydrocarbon density is highly temperature dependent. It is unscientific to use volume without some temperature specification.

If an unpackaged material flows then it is traded commercially by volume, if it does not flow, then it is sold by mass. Gasoline and diesel fuels are bought and sold by volume because it is difficult to put them on the scales. A local fuel distributor was involved in a dispute when it turned out they were delivering hot fuel to the underground tanks at the filling stations. They were profiting by the their thermal expansion of the fuel.

Miles per gallon, mpg, was used by drivers to estimate available range.
Litres per 100km, is now used by car buyers to estimate future economy.
But it is the mass of fuel that is always used in scientific and engineering discussions.
Since this is an engineering forum, drivers should leave their unscientific baggage outside the door.

The SI unit for specific energy is kJ/kg. https://en.wikipedia.org/wiki/Specific_energy
An old engineering measure of fuel economy was; pounds per (horsepower * hour).
Another often quoted engineering reference figure is that it takes 14.5 pounds of air to burn one pound of fuel.

All those specify mass so as to eliminate the changing effects of volume, temperature and density.

 

[cjl]

But not for the comparison between fuels, except by the uneducated public. That is because liquid hydrocarbon density is highly temperature dependent. It is unscientific to use volume without some temperature specification.

Who cares if it's unscientific? Fuel is sold by volume, vehicle fuel capacity is volumetric, and thus, for the vast majority of measures that matter when comparing diesel to gasoline, volumetric fuel energy content and fuel efficiency are the parameters that matter. Thus, it is perfectly reasonable to assume that's what Keggyleg was referring to, and it's annoyingly and unnecessarily pedantic to "correct" them, especially with a statement like "You need to stop making false statements about subjects you know nothing about".

 

[Baluncore]

Who cares if it's unscientific?

I do. This is a physics and engineering forum. If it is not scientific then it should be corrected or deleted. Your resort to rhetoric suggests you are emotional and so unable to appreciate the scientific analysis behind the arguments.

Fuel is sold by volume, vehicle fuel capacity is volumetric, and thus, for the vast majority of measures that matter when comparing diesel to gasoline, volumetric fuel energy content and fuel efficiency are the parameters that matter.

That is commerce and marketing, it leads to commercial rorts and misinformation based on fuel density. It is energy to mass ratio that regulates vehicle acceleration and climb efficiency. Volume is largely unimportant, there is ample space for fuel, there is critically limited payload. Every extra kg of unnecessary fuel reduces the payload by one kg, and that is true, both commercially and scientifically. You need to face that fact.

Thus, it is perfectly reasonable to assume that's what Keggyleg was referring to, and it's annoyingly and unnecessarily pedantic to "correct" them, especially with a statement like "You need to stop making false statements about subjects you know nothing about".

You need to go back and read all Keggyleg's statements that I have questioned. Then, if you analyse them, you will realize that they contain a number of false assertions. They do not rationally explain the significant efficiency gained by increased compression ratio. This thread was discussing improvement to the efficiency of expansion engines. Compression ratio and compounding of the expansion are much more important than even a factor of two in the density of the fuel.

@ cjl; You see an attack on a writer's unscientific and false statements as an attack on the writer. You then rush in late to defend the writer of the false statements. But at some point the stream of ongoing false statements needs to be stopped. If the use of scientific analysis and engineering principles cannot educate the writer, then it is necessary to use language understood by the writer to persuade the writer think again, or the thread needs to be closed.

 

[cjl]

I do. This is a physics and engineering forum. If it is not scientific then it should be corrected or deleted. Your resort to rhetoric suggests you are emotional and so unable to appreciate the scientific analysis behind the arguments.

Unnecessary pedantry helps nobody though, and jumping down people's throats for minor technical inaccuracies when their broad point is both correct and easily understood is not helpful to the discussion.

That is commerce and marketing, it leads to commercial rorts and misinformation based on fuel density. It is energy to mass ratio that regulates vehicle acceleration and climb efficiency. Volume is largely unimportant, there is ample space for fuel, there is critically limited payload. Every extra kg of unnecessary fuel reduces the payload by one kg, and that is true, both commercially and scientifically. You need to face that fact.

This would be true if we were talking about long range aircraft or rockets, where the fuel mass is a substantial proportion of the vehicle's overall mass. However, for cars (or trucks, or trains, or ships), fuel mass is a relatively insignificant portion of the mass of the vehicle, and volumetric constraints tend to be tighter than mass constraints (10-25 gallons of fuel takes up a fairly significant volume under a car), and the volume of the fuel is fixed by the design of the vehicle. When traveling somewhere, you really do not care about the mass of fuel your car can hold - you care about the volume.

You need to go back and read all Keggyleg's statements that I have questioned. Then, if you analyse them, you will realize that they contain a number of false assertions. They do not rationally explain the significant efficiency gained by increased compression ratio. This thread was discussing improvement to the efficiency of expansion engines. Compression ratio and compounding of the expansion are much more important than even a factor of two in the density of the fuel.

I have read the statements, and I agree there were some false assertions. However, you were quick to jump in and declare someone as knowing "nothing" about a subject when their point was relatively easily understood (and not fundamentally incorrect)

@ cjl; You see an attack on a writer's unscientific and false statements as an attack on the writer. You then rush in late to defend the writer of the false statements. But at some point the stream of ongoing false statements needs to be stopped. If the use of scientific analysis and engineering principles cannot educate the writer, then it is necessary to use language understood by the writer to persuade the writer think again, or the thread needs to be closed.

No, I am quick to become annoyed at excessive nitpicking and pedantry, as it distracts from the conversation and forces the reader to wade through large amounts of unnecessary and unneeded text. If you had simply commented "calorific value usually refers to mass energy density, not volumetric" and left it at that, I wouldn't have jumped in at all, since that is a relevant, interesting, and useful piece of additional information. You instead took the opportunity to declare the other poster as "knowing nothing", which (as I said before) was both needless and irrelevant.

In addition, your statements aren't even completely factual. There is no inherent reason why diesel must have a higher compression ratio than gasoline, and the compression ratio alone does not explain the differences in efficiency. Reduction of pumping losses due to the lack of air throttling, lean burn at part throttle, and lower RPM in the powerband also have significant effects on the efficiency, as do several other factors. In some cases, lowering the compression of a diesel actually helps its efficiency. For example, Mazda's last generation 2.2 liter diesel had a compression ratio of 16.3:1, and their new one lowered that to 14:1 (the same as their 2.0L gas engine, interestingly enough) as part of a major effort to improve efficiency, largely because it allowed for an improvement in the homogeneity of the burn and a reduction in cylinder wall friction, as well as a substantial reduction in weight (and therefore inertia) of internal components. Internal combustion engine efficiency is a complex topic, and there are many things involved in maximizing it.

 

[Baluncore]

Unnecessary pedantry helps nobody though,

So you quoted and accepted my first point, then attached your irrelevant personal statement.

This would be true if we were talking about long range aircraft or rockets, where the fuel mass is a substantial proportion of the vehicle's overall mass. However, for cars (or trucks, or trains, or ships), fuel mass is a relatively insignificant portion of the mass of the vehicle, and volumetric constraints tend to be tighter than mass constraints (10-25 gallons of fuel takes up a fairly significant volume under a car), and the volume of the fuel is fixed by the design of the vehicle. When traveling somewhere, you really do not care about the mass of fuel your car can hold - you care about the volume.

You have clearly not thought that through before you wrote it. You have most of it backwards.

Cars can always be designed to carry a greater volume of fuel at the expense of luggage capacity. 4WDs can get replacement tanks that mount in the same position but often with double the capacity because there is so much unseen and unused space under the vehicle.

A CI engine can run on gasoline so long as it is contaminated with oil. A CI diesel vehicle will then travel about half as far again as a SI gasoline engine for the same volume or mass of the same fuel. Gasoline is more expensive to process than diesel. Diesel is safer and more economic than gasoline. Consider a diesel truck with a 300 litre fuel capacity. With a gasoline engine it would require 450 litres of more expensive gasoline to have the same range, and the payload would be reduced by about 150kg.
Compression ratio trumps fuel density every time.

The only hard limits are GVM, the mass of the fuel and the distance between filling stations. Get yourself a truck license and then contemplate the fine if you are 1kg over GVM. Take a look under a truck to see where there is plenty of room for more tank capacity. As I wrote, every kg of fuel reduces the payload by 1kg.

No, I am quick to become annoyed at excessive nitpicking and pedantry, as it distracts from the conversation and forces the reader to wade through large amounts of unnecessary and unneeded text.

You mean like your post #49.
Where;

In addition, your statements aren't even completely factual.

And then follow it with;

There is no inherent reason why diesel must have a higher compression ratio than gasoline, and the compression ratio alone does not explain the differences in efficiency.

Yes there is and yes it does. You know NOT of what you write. Get your facts straight.

It takes at least a 15:1 CR for CI engines to start and run properly. SI engines running available ULP preignite when the CR is over about 10:1. Premium fuel is more expensive and gets you a little further before you must switch to ethanol. Only an idiot would build a CI engine with an effective compression ratio below 15:1 as it would be inefficient without a turbo or supercharger. You must multiply the air charger boost ratio by the cylinder ratio to get the effective CR. Many diesels operate at about 21:1 above which the heat of compression threatens piston material thermal limits and engine reliability.
You point to the Mazda Sky-D as having a 14:1 CR, but you fail to note that it takes a two stage turbocharger to recover the CR and the associated efficiency.

The compression ratio does not explain it all, but it totally dominates the economics.

Articles about the Mazda Sky-G claim the improvement in economy is due to compression ratio at the expense of premium fuel.
QED.

 

[Keggyleg]

I will probably biuld something someday when I have finished bitscope low level programming. I have 27 years experience of metrology and know that energy in compared with mechanical work out equals efficiency. I have noted in the past how much better a gasoline engine runs in a fog. Maybe this is the way to go, Maybe an alkahol engine with water in the fuel. You could run an engine on homebrew.!

Cheers and plenty of beers !

 

[Baluncore]

I have noted in the past how much better a gasoline engine runs in a fog.

Fog is a form of water injection. If it improves the performance of an SI engine by preventing knocking, then it indicates that the fuel you are using has too low an octane rating for the CR of your engine. It may also indicate that you are driving too fast in poor visibility.

You need to use a fuel with a slightly higher octane rating. Maybe in an old engine, you can compensate for previous head repairs by installing a thicker head gasket to return the CR to the original specification.

Water injection is an indication of an unresolved problem. There is something about water injection that makes it seem attractive. Maybe it is because everyone has the subliminal dream to run their car on water.

 

[Keggyleg]

An intersting artical you might like http://www.enginerunup.com/ with modern day electronics water could be injected even between strokes to cool the engine. A cross between steam and gasoline power.

 

[Baluncore]

A cross between steam and gasoline power.

There is no steam power involved.

This topic is about optimisation of external combustion, steam expansion engines.
That may include the flash generation of steam for expansion in the engine.

The injection of cooling water into IC engines to improve performance is getting well off the topic.