[steamer_ctn]

In the WIshes for Steam Locomotive advancement thread a number of contributors have raised question about the accuracy of some elements of the model for the steam locomotive. It has been agreed that some investigation would be undertaken to either validate the current model, or identify potential tweaks that could be undertaken.

This thread has been established to focus discussion on the very specific area of investigation agreed to, ie the operation of steam relief valves, and potential combustion impacts that may impact their operation.

For background, read from post #74 for any relevant posts relating to steam relief valves.

Following on from post #88 , I believe that there may be some merit in investigating the impact of draft to the fire at different speeds as this may impact the combustion rate of the fire.

As a starting point this publication provides an interesting start. It describes the change in draft as the locomotive moves, so we will need to study some similar documents to try and develop a reasonable working model to be incorporated into OR. In the introduction the document alludes to two other bulletins which provide additional information. Is any body able to identify and source these two bulletins.

This will not be a quick process, and will require some detailed research.

Please do not post to this thread unless your comment is specifically related to the above investigation process. Any wish list items or general steam locomotive comments should continue to be posted in the "Wishes for Steam Locomotive Advancement" thread.

[darwins]

The document may be useful in helping to determine the effects of the blower and the dampers on a coal fire. It also gives us some insight into using different sizes of coal and different thicknesses of fire. I was very pleased to see the following

Quote

The pressure drop, or draft, was produced as usual by the small steam jet or by discharging steam directly from the boiler- through the exhaust nozzle

as I thought this might help us to identify the impact of the blower in creating 'draft'. Unfortunately that was not the case as there is no differentiation in the results between those achieved with the blower and those which used the blast orifice.

I am not sure that this will directly help with the function of safety valves. As suggested in the oil firing thread I think we need to break things down in a more analytical way - particularly treating the fire (combustion), boiler (heat exchange) and engine (transmission) as separate entities. By setting up a hypothetical oil fire that allows the heat input to the boiler to be finely controlled we can focus only on heat exchange in the boiler, without the need to deal with the behaviour of the coal fire at the same time.

So even this thread is essentially proposing two different investigations:

( 1 ) Safety valve behaviour

( 2 ) The effect of pressure differences between the grate and the smokebox on the rate of combustion of coal (or oil?) and the associated rate of heat transfer to the boiler. Pressure differences in a static locomotive may be influenced by blower, dampers, blast, fire thickness and nature of coal. In addition to all of those in a moving locomotive the effect of moving air through will also have an impact and I am not sure if there is any data around related to that.

[ATSF3751]

I found Scott had posted this in a separate thread but thought it should be posted here as well. It is a whole guide on how to fire a steam locomotive in 1944. Lots of detailed and great information that could become very handy when we are working to get the everything corrected with firing in Open Rails. I hope it is okay I posted this here as I know Peter created this forum for Safety Valves alone.

Brandon

https://www.railarch...ring/index.html

[steamer_ctn]

darwins, on 26 January 2021 - 10:54 PM, said:

Pressure differences in a static locomotive may be influenced by blower, dampers, blast, fire thickness and nature of coal. In addition to all of those in a moving locomotive the effect of moving air through will also have an impact and I am not sure if there is any data around related to that.

The amount of draft impacts the heat generated by the fire, and absorbed by the boiler. Hence it is a key factor in the amount of Heat In to the Boiler.

We should read "draft" rather then "pressure differences", as the pressure difference is but a measure of how much draft is occuring.

However if we think of a few different scenarios the impact of the draft will be different on the fire, and hence the fire behaviour will be different.

i) Locomotive is running at full load and speed - draft will be a maximum, and be a mix of natural air flow due to motion, and the blast orifice

ii) Locomotive is running at same speed as above, but throttle closed (coasting) - draft will be natural air flow only

iii) Locomotive is stationary - no blast orifice, minimal natural air flow, perhaps some blower draft - fire should be at a minimum level.

I agree that it will be challenging to build a draft model due to the lack of detailed information, and this is one of the reasons why it is lacking in the OR model at the moment. OR in its own way attempts to cater for some form of draft effect by raising and lowering the burn rates, and unless we can develop a better understanding draft in more detail and how to "accurately" model it, I think that it will be difficult to improve upon the OR current model.

ATSF3751, on 27 January 2021 - 03:27 PM, said:

I found Scott had posted this in a separate thread but thought it should be posted here as well. It is a whole guide on how to fire a steam locomotive in 1944. Lots of detailed and great information that could become very handy when we are working to get the everything corrected with firing in Open Rails.

Thanks Brandon, however whilst this is a very good document describing fire behaviour at an operational level we are really in need of technical articles to provide us with sufficient information to build a representative model.

So some of the questions that Darwin has raised in terms of the contribution of natural airflow and blast orifice is the type of detail that we will require. Typically this is found in test reports, engineering or technical articles, such as the example that I provided.

So any of that type of information will be most welcomed.

I need to finish of some other development work that I am currently involved in before commencing this piece of work in any detail. I also want to stop and reflect for a little while on how to move forward, so it may be a little while before I respond further to this thread.

[ATSF3751]

Sounds good Peter! Thanks for the response and I will look around to see if I can come across any info that you are looking for.

Brandon

[steamer_ctn]

Just as an update, I have been giving this some thought and research in the background, and some possible changes are slowly being identified.

I came across a very good engineering paper presented by C. A. Cardew and called "The Blower, Its Origin and Its Function on the Locomotive". This provided some very useful information on Blowers and their operation.

It is a paper presented in the Journal of the Institute of Locomotive Engineers", and there are some other papers that I would be interested in viewing to build a complete picture. Can anybody access these documents, perhaps through their employment or a library that they are members of, etc?

[darwins]

Making a working model of the coal fire is proving a huge challenge, but Peter has come up with a number of potential improvements over the past two months. Work is still ongoing, but it looks like much improved fire behaviour may be possible. Appropriate control with the blower and damper(s) during manual firing should be amongst the most significant improvements.

[Weter]

It's obviously needed.

[copperpen]

A steam locomotive is a simple, but complicated machine to deal with. There are three things that are linked together, fire, boiler and front end.The boiler cannot make steam without the fire and the fire cannot function properly without the front end operating to provide the required draft to the fire. In post #4, Peter suggested that when coasting the throttle was closed and draft would be natural air flow. This for the most part is not true. The throttle was slightly opened to allow a small amount of steam to the cylinders thus preventing exhaust gas from the fire being drawn into the cylinders anfd destroying the lubrication. Some classes of locomotive had a "snifting valve" fitted that allowed outside air to be passed though the cylinders when the throttle was closed. In both cases there was a still a forced draft on the fire, albeit much lower than when the locomotive was working normally.

Several years ago I bought a book that specifically deals with the front end of the steam locomotive. It is filled with mathematical formulae that are way above my pay grade. What it all boils down to is that the fire will not burn efficiently if the front end is not working properly, and if the fire is not working properly the boiler is not making sufficient steam.

So, steam is taken from the boiler at pressure, passed through the cylinders, through the exhaust nozzle at the bottom of the smokebox and out to atmosphere via the chimney at the top of the smokebox. The speed of the steam between the exhaust nozzle and the chimney base is what makes the draft on the fire by pulling the hot gases through the boiler tubes and ejecting them along with the steam through the chimney. This ejection to atmosphere makes the air pressure in the smokebox lower than atmospheric which is filled by air from the firebox, thus we have the draft cycle. It is the strength of this draft that can pull live coals from the firebed, through the tubes and eject them trough the chimney thus causing line side fires.

For an extremely graphic illustration, https://www.youtube....annel=dawei2012

[Laci1959]

copperpen, on 06 April 2021 - 02:39 AM, said:

So, steam is taken from the boiler at pressure, passed through the cylinders, through the exhaust nozzle at the bottom of the smokebox and out to atmosphere via the chimney at the top of the smokebox. The speed of the steam between the exhaust nozzle and the chimney base is what makes the draft on the fire by pulling the hot gases through the boiler tubes and ejecting them along with the steam through the chimney. This ejection to atmosphere makes the air pressure in the smokebox lower than atmospheric which is filled by air from the firebox, thus we have the draft cycle. It is the strength of this draft that can pull live coals from the firebed, through the tubes and eject them trough the chimney thus causing line side fires.

When the locomotive is stationary it is not passed through the cylinders, at least not for all types. Fresh steam is led to the blower if they want to ignite the fire.
On the fly, tired steam from the rollers is led into the blower, but only if they want to ignite the fire. If there is a good thick fire, the tired steam is released next to the blower.
The blower is in the smoke cabinet, it works on the principle of the Venturi pipe.
It also includes a bit of the fact that when the locomotive is in motion, the steering lever is pulled back to the middle position, thus reducing the charge on the cylinders with the same control opening. This also affects the color and amount of combustion product flowing out of the chimney.
Sorry, Google doesn't translate.