Grand Canyon

Welshpool

Drawings completed by my Son to Nigels instructions.

W&LLR 19 test gear

Sorry for being quiet but design is complete, It just leaves me to try and sweet talk our Local Technical College to machine the nozzles so I will probably be quiet for a bit longer but as the project progresses I will update as soon as possible.

From Nigel

If you go to the Welshpool and Llanfair railway website you will find pictures of Joan on running in tests including a new Lempor. This is inside a casing similar to its spark arresting chimney. The reports and so far I have not seen it run are that it steams well and has substanshaly less back pressure.

Yesterday work started.
I have been successful in getting our local Technical College to machine the nozzles.Hopefully work will start on them next week.
Yesterday I machined the nozzle flanges that fit on the blast pipe from steel plate at my mates workshop. Hes very good, donates materials, his machinery, will do the welding, I guess he will enjoy a carton of beer.
With luck I will start cutting out the diffuser and mixing chamber.
Attached are images of the flanges test fitted on the blast pipe stand

Although the subject here has mostly been about building a lempor for Dennis and a loco that is coal burning in resent weeks I have been asked alot about lempors and oil firing. After this post Stephen will post my paper on lempors and oil firing. The writing of this was mostly due to another similar unconected Australian version of this type of web site 'Railpage' and the returning of R711 to its orgonal state. R711's situation is done and in the past. I was not involved in the project or wish to coment upon that. I simply wish to explain the lesser know facts relating to oil firing and the use of lempors with oil which I hope you will find intresting.

Nigel's paper: The Importance of Lempors for Oil Firing:
http://restorationstories.com/oilfiringpage.html

Progress is being made with the chimney components being rolled and welded.
The next step it to take the Diffuser and Mixing chamber back to the rolls to roll them round because the long edges slightly flatten along what will be the welded seam when they came out of rolls.
Hopefully I will get an update this week about the machining of the nozzles.

Oil Firing
My many days spent in the boiler rooms in Royal Australian Navy ships taught me that
Black Smoke = too much fuel and not air (cools the gas path)
White Smoke = too much air and not enough fuel. (Flue gas temperature would be high)
A light brown haze = good combustion.
However good combustion was not a hit and miss affair but the result of supplying the correct proportions of fuel to air or vice versa at the right temperature.
We used to get our bums kicked if we made too much smoke, if smoke persisted it was generally a problem with the sprayer (burner).
From reports I have heard about the results of Nigels lempor modifications to the West Coast Wilderness Railways oil burning rack locomotives is nothing short of spectacular, this result has not come from speculation but from Nigels knowledge of a steam locomotives heart, that is its front end design.

Dear Mr. Nigel Day

In your piece entitled “The Importance of Lempors for Oil Firing” you state the following. “The other down side is that a blast pipe has to have back pressure to provide the energy for the pumping of the air flow. Whilst the balance can be nearly achieved with a coal burning loco and a traditional non-scientifically designed front end there are additional factors relating to oil burning. Which means that any self-respecting oil burning loco must have a Lempor to achieve a reasonable air to fuel mixture.”

So by this statement are you suggesting that all oil burners were failure? If so then how do you explain the widespread use of oil on both the SP and AT&SF in the United States which by most accounts at the time were quite successful?

Respectfully
Robby Peartree

No I am not saying that all oil burners where a failure by the standards of the day. What I am saying is that with time all things including oil fired locomotives can be improved with the leasons learnt over time. What was acseptable then and regarded as good may not now be acseptable and ways have to be found to move things on to meet present conditions and changes in expectations. No doupt even what I have worked hard to try and achive will be bettered by someone in time.

How do these nozzles affect the locomotive besides back pressure? Would the increased flow affect draft by increasing the speed the gasses are pulled through the firebox and flues? If that is the case, is the fuel efficiency reduced but compensated by the loss of back pressure? How much does the smokebox temperature play a role?

The Chimney Insert complete.

John

Thank you for your question. I hope this is the answer you want.

The aim is to gain the most velocity for a given mass flow for the exhaust steam with the least friction. In traditional blast pipes the nozzle has a steep taper and probrably very rough serface. The result is a high level of friction and a high co-eficent number of greater than 2. Such nozzles have a terminal velocity which means that as the back pressure incresses the velocity dose not increase. A state which only reduces the presure drop across the cylinder and increses the steam demand whilst no aditional steam is produced.
Jump forward into jet and terbine technology and you find nozzles which are very slowly tapered and very polished so the friction and terbulence is low. Aditionaly they have a converging/ diverging section which allows the transition from sub sonic to super sonic speeds to be achived. The main points here are that the steam dose not reach a terminal velocity as it reaches super sonic speed but can continue to be reactive and give a more consitant relationship between back pressure and draft. Critical pressures for this are around 12 psi and velocities of 500 m per second. You can tell a locomotive working below terminal conditions as there is a distinct beat compered with an all out roar of terminal conditions. Lempor nozzles have a co-eficent of 0.99
The effects of all this.
Firstly reducing the back pressure by 1 psi can in some situations equal to increasing the inlet pressure to the cylinder by 5 psi.
Secondy the 'polishing and streamlining of the cylinder pasages and exhuast pipes' allows greater gas flows and velocities thus the cylinders can breath more easily and allow for a higher engine speed then eficentcy.
The aim is to produce higher velocities in the mixing chamber of the Lempor which is part of improving the efcentcy of the drafting rather than increasing the gas flow in the tubes for a given combustion gas flow rate.

The fundimental control on the combustion gas flow rate is the size of the mixing chamber. If its to small then not enough gas will flow and insuficent heat will pass the heating serfaces and insuficent steam. If its to big then to much gas flow will ocurr and excesive steam will be produce. Porta discribs the means of gaining eficentcy as a conservation of energy, what is ment is that you want to extract the most heat out of the cobusion gasses. Calculations for this can be long and complex but are compramised hevily if the boiler is scaled up and then everything goes out of proportion. The exhaust tempratuere is a way of measuring how efective the the heat exchanger is. Idealy the tubes need to be longer than conventionaly understood to allow for eficent heat transfer. In an atempt to improve the heat transfer roughening of tubes is done. Aditionaly the proportions of the mixing chamber can be altered to give a desired heat transfer and velocities through the tubes that will affect the final exhaust temprature. In most Lempor designs it is found that the mixing chamber is substanchaly smaller (The velocities there are higher than a traditional chimney)than the choke of an exsisting chimney and through that its posible to estimate the overal fuel savings. Relativly a saturated boiler can have a lower smoke box temprature than a super heated locomotive where you need to achive the desired super heat level.
The combusion gas velocities espeshaly through the tubes of a coal fired boiler with around 14% of the grate as gas flow area (GFA) through the tubes is a good situation where a Lempor would not be vastly difrent to a traditional chimney. If the GFA is less then it will control the evaporative rate of the boiler rather than the grate limit.

I hope that answers the questions.