I am impressed by the recent chart of performance figures from IMLEC, and I hope someone can help:

If all the carefully measured coal goes into the empty firebox (does it?) and you light the fire (adding energy), some of the dust will fall out of the bottom at once. As the fire gets going, some of it will be carried over up the chimney. As the fire progresses, some of the remaining coal will be turned to ash, and some of that to clinker. Some of the ash will go up the chimney with unburnt and coal debris, some will fall downwards. Some of the coal will be part burned – perhaps roasted, giving off its gaseous content, and leaving coke, perhaps just partly consumed leaving a grey mix of coal and ash.

To be certain (ie to within 1%) you need to know how much of the coal escaped unburnt, how much extra energy was added as ignition gas, kindling, etc, and how much of the remaining solid fuel is fully burnt clinker, part-burned coal, accidental stone inclusions, and ash.

I am interested to know, on the small scales we are involved with, how these calculations are carried out and verified. In industry, a similar test might take hours and involve hundredweights, and so the variations added from the kindling, and the amount of clinker counted as unburnt coal, could be determined fairly well, but I need to understand how this is done on the small scale. After all, the coal consumption is recorded for us in pounds to three places of decimals, ie to the nearest half a gram. (That is the mass of one dried pea).

I note too that the time taken is recorded and the coal consumption calculated. My understanding is that the work done is force time distance, whether done quickly or slowly, so my second question is: Are the Lb/hr figures charted merely for interest, or do they form a part of the final calculations of position? And, why is no listing of power output given (for further interest)?

My interest is prompted by noting that the Specific Consumption figures and the Efficiency figures are closely related mathematically*, and as one includes time and the other shouldn't I am doubly confused.

* ie multiply one by the other and the result is the same for all entrants (17.55)

Regards – Tim