[Stoves] Energy in different fuels

[Crispin Pemberton-Pigott]

Dear Paul

It is important to ensure that you are converting litres or converting kilograms because people are using the confusion to pretend their stoves or fuels are more effective than they really are.

I have collected the following notes from various sources and messages to this list:

Ethanol alcohol 31.8 MJ/Kg
Ethanol alcohol 26.7 MJ/Litre
Ethanol with 5% water (which is the normal water content of distilled ethanol)  24.5 MJ/Litre.  Gel fuels are typically 5% water + the gell and denaturing agents, giving about 24-25 MJ/Litre but often the literature claims it is 30 MJ which is the heat per Kilogram, not per litre. I have a particular bone to pick about this because the stoves are often compared with paraffin fuel heat measured in litres and alcohol fuel heat measured in kilos.

Fuel oil 40.3 MJ/Litre which is diesel by another name, slightly higher than paraffin.
Fuel oil 42 MJ/litre, different claim.  The heat per Kg is about 46 MJ.

Paraffin (Kerosene, 'Petrol' in French) 38.3 MJ/Litre but it varies a bit
Paraffin (Kerosene, 'Petrol' in French) 46 MJ/Kilogram but it varies a bit.  South Africa officially uses 44 MJ/Kg as their bench mark for testing paraffin stove performance.  The density of paraffin is variable but about 0.83.

Easy lighting Coal 22 mj/kg with 25-30% volatiles, from Middleburg/Witbank in South Africa but coal varies a great deal.
Anthracite 35 MJ/Kg - Swaziland
Coal gas is about 28 MJ/Kg, the same as good coal or ordinary charcoal.

Propane 46.44 MJ/Kg  That may be a LLV figure.  I think 49 is closer to the truth.
Propane 93.8 MJ/Cubic Metre

Methanol 0.796 gm/ml
Methanol is probably 25 MJ/Litre and 31.8 MJ/Kg

Rubbing alcohol 0.785 gm/ml but no heat content figure.

Naptha 43.6-44.8 MJ/Kg, mass 0.74gm/ml
Naptha 32.7 MJ/Litre

Wood gas: 4.6-5.2 MJ/M^3

Wood
In general, 19 MJ/Kg bone dry with Pine being as much as 21 because of the resins in it.
16 MJ/Kg air dried, 
11 MJ/Kg at about 20% moisture

Charcoal varies a great deal because it is made in various ways.
Try using 28 MJ/Kg unless you know the variety you have is different.
Charcoal briquettes with binders vary even more.  Use 22.5 MJ/Kg if you think the binder is not combustible.

Paper made without clay (brown paper, cardboard, newspaper and other 'mechanical' products made directly from pulp) are the same as wood = 19 MJ/Kg bone dry.
Paper - shiny type from magazines with lots of additives - hard to predict.  Perhaps as low as 11 MJ/Kg.

Paper + sawdust briquettes, the same as wood as long as it is mechanical paper.  Usually they have more moisture because they gain it more easily.

Butane (MJ/Kg)
Lower heating value 45.5 MJ/kg, 
Higher heating value 49.4 MJ/kg

I trust this is useful.

Regards
Crispin


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Crispin Pemberton-Pigott
Regional Technical Advisor
Programme for Biomass an Energy Conservation (GTZ/ProBEC)
Johannesburg
RSA