report on the efficiency of cob style materials

[smarty]

This report deals with the use of mud and straw style earthen mass rocket stoves for cooking on but I put it here because it is of general relevance:

services.lib.mtu.edu/etd/THESIS/2011/Civil&EnvironmentalEng/schreiner/report.pdf

The results show that rocket designs do not necessarily give improvements over traditional open cooking fires particularly where the stove is high mass. It has some useful methods for determining thermal efficiency of various materials by experimental means and some equations for modelling this.

The cautionary note it that the use of various different materials can have a marked impact on how well a stove actually operates under test conditions.

[Deleted]

Thanks for the laughs
The author is unable to interpret his own data.
And maybe the calculator was defect.

The "three stone" uses 1.3 times more fuel,
but gets a 1.4 times higher thermal efficiency attested.

OK, it burns less fuel per minute.

[smarty]

I think that the author doesn't have in mind the idea of thermal efficiency that would be my natural definition - i.e. the efficiency with which heat is generated from the wood but: "Thermal efficiency indicates how effective heat energy from the fire is transferred to the cook pot. High thermal efficiency may also coincide with the production of excess steam. Energy carried away by steam cannot be utilized in the cooking process (Balis, Ogle et al. 2007). For this reason specific fuel consumption is also presented as the amount of fuel consumed per unit output or in this case, the amount of wood burned to boil one liter of water."

This is I guess just one distinction that could be made between rocket heaters and cookers. Table 4-2 clearly shows that the rocket stove consumes less wood and releases considerably greater brute heat energy than the open fire. So from a heating point of view it wins hands down. Without doing the maths but just from a guesstimate it looks like the rocket stove despite its slightly lesser thermal efficiency - by the definition above would still come out ahead. This does however highlight one area of potential improvement. This is however a discussion that really does belong in the cooking section.

Table 4-5 had some useful comparisons between different materials for stove construction with sawdust and clay coming out surprisingly well.

The general point being that it matters more than you might naturally think what kind of material that you use in a high mass stove with regard to particulate emissions and CO levels.