[Stoves] benefits from reduced indoor air pollution.

[Crispin Pemberton-Pigott]

Dear Andrew

I need a further explanation please:

>The oxygen in the wood is already bonded to hydrogen and carbon, true it is not in it's lowest energy state but it's close. So the oxygen in wood does not significantly contribute at all. 

Contribute significantly to what? I don't follow. I presume you meant for heat generation (?), but I was talking about the chemistry of combustion.  We know the O in fuel ends up in the exhaust gases. The thermal decomposition of biomass releases H and O and N and S approximately in the same ratio as they occur in the fuel (with some exception made for S which sometimes clings to C.) 

For this reason the air demand of any fuel containing oxygen is lower than any otherwise similar fuel that does not. It happens that I gave a presentation on this to the CFD modeling group at the Chinese Academy of Sciences today. Lambda (total air demand) for a fuel containing oxygen is not Excess Air Factor +1, because the "1" is not correct for any fuel that contains oxygen. For wood it is about 0.76 if it is burned homogeneously and varies from about 0.2 to 0.99 in a real fire depending on what fraction of the fuel happens to be burning at the time (i.e. ignition volatiles v.s. char burning).

Wood doesn't contain nearly enough oxygen to burn the carbon (which can remain behind), but does contain nearly enough to burn all the hydrogen (which can't). When it is heated to a low temperature the O and H disassociate to make water vapour, leaving the char (carbon) behind. 

You are quite correct about the energy released, net, being low. That is why it is important to determine the ultimate analysis of what just burned in real time, so that the energy available can be calculated and the true efficiency determined in real time. The determination of what just burned requires separating the water vapour originating as fuel moisture from water vapour that results from combusting hydrogen - something heretofore not possible using carbon balance or chemical mass balance analysis methods. The presentation was on a method of doing exactly that: solving the water vapour split.

By the way that group is modeling combustion of fuels and particle formation using a very nice computer: 2.5 peta-flops; $100m. The simulation takes three days to run. I think I need a new laptop.

Regards
Crispin