[Stoves] Analysis of a two-stove cooking system

[Crispin Pemberton-Pigott]

Dear Frank

 

Good question.

 

> Where does energy need to come in?

 

Fuel mass is a proxy for energy. We need the energy number, not the ‘mass’. As there are different types of wood, and we need to normalise the calculations, we convert the mass into total energy. Thus ‘fuel efficiency’ is just a way of talking about energy efficiency as fuel mass represents energy, not the other way round.

 

When I say “1 kg of fuel” I am referring indirectly to 15 MJ of energy.  When I say “15 MJ of energy” I am not referring indirectly to a certain mass of fuel. I don’t care about what the fuel is, I care about the total energy. Fuel mass is the proxy for what is real.

 

Regards

Crispin

 

 

Dear Crispin,

 

Before I sit quietly I would just like to ask one question regarding this following section:

 

Where does energy need to come in?

 

We gather some wood and we cook a meal and sit down to a bowl of rice, some meat grilled over char and a cup of tea. How much wood did we use from the forest to boil water, cook some rice, and use the char left to cook the meat. 

 

The more fuel the less efficient. 

The less fuel the more efficient.

 

 

All based on weight of dry fuel per tasks completed. 

 

Regards

 

Frank

 

Frank Shields

 

 

 

 

 

 

 

 

On Nov 28, 2015, at 1:33 PM, Crispin Pemberton-Pigott <crispinpigott at outlook.com <mailto:crispinpigott at outlook.com> > wrote:

 

>A ) (Fuel Efficiency%) = ((task 1 + Task 2) / (dry wt biomass fuel) ) X 100

This is the dry fuel taken from the forest required to complete task 1 and task 2. Doesn’t matter the energy or time it takes to do it. As long as the stove(s) can complete the task(s) the stove(s) can be tested. There must be a very sharp endpoint telling when the task(s) are completed. Excess fuel left in the stove is wasted. 

 

This takes a mass-based approach and it has little use for stove performance rating. The problem is there is more than one fuel and as they have different energy contents, comparing the mass consumed doesn’t tell us precisely the performance. It has to be done on an energy basis because the work done is based on energy (we have to use something). Similarly emissions per kg of fuel burned are not ideal for measuring stove performance. They are useful for air-shed modelling but are usually misconstrued because a fuel does not by itself, have ‘characteristic emissions’.

 

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