# Saving lives and the environment with improved cookstoves in Darfur, Sudan {#saving-lives-and-the-environment-with-improved-cookstoves-in-darfur-sudan .unnumbered}

**End of Semester Report**

**ER291: Design for Sustainable Communities**

![](media/image1.jpeg){width="6.192361111111111in"
height="4.658333333333333in"}

Charles Kirubi

Jesse Woo

Susan Amrose

Teddy Kisch

5/10/06

#  {#section .unnumbered}

# Introduction

## Overview of Conflict in Darfur

> Covering an area of 2.5 million square kilometers, or ¼ the areas of
> the US, Sudan is the largest country in Africa, located in the
> northeast just south of Egypt. Around 200 different languages and
> dialects are used by the 40 million Sudanese people. The majority of
> the country (93%) is desert and the per capita GDP is about \$1820[^1]
> (ppp US\$). The nation has just recently (as of January 2005)
> negotiated a difficult peace after 50 years of devastating civil war
> between the Muslim north and the Christian and animist south. However,
> even as this peace was being negotiated, armed conflict broke out in
> the western region of Darfur.

Darfur is a very poor region about the size of France. There has been
tension there for many years, mostly over land and grazing rights
between nomadic Arabs and black African farmers from the Fur, Massaleet
and Zagawa communities. Warfare erupted in early 2003 when the non-Arab
African rebel group known as the Sudanese Liberation Army/Movement
(SLA/SLM), later to be joined by the Justice and Equality Movement
(JEM), attacked the Sudanese government forces and ethnic Arab militia.
Their demands were for the government to bring an end to the region\'s
chronic economic and political marginalization and to provide protection
for their communities against attacks by armed nomadic groups. In
response, an Arab militia known as the Janjaweed, widely believed to
have been supported by the Khartoum government, began terrorizing and
destroying the homes of unarmed civilians belonging to the same ethnic
groups as the rebel groups. Human Rights Watch[^2], an NGO dedicated to
protecting human rights, reports that the Janjaweed focus their attacks
on looting, burning, and plundering villages and killing civilians, and
that they have complete immunity from any sort of criminal prosecution
from the government.

As a result, about 2.3 million people (out of a population of about 6
million) have been displaced in Darfur during the past three years. Most
of the Internally Displaced Persons ("IDPs") are black Africans, but
there are also displaced Arab communities whose villages were attacked
by African groups and who are victims of inter-African ethnic fighting.
The displacement of over 2 million people has turned into a humanitarian
crisis of which supply and demand of energy for cooking is but one
critical dimension of the escalating crisis.

## Project overview and statement of the problem 

The energy challenges arising from over 2.3 million IDPs living in dense
scattered camps in Darfur unfold in multiple dimensions. First, as
Darfur is an arid region with limited vegetation cover, women and
children spend over 7 hours per day gathering fuelwood at the expense of
other more productive activities (Galitsky et al. 2006). Second,
unsustainable fuelwood harvesting contributes to severe denudation of
arid land, inhibits natural regeneration of vegetation, accelerates soil
erosion and exacerbates overall land degradation. Third, venturing
outside the camps to collect fuelwood exposes women and children to
incidents of abuse and rape by the Janjaweed militia. Doctors Without
Borders issued a statement in March 2005 noting that it alone treated
almost 500 rapes in a four-and-a-half-month period. When asked why only
women collect firewood when they are raped, one woman reportedly
explained, \"It\'s simple. When the men go out, they\'re killed. The
women are only raped\" (Kristof 2005). According to the head of UN
Humanitarian Affairs in Darfur, fuelwood collection has become the
"largest security operation" in the region[^3].

To address the energy crisis, a team from Lawrence Berkeley National Lab
(LBNL) visited Darfur region in November 2005. In conjunction with CHI
International (a non-profit operating in Darfur), the LBNL team visited
different camps, assessed the fuelwood crisis and tested a few
alternative designs of improved cookstoves from India. The team
identified five principal factors that influence fuelwood consumption in
a cookstove: the cook's fire tending skills, the fuel, the stove, the
pot and the food and how it is cooked. The final recommendations for the
most feasible and effective way to influence fuelwood consumption were
aimed at modifications of the stove (along with training of cooks).
Based on their preliminary field tests, the team recommended further
modifications on an Indian model known as the Tara Stove - in two key
ways. The objective of the first modification was to accommodate the
vigorous cooking style employed by the IDPs in Darfur. The objective of
the second was to minimize convective heat loss from the stove,
particularly during the breezy weather in which food is commonly
prepared in Darfur[^4]. These recommendations defined the problem and
scope of work undertaken by our group during the class "Design for
Sustainable Communities" during the Spring Semester (January-May) 2006.

## Broad Objectives

Building on the previous work by the LBNL team, our broad goal was to
continue their efforts towards designing and disseminating a cookstove
for the Darfurian IDPs that would ***save fuel,*** be ***low cost*** and
***culturally appropriate*** in Darfur. The best way to do this was to
try to implement the two recommendations of the LBNL team. Thus our
broad objectives for the semester were to design, fabricate and test
mechanical modifications of the Indian Tara stove with a view to (1)
make the stove stable in the presence of vigorous stirring; and (2)
minimize convective heat loss from the stove during breezy weather.

In addition, we would strive to meet both objectives in a way that would
not significantly increase the cost of the stove and would allow for the
possibility of local manufacture.

The design was also to embody other user-friendly attributes such as
portability and safety.

## Specific objectives

> With the aim of achieving our two broad objectives by the end of the
> semester, our group came up with the following specific objectives:

-   Come up with a robust design that could be fabricated and tested
    within the time and resource constraints of one semester (this
    includes evaluating design ideas according to set criteria).

-   Develop appropriate protocols to compare fuelwood savings between
    the modified and unmodified Tara stove for traditional IDP meals, in
    both windy and non-windy conditions.

-   Develop an appropriate protocol to compare the stability of the
    unmodified and modified Tara stove taking into account vigorous
    stirring of traditional IDP meals.

-   Fabricate and test the modified Tara stove according to the above
    protocols.

## Motivation and significance of the project

Despite a disproportionately large share of security personnel involved
in protecting women and children who gather fuelwood in Darfur, their
safety outside the camps cannot be guaranteed. Moreover, in severely
resource-poor conditions as is the case in Darfur, the more security and
other resources (financial, administrative, etc) devoted towards
fuelwood gathering, the less the resources available for other endless
and equally important humanitarian services. Thus addressing the
fuelwood crisis is of fundamental importance and priority. In addition,
modifications that enable the final stove design to deliver substantial
fuel savings will go a long way in mitigating land degradation in Darfur
and surrounding areas.

But why did we exclusively focus on improved stoves and not other types
of fuels? Alternative cooking fuels and technologies such as solar
cookers, liquefied petroleum gas (LPG), and kerosene are inappropriate
in Darfur for a variety of reasons. At first glance, solar cookers
appear to be a suitable alternative as Darfur experiences tropical (hot)
sunny weather most of the year (over 100F in summer). However, the local
staple foods are vigorously stirred during cooking and require constant
attention, making the solar cooker untenable. Low cost solar box cookers
are more suitable for meals that do not require constant attention
and/or stirring such as rice[^5]. Other fuels such as LPG and kerosene
pose acute and significant fire, health, and security hazards because
the IDPs' hutments are made from straw and tarpaulin. In addition to
this, the costs of importing and supplying the fuel and requisite
appliances are prohibitive (Galitsky et al. 2006). Other alternative
fuels such as biomass briquettes and biogas are severely constrained by
the lack of sufficient and reliable supplies of feedstock or raw
materials.

For these reasons, and given the limited time and resources available,
improved woodstoves are the best bet for responding to the energy crisis
in Darfur. That the stoves can be locally and rapidly fabricated and
deployed at relatively low capital cost is another major advantage for
supporting this intervention[^6]. Another critical motivation was to
undertake a project that permitted hands-on learning and application of
the principles underpinning designing for sustainable communities
discussed in class. We selected the improved stove project because it
permitted direct exploration and contending with a wide range of
sustainability challenges including affordability and cultural
appropriateness of the final stove design. Further, the stove project
permitted and benefited immensely from the inter-disciplinary character
of the class team, which included a physicist (Susan Amrose), mechanical
engineer (Jesse Woo), environmental scientist (Teddy Kisch) and energy
specialist (Charles Kirubi).

# The Design Process

## Conceptual framework

We began our brainstorming process by researching some of the theory
behind woodstoves and sustainable design process. Conceptually, two
principles underpinned and guided the design process in this project:
(1) the theory of combustion and heat transfer in a typical woodstove,
and (2) designing for sustainable and resource-poor communities.

### Basic stove theory of combustion and heat transfer 

The primary goal of an energy efficient stove is twofold: convert as
much wood as possible into energy (combustion efficiency) and transfer
as much of the released energy into cooking the contents in the pot as
possible (heat transfer efficiency). An open fire is often 90% efficient
at the work of turning wood into energy but only 10-40% of the released
energy makes it to the pot (Aprovecho, undated[^7]). Improving
combustion efficiency helps to reduce harmful smoke and emissions while
improving heat transfer efficiency helps save fuel. To achieve the twin
objectives of reducing emissions and saving fuel, the stove designer's
job is to first clean up the fire and then force as much energy into the
pot or griddle as possible (Aprovecho, undated). In theory, both
functions can and should be accomplished in a well-engineered cookstove.
In practice, however, not every "improved stove" saves fuel and some can
even be worse than three-stone fires. For instance, the LBNL team
documents the disappointing performance of the "improved mud-stoves"
introduced by ITDG (Practical Action) in Darfur (Galitsky et al. 2006).
Since our group was starting from an existing Tara design, our project
placed more emphasis on enhancing fuel savings (via heat transfer
efficiency) than on reducing emissions (via combustion efficiency).

In wood burning stoves, a lot of heat is transferred to the pot by
convection. Forcing hot flue gases to flow past the surface area of a
pot in a narrow channel (flue gap) is a stove strategy promoted by both
Dr. Samuel Baldwin and Dr. Larry Winiarski (Aprovecho, undated; Baldwin,
1987). Popularly known as the "rocket" stove design, Dr. Larry Winiarski
created the pot skirt (or collar), which is a cylinder of sheet metal
that surrounds the pot and forms a narrow channel increasing heat
transfer efficiency (see Figure 1).

![](media/image2.png){width="2.920138888888889in"
height="1.8736111111111111in"}

Figure 1: The narrow channel (flue gap) close to the pot increases
convective heat transfer (Aprovecho, undated).

The Aprovecho Research Center on wood cookstoves identifies three key
ways to increase convective heat transfer: (a) the flue gases scraping
the surface to be heated should be as hot as possible; (b) the surface
area of the heat exchanger (e.g., pot or griddle) should be as large as
possible; c) the velocity of the hot flue gases should be increased as
much as possible (Aprovecho, undated). A faster flow over the exterior
of the pot disturbs the stagnant boundary layer of air that slows
effective heating. To permit smooth flow of air via the flue gap, the
size of the flue gap must be well balanced in relation to firepower and
surface area of the firebox. This is important because narrowing the gap
increases heat transfer efficiency but also decreases the flow of air
through the stove. As more wood is burned per minute, more air is needed
to support both the combustion and the necessary flow to avoid a back
draft into the room, which would increase indoor pollution. If the gap
is too small, the fire may burn well while simmering but will be short
of air when operated at high power. Conversely, very large channel gaps
will sustain a large fire (high power) but some amount of heat will be
lost unnecessarily due to poor heat transfer, resulting in low fuel
savings.

### Designing for sustainable and resource-poor communities in Darfur

The overarching theme running through the class was the challenge of
designing for sustainable communities with a special emphasis on
resource-poor regions. The energy crisis unfolding in Darfur poses three
key sustainability challenges: humanitarian, financial and ecological.
With over 2 million IDPs in densely populated camps, the lack of
adequate energy supply, particularly for cooking, is but one dimension
of the humanitarian crisis. As in other refugee-type and resource-poor
conditions, the energy crisis has both supply and demand-side
components. Energy supply is particularly complicated by the fact that
Darfur is an arid region with scarce supply of biomass for use as
fuelwood. Moreover, supply of alternative fuels to fuelwood is
(currently) unsustainable and untenable for a variety of reasons (see
sec 1.5 above). From a sustainability perspective, however, we hesitate
to conclude that fuelwood and improved woodstoves should be viewed as
the "silver bullet" to the energy crisis in Darfur. That would be a
static and limiting strategy whereas sustainability ought to embody
dynamic innovation and flexibility. Thus, as more experience and
capacity are established locally and (hopefully) more resources become
available for energy services, additional innovation could be devoted
into expanding the fuel and technology choice available to IDPs (e.g.,
fireless cookers[^8], solar cookers, etc.).

The demand side presents other constraints too. As noted earlier, the
traditional method in which the food is cooked has, among other factors,
significant influence on fuelwood demand. This aspect represents the
cultural dimension of the sustainability challenge our design had to
grapple with. But who cares about culture in a humanitarian crisis of
Darfur's magnitude? Despite severe deprivations and poverty in Darfur,
our advisor and part of the LBNL team, Ashok Gadgil strongly argues that
the IDPs intimately value their indigenous foods (specifically *mulah*
and *assida*, which will be discussed at length in section 4) as well as
their cooking pots (round-bottomed pots or "Tungutungus") and will go to
great lengths to retain this culture. Studies show this cultural aspect
is not unique to Darfur. Masera et al. (2000) have noted that cultural
factors (such as specific cooking practices, habits and religious
beliefs) constitute a wider set of complex interactions that determine
fuel choice in households in many parts of developing countries.

## Design Ideas

During the course of the semester, our team met for several
brainstorming sessions with Ashok Gadgil in order to put our conceptual
framework to use. These sessions served as a forum for discussing the
feasibility and effectiveness of numerous design modifications aimed at
meeting one (or both) of our two broad objectives. These sessions were
invaluable in determining the final product design. This section of the
report delves into examining the many ideas that were generated and
considered along with an analysis of why each idea was either accepted
or rejected for fabrication.

The unmodified Tara stove fabricated by the LBNL group and tested in the
field was found to be 50% more efficient at burning firewood than the
local three stone cooking method (Galitsky et al. 2006). However, room
for improvement was obvious just from looking at the traditional round
bottom pot on the stove. The size and shape of the pots used by the IDP
community were never considered in the design of the original Tara stove
(it was for use in India), and so it was designed to house a cylindrical
flat bottom pot. This resulted in the small and large traditional pots
resting slightly above the stove with a large gap (see Figure 2). This
position exposed the pot's bottom to the high winds, killing off the
heat transfer from the fire to the pot. Simply reducing this gap would
improve the heat transfer and save even more fuelwood. In addition the
unmodified Tara had large air hole openings around the bottom as well as
in the firewood door. These shortcomings were all places where we could
potentially modify the stove.

![](media/image3.jpeg){width="2.259027777777778in" height="3.0in"}

Figure 2: (Left) Small pot sitting on top of unmodified Tara stove.
(Right) Large pot sitting on top of unmodified Tara stove.

In order to address the gap, our first idea was to cut down the three
bracket points and thus allow the round-bottomed pots to sit further
inside the stove (see Figure 3a). The brackets existed to maintain some
gap between the pot and stove, so we did not was to remove them
entirely. Since this was an easy modification and ill side effects were
unlikely, we immediately accepted this idea and cut down the brackets by
2mm. To further shield the stove-pot gap from the wind, a metal
windshield was devised to be offset from the top of the stove itself
(see Figure 3b). This would further reduce the ability of the wind to
blow heat away from the sides of the pot as it was rose from the hot
center of the stove. Finally, we also agreed on reducing the effective
air hole area that was directly in line with the wind by changing the
stove's lower air *holes* into air *slats*. That is, instead of cutting
holes into the lower rim of the stove (as seen in Figure 3a and 3b),
slats would be cut forming metal tabs, with each alternate tab being
pressed in by hand so that air could enter from the sides (see Figure
3c). This would prevent high velocity wind from blowing directly into
the stove and increasing the speed with which hot air was forced out.
These three modifications were accepted as the winning ideas to
fabricate and test.

![](media/image5.png){width="4.990972222222222in"
height="1.6944444444444444in"}

Figure 3: Accepted wind modifications: (a) shortened brackets on
original Tara; (b) wind collar (note that the stove handles have been
removed); (c) wind collar plus slats instead of holes around the bottom
of the stove.

One idea for combating the wind that was rejected is listed below:

1)  Latch door to shut the stove's opening that feeds firewood (see
    Figure 4).

Pro:

-   The constant high winds will make the initial combustion of firewood
    difficult. In addition, excess air must be minimized.

Con:

-   Psychologically, people find it cumbersome to have latch doors. A
    latch door will fail after several repetitious usages.

![](media/image6.png){width="1.7444444444444445in"
height="1.5986111111111112in"}

Figure 4: Rejected wind modification: a latched door to close off the
firewood opening.

The second problem with the unmodified Tara was its tendency to tip
during the rigorous stirring involved in IDP cooking. The LBNL team
noticed some IDP women secure the instable stove-pot system with a rod
either laid horizontally on top of the pot or through the bottom air
feed holes. This quick fix required several people and made the stove
difficult to use. We thought of many possible ways to stabilize the
stove, finally settling on attaching a set of three bent steel rods
(like tent stakes) to the side of the stove. The rods would be free to
move within brackets, and so could be hammered into the ground several
inches and prevent tipping even in the presence of strong horizontal
forces (see Figure 5).

![](media/image7.png){width="1.8145833333333334in"
height="2.1034722222222224in"}

Figure 5: Accepted design for stability (after wind modifications):
three bent rods attached by brackets to the stove. These rods can be
pounded into the soil to create stability.

Again, we rejected numerous ideas before coming to our final design.
They are listed below followed by a list of pros and cons (the cons
ultimately outweighing the pros):

1\) A cookstove with a wider diameter to fit the Assida pot.

Pro:

-   Initially, the team believed the rod was used to secure the large
    Assida pot from slipping off the stove's bracket tabs.

Cons:

-   During an assessment of another Sudanese region's test site and
    consultation from Christie, there was a breakthrough realization
    that the main problem was the instability of the stove-pot system
    and not isolated to the stove's inability to secure the pot.

-   If the stove's diameter increased, the Assida pot would sink deep
    into the stove but it would not solve the problem of the stove-pot
    system from tipping over.

2)  Stainless steel spring loaded brackets to secure the Assida pot.

Pro:

-   If installed, the brackets would press upon the surface of the pot,
    increasing the contact surface area between the tabs and the Assida
    pot.

Cons:

-   The 3 point contact with the three tabs is an effective method in
    holding the pot in place.

-   The problem isn't the Assida pot slipping off from the bracket tabs.

3)  Unused stones from the three stone method used to stabilize the
    stove (see Figure 6a).

Pro:

-   Figuring it was a stove-pot system problem, the use of stones would
    be a cheap and effective method of stabilizing the problem.

Con:

-   There is a limited supply of stones in the Darfur refugee camps. In
    addition, stones could be too small to secure the stove.

4)  Tripod rods stabilizing the stove (see Figure 6b).

Pro:

-   Easily able to withstand large lateral forces.

Cons:

-   If implemented, the design would be bulky and more material would be
    used in the manufacturing of these stoves.

-   The tripod legs can fail if bent slightly.

-   There is no assurance of a leveled ground which will hinder the
    effective use of the tripod.

![](media/image8.png){width="4.993055555555555in"
height="1.5659722222222223in"}

Figure 6: Rejected stability modifications I: (a) use of local rocks to
stabilize stove; (b) tripod attached to wind collar (note: third leg is
behind the stove).

5)  Hinged brackets to hold the pot in place with the upper tab limiting
    the movement of the pot (see Figure 7a).

Pros:

-   Contained within the stove (no protruding parts).

-   No directions needed - the mechanism would be triggered by normal
    use of the stove.

Cons:

-   There is a history of products failing with the presence of moving
    parts in developing countries.

-   Once the hinge is loose and breaks down, replacing the piece can
    take horrendous time in developing countries.

6)  Long rods run through air holes and attached to ground via bent
    horseshoe-shaped rods (see Figure 7b).

Pro:

-   This models the design that some IDPs were already using to
    stabilize the stove.

Cons:

-   Requires extra pieces that may be lost.

-   Requires holes instead of slats around the bottom rim (incompatible
    with our wind modifications).

![](media/image9.png){width="4.367361111111111in"
height="1.7722222222222221in"}

Figure 7: Rejected stability modifications II: (a) hinged brackets that
grip the pot as it is lowered into the stove (wind collar not shown);
(b) long rods through air holes held in place by horseshoe-shaped rods.
Note that this is incompatible with the slat air hole design.

7)  Interior horizontally flat annular ring with point welds to the
    stove.

Pro:

-   Theoretically, there would be a constant support if the pot is
    tilted for cooking purposes but again it should be emphasized that 3
    points stabilizes anything.

Cons:

-   The idea is an example of a ball and socket joint. The pot could
    actually slip off more easily than the 3 points method.

-   The idea can introduce the piston-cylinder problem. It is dangerous
    to limit the gap between the stove and pot. There needs to be a
    proper size gap to optimize the heat transfer to the sides of the
    pot or the exit of the hot flue gases generated from the fire.

# Fabrication

After the stove design was finalized, fabricating the necessary
modifications was the next step. The group used the machine shop at LBL
maintained by Jonathan Slack. Through his guidance, the group
independently machined and assembled the additional parts to the
existing Tara stove.

Approximately several millimeters of the upper bracket tabs were cut
with a hacksaw. The stove was held inside a vice and after several
iterations of adjustments to attain a comfortable position, the tab was
sawed off with a hacksaw.

The sheet metal wind collar was bent into an open ended thin cylinder.
Punched holes at the ends were fastened with a screw-nut combination. At
the bottom of the sheet metal wind collar, cut out rectangular pieces
were bent inward, which were then used to attach to the original Tara
stove. The bottom gap between the stove and the wind collar would
eventually be sealed with aluminum foil during testing. It is imperative
to seal the gap because high pressure from the hot flue gases mixed with
the low pressure from the ambient air will cause a decrease in heat
transfer efficiency.

In addition, a thin sheet metal rectangular piece was cut, punched and
installed in the region below the grate holding the firewood. The
purpose of this thin rectangular piece is to block out the high winds
entering into the air feed holes. This was done to simulate the slat
geometry of our final design. Unfortunately, we did not have the ability
to fully implement the slat design for our initial tests.

Lastly, the brackets to hold the "L" shaped 1.5 foot metal rods were
installed (the stability modification). Using a power drill, the
bracket's position holes in the stove were created. The brackets were
then fastened to the Tara stove with a screw-nut combination.

Figure 8 shows the final modified stove and how it holds both the large
and small traditional pots.

![](media/image10.jpeg){width="1.882638888888889in" height="2.5in"}

Figure 8: (Left) The modified Tara stove with the small traditional pot.
Note how far it sinks into the stove. (Right) The modified stove with
the large traditional pot. The wind collar effectively shields the large
air gap that was present on the unmodified stove.

# Methods

## Fuelwood Savings Tests

One of our tasks was to design test protocols for computing the fuelwood
savings between the modified and unmodified Tara stove while cooking a
traditional IDP meal in traditional IDP pots. This required us to think
more closely about the meal and the pots in order to simulate each in a
(relatively) controlled environment. The staple meal of the IDP camps
includes *assida* and *mulah*. *Assida* is a dense bread-like substance
made from flour and water that is cooked until the water is completely
absorbed and the starches coalesce. It is commonly prepared in the
largest round-bottom pot and involves the vigorous stirring mentioned
earlier. *Mulah* is the sauce poured over the top, traditionally
prepared from sautéed onion, garlic, okra, dried meat, (or yogurt in
place of meat), dried tomato, rock salt, and chili (Galitsky et al.
2006). It is commonly prepared in the smaller round-bottom Tungutungus
pot that we were lucky enough to inherit from the LBNL group. We
developed two separate protocols for simulating these meals, an Onion
Test (OT) to simulate the *mulah* and a Water Boiling Test (WBT) to
simulate the *assida*.

### Mulah Protocol

We started with the *mulah* because we already had possession of the
small pot that *mulah* is traditionally prepared in. Most of the heat
used in making *mulah* goes to the task of frying its primary
ingredient - the chopped onions. Thus we ignored the other ingredients
and simulated the *mulah* using a mixture of corn oil and chopped white
onions, both of which are readily available and can be quickly prepared.
Traditionally, *mulah* contains about 400mL of oil and 3.5 cups of
onions. Since we were interested in comparison testing and not in
absolute wood use, we chose to use half of this amount (200mL oil and
1.75cups of onions) in order to decrease the total time of each test. We
also knew that convective heat loss was aided by the constant stirring
of the *mulah* and the lack of a lid. Thus all of our tests would
include constant stirring and no lid.

Onions are considered fully cooked when they become translucent and
begin to brown. We found that this state was hard to gauge by eye alone
in a way that was consistent enough for our purposes. Some basic physics
principles allowed us to establish a more accurate and reproducible end
point. In order for the onions to become translucent and brown, the
water in the raw onion pieces must be completely boiled off. We know
from thermodynamics that as water approaches its boiling point, the
energy going into the water ceases to increase its temperature and
begins to go into changing the water's phase from a liquid to a gas.
When all of the water has changed phase, the heat again begins to
increase the temperature of whatever is left, in our case solid onions.
The dried out onions then brown and eventually burn. Having the ability
to measure the temperature of the oil/onion mixture during cooking, we
set out to see if we could determine by eye the point when the
temperature started to increase again after flattening out during the
boiling phase. We called this the *elbow point* because it bends upwards
like an elbow on the temperature with time graph.

We first set up a series of tests using the oil/onion mixture in a
standard American flat-bottomed pot on a gas stove range. For each test,
we used a thermocouple taped to a wooden spoon to record the temperature
of the mixture as it was heated. All of our tests spanned the time
between turning the heat on and the time when the onions were clearly
burned. The purpose was (1) to determine if we could see the elbow point
and (2) to characterize that point either by its temperature or time of
onset. We also changed the stirring speed and power level on the range
to see if and how these would affect the elbow point. The results of our
initial stovetop tests are shown in Figure 9.

![](media/image12.png){width="4.742361111111111in"
height="2.972916666666667in"}

Figure 9: Heat curves from initial onion tests. The change of slope near
120°C is the *elbow point*. It designates that all of the water in the
onions has boiled off.

The initial large slope in all of the tests occurs as the temperature of
the oil/onion mix rises from room temperature to the boiling point of
water (100°C). The first change in slope occurs when the boiling point
is reached and the slope flattens out as heat is used to turn the water
into steam. The second change in slope occurs when the water has
completely boiled off (the elbow), and the heat begins to raise the
temperature once again. We found that the elbow *is* visible in the
graph (though not as sharply defined as we had hoped) and occurs around
120°C regardless of power level or stirring speed.

However, these tests were not completely satisfying. We saw the expected
increase in total cooking time as the power was lowered or the stir
speed was slowed, but we also saw large differences in total time
between tests that were supposed to be identical (in terms of stir
speed, power level and initial temperature). The most likely explanation
was that the rate of natural gas coming to the burner was changing
slightly with time, thus affecting the actual power produced from a
given power setting. To test on a more stable power setting, we repeated
the stovetop tests using an electric range. Our first attempt failed due
to effects from other burners on the range that were turned on during
our tests. However, our second electric range test (with all other
burners off) showed the results in Figure 10. These tests show cooking
times within 10% of each other (using the time to reach 120°C) for
identical stirring speeds, power settings, and initial temperatures. We
verified by eye that 120°C was a reasonable temperature to end our
future tests.

![](media/image13.png){width="5.997916666666667in"
height="2.9916666666666667in"}

Figure 10: Identical onion tests on an electric range (\<10% variation
between tests).

Our final testing protocol for simulating *mulah* was to bring a mixture
containing 200mL corn oil and 1.75 cups of onions chopped into small
(\~3-4 cm) pieces from room temperature to 120°C. The mixture was
constantly stirred at a rate of about 1 bowl diameter per second. This
protocol was dubbed the Onion Test.

The first time we tried this test in the field, we recorded the
temperature every few seconds just as we had for the stovetop tests. The
resulting heat curve from our first test (Figure 11) verifies that the
behavior is the same over a wood fire as it is on an electric range.
Note that we stopped the field tests once the temperature reached 120°C,
so the behavior above the elbow is not visible. In additional, the heat
curve shows that the onions take longer to rise to their boiling
temperature on the unmodified stove, verifying that the modified stove
does improve heat transfer to the pot.

![](media/image14.png){width="5.368055555555555in"
height="3.3229166666666665in"}

Figure 11: Heat curve for the first onion test in the field. Note that
field tests are ended when the temperature hits 120°C.

### Assida Protocol

To simulate the cooking of *assida*, we first needed to find a large pot
similar to the traditional one. Specifically, we needed the pot to have
a similar arc length around the bottom. It was because of this shape,
and the resulting gap between the stove and pot, that the original stove
was losing so much heat in the presence of a small breeze. In addition,
the fit between the stove and pot was a key cause of the stability
problems we were trying to fix. Ideally, we would use an actual
Tungutungus pot from Darfur, however we initially felt it would take too
long to arrive for it to be useful. Thus we set out to find a pot with a
similar arc length and diameter. We searched ebay, flea markets, thrift
stores, and both Indian and Mexican themed shops. We tried copper
kettles, metal mixing bowls, woks, plastic mixings bowls (for stability
tests only) and finally ordered a wrought iron pot of a remarkably
similar shape from an online store. That pot never actually arrived. In
the end, we were able to receive a genuine large Tungutungus pot used to
make *assida* in Darfur through the mail from Sudan after all. Thus all
of our *assida* tests were completed in the same pot.

The *assida* is mostly water and flour, which must be brought to a boil
and simmered until the water is boiled away and the starches coalesce.
The heat is mostly used to boil off the water, so using water alone was
accepted as a good proxy. We had hoped to use the same amount of water
as the IDPs use in *assida* (2500mL), but we found ourselves limited by
the height of a hole in our *assida* pot. The hole limited the water to
2000mL.

Because using less wood is more efficient, the fire tender tried to use
as little wood as possible when bringing the water to a boil. We found
that we still needed to use more wood than we used in the Onion Test in
order to make sure we could complete the tests in a reasonable (\< 2
hour) time. However, the fire tender still aimed to be as efficient as
possible given the time constraint. Since our goal was to compare the
wood use between stoves (rather than estimate the absolute wood use for
making *assida*), our original protocol called for only 5 minutes of
simmering. We later changed this to 15 minutes of simmering to avoid the
strong urge to stuff the fire for the remaining 5 minutes (we wanted to
get a good idea of the simmer stage as well as the initial heating
stage).

Frequently, while trying to use as little wood as possible, the fire
would lose some power after boiling had been reached and so the
temperature would fall below boiling for some portion of the 15 minute
simmer period. We chose not to stop the clock when this happened, but
rather to try to bring the water back up to boiling as quickly as
possible, noting any lapses in our log. This happened more frequently
with the unmodified stove than with the modified stove. However, this
would only increase the wood used on the unmodified stove and so
increase the fuel savings even further.

### Wind

We wanted to find out the fuelwood savings both in the presence of wind
and in still air (without wind). To create wind, we used a simple table
fan on a low setting facing the stove. A weather station was used to
measure the wind, both for tests with wind and without wind (to measure
the ambient breeze). Figure 12 shows the team engaged in a wind test.
Note the fan blowing towards the stove. We wanted to simulate a medium
breeze, so we aimed for a wind speed near the stove of 5-6mph.

![](media/image15.jpeg){width="2.504166666666667in"
height="1.8784722222222223in"}

Figure 12: The team tends the unmodified stove during a *mulah* test
with wind (note the fan in the lower right).

### Doubled-Up Tests

As a group, we divided ourselves into two person teams in order to
increase our total available testing time. Initially, we tried to save
time as well by testing two stoves (one modified and one unmodified)
side by side. One person was designated to tend the fire on both stoves
and the other stirred the contents of both pots. After some time, we
realized that this was compromising our test results. It was too hard
for the fire tender to carefully watch and tend both fires at once. In
addition, the *mulah* test always went faster, so we would be stuck
dousing the fire on one stove and neglecting the other for a time.
Because the *assida* test was always the neglected one, the doubling up
had more effect on the *assida* tests than on the *mulah* tests (where
it was not observed to have an impact). In addition, when the fan was
providing wind, the neglect of the *assida* stove was far more
disruptive than during the tests without wind. Thus we had to throw away
any results for *assida* tests with wind that were completed during a
doubled up test. This accounts for the disproportionate number of
*mulah* tests and *assida* tests without wind reported in our findings.

## Stability Protocol

The test the increase in stability added by our modifications, we
compared the lateral force required for the stove to just begin to tip.
The *assida* pot was filled with 3.4kg of water to simulate the 3.4kg of
combined water and flour that usually fills the pot when making
*assida*. We then tied a cord around the widest point on the pot and
applied a lateral force to the cord (Figure 13). This simulated the
force applied by the stirring stick while stirring *assida* (the stick
tends to push out on the pot from the widest point). We used a hand held
scale (essentially a spring balance) capable of measuring up to 12kg
weight (117N of force) to measure the lateral force required to tip the
stove.

![](media/image16.png){width="2.9944444444444445in"
height="2.613888888888889in"}

Figure 13: Schematic of the setup for stability testing (showing the
unmodified Tara stove). The spring balance was pulled laterally until
the stove just began to tip.

# Findings

## Fuelwood Savings

### Mulah tests

The *mulah* test was repeated several different times, both with and
without the wind. The resulting fuelwood savings are summarized in
Tables A and B. Figure 14 compares the fuelwood savings for the test
with and without wind.

**[Table A:]{.underline}** *Mulah* test without wind: unmodified vs.
modified Tara stove

  ---------- -------------- -------- -------------- ------------- -------------------------
             **Unmodified            **Modified                   
             Tara**                  Tara**                       

  **Test     **Time-reach   **Fire   **Time-reach   **Fire wood   **Relative Firewood
  Date**     120C**         wood     120C**         used (g)**    Savings \[Wood
                            used                                  (unmodified) - Wood
                            (g)**                                 (modified)\] x 100/
                                                                  \[Wood (unmodified)\]
                                                                  \***

  3/10/06                   171                     106           38.01%

  3/14/06                   302                     122           59.60%

  4/4/06     23 min         201      17 min         107           46.77%

  4/15/06    20 min         215      12 min         132           38.60%

  4/18/06    31 min         229      17 min         156           31.88%

  4/24/06    35 min         321      32 min         236           26.48%

                                                    **Mean**      **40.22%**

                                                    **Standard    **11.70%**
                                                    Deviation**   
  ---------- -------------- -------- -------------- ------------- -------------------------

\*Regarding all tables, the wide range of values is due to various
variables such as rainy conditions, doubled up duty of the fire tender,
the absence of a consistent fire tender and stirrer, hot/cold stove,
size and age of chopped onions, uneven distribution of wind generated by
the fan, and periods of low level flames.

**[Table B:]{.underline}** *Mulah* test with wind: unmodified vs.
modified Tara stove

  ---------- -------------- -------- -------------- ------------- --------------------------
             **Unmodified            **Modified                   
             Tara**                  Tara**                       

  **Test     **Time-reach   **Fire   **Time-reach   **Fire wood   **Relative Firewood
  Date**     120C**         wood     120C**         used (g)**    Savings**
                            used                                  
                            (g)**                                 

  4/17/06    21 min         354      8 min          175           50.56%

  5/1/06     14 min         357      12 min         152           57.42%

  5/1/06                    313                     120           61.66%

                                                    **Mean**      **56.55%**

                                                    **Standard    **5.60%**
                                                    Deviation**   
  ---------- -------------- -------- -------------- ------------- --------------------------

![](media/image17.pct){width="5.499305555555556in"
height="3.4090277777777778in"}

Figure 14: *Mulah* test: Relative fuel wood savings "with" and "without"
wind test conditions

A 40.22% relative savings in firewood under the absence of wind clearly
shows an increase in heat transfer efficiency once the *mulah* pot is
sunk deeper into the stove's cavity. It can be attributed to how the
generated heat travels a shorter distance to reach the bottom of *mulah*
pot as well as the increase of heated surface area. The simple
modification of cutting off 2 mm from the three bracket's upper tabs,
can contribute to an enormous savings in firewood.

In the presence of wind at speeds up to 6 mph, the addition of a wind
collar plus the sunken pot contributed to a 56.55% relative savings in
firewood. The wind collar is effective in blocking out wind currents
cutting off the heat transfer path.

Testing the unmodified Tara stove in the Darfur refugee camps,
scientists calculated that the stoves contributed to a 50% savings in
firewood compared to the local three stone cooking method. Now with the
additional modifications, the Tara stove would achieve even greater
savings in firewood. With our collected experimental values and the
following equation \[50% + X (mean)%\*50%\], we can make a general
calculation of how much the modified Tara stove saved on firewood
compared to the three stone fires.

Under the conditions with and without wind, the modified Tara is
calculated to save 78% and 70% of the firewood used in the three stones
method cooking *mulah*, respectively.

### Assida

The *assida* test was also repeated several different times, both with
and without the wind. The resulting fuelwood savings are summarized in
Tables C and D. Figure 15 compares the fuelwood savings for the test
with and without wind.

[Table C:]{.underline} *Assida* test without wind: unmodified vs.
modified Tara stove

  ------------ -------------- -------- -------------- ------------- --------------------------
               **Unmodified            **Modified                   
               Tara**                  Tara**                       

  **Test       **Time-reach   **Fire   **Time-reach   **Fire wood   **Relative Firewood
  Date**       98C**          wood     98C**          used (g)**    Savings \[Wood
                              used                                  (unmodified) - Wood
                              (g)**                                 (modified)\] x 100/ \[Wood
                                                                    (unmodified)\] \***

  4/15/2006+   27 min         521      27 min         473           9.21%

  4/18/06      34 min         545      42 min         490           10.09%

  4/26/06      21 min         492      19 min         464           5.69%

                                                      **Mean**      **8.33%**

                                                      **Standard    **2.33%**
                                                      Deviation**   
  ------------ -------------- -------- -------------- ------------- --------------------------

\* Please refer to footnote under Table A

\+ 5 minutes simmer time compared to 15 minutes

**[Table D:]{.underline}** *Assida* test with wind: unmodified vs.
modified Tara stove

  ---------- -------------- -------- -------------- ------------- --------------------------
             **Unmodified            **Modified                   
             Tara**                  Tara**                       

  **Test     **Time-reach   **Fire   **Time-reach   **Fire wood   **Relative Firewood
  Date**     98C**          wood     98C**          used (g)**    Savings**
                            used                                  
                            (g)**                                 

  4/29/06    72 min         2269     9 min          460           79.73%

  5/3/06                    1459                    454           68.88%

                                                    **Mean**      **74.30%**

                                                    **Standard    **7.67%**
                                                    Deviation**   
  ---------- -------------- -------- -------------- ------------- --------------------------

![](media/image18.pct){width="5.496527777777778in"
height="3.4229166666666666in"}

Figure 15: *Assida* test: Relative fuel wood savings "with" and
"without" wind test conditions

An 8.33% relative savings in fuelwood under the absence of wind
demonstrate how minor the *assida* pot would benefit from the cut upper
bracket tabs. Since the *assida* pot has a greater diameter and median
arc length than the *mulah* pot, the larger pot sunk only several
millimeters, a distance that doesn't significantly change the fuelwood
savings. The collar served no purpose since there was no wind.

However, under breezy conditions, boiling the water with the *assida*
pot with the modified Tara stove was substantially beneficial. The
addition of the wind collar was the main contributor to the 74.30%
relative savings in firewood. Several times during test runs, the fire
slowly died out because of the constant wind currents suppressing the
direct heat transfer path. When temperatures remained constant for
several minutes, the fire tender improvised and overstuffed the stove
cavity with firewood. The medium fire level that the fire tender aimed
off was insufficient to reaching the 98ºC boiling temperature mark.
Under the breezy condition without the collar, the flames that reached
the bottom of *assida* pot swayed and drifted off away from the central
concentrated zone. Under the same conditions with the collar, the
observed flames focused on a central location at the bottom of the
*assida* pot.

Under the conditions with and without wind, it is calculated that the
modified Tara saved 54% and 87% of the firewood used in the three stones
method cooking *assida*, respectively.

## Stability

The stability test was carried out on both the modified and unmodified
stove once. The results are summarized in Table E.

**[Table E: Mechanical Stability]{.underline}**

Terrain conditions: well packed dirt

  ----------------- -------------------------- --------------------------
  Date              Lateral Force (N)          

  5/5/06            Unmodified Tara Stove      Modified Tara Stove

                    22                         \> 117
  ----------------- -------------------------- --------------------------

The force required to tip the unmodified Tara was quite small - only 22
N, equivalent to lifting about 2.25kg. It is not surprising that the
IDPs had problems with this stove tipping during the November 2005
visit. However, once the stability modifications are added and pounded
into the ground, the stove could not be tipped even when the maximum
force measurable on our scale (\> 117N or lifting 12kg) was applied. We
were able to continue applying force beyond the capacity of the scale
and found that it would not tip even with what felt like double the
force applied. However, as we attempted to lean with our entire body
weight (far more than one would ever push on the pot during normal
cooking), the *assida* pot threatened to slide off of the stove and soak
us with water, so we felt it was a good place to stop.

This test was completed in an area with fairly moist compact dirt. We
would like to repeat this test on sandy terrain to get a lower limit of
the force (Darfur is neither loose like a beach nor hard and compact
like moist dirt).

# Implications

The modified Tara stove has great potential for improving the safety and
security of women. As indicated in Galitsky et al. (2006), women
(primarily in North Darfur) are facing significant health and nutrition
problems associated with the lack of fuel wood. Currently, the refugees
burn a type of wood called *oudar*, a stick whose smoke can produce
blindness (Galitsky et al. 2006). The improved efficiency will reduce
the volume of oudar burned, resulting in decreased exposure to its
harmful effects.

The greatest impact of the stove on the women would be its reduction in
fuel needs. The women who were collecting fuel wood would have the
option to only collect fuel wood a quarter of the time. They could also
sell additional wood in the market. If the women only collected wood for
their own family, then the new stove would result in the women going out
four times less often, barring any increase in wood consumption.[^9]
This could translate into a four times decrease in the incidences of
rape and brutality, making the community more secure than before.
Regardless of whether women continue to harvest wood or they choose to
stay home, the introduction of the stoves will result in a major
improvement in community health and safety.

## Impact on the local environment

Galitsky et al. (2006) indicate a 260,000,000 kg wood saved per year
with the Tara stove. However, the modified Berkeley Tara stove consumes
on average half the wood of the original Tara. Therefore, the potential
wood savings can be estimated at 520,000,000 kg wood per year with the
modified stove. However, this model is based on 100% saturation and no
'takeback' (i.e. increased wood consumption due to the increase the
number of meals per family per day) (Galitsky et al. 2006). They note
that the average walk for fuel wood is one hour farther than last year.
Assuming they walk 5-6 kilometers per hour, that means that the fuel
source is retreating by 5-6 kilometers each year. A four-time reduction
in fuel wood consumption will drastically slow down their advance on the
forest, prevent soil erosion, and therefore fight the spread of
desertification. It will also help to maintain the current distance from
the camps to the wood area, instead of a continual increase of space
between the two. This will promote plant and wildlife conservation by
dramatically reducing the impact on the ecosystem, allowing it ample
time to recover.

## Dissemination Plans

Initially, CHF International has a plan to disseminate 10,000 stoves in
a pilot study. The stoves will be disseminated through the sheiks, who
are the heads of individual family groups. The current dissemination
plan is to market the stoves through a micro-lending program, which
allows the individuals to pay for the stove with the savings they
receive from the stove's increased efficiency. This process eliminates
any extra capital that the family might need to purchase the stove.
While this may reinforce the current power structure and divide the
haves and the have-nots, we hope that eventually each family will be
provided in with a stove. In the past, the refugees have shown
resilience and co-operation against harsh conditions[^10], so it would
not be surprising to have families with stoves helping out others.

Since the average family pays USD \$160 in fuel wood costs per year, it
will not take long before the families have paid for the stoves.
Payments for each stove will be used to manufacture additional stoves,
which will allow the program to continually fund more cook stoves.
Through this micro-lending program, the initial stove investment will
provide funding for more stoves. In this manner, we hope to ultimately
manufacture 40,000 stoves by the end of 2006.

To make sure the families get the most out of their new cook stove, our
group plans to have assistants on the ground in Darfur. We will have a
two-student team lead demonstrations to educate women how to efficiently
operate the stove. The major points of this presentation will focus on
constant feeding of the fire, avoiding the overstuffing of the stove,
minimizing high power and high flame (unless in severe wind) and
preventing the flame from dying. The team will also address any problems
in the field that may come up.

# Conclusions

Based on robust protocols we developed to simulate traditional foods and
cooking habits in Darfur, our findings demonstrate that the modified
Tara stove has potential to yield significant benefits in multiple and
compelling ways. First, relative to three-stone fireplace, the modified
Tara yields 54% and 87% fuelwood savings with and without wind test
conditions, respectively. Second, using the modified stove is projected
to reduce the time spent collecting fuelwood by a significant factor of
four. Third, extra-polating from the fuelwood savings per capita, we
estimate that if every household used the modified Tara stove, the
resultant fuelwood savings would be in the order of over 500 million Kg.
While additional improvements are possible, the current modified Tara
stove design represents a win-win design for the IDPs and the
environment.

# References 

Aprovecho Research Center, undated, [Design principles for wood burning
cook]{.underline}

> [stoves]{.underline}. Aprovecho Research Center, Shell Foundation
> Partnership for Clean Indoor Air. Eugene, Oregon.

Baldwin, S., 1987, [Biomass cookstoves: engineering design, development
and]{.underline}

> [dissemination]{.underline}. In: Aprovecho Research Center, undated,
> "Design principles for wood burning cook stoves." Aprovecho Research
> Center, Shell Foundation Partnership for Clean Indoor Air. Eugene,
> Oregon.

Galitsky, C., Gadgil, A., Jacobs, M., Lee, Y., 2006, "Fuel efficient
stoves for Darfur IDP

> camps: Report of field trip to North and South Darfur, Nov. 16-Dec.
> 17, 2005." Lawrence Berkeley National Laboratory (LBNL)- 59540.
> University of California, Berkeley.

Kristof, N.D., "A policy of Rape." *The New York Times*, Op-Ed June 5,
2005.

Masera, O.R., Saatkamp, B.D., and Kammen, D.K., 2000, "From linear fuel
switching to

> multiple cooking strategies: a critique and alternative to the energy
> ladder model." *World Development*, 28(12), 2083-2103.

[^1]: This is the number cited by Africare at http://www.africare.org
    for 2004. The world Factbook cites per capita GDP as \$2100 for 2005
    at http://www.cia.gov/cia/publications/factbook.

[^2]: http://www.hrw.org - 2006

[^3]: Randa Hassan 2006- email communication

[^4]: For about half the year, IDPs cook outside in breezy weather. The
    other is done indoors but their shelters do not provide sufficient
    protection in windy conditions (Galitsky et al 2006).

[^5]: For instance, solar book cookers are widely used in refugee camps
    in Northern Kenya where the dominant community is Somali and rice is
    the staple food. Parabolic solar cookers are also appropriate for
    communal cooking (e.g., in schools, community centers, hospitals,
    etc) (Kirubi, personal observation). Communal cooking was beyond the
    scope of our project, however.

[^6]: The "willingness to pay" for an improved stove in Darfur is
    \$20/stove (Galitsky et al. 2006). Other factors equal, we estimate
    our final design could retail for approximately \$15/stove.

[^7]: There was no date anywhere on the pamphlet or on the website where
    it can be downloaded. The date must be later than 2002 based a date
    mentioned in the text.

[^8]: Fireless cookers are insulated boxes into which food that has come
    to boil is transferred for simmering without additional fuel input.
    By keeping food warm for longer periods, these devices save fuel
    that would otherwise have been spent in re-heating.

[^9]: For example, if each woman brings home 5 kg of wood a day and uses
    2.5kg per day with the traditional three stone fire, she would need
    to go out once every other day. With the modified Tara stove,
    fuelwood consumption is reduced by a factor of four, or a
    consumption rate of 0.625 kg per day. This means the same 5 kg lasts
    eight days instead of two, reducing the number of trips by a factor
    of four.

[^10]: Ashok Gadgil 2006 -Personal Communication