A review of injera baking technologies in Ethiopia

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Review

A review of injera baking technologies in Ethiopia: Challenges and gaps

Kamil Dino Adem ⁎ , Demiss Alemu Ambie

School of Mechanical and Industrial Engineering, Addis Ababa Institute of Technology, Addis Ababa University, P.O. Box 385, King George IV Street, Addis Ababa, Ethiopia

a b s t r a c t a r t i c l e i n f o

Article history:

Received 7 January 2017 Revised 3 August 2017 Accepted 11 August 2017 Available online xxxx

Most of the people living in the Third World cook/bake food using biomass as their primary energy sources. There are a number of efforts undertaken to improve the efficiency, lessen the indoor air pollution and reduce emission of a three-stone-open-fire stove by introducing improved cooking stoves. The major purpose of this review is to organize, and document research and development efforts, showing gaps for researchers and developers working in the area of improved biomass and other stoves more specifically for bakinginjera. The information in the review, which is mostly in chronological order, is obtained from governmental and non-governmental reports, patents and journals written in the area ofinjerabaking stoves. The most important results of the review show that a number of efforts were undertaken to improveinjerabaking stoves, though there were no organized reviews earlier to show the efforts made by various institutions. The review also shows that other alternative energy sources forinjerabaking stoves have been used to address the problem of the majority of the people living in rural areas. In the end, the review indicated a research direction for the future in relation to the supply of alternative energy sources such as solar, biogas, gasifier and electric power forinjerabaking stoves.

Keywords:

Biomass stove Injerabaking stove Gasiﬁer stove

Electricinjerabaking stove Patent oninjerabaking stove Solarinjerabaking stove

Contents

Introduction . . . 69

Injeraand its baseline baking technology . . . 70

What isinjera? . . . 70

Three-stone-ﬁre for bakinginjera . . . 70

Early research and development efforts for improvements ofinjerabaking stoves . . . 70

Biomassinjerabaking stoves . . . 70

Injerabaking pan . . . 73

Electricinjerabaking stoves . . . 73

LPG and keroseneinjerabaking stoves . . . 73

Recent research efforts towards improvinginjerabaking stoves . . . 73

General research outputs . . . 73

Summary of research outputs . . . 75

Improved biomassinjerabaking stoves . . . 75

Electric and heat transferﬂuidinjerabaking stoves . . . 76

Solar poweredinjerabaking stoves . . . 76

Patents acquired forinjerabaking stoves . . . 76

The beneﬁts of the hitherto improvedinjerabaking stoves . . . 76

Indoor air pollution reduction and speciﬁc fuel consumption . . . 76

Carbon emission reduction potential . . . 76

Research directions . . . 79

References . . . 79

⁎ Corresponding author.

E-mail address:[email protected](K.D. Adem).

http://dx.doi.org/10.1016/j.esd.2017.08.003

Contents lists available atScienceDirect

Energy for Sustainable Development

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Introduction

The number of people in the world using traditional biomass energy is 2.7 billion (IEA, 2015). In Ethiopia, 95% of the population relies on the use of traditional biomass for cooking application (IEA, 2015) among which 50% of the energy is used to bakeinjera—traditional pan cake like bread. Due to the low efficiency ofinjerabaking biomass stoves, large amounts of firewood are used, resulting in high indoor air pollution, greenhouse gas emission and rampant deforestation. The attempts to improve theinjerabaking stove resulted in incremental change in efficiency and reduction in emission of pollutants without major breakthrough hitherto.

Injeratogether with‘wot’(sauce) is the major staple food eaten by Ethiopians and Eritreans as well as people from some areas of Somalia and Sudan (Asfafaw et al., 2014) both living in their country and abroad.

The standardinjeraweighs 310 g and it is 52 cm in diameter.Injerais a pancake-like thin bread which isﬂat at the bottom and has many“eyes” on top and looks like a‘thin sheet’. The majority ofinjerais prepared from the local indigenous grainteff.Teff(Eragrostistef) even if eaten by most Ethiopians and Eritreans, was not appreciated until recently.

Researchers found out thatteffis gluten-free which makes it very attractive for healthy nutrition (Kaleab, 2014). The details of theinjera baking process which starts from preparation and ends in baking is described byStewart and Getachew (1962).

Most of the people living in Ethiopia bakeinjerausing biomass on open-fire stoves. The inefficient open-fire stove consumes large amounts offirewood and produces high indoor air pollution and CO2

emission. A three-stone-stove or a three-stand-stove is where three stones with a similar size are made from clay. The three stones are placed in a triangle to support or carry the baking pan with a diameter of 60 cm and thickness of 20 cm on average. Then,ﬁrewood is inserted into the openings between the stands for burning. While burning is taking place below the pan,injerais baked on it. In the process, 90% of the energy supplied is lost to the environment. Moreover, the cook and her child is exposed to large amounts of CO and PM which is above the WHO standard set for safe cooking (Beyene and Koch, 2013).

Researchers in Ethiopia and abroad have made attempts to improve the efficiency ofinjerabaking stoves to save energy, reduce indoor air pollution and CO2emission. This includes early efforts by the Ministry of Water, Irrigation and Electricity, i.e. by the Alternative Energy Development and Promotion Directorate, and GIZ-Energy Coordination Office in the late 1980s and early 1990s. Significant achievement is registered by the GIZ-Energy Coordination office-Ethiopia in disseminating around 455,000 improvedinjerabaking stoves—Mirt,¹throughout the country (GIZ-ECO, 2011). A number of studies were conducted to see the reduction in specific fuel consumption ofMirtcompared to open fire baking which was in the range of 30–49% (Workeneh, 2005;

Alemayehu et al., 2012; Walelign et al., 2013; Anteneh, 2014; Yosef, 2007; Anteneh and Walelign, 2011; Dresen et al., 2014). However, improving the performance of biomass stoves, especially for bakinginjera still remains to be a challenge for researchers.

This review discusses the following issues: i) early development of injerabaking stoves, ii) current research, and iii) the way forward in terms of research and development regardinginjerabaking stoves. Since the information collected is mostly from reports from governmental and non-governmental institutions in the country, most of the references are not published in peer reviewed journals.

Our effort will present signiﬁcant beneﬁts to a wider public.

Besides, it will serve as a starting point for researchers who are inter- ested in designing, manufacturing and testing of stoves particularly for the purpose of baking not only in Ethiopia but also elsewhere in the world.

Injeraand its baseline baking technology

What is injera?

Injerais aﬂatbread with a unique taste; it is a circular pancake that is sour and tasty and has a soft-spongy like structure with a thickness of 2–4 mm and a diameter of around 58 cm. The major ingredient for bakinginjeraisteff, though other cereals such as sorghum and barley are sometimes used. These days, some consumers tend to add a few grams of riceﬂour for whiteninginjera. The knowledge and skill of bakinginjerais well known by Ethiopians and it has been transferred from generation to generation for a long time. The general structure of well bakedinjerais shown inFig. 1.²

Injerais made fromteffﬂour which is mixed with water and allowed to ferment by adding left over batter from the previous baking session as a starter. When it is ready,ﬁre will be lit from the bottom of the clay pan for biomass stoves and in the case of electricinjerabaking stove resistors will be turned on. When the pan's temperature reached around 200 °C, the dough will be poured into the baking pan. The viscosity allows it to be poured into the baking pan rather than rolling out. Finally, the bakedinjerawill be removed from the baking pan.

The majority of Ethiopians still bakeinjerausing three-stoneﬁre.

Starting from1980s efforts have been made to improve biomassinjera baking stoves and introduce electricinjerabaking stoves for urban dwellers.

Three-stone-ﬁre for baking injera

As the name indicates, a three-stone open-ﬁre stove uses three sep- arate stones to support themitad(clay pan) for baking. The types and sizes of stones used varies according to the availability of the stones.

Usually three (10–15 cm) high stones are used to support themitad (Fig. 2a).

A number of developers have used a three-stone open-fireinjera baking stove as a reference for showing the improvements with various versions of theMirtstove. The specific fuel consumption of a three-stone open-fire stove on average is 929 g of wood/kg ofinjerausing CCT protocol for testing (Table 1).Yosef (2007)conducted tests onMirt and three-stone open-fireinjerabaking stove and obtained indoor air pollution parameters for three-stone open-fire stove as 80 ppm for CO and 1.10 mg/m³for PM.

Early research and development efforts for improvements ofinjera baking stoves

Biomass injera baking stoves

The need for efficientinjerabaking stoves had not been addressed for a long time until governmental institutions laid the foundation in the 1980s. Early efforts included manufacturing of mudinjerabaking stoves by theBurayouBasic Technology Center (BTC), under the Minis- try of Education in the early 1980s. The name of the stove was‘Burayou mud-stove’. The then Ethiopian Science and Technology Commission (now Ministry of Science and Technology of Ethiopia) hired a consultant in 1981 to assess traditional closed stove in selected areas of the country (Ali, 1981). The major aim of this study was to make a survey of the types of stoves in use in the country. The numbers of stoves surveyed were 113 with a diameter of 60–65 cm and thickness of less than 2.5 cm earthen stove (mitad). Out of the total, 109 types of stoves were identified for further evaluation. Then, depending on the similarities of the stoves, the stoves were reduced into 20 stove types andfinally, six stoves were selected for further testing. The performance evaluation was made based on water boiling test. It was performed at

1 Mirt stove—means‘best’in local language and is used to name a biomass improved

injerabaking stove. ² http://www.diretube.com/articles/read-injera-got-standardized_4311.html.

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the Appropriate Technology Center of the Adult Education Department of the Ministry of Education. The report indicated that a pit type stove (Stove E) was found to be the most efﬁcient stove. This stove was constructed out of a mixture of clay, andchid(teffstraw). All of the stove parts were made out of clay andchidand they named itBurayou mud-stove (Ali, 1981).

The total weight of the stove is about 100 kg. The stove is massive and fragile, and it needs at least two persons for installation. This also makes transportation very difﬁcult. The sketch of the Burayouinjera baking stove is shown inFig. 2b.

In 1986, theAmboteam modiﬁed theBurayoumud-stove and came- up with theAmbomud-stove used forinjerabaking (ITDG-GTZ, 1991).

In the early 1990s, a team of experts at the then Ethiopian Energy Authority with consultants from abroad started a survey to make a starting point for the development ofinjerabaking stove in the country.

The assessment made throughout the country revealed that the Burayou,AmboandTigrianmud stoves were the more efﬁcient stoves at the time of the study, in 1991 (Endale et al., 1992). When tests were conducted on the above mentioned threeinjerabaking mud stoves, the variation in performance was associated with thickness and seasoning skill of themitad(Shimelis, 1991).

Enclosed traditionalinjerabaking stoves are commonly used in the northern part of Ethiopia, mostly inTigray(TigrayNational Regional State) andWollo(a province in Amhara National Regional State). They are named after the area where they are most popular in Tigray and hence, it is commonly referred asTigrianstove. These stoves, unlike three-stoneinjerabaking stoves, are permanently built on the ground or on a raised platform made up of mud and stones. Users build the stove according to one's estimate of dimensions. In some places, the height of the stove varies from 28 to 40 cm with one or two smoke outlets. A typicalTigrian injerabaking stove has usually two smoke outlets and a height of about 35 cm.

The efﬁciency of a well-built enclosedTigrian injerabaking stove is about 12% (Tim, 1991). Compared to the three stone openﬁreinjera baking stove, it consumes less fuel, and is easier to use and protects from burns.

Tehesh injerabaking stove was developed by GIZ (previously GTZ) and the Rural Technology Promotion Center ofMekele. The idea of designing Tehesh came from improving the existingTigrian injera baking stove.Fig. 2c showsTehesh injerabaking stove.

The raw materials needed for the making ofTeheshare mud, stones, and straw. Small amount of fresh dung is mixed together with mud to increase its adhesion. This mixture is smeared over the vertically stacked stone from inside and outside. The straw is used as insulation by placing it between the outer and inner walls of the stove and under the combustion chamber (RTPC, 1998).

Sodoinjerabaking stove is made by the Rural Technology Promotion Center inSodo. The name of the stove is taken from the place it wasﬁrst

designed. It is an enclosed stove made of 2 mm sheet metal. TheSodo injerastove can supportmitad(stove) sizes between 54 and 56 cm.

The total height of the stove is 42 cm. The combustion chamber is 60 cm in diameter and 15 cm in height. It has an ash-collecting box under the perforated metal grate (Fig. 2d). The controlled cooking test conducted by Sodo RTPC on a 45 cm diametermitadshows that the average fuel wood consumption of the stove was 0.343 kg wood per injera(MoA/GTZ, 1999).

Tests were conducted on theBurayou, Ambo andTigrianstoves, and Ambowas found to be the most efficient compared to the other two injerabaking stoves, but the fuel consumption reduction was not satisfactory. Later on, important modifications were made and the team of experts came up with a mudinjerabaking stove which is efficient, and they named it‘Mirt’, which means‘best’(Endale et al., 1992).

Consequently, the mud structure ofMirtis changed into cement- mortar mixture to build theﬁre chamber enclosure as shown inFig. 2e.

And this stove is widely promoted by the GIZ-Energy Bureau Ofﬁce in Ethiopia and namedMirt.

The speciﬁc fuel consumption ofMirtstove has been determined by a number of researchers and developers. The average speciﬁc fuel consumption ofMirtstove is 535 g of wood per kg ofinjera(Table 2).

Mirtstove was tested at the Aprovecho Research Center; the test was conducted using the water boiling test procedure where the time to boil is 35.8 min and 6407 g of fuel was used. The CO observed was 192 g and PM was 5322 g. The improved design brought about a percentage reduction of 18% (time to boil), 81% (fuel use), 90% (CO), and 83% (PM).

Fig. 2f shows the experimental modiﬁcation made to Mirt stove (Hatﬁeld et al., 2006).

The other improvedinjerabaking stove is made out of clay and its name isGonziye(Fig. 2g). It is a multipurpose improved cooking stove to be used both forinjerabaking and other types of cooking such as water heating, coffee making andwot³preparation. The speciﬁc fuel consumption of Gonziye injerabaking stove is 617 g/kg of injera (Anteneh, 2014).

Awrambais the other improvedinjerabaking stove which is named after theAwrambacommunity inAmharaRegional State.Thisinjera baking stove has been in use in the community since 1971. This stove also integrates other cooking applications in addition toinjerabaking.

It has a speciﬁc fuel consumption reduction of 35% compared to the open-ﬁreinjerabaking stove.Fig. 2h shows the simultaneous operation of theinjerabaking and cooking using theAwramba injerabaking stove (Walelign et al., 2013).

Biogas cooking stove is widely used in developing countries; however it is not yet popular forinjerabaking. There are a number of efforts by Fig. 1.A picture of top and bottom side of a typicalinjera.

3Wot—traditional sauce eaten withinjera.

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the Ministry of Water, Irrigation and Electricity—Alternative Energy De- velopment Directorate and SNV to develop a bio-gas stove for baking injera.

In 1996, a biogasinjerabaking stove was tested. It was a three ring stove consisting of three concentric rings made from a 1/2″steel pipe.

Fig. 2i shows the biogas burner tested forinjerabaking application.

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(c) (d)

(e) (f)

(g) (h)

(i) (j)

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Fig. 2.Biomassinjerabaking stoves: a) three-stone open-ﬁre, b)Burayou, c)Tehesh(actual & sketch), d)Sodo, e)Mirtwith cooking stove, f) modiﬁedMirt, g)Gonziye, h)Awramba, i) biogas burner (old), j) biogas burner (recent).

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The performance of the concentric three-ring injerastove was determined by bakinginjera. The power output of the stove was 11 kW, corresponding to gas consumption of 41 l/min. The gas consumption perinjerawas 193 l (3108 kJ/injera). The average efﬁciency of the three-ring biogas stove was 16% in the range of improved biomass stove. Thisﬁgure is quite low for a gas stove (Dereje, 1996).

Ethiopia has also recently established the National Biogas Program (NBPE) with the support from the Netherlands Development Organiza- tion (SNV) to promote the use of biogas for cooking. NBPE assisted a company to develop aninjerabaking stove which uses biogas as a fuel (Hivos, 2016). Combustion of methane using proper fuel-to-air ratio will create a non-polluting and comfortable kitchen forinjerabaking.

The amount of biogas or the feed stock required for bakinginjerafor a household, on average 25–30injeraat a time, is quite signiﬁcant. Thus, improving the development of aninjerabaking biogas stove requires further efforts by researchers and developers in the area.Fig. 2j shows aninjerabaking stove using biogas.

Injera baking pan

Improved biomassinjerabaking stove was also functionally tested using metal as aninjerabaking pan (Putz and Muller, 2011). The quality ofinjerabaked on a metal pan is not as good as the clay-madeinjera baking pan. The circular metal pan used to bakeinjerahas a higher thermal conductivity compared to clayinjerabaking pan which allows heat transfer rapidly generating small amounts of burns and less‘eyes’ in the bakedinjera.

Electric injera baking stoves

Electricinjerabaking stove (electricinjera mitad) was introduced to Ethiopia 40 years (EEA, 2015) back through the then Ethiopian Electric Light & Power Authority (EELPA). In order to disseminate the electric injerastove, various government and private organizations produced the stove and sold it to the market. Since the electricinjerabaking stove is not standardized, the performance of the electricinjera baking stove depends on the experience of the company and the quality of the workmanship. The average power demand of a single household electricinjerabaking stove is in the range of 3 to 4 kW.Fig. 3shows a commonly manufactured electricinjerabaking stove. Currently, small manufacturing enterprises are involved in the manufacturing of the

electricinjerabaking stove. The number of electricinjerastove in use is estimated to reach 850,000 in the year 2020 (EEA, 2015), which demands corresponding energy efﬁciency measures to improve the peak hour load created by households.

The Ethiopian Energy Authority is in the process of preparing the Ethiopian standard for labeling electricinjerabaking stoves in order to create awareness for the users to select their preference according to their interest based on the performance of the stove (MWIE, 2016).

LPG and kerosene injera baking stoves

The number of LPG users in Ethiopia is relatively low for decades due to the high prices of the gas and its appliances. LPG stove was also tested forinjerabaking appliance. During the test, a gas burner imported from Krampous, in France, with clay plate of 50 cm diameter was used. The Krampous burner was designed for the preparation of “crepes” (pancakes). Forinjerabaking purpose, the cast iron baking plate was replaced by a clay plate. The speciﬁc energy consumption with LPG was much higher than wood and electricity which might have been caused by the high power of the gas stove with about 6 kW. The energy consumption with LPG using the Krampous burner was 16 to 43%

higher than with wood and more than twice as high when compared to electricity (Yahaya, 1984).

Recent research efforts towards improvinginjerabaking stoves

General research outputs

Conducting research on improving the performance ofinjerabaking stove has increased in recent years due to environmental and health concerns, in addition to the possible reduction in the amount of energy lost duringinjerabaking. As shown inFig. 4, the path followed in recent researches consists of, atfirst, with optimization of a numerical model to come up with an improvedinjerabaking thin plate made of ceramic or other material in order to minimize specific energy consumption with experimental validation. The second direction is the use of thermic fluid and steam as workingfluid in order to use solar energy to bake injera.

The numerical investigation mainly focused on application of the finite element method to see the possibility of using numerical methods to solve the performance indicators of electricinjerabaking stoves. A 2D transient Finite Element Method is used to see the temperature distribution during baking ofinjerawith a conventional clay plate and a new ceramic plate. Both showed a reasonable heat-up and baking time during the test (Assefa, 2010; Abulkadir and Demiss, 2013). When the numerical investigation was compared with experimental results for various power supplies and thermic oil temperature, the result showed a minimal error. The experimental results on the electricinjerabaking stove with a clay pan⁴(thickness: 20 mm) and a ceramic pan⁵(thickness: 8 mm) have been compared and the results showed a thermal efficiency of 53% for the clay baking pan and 66% for the ceramic plate baking pan (Gashaw, 2011). Similarly, the thermal efficiency for baking 10–15 injerawas 53–66% for the clay pan and 66–72% for the ceramic pan (Awash, 2011). The ceramic pan was manufactured at a ceramic factory in Ethiopia (Tabor Ceramic Factory). In these studies, the output of the numerical computations cannot directly be compared with electricinjerabaking stove efficiency.

The other effort made by this study was on the possibility of using indirect heating for bakinginjerawith thermic-ﬂuid and steam as a

4Clay pan—made of ordinary plastic clay sintered between temperatures of 800 and 900 °C made at household level.

5Ceramic pan—made of plastic clay, silica sand, kaolin, feldspar and quartz which is sintered at a temperature of 1200 °C.

Table 2

Speciﬁc fuel consumption ofMirtstove.

No. Speciﬁc fuel consumption (g/kg ofinjera)

Injerabaked per session

Reference

1 460 Workeneh (2005)

2 524 Yosef (2007)

3 596 23–25 Alemayehu et al. (2012)

4 528 25–30 Anteneh and Walelign (2011)

5 575 23–25 Alemayehu et al. (2012)

6 667 23–25 Alemayehu et al. (2012)

7 393 Dresen et al. (2014)

Average 535 Table 1

Speciﬁc fuel consumption of three-stone open-ﬁre stoves.

No. Speciﬁc fuel consumption (g/kg ofinjera)

Injerabaked per session

Reference

1 630 Workeneh (2005)

2 1029 23–25 Alemayehu et al. (2012)

3 1031 25–30 Anteneh and Walelign (2011)

4 1025 25–27 Walelign et al. (2013)

Average 929

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workingfluid (Fig. 5). This was verified experimentally at two locations in Ethiopia (Addis Ababa and Mekele). In thefirst case, the solar energy was simulated with an electric heater to supply heat to the thermic- fluid so thatinjerais baked before the whole system is connected to the parabolic trough since the overall objective of the project was bak- inginjerausing solar energy using thermic-fluid. The surface temperature of the baking pan was in the range of 180–220 °C. The proposed injerabaking system for the thermic-fluid is shown inFig. 5. The test result showed a reasonableinjeratexture with a surface temperature of 215 °C (Abdulkadir et al., 2011; Mekonnen, 2011).

The second experimental study was a solar thermal stove which generates steam by concentrating suns ray using a parabolic dish on the receiver. The steamﬂows through a pipe to theinjerabaking stove and condenses by transferring heat to the baking pan which is placed on the steel plate that is in contact with steam (Fig. 6). The important

conclusion drawn from this study was the possibility of bakinginjera using indirect steam in a temperature range from 135 to 160 °C. The indicated temperature was less than the literature or experimental values obtained earlier by other researchers or developers working on aninjerabaking stove (Asfafaw et al., 2014).

The usual operation temperature was around 250 °C to obtain a well-bakedinjera. As it has been stated in this study, it requires further testing and veriﬁcation.

Direct solar radiation through a mirror was also tried in the USA using a frying pan for bakinginjera. A prototype was tested with a diameter of 46 cm of the baking pan with baking capacity of 4 kg per hour.Fig. 7shows a frying paninjerabaking prototype apparatus. The reported baking time was 2 min. The researcher states that the design is scalable to any required size (Gallagher, 2011). It is a good attempt to be explored and veriﬁed for a larger scale application.

a) b) c)

Fig. 3.Electricinjerabaking stove: a) back side before sealing, b) backside sealed with gypsum, and assembled electricinjerabaking stove (EEA, 2015).

Recent research on injera baking

Numerical optimization of Electric injera baking

stoves

Experimental investigation of injera

baking stoves

Thermic fluid as a working fluid using ceramic pan

Steam as a working fluid using clay pan Electric power as

energy source using clay/ceramic

pan Clay injera

baking pan

Ceramic injera baking pan

Fig. 4.Process of recentinjerabaking stove research.

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Summary of research outputs Improved biomass injera baking stoves

As the primary purpose of improvinginjerabaking stoves is to reduce fuel consumption for economic and environmental reasons, speciﬁc fuel consumption has been used as a tool for comparison.

The maximum reduction in speciﬁc fuel consumption of improved injerabaking stoves relating to open-ﬁre stove in Ethiopia is 49%

while the minimum is 34% (Table 3). Similarly, the maximum percentage reduction in CO during the test period was 91% while that of PM was 19.3% in comparison with an open-ﬁreinjerabaking stove (Yosef, 2007).

Fig. 5.Injerabaking using solar power with thermic-ﬂuid as a workingﬂuid (Abdulkadir et al., 2011).

Fig. 6.Parabolic dish solar thermalinjerabaking stove (sketch & actual test-rig) (Asfafaw et al., 2014).

Fig. 7.Prototypeinjerabaking frying pan (Gallagher, 2011).

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Electric and heat transferﬂuid injera baking stoves

Electricinjerabaking stoves have wider use in urban areas where grid electricity is available. Numerical and empirical investigation of electricinjerabaking was conducted by many researchers. The baking pan (mitad) was originally made out of clay, but a ceramic baking pan was also introduced for research. The average thermal efﬁciency obtained is 50% for the clay and 60% for the ceramic plate.Table 4 shows the major output of research on Electricinjerabaking using both clay and ceramic baking pan.

Solar powered injera baking stoves

Injerabaking stove operated by solar energy was another option investigated by various researchers. The major outputs obtained by experimental investigation are mainly the possible use of steam for bakinginjerawith a temperature range of 135–160 °C and a direct solar radiation reﬂector to bakeinjeraon a cooking pan at 180 °C.

Numerical investigation of bakinginjerawith solar energy showed a promising result. The experiment was conducted based on a simulated electric heater to heat the thermic ﬂuid circulating in the baking process.Table 5shows the reviewed journals available on the development of a solar assistedinjerabaking stove and research oninjerabaking pan.

Patents acquired forinjerabaking stoves

In addition to research and development efforts on biomass and electricinjerabaking stoves, a number of patents were acquired for mass production ofinjeraat industrial level. All the proposedinjera baking machines operate either with electricity or gas. So these studies oninjerabaking machine were catering only for urban areas. Out of 6 patents acquired from the US patent ofﬁce, one is currently operating which is invented by Admassu (Kloman, 2013). Admassu'sinjerabaking machine (Fig. 8c) has the capacity of producing 1000injeraper hour;

this is an industrial sizeinjeraproduction method.Fig. 8shows the patents claimed by various developers (Kindie et al., 2003; Desalegn, 2005; Admassu, 2004; Temesgen, 2008; Mulugeta, 2011; Ma, 2012).

Table 6shows a summary of the patents achieved up to now regarding the mass production ofinjerawith their respective invention outputs.

The beneﬁts of the hitherto improvedinjerabaking stoves

Indoor air pollution reduction and speciﬁc fuel consumption

Although a large number of tests have been undertaken to evaluate the performance ofMirtstove, there were only two reports on the environmental performance ofMirtstove.Yosef (2007)reported that the percentage reduction in CO during the test was 91% while that of PM was 19.3%. The second test conducted at the Aprovecho Research Center did not show percentage reduction compared to a three stone openfire stove. However, a water boiling test conducted at the center onMirtand‘improvedMirt’stoves showed remarkable improvement in terms of indoor air pollution and fuel consumption (Hatfield et al., 2006). The majority of tests conducted are attributed to GIZ and Ministry of Water, Irrigation and Electricity—Alternative Energy Promotion Center. The percentage reduction in specific fuel consumption of Mirt compared to an open-fire stove obtained by various researchers is between 30% and 49% (Workeneh, 2005; Yosef, 2007;

Anteneh and Walelign, 2011; Alemayehu et al., 2012; Anteneh, 2014;

Walelign et al., 2013).

Carbon emission reduction potential

Most of the improved injerabaking stoves have contributed to emission reduction compared to the three-stone open-fire, which is used by the majority of the people in Ethiopia. A few researchers and developers attempted to measure the CO2emission reduction potential of Table3 Reductioninspecificfuelconsumption,timetobake,COandPMforimprovedbiomassinjerabakingstovesinEthiopia. No.TypeofstoveDevelopedbyPerformanceReference Specificfuelconsumption (g/kgofinjera)Totalbakingtime (min.)%reductioninspecificfuel consumptioncomparedto open-fireinjerabakingstove

%reductionintimetoboil comparedwithopen-ﬁre injerabakingstove

COconcentration (ppm)PMconcentration (mg/m3) 1MirtstoveEthiopia-MinistryofWater, Irrigation,andElectricity (AlternativeEnergy Development&Promotion Directorate)/GIZ

460–30–––Workeneh(2005) Three-stoneopen-fire630––––– 2Mirtstove52412949−77.20.88Yosef(2007) Three-stoneopen-fire1031121––801.10 3Mirtstove(withintegrated chimney)5961024215––Alemayehuetal.(2012) Three-stoneopen-fire1031121–––– 4InstitutionalMirt5281014917––AntenehandWalelign (2011)Three-stoneopen-fire1031121–––– 5Yekuminjeramitad5751004415––Alemayehuetal.(2012) Three-stoneopen-fire1026117–––– 6YekumMirtType-I596116421––Alemayehuetal.(2012) Three-stoneopen-fire1029117–––– 7YekumMirtType-II667110347––Alemayehuetal.(2012) Three-stoneopen-fire1029117–––– 8Gounziestove617106417––Anteneh(2014) Three-stoneopen-fire1038114–––– 9AwrambastoveAwrambacommunity573107355––Walelignetal.(2013) Three-stoneopen-fire1025120–––– 10MirtstoveGIZ393–24–––Dresenetal.(2014) Three-stoneopen-fire520–––––

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Table 4

Electric & heat transferﬂuidinjerabaking stoves research output.

No. Authors Year Title of the research Major outputs Reference

1 Mekonnen Mesele Tsegaye

2011 Design and manufacturing of laboratory model for solar poweredinjerabaking oven

•Design and manufacturing a laboratory model for solar powered injerabaking oven system consisting of oil storage and heating tank, pumping and piping system, baking pan assembly and support structure.

•The system uses electrical heater to heat the thermicﬂuid to be used for baking.

•A temperature of 215 °C is achieved on baking pan and bakedinjera.

Mekonnen (2011)

2 Gashaw Getenet 2011 Heat transfer analysis during the process of injerabaking byﬁnite element method

•Developed mathematical models andﬁnite element formulations for baking pan andinjeraduring baking.

•Simulation was done in terms of temperature proﬁle during heat-up and cyclicinjerabaking using MATLAB.

•Performed simulation for four different electric power sources (1.867 kW, 2.2 kW, 2.5 kW, and 3 kW) using two types of baking pans (clay and ceramic).

•Efﬁciency achieved for baking cycle of 10–50injerais 53–66% for clay pan and 66–72% for ceramic baking pan.

Gashaw (2011)

3 Awash Tekle Tafere 2011 Experimental investigation of performance characteristics and efﬁciency of electric injerabaking pans (‘MITAD’)

•Maximum energy losses occurred at the bottom of conventional and improved (ceramic) baking pans with the efﬁciency of 52%

and 75%, respectively.

•Increasing the number of baking cycles and density of batter increases the efﬁciency of theinjerabaking by 5–10%.

Awash (2011)

Table 5

Solar thermalinjerabaking stoves andinjerabaking pan research outputs.

No. Authors Year Title of the research Major outputs Reference

1 Assefa Ayalew Tareke 2010 Heat transfer analysis ofInjera baking pan by FEM

•FEM is used to model heat transfer process duringinjerabaking using clay plate. This was experimentally veriﬁed using electricinjerabaking stove.

•Major improvements are predicted if the cooking plate thickness is minimized or thermal conductivity increased.

Assefa (2010)

2 Asfafaw Haileselassie, Mulu Bayray Kahsay, and Ole Jorgen Nydal

2013 Design and development of solar thermalinjerabaking: steam based direct baking

•Introduces indirect solar stove

•A parabolic dish with an aperture area of 2.54 m²with well insulated pipes and stainless steel heat exchanger to bakeinjera.

•The experiment demonstrated that a high temperature indirect steam baking ofinjerais possible

•The authors claim thatinjeracould be baked at a temperature of 135–160

°C with acceptable quality

Asfafaw et al. (2014)

3 Abdulkadir Aman Hassen, Demiss Alemu Amibe and Ole Jorgen Nydal

2011 Performance investigation of solar powered injera baking oven for indoor cooking

•A new type of baking system is proposed where solar energy is used as a power source. The solar thermal energy is transferred to the kitchen by means of a circulating heat transferﬂuid which is heated by a parabolic trough.

•A new type of baking pan made from ceramic is manufactured and used for bakinginjera

•In order to heat the ceramic baking pan a steel pan withﬁns is put underneath and the oil enters the cavity to transfer the heat to the steel andﬁns.

•It takes approximately 1 h to start circulating the oil and 40 min to reach the optimum baking temperature (~180 °C–220 °C).

•5injerawas baked at an interval of 2 min and idle time of 3 min between eachinjera.

Abdulkadir et al. (2011)

4 Abdulkadir Aman Hassen and Demiss Alemu Amibe

2013 Finite element modeling of solar poweredinjerabaking oven for indoor cooking

•A 2D transientﬁnite element analysis was carried out for a new type of solar poweredinjerabaking system.

•In the proposed system, heat transfer oil is heated using solar energy by parabolic trough and the oil circulates through the space below the baking pan in the kitchen.

•Based on previousﬁnite element study on existing electricinjerabaking pans, a new type of baking pan made from ceramic with 8 mm thickness was manufactured and used for the proposed system

•The proposed baking pan that uses solar energy gives acceptable heat up and baking time compared to existing conventional baking methods.

•Theﬁnite element model predicts well the temperature distribution during initial heat up and cyclic baking.

Abulkadir and Demiss (2013)

5 Alan Gallagher 2011 A solar fryer •A 42 cm diameterinjerabaking pan was heated using solar radiation through a mirror reﬂector.

•Capacity of solar fryer was 4 kg/h.

•The pan reaches a temperature of 180 °C in 20 min.

Gallagher (2011)

6 Katrin Putz and Joachim Muller

2011 Development of a multi fuelmitad as stove extension forinjerabaking in Ethiopia

•Developing a multi fuelinjera mitadapplicable in combination with existing energy saving and relatively cleaner stoves.

•To better exploit the available heat theﬁrst prototype was realized with metal.

•The lower heat capacity of metal compared to clay inﬂuences the distinctive appearance ofinjera—it leads to a slightly different formation of the eyes (holes) on the pancake's surface.

•The proven high demand for a fuel savinginjerabaking appliance in Ethiopia justiﬁes the further optimization of the multi fuelinjera mitad.

Putz and Muller (2011)

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(a)

(f) (c)

(b)

(e)

(d)

Fig. 8.Schematic diagram of patents obtained on mass productioninjera(Kindie et al., 2003; Desalegn, 2005; Admassu, 2004; Temesgen, 2008; Mulugeta, 2011; Ma, 2012).

Table 6

Invention regardinginjerabaking stove and their major outputs.

No. Title of the invention Inventor Year of invention

Major inventions Reference

1 Method and apparatus for making bread

Mengistu A. Kindie, Robert J. Sweeney, and Jim Aitken

2003 A device used to bakeinjeraand bread by making use of a dispenser. The dispenser pours the batter in the baking surface which is heated by an electric power supply from the bottom. The device is automated for continuousinjerabaking operation

Kindie et al.

(2003) 2 Method of and apparatus for

making Ethiopian bread

Emiru Y. Desalegn 2005 A measured amount of batter dispensed into a horizontal moving conveyor where injerais baked and transported to a cooling zone. The machine is automated to bake injeracontinuously with the help of electric power.

Desalegn (2005) 3 Injeramanufacturing

system

Wundeh Mulugeta 2006 A continuousinjerabaking machine consisting of storage, dispensing, baking and cooling stages. The machine is capable of producinginjerain mass continuously.

Admassu (2004) 4 Injerabaking machine Yoseph Temesgen 2008 Automatedinjerabaking machine starting from polishing the surface of baking plate,

dispensing and removing using spatula attached to a reciprocating conveyor. The batter dispensing mechanism can rotate and reciprocate simultaneously.

Temesgen (2008) 5 Rotary baking system and

method

Wassie Mulugeta 2011 An automatic rotaryinjerabaking machine which consists of a movable dispensing unit with a rotary system for baking using a gas burner. The gas will be fed to each baking surface from the gas cylinder.

Mulugeta (2011) 6 Method and apparatus for

rapid production ofinjera bread

Michael Ma 2012 Injerabaking machine with a large production capacity consisting of a batter dispenser coupled with a conveyor belt for transport. A perforated cylinder is used to dispense the batter to produce a number ofinjera. The bakedinjerawill be transported into a cooling and packaging unit after baking.

Ma (2012)

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the improvedinjerabaking stoves such asMirtstove.Dresen et al.

(2014)showed that 2.145 tons of CO2per ICS per year could be saved by usingMirt. Similarly, World Food Program—Ethiopia and World Vision Ethiopia through the Project Design Document (PDD) for programmes of activities registered a carbon saving potential of 1.14 tCO2/device/year (World Vison Ethiopia, 2013; World Food Pro- gram, 2014).

Research directions

Injerawill continue to be the staple food of Ethiopians and Eritreans in years to come. In order to efﬁciently bakeinjerausing various types of stoves, research and development work forinjerabaking is critical.

Currently, biomass is the dominant source of energy used forinjera baking followed by electricity. Electricity is mainly used in urban areas of the country. Alternative energy sources such as solar, thermal and biogas can be used for bakinginjera(Fig. 9).

As it has been stated in the early study ofinjerabaking stove, and subsequent studies using numerical methods, improving theinjera baking pan will directly minimize the losses associated with baking. A number of efforts are being undertaken to improve the baking pan, such as ceramic materials and combinations of steel chips combined with clay and glass. Research directions could also focus on improving the thermal conductivity of the baking pan without compromising the quality ofinjera. A compositeinjerabaking pan could also be an area to be explored further.

The case of electricinjerabaking is relatively well established except for possible improvements in efficiency. Solar thermal, gasification and biogas, which are potential future research areas of focus, will have enormous contributions for improvements on the health of women and children exposed to indoor air pollution. However, most research efforts oninjerabaking stoves were focused on improving specific fuel consumption and little attention was given to the reduction of indoor air pollution such as CO and PM as well as reducing carbon emissions.

Therefore, future research efforts should also address such issues as these which are also important factors in the development ofinjera baking stoves.Fig. 9shows the possible layout for research in the areas ofinjerabaking.

Although the long term solutions for developing countries such as Ethiopia is connecting electricity to all of its inhabitants, the short and middle term solution is improving the performance of biomass stoves through research collaborations of the governmental institutions with other partners. The development of biomass technology will be instru- mental in the energy mix in the long term solution strategy, particularly for decentralized energy generation systems. Speciﬁcally, the use of clean biomass stoves for bakinginjerais a vital issue for alleviating air pollution, greenhouse gases and energy efﬁciency. This is a grave concern not only for the majority of Ethiopians but also for people living in rural parts of the world, such as most developing countries in Africa.

Besides, biomass is a key factor in the energy mix; it requires further research undertakings for more efﬁcient utilization.

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Injerabaking plate- Mitad

Energy

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Energy Source Type of Stove Injerato be baked

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MirtStove

Gasifier Stove

Biogas Stove Biomass Fuel

Household Electric Injera Baking Stove Electric Energy

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Stove Solar Thermal Injera

Baking Stove

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