Performance evaluation of three methanol stoves using a contextual testing approach

Energy for Sustainable Development 55 (2020) 13–23

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Energy for Sustainable Development

Performance evaluation of three methanol stoves using a contextual testing approach Tafadzwa Makonese a,⁎, Harold John Annegarn b, Johan Meyer c a b c

Sustainable Energy Technology & Research Centre, Faculty of Engineering and the Built Environment, University of Johannesburg, P. Bag 524, Auckland Park 2006, South Africa. School of Geo and Spatial Sciences, North-West University (Potchefstroom Campus), P. Bag X6001, Potchefstroom 2520, South Africa. School of Electrical and Electronic Engineering Sciences, Faculty of Engineering and the Built Environment, University of Johannesburg, P. Bag 524, Auckland Park 2006, South Africa.

a r t i c l e

i n f o

Article history: Received 9 July 2018 Revised 7 November 2019 Accepted 18 December 2019 Available online xxxx Keywords: Water boiling test Methanol stoves Uncontrolled cooking test Kitchen performance test Contextual testing ISO/IWA tiers Stove ranking

a b s t r a c t Over the years, a significant need has been established to develop stove testing protocols that reflect the performance of fuel/stove combinations in the field better. This is particularly true for alcohol-based liquid fuels, widely seen as a future replacement for kerosene fuels in the informal and less affluent communities of South Africa. This paper aimed to evaluate three liquid-fuelled stoves using cooking sequences derived from a typical township in Johannesburg, South Africa based on a contextual testing approach, which is a revised in-situ testing protocol based on the Uncontrolled Cooking Test (UCT). The devices were evaluated and rated based on their intended contexts-of-use in South Africa using the new contextual testing protocol, which was combined with the old Heterogeneous Stove Testing Protocol (HTP). Overall, results showed that there are no significant differences (p N 0,05; α = 0,05) between the averaged cooking sequences and the uncontrolled cooking task of individual methanol stoves regarding energetic and emissions characteristics. Although the Dometic and the Meca stoves were designed for ethanol, they performed well with methanol fuel delivering adequate cooking power (at least 1 kW into the pot) and fewer CO and PM emissions. Results show that a laboratory test sequence with the same power levels for cooking food or for heating water produced nearly the same results as a UCT of a typical meal in the Township. © 2020 International Energy Initiative. Published by Elsevier Inc. All rights reserved.

Introduction This paper addresses three interlinked topics related to the introduction and testing of methanol as a fuel in improved liquid-fuelled cookstoves. The use of methanol as an alternative to kerosene and ethanol as a domestic liquid fuel is evaluated by testing three stoves, two designed for ethanol and one designed for methanol. Established performance and emissions testing protocols are used. Secondly, the paper illustrates how observations of the context of use can be incorporated into a laboratory test sequence. The contextual approach is indicated by deriving a test sequence based on observations of cooks preparing staple meals in accordance with their own customs and combining these observations into a laboratory test sequence that mimics the contextual behaviour, but which can be carried out in a laboratory under controlled conditions. Thirdly, the three stoves are evaluated against South African and International Organization for Standardization (ISO) International Workshop Agreement (IWA) (ISO/IWA, 2012)

⁎ Corresponding author. E-mail address: [email protected] (T. Makonese).

performance criteria for energetic, emissions and safety performance for international comparability. In South Africa, energy poverty is a crucial driver of burn injuries from flame-based cooking mishaps and accidental home fires (Kimemia & van Niekerk, 2017), poisoning due to ingestion of kerosene fuel, and loss of property and dignity in informal settlements or shack dwellings. These are often small and primitive types of dwellings built from available materials. About 5000 informal settlement shack fires were recorded between 2009 and 2012 (Fire Protection Association of Southern Africa, 2014) leading to loss of economic capital, injuries and impairments, and even death (Kimemia & van Niekerk, 2017). Overall, 200,000 injuries per year were reported due to kerosene accidents, including fires, burns and ingestion poisoning (Kimemia, Vermaak, Pachauri, & Rhodes, 2014). Ingestion poisoning in children alone led to over 40,000 cases per annum (Lam, Smith, Gauthier, & Bates, 2012; Matzopoulos et al., 2015). Faulty and sub-standard kerosene appliances have been implicated as major causes of accidental fires in low-income households and informal settlements (Truran, 2009). Specifically, the non-pressurised wick kerosene stove is identified as the most hazardous cooking appliance and the proximate cause of many of these accidents. Respiratory illnesses, aggravated by indoor emissions of

https://doi.org/10.1016/j.esd.2019.12.002 0973-0826/© 2020 International Energy Initiative. Published by Elsevier Inc. All rights reserved.

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particulate matter and carbon monoxide from unvented stoves, are a further manifestation of energy poverty. The adverse health effects of indoor air pollution have been extensively discussed and are drivers of international campaigns to introduce improved stoves (Newell, Kartsonaki, Lam, & Kurmi, 2018; Cohen et al., 2017; Gordon et al., 2014; www.cleancookstoves.org). Studies in South Africa of commercially distributed kerosene wick stoves have shown that some of the leading brands are inefficient, poorly designed with respect to safety and durability, and emit harmful levels of gases and particles (Kimemia & van Niekerk, 2017; Truran, 2009; Makonese, Pemberton-Pigott, Robinson, Kimemia, & Annegarn, 2012; Lloyd, 2014). In 2006, the South African Bureau of Standards (SABS) promulgated a national standard for non-pressurised kerosene stoves, which was later declared a compulsory product specification (Kimemia & van Niekerk, 2017; SANS 1906:, 2012). Since the homologation of this specification, certain kerosene wick stove products have been approved by the SABS and carrying the SABS mark for efficiency and safety. Specifically, the CO/CO2 ratio should not exceed 2%. However, some of these so-called improved kerosene stoves do not show satisfactory improvements over the kerosene stove model that dominated the market prior to the introduction of the SANS 1906 Standard (Makonese & Meyer, 2018). These devices exacerbate the problem that they are intended to alleviate - that of indoor pollution - partly because the new stoves are not adequately tested against baseline criteria (Taylor, 2009). At a social level, the lingering odours associated with kerosene combustion are regarded as an embarrassing outward manifestation of poverty; the soiling of pots, ceilings, and walls by black fumes from kerosene flames is likewise an undesirable side effect. These fumes are associated with adverse respiratory health effects. Considering the above, alcohol-based fuels, including ethanol and methanol, have been considered as replacements for kerosenefuelled cooking appliances. Because of the short-chain linear carbon structure of alcohol molecules, PAH (polycyclic aromatic hydrocarbon) emissions are reduced when using such fuels, along with inherently low particulate emissions and minimal soiling. Alcohol flames do not have strong odours such as those associated with kerosene flames and barring impurities, these flames are odourless. Accidental fire risks are reduced as alcohol fires may be extinguished with water (fully miscible), whereas kerosene is immiscible and floats on top of water, potentially spreading the flames when doused with water. On the downside, alcohol flames are nearly invisible in bright sunlight, and this poses a safety risk. Alternative formulations of ethanol gel fuels reduce the risk of spillage and liquid fires (albeit at the cost of reduced energy density and higher cost). A wide range of ethyl alcohol liquid and gel stoves are available in the South African market, and elsewhere. Methanol, the simplest alcohol (CH3OH), has not been considered much as cooking fuel and as part of a clean cooking solution, even though in South Africa there is an adequate source of methanol available as a by-product of the coal-to-gasoline process carried out by SASOL Limited – an integrated energy and chemical company. Because methanol has an approximately 50% lower thermal capacity per volume compared to kerosene or ethyl alcohol, there is an inherent disadvantage to methanol-fuelled stoves. Methanol is a poisonous liquid that may cause blindness or death when ingested (Cursiefen & Bergua, 2002), which is a further disadvantage. Nevertheless, if these challenges can be appropriately addressed, a case can be made for developing methanol stoves and a marketing distribution chain for the fuel, based on social, utility, safety and economic criteria. Mudombi et al. (2018) have argued that methanol can improve household cooking efficiency and provide auxiliary health and environmental benefits. The lower energy density of methanol can be compensated by stove designs with higher thermal efficiency that have enough cooking power (minimum 1 kW delivered to the contents of the pot) and economic fuel consumption (cost per cooking task) (Masekameni, Makonese, & Annegarn, 2015). There is a need to address ingestion poisoning risk

factors associated with methanol, especially in toddlers who do not have well-developed senses of smell and taste (Schwebel, Swart, Hui, Simpson, & Hobe, 2009). However, the poisoning risk is a generic problem with all domestic liquid fuels, especially kerosene (Kimemia & van Niekerk, 2017). The design of child-safe packaging and refuelling procedures must be an integral part of any new methanol distribution system. It has been argued that improved stoves have the potential to address a comprehensive set of issues ranging from local health (Barnes et al., 2004; Bruce, Perez-Padilla, & Albalak, 2000) and environmental implications to global impacts associated with greenhouse gas (GHG) emissions and particulate emissions of black and brown carbon that have global impacts on climate. However, experiences from past fuel/stove campaigns have shown that a successful stove program is more than just building or disseminating novel stove technologies (Makonese, 2018). Masera, Díaz, and Berrueta (2005) contended that before rolling out stoves en masse, the whole ‘cooking system’ (fuel/stove/pot combination) needs to be considered through integrated approaches that work simultaneously with technology innovation, creative financing, market development, and the monitoring of health and environmental benefits. Such programmes encourage bottom-up participatory approaches that seek to involve end-users, specifically the cooks (usually women in the household), to address issues of priority and preference correctly (Masera, Díaz, & Berrueta, 2005). Again, the stoves must be evaluated in the context of their intended uses in the targeted communities. Over the years, this critical factor has been overlooked in many fuel/stove campaigns. It is arguable that some stove campaigns failed because they did not address human behaviour and cooking needs (Rhodes et al., 2014). Abdelnour and Pemberton-Pigott (2018) opined that current policy strategies championing the benefits of improved stoves are not in tandem with the uncertain outcomes of most fuel/stove campaigns. Many researchers have attributed the failure of fuel/stove campaigns to poor stove designs, testing protocols, and rating procedures (Lombardi, Riva, Bonamini, Barbieri, & Colombo, 2017). Central to the issue of access to clean and safe cooking energy fuels is the performance evaluation of fuel/stove combinations. Over the years, there has been heightened interest for specifying energetic and emissions performance of stoves powered by solid and liquid fuels, given an impetus by the then Global Alliance for Clean Cookstoves (GACC) and now Clean Cooking Alliance (CCA), whose mission is to foster the adoption of clean cookstoves and fuels in 100 million households by the year 2020. (Taylor, 2009) believed some cooking devices are designed to meet specific requirements of commonly used stove testing protocols rather than the needs of the potential users. Several of the more widely used protocols for solid fuel stoves including the Indian Standard on Solid Biomass Chulha-Specification (CIS 1315 Z) are prescriptive in the type of fuel used, to derive a standardised test. The imposition of prescriptive conditions on the stove test sequence (and fuels) was argued to be necessary to allow “international inter-comparability” of stove test results (Makonese, Chikowore, & Annegarn, 2011). However, the introduction of standardised burn sequences, lid on or off and prescribed fuel types resulted in tests that were not representative of real-world uses or likely combinations of the way fuels, stoves and pots may be used (Makonese, Pemberton-Pigott, Robinson, Kimemia, & Annegarn, 2012). Up until June 2018 when the ISO 19867-1 standard was promulgated, there was no agreed international stove testing protocol that had been developed under the guidance of a professional standards-setting agency or validated and approved by such professional standard certifying bodies. National testing protocols and performance standards, differing in critical details, have been used in India, China, Indonesia and elsewhere. The Global Alliance for Clean Cookstoves has maintained the widely used Water Boiling Test, but many variations have been used to meet specific needs. As a result, ad hoc protocols are designed for specific stove testing entities or stove programmes. Such non-uniformity of the testing regimen makes it

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difficult to compare stoves tested in different areas and using a variety of testing protocols (Makonese & Meyer, 2018). A drive to develop an international stove-testing standard through the International Organization for Standardization Technical Committee (ISO/TC) 285 (Clean Cookstoves and Clean Cooking Solutions) with the support of the GACC reached maturity in June 2018, when the ISO released a voluntary standard on harmonized test protocols for clean cooking solutions (ISO 19867-1:, 2018). Standards-setting bodies and research institutes in numerous countries were involved in this process. Although this voluntary standard is a welcome addition, some researchers have argued that the ISO standard does not adequately capture the contextual uses of fuel/stove combinations for different parts of the world. Such evaluations of stoves have been reported to be flawed because they do not reflect conditions under which the devices are used in the field. Abdelnour and Pemberton-Pigott (2018:196) argued that “although improved stoves have been promoted to address health and environmental concerns for over 50 years, changing the cooking and fuel use behaviour of poor and rural people remains an indeterminate task”. Emission measurements from laboratory tests may not reflect typical domestic emissions during daily activities. The user/fuel/stove/pot nexus is often ignored, with the fuel/stove nexus being the lowest common denominator in most stove testing standards. As such, these evaluation methods may not provide an accurate assessment of the performance of the stoves under real-world conditions, and they may provide inadequate decision support about which cooking devices to promote. An important aspect that has been omitted from the ISO 19867-1:, 2018 standard is a provision of laboratory testing sequences that better reflect the context of actual cooking (Makonese & Meyer, 2018). However, there are challenges of defining a lab test that is representative of actual use with typically large variation between seasons, households, communities, regions, income levels, cooking sequences, and many other factors. In the forefront of every stove project should be the specification of robust testing protocols that allow for representative and reproducible testing and inter-comparison of the thermal performance and emissions from a diverse range of user/fuel/stove/pot combinations (Robinson, Ibraimo, & Pemberton-Pigott, 2011). While thermal performance and emissions may be important, many other characteristics may also be important in a stove project. Even though there are other important characteristics in a stove, the thrust of past stove dissemination projects has placed emphasis on these two metrics and stove projects that do not meet targets on these two parameters may be less likely to receive international funding. Such standardised protocols should be representative of either the stove design parameters or contextual uses of the fuel/stove/pot combination. Region-specific cooking regimes – cooking sequences – are an essential part of a stove-testing regimen (Arora, Jain, & Sachdeva, 2014; Lambe & Atteridge, 2012). The concept of ‘burn sequences’ or ‘cooking sequences’ was first introduced by Johnson, Edwards, Berrueta, and Masera (2009) and later adopted and adapted by the Sustainable Energy Technology & Research (SeTAR) Centre, the University of Johannesburg as a contribution to the Indonesian Clean Stove Initiative (CSI) stove programme. Cooking sequences have been considered a critical factor in assessing the real-world performance of stoves. The uncontrolled cooking test (UCT) (Robinson, Makonese, Pemberton-Pigott, & Annegarn, 2010) has the potential to be a better method for testing stoves as it can quickly capture the intricate details of cooking sequences. Information from UCT is useful to both stove designers and energy researchers with interest in the development of clean fuels and efficient stoves that have the potential to be adopted by user communities (Arora, Jain, & Sachdeva, 2014). Although the UCT can provide useful information on the actual use of a stove, it has limitations due to the wide variation of actual use conditions between users, seasons, households, communities, regions, socioeconomic status, and many other factors. UCT testing with a statistically representative sample of the population may be costly or outside the budget for a project.

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The literature has limited information regarding the evaluation of fuel/stove combinations using cooking sequences developed for rural or township South African households. Arora, Jain, and Sachdeva (2014) have attempted to evaluate the performance of a variety of fuel stove combination using cooking sequences derived from regions of India. There are no similar published studies that have been undertaken in South Africa to evaluate the performance of stoves using locally derived cooking sequences. This paper illustrates that once a cooking sequence test has been derived for a community, this simplified test may be used in a laboratory without loss of contextual relevance to the intended user community. The results of tests on three methanol stoves, using a locally derived test sequence, will be evaluated against South African national standards and the IWA/ISO tier performance guidelines, to demonstrate that test results may be compared to such metrics. The study is presented in subsections dealing respectively with: (a) the choice of methanol and of three stoves for testing, and the test protocols; (b) a description of the cooking observations and derivation of a laboratory test sequence, (c) test results to show the equivalence of observed and derived test sequences; and (d) evaluation of the methanol stoves against performance criteria. Methods and experiments Study design and sampling The cooking observation studies were done in Alexandra Township, Johannesburg, South Africa in an informal settlement called Setswetla, with approximately 2000 informal dwellings. The population has a rapid turnover, as this settlement is first stay for new arrivals, who move on to better backyard shacks or rented rooms in formal housing. A new initiative by the government entails that when the residents are moved to new Reconstruction and Development Programme (RDP) houses, the informal dwellings should be destroyed, and the place secured to avoid people from occupying the area. The provision of RDP houses is a government initiative to redress inequalities of the past through building cheap and subsidised houses for South African nationals staying in informal settlements. The informal settlement lies on a narrow strip between the Alexandra cemetery and the Jukskei River, about 5 km from the Sandton Central Business District. Despite close spatial access to grid electricity, residents of Setswetla continue to rely mostly on kerosene for meeting their essential space heating and cooking needs. Kerosene is used by 99% of Setswetla households for cooking (Kimemia & Annegarn, 2011). Many of the respondents expressed an interest in adopting an improved stove to reduce their energy burden, reduce risks of shack fires and to mitigate domestic air pollution (Kimemia & Annegarn, 2011). Three types of methanol stoves with enough methanol to carry out the cooking experiments were provided to identified focus groups in Setswetla. Five focus group meetings (each with a minimum of six members randomly selected from the settlement) were carried out before the replicate tests in the laboratory. Unit numbers making up the settlement were written on pieces of paper and the papers were randomly picked from a hat. Only the randomly selected participants were interviewed and took part in the surveys. The final sample consisted of 42 participants across five focus groups. All participants consented to take part in the study and were aware that they had the right to withdraw from the survey at any point. The University of Johannesburg advised the researchers that formal ethical clearance was not required, as the study did not request any personal information. Experimental stoves Three liquid-fuelled single-burner stoves were selected for this study and are amongst a suite of alcohol-based cooking devices being promoted in South Africa as a replacement for kerosene stoves [Fig. 1].

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Fig. 1. Photographs of the experimental stoves evaluated: (a) Protostar (b) Dometic (c) Meca.

The three devices differ from each other concerning the material used to build them, size of the fuel reservoir, and re-fuelling styles. The Protostar stove was manufactured by a local industrial designer and was primarily designed to burn methanol. The designer claims that the stove can also be used to burn ethanol in the absence of methanol. For purposes of this study, the stove was tested with methanol and not with ethanol. A local business bought the distribution rights of the Dometic stove from a Swedish company - Dometic AB™. The Meca stove was artisan manufactured in Madagascar and is available as a single ethanol burner. Note that the Dometic stove and the Meca stove were designed for ethanol and not methanol. However, in this study, the stoves have been tested with methanol fuel, as it is a readily available (in bulk) fuel in South Africa, but not yet widely distributed as domestic cooking fuel. The methanol fuel was sourced from a local supplier enough to carry out cooking observation tests and the replicate laboratory tests. The methanol had a calorific value of 22.87 MJ/kg (Rumble, 2017). Test apparatus Metrics and calculations. Thermal efficiency (ŋ) is defined as the ratio of work done by heating a known volume of water to the energy available from the fuel (not all the available energy may be generated due to incomplete combustion of the fuel), and is mathematically represented as: η ¼ ½4:186 ðPci –PÞðTcf –Tci Þ=ð f cd  LHVÞ

ð1Þ

where P (g) is the dry weight of the empty pot, Pci (g) is the mass of the pot and water, (Pci − P) (g) is the initial mass of water in the pot, 4.186 (J/g/°C) is the specific heat of water, (Tcf − Tci) is the change in water temperature, fcd (g) is the mass of the fuel used, and LHV (MJ/kg) is the lower heating value of the fuel. This calculation assumes that water loss through evaporation is negligible, as the water in the pot is not heated until boiling, but until 70 °C, and after that, the pot is replaced with a fresh pot of water of equal mass. The net heat gained (HNET) (MJ) is the heat retained by the contents of the cooking vessel during a burn sequence. It includes the energy needed to heat contents of the pot but excludes other heat flows through the cooking vessel, specifically radiative and convective losses from the cooking vessel's sides and top (Makonese, Masekameni, Annegarn, & Forbes, 2017). In this study, emission factors were calculated as in Bhattacharya, Albina, and Salam (2002) albeit with some adjustments. For example, methane and non-methane hydrocarbons were included in their estimations. These pollutants were not measured in the experiments, and as such, they are not reported herein. It is assumed that CO and CO2 comprise the bulk of emissions from the experimental combustion processes. Both useful energy-specific emission factors (g/MJ) and mass-specific emission factors (g/kg) of dry fuel fed are reported. Emission factors of CO2 and CO were calculated as a function of the net heat gained by the

contents of the cooking vessel - (HNET) in kJ: CO2 EFenergy−specific ¼ n CO2  MCO2 =ðHNET Þ

ð2Þ

COEFenergy−specific ¼ n CO  M CO =ðHNET Þ

ð3Þ

n

ð4Þ

COEFmass−specific ¼

CO

 M CO = f cd

where M is the molecular mass of the pollutant, n is the number of moles of the pollutant, and fcd (kg) is the mass of the fuel used. The number of moles of carbon in the flue gas is calculated using Eq. (5): n ¼ n CO2 þ n CO

ð5Þ

where nCO2 is the number of moles of CO2 and nCO is the number of moles of CO. This equation assumes that all the carbon from the fuel is converted to CO and CO2 gas only. It does not include CH4 and total non-methane organic compounds (TNMOC) as these were not measured in the experiments. For PM2.5 emissions measured using a DustTrak aerosol monitor (DustTrak 8530, TSI Inc.) (Makonese, Masekameni, Annegarn, & Forbes, 2017), emission factors were reported in milligrams of particulate matter emitted per net heat gained or per net fuel mass used (Makonese, Masekameni, Annegarn, & Forbes, 2017). The energy-specific emission factor of PM2.5 emitted during a burn sequence is determined as follows: PM2:5 EFenergy−specific ¼ PM2:5 =ðHNET Þ

ð6Þ

where PM2.5 is the mass of particulate matter with aerodynamic diameter ≤ 2.5 μm (mg), and HNET is the net heat gained by the contents of the cooking vessel from the fuel (kJ). The mass-specific PM2.5 emission factors were calculated as: PM2:5 EFmass−specific ¼ PM2:5 =f cd

ð7Þ

where fcd (kg) is the mass of the fuel used and the other symbols as above. Statistical analyses A two-tailed student t-test at the 95% confidence level (p = .05; α = 0.05) is used for statistical evaluation of the thermal and emission factor results. These tests were applied when comparing emissions factor results from the Protostar stove, using the observed cooking sequences and the derived laboratory sequence, to test the hypothesis that there is no significant difference between emission factors derived from the laboratory test sequence and from the observed cooking sequence.

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Other trace gases Even though gases such as SO2, H2S, NO, NOX, and H2 can be measured with the equipment in the SeTAR laboratory, only carbon monoxide and PM2.5 have been chosen as our indicator pollutants. Sulphur and nitrogen pollutants are omitted for the following reasons. In South Africa, the methanol available on the market has insignificant amounts of sulphur content. Thus emissions of SO2 and H2S were below the limit of detection in the evaluation of alcohol-fuelled stoves. Quality control For each fuel/stove combination, a series of preliminary experiments were carried out to standardise the burn sequence derived from the cooking observation tests and minimise the natural variability due to differences in operator behaviour. The trial runs were conducted repeatedly until a stable mode of operation was established to familiarise the operators with the testing procedure and with the characteristics of the stove. Thereafter, five replicate tests were conducted for each fuel/ stove combination. Continuous gas and particle monitoring instruments were sent for calibration by the manufacturers' prescribed intervals, or at least once in a year, and were periodically verified with laboratory standards. Zero and span calibration were performed on all analysers before and after every test run, which was performed daily. The DustTrak aerosol monitor was zeroed with filtered air before each test run. The DustTrak was also calibrated with gravimetric (filter) measurements of PM2.5 emissions from methanol-fuelled stoves using the method detailed in Language, Piketh, and Burger (2016). The gravimetric sampling was carried out by exposing 37 mm cassettes fitted with 37 mm Nucleopore membrane filters, at a constant flow rate of 1.7 L.min−1, using Gilian GilAir 3 (Sensidyne, Clearwater, FL, USA) pumps. The pumps were fitted with 10-mm Nylon Dorr Oliver Cyclone (TSI Inc., Shoreview, MN, USA) inlets to obtain the 50% cut size at 4 μm (Language, Piketh, & Burger, 2016). The gravimetric sampling occurred in line with the DustTrak aerosol monitor. The Nucleopore membrane filters were weighed before and after sampling using a Sartorius Microbalance with a sensitivity of 1 μg. The calibration factor was calculated as follows: Cal:Factor ¼ Grav:Conc=Inst:Conc

ð8Þ

where Cal.Factor is the calibration factor, Grav.Conc is the gravimetric concentration and Inst.Conc is the instantaneous measured value reported by the DustTrak aerosol monitor. The calibration factor was found to be 0.70 (Fig. 2). The DustTrak measurements were then corrected by multiplying the obtained average measured

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concentrations over the entire cooking sequence and the photometric calibration determined experimentally for the instrument. After each fuel/stove combination was tested, the combustion gas sampling probes were cleaned, and the pumps for the gas and PM2.5 analysers checked and zeroed. Derivation of contextually relevant test sequences Participants in the Setswetla focus groups were provided with stoves and fuels, and food items to cook at most three different meals (each enough for a family of five – about 65% of the sampled households had 5 members or more) common in the township under investigation. The food items and dishes that were prepared using each methanol fuel/ stove combination are summarised in Table 1. These meals were prepared using 6 L aluminium pots with lids. The stove users were not given instructions to use all the ingredients provided. Recipe cards and cookbooks were not used in the experiments, as the aim of the study was to allow the stove users to prepare dishes as they usually would without being constrained. The stove users were video recorded during the preparation of the meals. All other aspects of the experiment (i.e. preparation of the meal, stove operation, allotted time, cooking sequences) were not controlled during the cooking observation tests. Note that full sociological surveys for a statistically significant number of meals are beyond the scope of this paper. The community partner in this project was resident in the suburb and is a member of the ethnic group comprising a large fraction of the residents. Food types comprising the staple diet of lower socio-economic sectors are common knowledge within communities. Despite this, in cosmopolitan cities like Johannesburg, there are wide ranges of ingredients and food types available. However, the absence of a detailed survey does not necessarily invalidate the main line of argument of this paper. Contextual testing Preparation of food dishes. Two female cooks from each focus group who were residents of Setswetla within Alexandra Township prepared the meals in households using UCTs, while the SeTAR stove testing team recorded the activities. The other members of the group assisted with preparing for the cooking tasks (e.g. washing the dishes, cutting of tomatoes and onions, and advising the cooks) Observations were made during the UCTs of some everyday meals in households as suggested by Robinson, Ibraimo, and Pemberton-Pigott (2011). The stove users were asked to identify the utensils (pots, lids, cooking spoon, and cooking stick) to be used during the meal. All cooking utensils were

0.9 y = 1.047x + 0.1522 R² = 0.9273

0.8

PM4 DustTrak (g)

0.7 0.6 0.5 0.4

0.3 0.2

Cal. Factor = 0.70

0.1 0 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

PM4 Gravimetric (g) Fig. 2. Relationship between the light scattering DustTrak and gravimetric concentrations for PM4.

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Table 1 A summary of the ingredients and dishes prepared using the experimental stoves. Dish Rice and chicken stew Pap and beef stew Sampa and beans a

Ingredients: staple

Ingredients: sauce/relish

Rice, water, salt, cooking oil

Whole chicken, tomatoes, onions, cooking oil, salt and pepper, water

Maize meal, water Sampa, water, salt

Beef, tomatoes, onions, cooking oil, salt and pepper, water Sugar beans, tomatoes, onions, cooking oil, salt and pepper, water

Samp – crushed maize.

cleaned, dried, weighed and the measurements were recorded in a logbook. The amount of fuel and lighting material needed to make the meals were weighed on a mass balance. Before cooking, each food item (mealie meal – a course powder made from maize, rice, samp, beans, water, salt, cooking oil, onion, tomatoes, and meat) was weighed and the results recorded in a logbook. The test began with the cook being asked to make and light a fire as they usually would, with the method and the start time noted. The cook was then video recorded while preparing the meal. The cooking observation test involved recording the time taken to cook each meal from start to finish, noting the time of changes between the power levels as required by the cooks. The observed cooking sequence was determined by the cook, according to her own experience and recipe for preparing the supplied ingredients and the power range of the stove, rather than by the technician. The technician's job was to observe and record the happenings, precisely the time of operation at each power level; the operation of the stove was demonstrated to the cook prior to starting the cooking task. Note that for purposes of this study, the firepower settings were arbitrarily divided into high, medium, and low according to Makonese (2018). The highest power setting was indicated by N67% of the highest recorded firepower values, with medium power ranging between 33% and 67% of the highest firepower recorded, while the low power setting was below 33% of the highest recorded firepower (Makonese, 2018). When the cook had finished preparing the meal, the time was noted. The food was then weighed, photographed, and removed from the cooking area (Robinson, Ibraimo, & Pemberton-Pigott, 2011). The cook was free to start serving the food. This exercise shows that the test was not wholly uncontrolled although an effort was made to ensure there was as little interference with the cooks as possible. During the cooking observation exercises, the researcher asked questions relating to cooking, fire management practice and socioeconomic issues (Makonese & Meyer, 2018). These questions did not interfere with the cooking exercise. The cooks were not asked to stop preparing the dishes and operating the stoves in the manner that they deemed necessary. The questions were meant to capture the cooks' thoughts as they were carrying on with their tasks regarding food preparation, fire management, and other socio-economic factors without coercing or forcing them to change their mode of operation. The observed cooking sequences (duration of operation at each power level from ignition to completion of the cooking) for the three meals were combined into a laboratory burn sequence, intended to represent the typical use of the stove by the target user communities. Burn sequence and the testing protocol The laboratory test sequence was performed in the SeTAR laboratory on the testing rig (under an emissions collection hood) with a pot of water to be heated as a surrogate for a pot of food. The test under the emissions collection hood is carried out to determine the thermal and emissions performance of the experimental devices. The Heterogeneous stove Testing Protocol (HTP) was used to determine the thermal and emissions performance of the experimental devices (Makonese, Pemberton-Pigott, Robinson, Kimemia, & Annegarn, 2012). The protocol refers to evaluating the performance of a combustion device at multiple power levels, with water in any pot size and corresponding pot lids, but

for this study, only three power levels and pot sizes like those in actual use were used. The stove evaluations are based on laboratory test sequences derived from the context of use cooking observation tests. In the HTP, upon reaching 70 °C, the pot of water was substituted with a fresh pot of water at room temperature to avoid complexities due to water evaporation. The water temperature was monitored with a thermocouple placed inside the pot and hanging about 50 mm from the base of the pot. The stoves were tested for thermal and emissions performance using the ‘direct’ hood method (Ahuja, Joshi, Smith, & Venkataraman, 1987). According to Ahuja et al. (1987:251), “…the approach has been to design the emissions monitoring system such that it can be operated simultaneously with the determination of thermal performance. Thus, trade-offs between thermal and emissions performance can be investigated.” This method entails the tested device being placed under a hood, into which the flue gases are drawn by thermal drafting, with or without the assistance of forced draft by a fan (Ahuja, Joshi, Smith, & Venkataraman, 1987). The total-capture method with a forced draft is preferable for accuracy and for ventilation of the laboratory. The partial-capture method with a sampling probe or with a natural convection hood may be advantageous for portability in field measurements. For this study, a carbon balance method was employed to complement the partial capture method used in our experiments. The stoves were placed under a collection hood, and a gas-sampling probe was placed inside a hood exhaust duct. Two Testo™ 350 XL flue gas analysers were used to monitor gaseous pollutants including CO, CO2, H2S, SO2, NOx and O2. The gas stream was measured directly from the stove without being premixed with filtered air in the dilutor. Gas probes for the determination of the dilution ratio/factor were placed in the emissions collecting hood and channelled the combustion products to the gas analysers. The probe of the second analyser was connected to a variable dilution system. A dilution system was employed which injected compressed air into the drawn flue gases because the particle analyser has an upper detection limit that is regularly exceeded during testing of solid fuels including wood and coal, especially during ignition. The measurement of CO2 levels determined the level of dilution achieved using two flue gas analysers fitted with filters to avoid clogging (Makonese, 2018). A DRX DustTrak™ was used for in-situ monitoring of particulate emissions. The stove/pot combination was placed on a mass balance and remained there from ignition to completion of the test. The readings for fuel burnt, trace gases and particulate matter emissions were logged at 10 s intervals. The laboratory test provided information on gaseous emissions (e.g. CO, CO/CO 2 and PM2.5) and thermal performance (e.g. fuel burn-rate, cooking power, and cooking efficiency) of the test stove. The diagrammatic representation and full sampling set-up of the SeTAR dilution system are described elsewhere (Makonese, Masekameni, Annegarn, & Forbes, 2017).

Ranking of the stoves and safety considerations In 2012, a group of international researchers and stakeholders came together to form the International Workshop Agreement (IWA), with the mandate to develop a protocol for ranking stoves into different tiers of performance. The IWA places stoves into a tier system based on their performance against selected performance metrics including thermal efficiency, indoor emissions, total emissions and safety (Gallagher, Beard, Clifford, & Watson, 2016). A stove may fall into different tiers of performance for each performance indicator. A stove with a tier ranking of “0” shows “the lowest performance” similar to a threestone fire, and a ranking of “4” indicates “best” performance outcomes (Gallagher, Beard, Clifford, & Watson, 2016; Masekameni, Makonese, & Annegarn, 2015). Johnson and Bryden (2015) first developed the safety protocol, which was later adopted by the Global Alliance for Clean Stoves (GACC).

T. Makonese et al. / Energy for Sustainable Development 55 (2020) 13–23

Safety tests – tilting angles The purpose of this test was to establish if the stove could selfextinguish in the case of accidental tipping during operation, which reduces the risks of fire hazards or burns injuries. This test was done using a tiltometer developed at the SeTAR Centre, University of Johannesburg. The tiltometer is made from two wooden boards that are joined together by hinges at the short edge (Kimemia, Niekerk, Govender, & Seedat, 2018). The stove is placed on the top board, which is slowly lifted to put the stove in a tipping position. The angle between the boards is measured using a protractor. The detailed discussion of the functionality of the tiltometer is presented elsewhere (Kimemia, Niekerk, Govender, & Seedat, 2018). It was also noted during the tipping experiments whether the stoves self-extinguished after reaching the tipping angles specified in the SABS standard for liquid-fuelled stoves (SANS 1906:, 2012).

Temperature of touchable parts and fuel reservoir During the cooking observation tests, the surface temperatures of the touchable parts (i.e. flame regulators and handles) and fuel reservoirs of all experimental stoves (Kimemia, Niekerk, Govender, & Seedat, 2018) were recorded after every 10 min for the duration of the cooking sequences. Lutron™ Contact Thermometers (model TM-946) were employed in the study to document the surface temperatures.

Leaking fuel and dismantling of parts The fuel canisters in all the three experimental stoves were filled with methanol to recommended levels. Any spillage was wiped off from the fuel canisters before the fuel/stove combination was placed on a digital scale (32 kg ± 0,001 kg). The stoves were then put on a level table and allowed to stand for 3 h before being re-weighed and any mass loss attributed to fuel vaporisation and leakage. Any fuel spills were noted qualitatively through physical observations. The stoves were further overturned and allowed to stand in that upset position for 10 min, noting if any fuel leaks out of the fuel canister. After each leaking test experimental run, the stoves were re-weighed, and the mass loss observed. These values were compared against the SABS standard limit of 10 g per minute (SANS 1906:, 2012). After the leak tests, the stoves were placed on a flat table about 100 mm from the floor. Each stove was knocked off from the table several times, with the technician noting if any parts of the stove dismantled during this exercise or if the stove was otherwise damaged during the experiments. The technicians had to observe if the stove extinguished within 2 s of falling and hitting the ground. This requirement is stipulated in the SABS standard for non-pressurised kerosene stoves (SANS 1906:, 2012).

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Results and discussion Comparison of cooking observations with the derived laboratory test sequence Observed and derived laboratory sequences The cooking observation test involved recording the time taken to cook each meal from start to finish, noting the time of changes between the three power level settings on the cooking device (i.e. low, medium, and high) as required by the cooking sequence, following the method highlighted in Makonese (2018). The burn sequence for the staple dish and relish averaged over three common dishes prepared in Setswetla was 95 min (Table 2). Note that the beans and samp were soaked in water overnight to reduce the cooking time, which is a common practice in the townships as the users try to save on time and the fuel used to prepare any dish. For example, it would take twice as long to cook the samp and beans meal if the ingredients were not pre-soaked. This method is used all the time and the communities follow it religiously. The time taken to make each dish varied between the cooks as they were unconstrained in the manner they prepared the food items – they were requested to follow their usual domestic practices. Note that it is necessary not to combine sequences from stoves with different thermal characteristics. Low-to-high and high-to-low power sequences cannot be combined to make a representative lab test. Ideally, the sequences should be derived separately for each fuel/ stove combination. The laboratory test shown in Table 2 follows the highmedium-low sequences as demonstrated in the field. As such, averaging the sequences will result in a representative laboratory test. Comparison of laboratory test sequence with the average of five replicates of the UCT for one meal for the Protostar stove The comparative tests were done in the laboratory using the waterheating test. To demonstrate the benefits of averaging cooking sequences derived from a variety of cooking tasks in an area, Table 3 compares the relationship between the energy metrics of the observed (contextual) cooking tasks and the values obtained when cooking a meal using a laboratory cooking sequence (i.e. samp and beans – which was the most extended cooking sequence) on the Protostar stove. Results show there were no statistically significant differences (p N .05) between the metrics average cooking cycle and the cooking tasks in terms of fuel consumption rate (kg/h), cooking power (kW), CO/CO2 ratio (%), PM2.5 emission factors (mg/MJ), and CO emission factors (g/MJ). It is envisaged that by studying the context of use of a variety of cooking systems and developing laboratory tests based on the observed cooking sequences, a better picture can be gained of the way the

Table 2 Observed (uncontrolled) cooking sequences of three meals for each of the three stove types and the derived (laboratory) testing sequence to be used in further laboratory tests. Cooking time at different cooking power levels (minutes) Staple dish Meala Pap & beef stew

Rice & chicken stew

Samp & beans Derived (laboratory) burn sequence a

Stove type Protostar Dometic Meca Protostar Dometic Meca Protostar Dometic Meca

Dish 1 Pap (stiff maize porridge)

Rice

Samp (crushed maize)

Relish/sauce High

Med

Low

30 18 25 33 24 24 55 53 50 35

10 12 7 10 9 11 8 10 15 10

0 0 0 0 0 0 0 0 0 0

Dish 2 Beef stew

Chicken stew

Beans

High

Med

Low

39 18 36 27 10 35 44 38 48 33

10 16 12 15 27 6 20 10 13 14

0 15 0 0 9 0 0 8 0 3

Three meals were observed for each stove and no replicates of the meals were done for the same stove. The laboratory test sequence is an average of the duration taken to prepare the three meals (including a staple dish and relish/sauce) at each power setting. The three stoves were evaluated for thermal and emissions performance under a lab-controlled environment using the averaged laboratory sequence.

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T. Makonese et al. / Energy for Sustainable Development 55 (2020) 13–23

Table 3 Comparison of the average energetic and emissions performance of the Protostar stove for the observed (contextual) and derived (laboratory) sequences. Performance metric

Observed cooking sequenceb

Derived (laboratory) cooking sequence

p-Value

Na Fuel consumption rate Cooking power CO/CO2 CO emission factor PM2.5 emission factor

5 0,17 ± 0,01 0,94 ± 0,05 1,9 ± 0,3 0,76 ± 0,1 0,061 ± 0,006

5 0,18 ± 0,01 1,0 ± 0,04 1,9 ± 0,3 0,75 ± 0,1 0,063 ± 0,007

N0,05NS N0,05NS N0,05NS N0,05NS N0,05NS

(kg/h) (kW) (%) (g/MJ) (mg/MJ)

N0,05NS = no significant differences at the 95% confidence for one standard deviation a N = number of replicates b Cooking sequence for samp and beans meal using a Protostar stove

cookstove performs in real-world scenarios. Considering this, it will be possible to carry out test experiments in the laboratory to obtain test results that are comparable with field results (Makonese & Meyer, 2018). According to Arora et al. (2014: 20), “these types of user-centric studies focused on cooking cycles in different regions can help in identifying the power levels involved in specific cooking tasks. This will further benefit to test cookstoves using only those power levels that are dominant in certain regions…thus making it easier to compare cookstoves on their actual performance, based on specific cooking cycles”. Information obtained in the field on actual use conditions may be valuable to both stove designers and researchers engaged in the development of cookstove testing protocols as well as stove dissemination programmes. Metrics of methanol stove performance using the laboratory test sequence Energetic performance The energetic performances of the three methanol stoves were evaluated using the Heterogeneous Stove Testing Protocol integrated with a new contextual testing protocol. Results are shown in Table 4. A twotailed Student t-test at the 95% confidence level (p = .05) was used for all statistical analyses in this study. Results are presented as average ± one standard deviation (N = 5). The differences between fuel consumption of the three stoves tested were not statistically significant (p N .05). The Protostar stove gave a fuel consumption rate of 0,18 ± 0,01 kg/h and total fuel consumption of 280 ± 11 g over the duration of the cooking sequence. Average test replicates across the entire burn sequence showed that the stoves gave cooking power of 1,0 kW at high power, thereby meeting the South African National Standards for liquid-fuelled heating and cooking devices. The standard specifies that a stove must produce a minimum of 1,0 kW when operated at a high-power setting (SANS 1906:, 2012). The Meca stove gave the lowest cooking power of 0,97 ± 0,07 kW although this was not significantly different from the cooking power values exhibited by the Protostar and Dometic stoves. The low cooking power shown by methanol stoves can be a severe concern for consumers to accept the fuel as a cooking solution or to replace existing kerosene stoves that produce on average a cooking power of 1,5 kW (Makonese, Pemberton-Pigott, Robinson, Kimemia, & Annegarn, 2012). This could mean that the stoves are underpowered, taking the users a significant amount of time to prepare dishes. Rehfuess,

Table 4 Comparative energetic performance of the three methanol stoves. Stove type

Protostar

Dometic

Meca

Na Fuel consumedb Fuel consumption rate Cooking power Thermal efficiency

5 280 ± 11 0,18 ± 0,01 1,00 ± 0,04 58 ± 4

5 280 ± 12 0,21 ± 0,01 1,00 ± 0,06 61 ± 3

5 300 ± 22 0,20 ± 0,02 0,97 ± 0,07 60 ± 4

a

(g) (kg/h) (kW) (%)

N = number of replicates Total fuel consumed over the duration of the derived laboratory test sequence. As fuel costs are market dependent and variable, the economics of the devices may be obtained from the fuel consumption per task and prevailing fuel prices. b

Puzzolo, Stanistreet, Pope, and Bruce (2014) believed timesaving is a critical factor in stove adoption programmes. The time can be saved by less fuel collection (i.e. stove has lower specific fuel consumption), and through more efficient cooking because of high heat transfer efficiencies or using multiple pots (Rehfuess, Puzzolo, Stanistreet, Pope, & Bruce, 2014). Thus, methanol-fuelled stoves could save time by displacing solid-fuel stoves that require fuel collection. The three stoves show a similar performance concerning energy metrics. Average of fuel consumed for the three stoves is 287 g to cook meals for 95 min, which translates to 181 g/h. Although Dometic and Meca stoves are originally ethanol-fuelled stoves, their performance compares to that of the Protostar stove (designed for methanol). This indicates that the energetic performance of the liquid-fuelled stoves used in this study is not influenced by the configuration of the stove designs. The thermal efficiency numbers are comparable (Table 4). Gaseous emissions The gaseous emissions of the three stoves were compared using the cooking sequences derived in Setswetla within Alexandra Township, South Africa. Amongst the stoves, the Meca stove had the highest emissions factors of CO, producing 3,1 ± 0,5 g/MJ over the entire combustion sequence (Table 5). These values are a factor of approximately three higher compared to the CO emission factors produced by the Protostar and the Dometic stoves. The mass-specific emission factors (g/kg of fuel used) show a similar trend. These results are comparable to those reported by Masekameni, Makonese, and Annegarn (2015) for a cooking sequence derived from a local township. The average modified combustion efficiency (MCE) for the Meca stove during the laboratory test sequence was 94 ± 0,9 which is statistically different (p b .05) from the 98 ± 0,3 for the Protostar and 98 ± 0,6 for the Dometic stove. Both the Protostar and Dometic stoves met the South African Bureau of Standards (SABS) requirements for combustion efficiency, measured using the CO/CO2 ratio. The SANS (1906:, 2012 provides a specification for limiting harmful emissions with the CO/CO2 ratio expected to be lower than or equal to 2% for all qualifying non-pressurised liquid-fuelled cooking appliances. Considering the uncertainty, both the Dometic and the Protostar stove were marginal - on the border of non-compliance according to the SANS 1906 criterion for kerosene stoves. The differences in gaseous emissions can be attributed to a difference in the combustion conditions as a function of the stove type. The Meca stove is an artisan-manufactured device; no component of the stove was machine-tooled. This raised questions about the quality and Table 5 Comparative CO emissions performance of experimental stoves. Stove type N* CO emission rate Modified combustion efficiency CO/CO2 ratio CO emission factor – energy specific CO emission factor – mass specific

(g/h) (%) (%) (g/MJ) (g/kg)

Protostar

Dometic

Meca

5 2,6 ± 0,4 98 ± 0,3 1,9 ± 0,3 0,75 ± 0,1 15 ± 3

5 4,3 ± 1,0 98 ± 0,6 2,0 ± 0,6 1,2 ± 0,3 20 ± 5

5 11 ± 1,0 94 ± 0,9 5,8 ± 1,0 3,1 ± 0,5 55 ± 8

T. Makonese et al. / Energy for Sustainable Development 55 (2020) 13–23 Table 6 Comparative PM2.5 emission performance of the three methanol stoves. Stove type N* PM2.5 emission rate PM2.5 emission factor – energy specific PM2.5 emission factor – mass specific

Dometic

Meca

5 0,23 ± (mg/h) 0,03 0,06 ± (mg/MJ) 0,01

Protostar

5 1,35 ± 0,17 0,37 ± 0,03

5 0,21 ± 0,08 0,06 ± 0,02

(mg/kg)

6,4 ± 0,6

1,1 ± 0,2

1,3 ± 0,1

consistency of the stove. The design of the stove could have allowed the flames to be quenched by contact with the pot before combustion had proceeded to completion (i.e. low fire temperatures and insufficient oxygen). It is likely that the stove design influenced the CO emissions performance of the Meca stove. Particulate matter emissions For the three stoves tested, high PM emissions were noticed during ignition possibly because of low flame temperatures. Soon after (within the first 2 min of igniting the stove), the fire equilibrated and the PM emissions dropped significantly. The Dometic stove exhibited high PM2.5 emissions compared to the other two stoves. Results showed there is no statistically significant difference (p N .05) in PM 2.5 emissions between the Protostar and the Meca stove (Table 6). A statistically significant difference existed (p b .05) in PM2.5 emissions between the Protostar and the Dometic stove, and between the Dometic and the Meca stove. Ranking of the experimental stoves Rating the stoves against the South African Bureau of Standards - SANS 1906:, 2012 The three stoves were rated as pass or fail according to the South African Bureau of Standards – SANS (1906:, 2012 as they are earmarked for dissemination in South Africa. Table 7 shows that the Protostar satisfies all the requirements of the standard. The Dometic and the Meca stoves satisfied some of the provisions of the legislation. Notably, the Dometic stove fails to self-extinguish within 30 s if the device is tilted at an angle of N45° or within 2 s if the stove falls over from a cooking surface. The same applies to the Meca stove. The Protostar has an auto shut off system that is triggered when the stove is tilted at a 45° angle or when it falls over from a cooking surface. The self-extinguishing mechanism is needed to switch off a toppled stove immediately to prevent conflagrations (Kimemia, Niekerk, Govender, & Seedat, 2018). The lack of a self-extinguishing mechanism in the other two stoves heightens

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the risks of burn injuries, fire hazards and the loss of lives. On the other hand, the three experimental stoves could extinguish entirely within 30 s when the flame control lever was turned to the off position. The self-extinguishing safety feature could be a pivotal contributor to the success of methanol stoves as safe and clean cooking solutions for households in informal settlements. Only the Meca stove failed to satisfy the requirements for combustion efficiency measured as a ratio of CO to CO2, with an average ratio of 6%. (Table 5). The temperature of the fuel reservoir in all stoves tested did not exceed 35 °C at any stage during the 95 min laboratory test sequence. The highest recorded fuel reservoir temperatures recorded were 32.6 °C, 33.8 °C and 34.6 °C for the Protostar stove, the Dometic stove, and the Meca stove, respectively. This implies that after 3 h of normal operation all stoves were compliant with SABS requirement. All stoves were compliant with the SANS 1906:2012 requirement of a rigid construction framework for the stove. On being dropped 100 mm from an elevated platform, none of the stoves fell to pieces. The different parts of the stoves fit together rigidly. Even though the Meca stove was handcrafted, it showed a rigid construction that withstood distortions and dismantling when accidentally dropped from an elevated platform such as a table. Ranking the stoves using the ISO/IWA tiers The three experimental stoves were ranked according to the ISO International Workshop Agreement (IWA) tiers of performance (Table 8). Results show that all three stoves are ranked Tier 4 for thermal efficiency (%), CO emissions factors (g/MJ), PM2.5 emission factors (g/MJ), CO emission rates (g/min), and PM2.5 emission rates (mg/min). Based on the specified criteria, these stoves would be considered cleanburning technologies. The Meca stove has many sharp edges and points. This is because the Meca stove was handcrafted and has many undeburred sharp edges. The sharp edges and points test was designed to identify sharp edges or points on the stove body that could injure the user or catch on clothing thereby causing the stove to tip (Gallagher, Beard, Clifford, & Watson, 2016). The Dometic and Meca stoves lack an automatic flame extinguishing mechanism in case of accidental tipping or slipping. In both stoves, the fuel canister can be removed from the devices during normal operation by pulling at the flanges holding the fuel canister in place, thereby presenting risks of burn injuries. Overall, the Protostar stove has the potential to replace existing polluting and less efficient liquid-fuelled stoves on the market in South Africa. Risks of injuries from hot surfaces and liquid burns are minimised due to low surface temperatures – touchable surfaces and the fuel canister do not exceed 40 °C after 3 h of stove operation. However, there is a need for design improvements to raise the cooking power of the stove

Table 7 Performance of methanol stoves against the SANS (1906:2012) requirements. Parameter in SANS 1906

Protostar Dometic Meca

The appliance should not fall to pieces if knocked over – “If not fully assembled, the appliance shall be assembled according to the manufacturer's instructions as supplied. Removable components shall fit in a positive, unique and rigid manner.” (Lloyd, 2009) The appliance should be easily filled, and it should not be possible to refill it while in operation The burner should give a power outputa of at least 1 kW and have a lifetime of at least 500 h. During that 500 hb, no part of the appliance essential to its operation or integrity should deteriorate or otherwise be weakened to compromise its designed performance The appliance should self-extinguish within 30 s if tilted at 45° or greater The appliance should self-extinguish within 2 s of falling over When switched off, the flame should extinguish within 30 s, and once extinguished the appliance should not emit flammable vapours for N60 s When the burner is evaluated for performance using a water boiling/heating test, the device should emit no N0.03 g particulate matter per minute, and the CO/CO2 ratio should b0.02

✓

✓

✓

✓ ✓

✓ ✓

✓ ✓

✓ ✓ ✓ PM ✓ Ratio ✓

x x ✓ PM ✓ Ratio ✓

The maximum temperature of the fuel canister should not exceed 40 °C after 1 h of cooking The maximum temperature of any surface that can be touched while the appliance is in operation should not exceed 40 °C The appliance should not leak during operation or in a standing position

✓ ✓ ✓

✓ ✓ ✓

x x ✓ PM ✓ Ratio x ✓ ✓ ✓

a The standard is not clear whether this refers to the cooking power or firepower. Note that, if the standard refers to cooking power, then the Meca stove does not meet the 1 kW requirement. b In this study the stoves were not tested continually for 500 h, but only for the duration of the cooking sequences. Even so, the total number of cooking sequences cooked did not add up to 500 h.

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Table 8 Methanol stoves high power performance and ranking according to the ISO/IWA tiers of performance. Stove type Parameter High-power thermal efficiency

(%)

High-power CO emission factor

(g/MJ)

High-power PM2.5 emission factor

(g/MJ)

High-power indoor emission rate CO

(g/min)

High-power indoor emission rate PM2.5

(mg/min)

while operating at the high-power setting to about 1.5 kW. Attaining higher firepower could come at a cost - if the flame and pot are not well-matched, there could be larger heat losses in hot gases passing the sides of the pots, leading to higher fuel consumption despite a shorter cooking time. It is expected that the cooking power would increase with an increase in specific fuel consumption. The designers of the stove will need to consider alternative ways of improving the cooking power of the stove at least cost to both manufacturers and the end-users. Conclusion The study aimed to evaluate three liquid-fuelled stoves using cooking sequences derived from a typical township in Johannesburg, South Africa. The contextual testing approach is a revised in-situ testing protocol based on the Uncontrolled Cooking Test developed at the SeTAR Centre, University of Johannesburg. It seeks to assess the taskbased performance of the system (i.e. fuel/pot/stove/meal/user) when the stove is operated according to local conditions and practices to prepare meals. Cooking sequences were integrated into the overall assessment of the stove using a Heterogeneous stove Testing Protocol. Information obtained in the field on actual use conditions may be valuable to stove developers and disseminators. Although the Dometic stove was designed for ethanol, it performed well with methanol fuel delivering adequate cooking power (at least 1 kW into the pot) and fewer CO emissions compared to the Meca stove. Results have indicated that if a stove is not well designed, the CO emissions increases. Again, testing for CO emissions is an essential aspect for any liquid-fuelled stove. Even when the PM values are lower, the CO emissions can differ by a factor of three between competing stoves. There is, thus, potential for optimisation of these and other methanol fuelled stoves in order to meet user expectations, and to meet current standards for liquid-fuelled stoves through lower CO emissions, improved combustion efficiencies, and the provision of automatic shut off systems in case of the stoves tipping over or falling from a raised platform. The significance of this study is that it demonstrates methanol powered stoves as cleaner devices for the lower economic strata of society who cannot afford modern energy carriers like electricity for thermal energy services, and as an improvement on the market-dominant kerosene stove technologies. The paper shows that observations of cooking can be used to design a lab test with a sequence of power levels. The data show that a laboratory test sequence with the same power levels for cooking food or for heating water produced nearly the same results as a UCT of a typical meal in the Township. In stove studies that are intended to measure and predict likely performance of stove/ fuel/user behaviour combinations, irrespective of laboratory instrumentation used, the approach of deriving contextually appropriate test sequences as demonstrated in this paper may be more useful than alternate “International comparative” test sequences.

Protostar

Dometic

Meca

58 Tier 4 0,8 Tier 4 0,06 Tier 4 0,04 Tier 4 b0,01 Tier 4

67 Tier 4 1,2 Tier 4 0,37 Tier 4 0,07 Tier 4 b0,01 Tier 4

60 Tier 4 3,1 Tier 4 0,06 Tier 4 0,18 Tier 4 b0,01 Tier 4

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