Thermal performance of gasifier cooking stoves: A systematic literature review

Search and selection strategy

A literature search was conducted to cover the period from January 2008 to August 2022. Scopus, Web of Science, Google Scholar and Science Direct databases were selected as search strings. Boolean operators “AND” and “OR” between Keywords and database searching fields. The searching keywords were gasified cooking stoves, producer gas cooking stove thermal performance and cooking fuels. The gasified cooking stove also called as producer gas cooking stove therefore both of the terms used as keywords. EndNote X 9.0 software was used to exclude duplicates from searched data. The protocol of the review discussed in Table 1.

Data extraction and analysis

To conduct this study, the author, date, name and types of study, study location, stoves types, material used, fuels/energy sources, thermal performances and emission of pollutants were reported by using Microsoft Excel.

Publication year

The publications year of the selected articles is summarized in Figure 2, which was obtained from Table 2. The figure shows that the selected articles were published in 2022, 2021, 2020, 2019, 2017, 2016, 2015, 2014, 2012 and 2008. The result also highlights that the highest amount of research on gasified cooking stoves was conducted in 2019 at 18% and the lowest amount of research was conducted in 2012 at only 4%. From the beginning to the mid of the current year 2022 almost 14% studies were identified from the selected literature which reflects that the investigation demand on gasified cooking stoves is recently also a high priority to researchers.

Figure 2. Year wise publications percentages.

Identified gasified cooking stoves

From the literature search, this review identified different types of gasified cooking stoves wherein modification and improvement were applied. Based on the findings from Table 2 the identified gasified cooking stoves are summarized in few categories, which are:

From the table it can be seen that most of the studies worked on general gasified cooking stoves while lowest number of studies worked on micro, and other gasified cooking stoves. Due to the easy design consideration and fabrication, most of the studies considered general gasified cooking stoves for their investigation. A short description of the categorized cooking stoves are as follows:

General gasified cooking stove

Few published articles have focused on gasified cooking stoves, but have not mentioned any particular type. These stoves are generally referred to as 'general gasified cooking stoves' in the literature. Biomass, Chinese, and biochar are identified as general gasified cooking stoves in literature. A bio-char general gasified cooking stove of Shahi et al. (2014) is presented in Figure 3. The stove mainly consists of outer cylinder ad inner cylinder. Inside the inner cylinder the combustion and then gasification occurs. The working procedure of these stoves depend on two processes. Firstly, charcoal and hydrocarbon-containing gases are combined with solid biomass in the gasification process. Second, a clear (smokeless) flame is used to burn the gases. At this stage, the stove's operation is halted when making charcoal, and the charcoal is taken out as a residue. For gasification, a primary air flow is necessary, and to help the gas ignite, a secondary air flow is added to the hot gas above the fuel.

Figure 3. Bio-char general gasified cooking stoves (Shahi et al., 2014).

Updraft gasifier cook stove

Updraft gasifier cook stoves are a type of biomass stove that produce a clean and efficient flame through a process of partial combustion and gasification of the fuel. The basic principle of the updraft gasifier cook stove is to burn the fuel in an oxygen-limited environment, creating a syngas consisting of hydrogen, carbon monoxide, and other combustible gases. This gas is then burned cleanly in a secondary combustion chamber, producing a hot and efficient flame.

Figure 4 illustrates the schematic diagram of a Top-Lit Up Draft (TLUD) gasifier cook stove (Scharler et al., 2021). The TLUD, known as the reverse downdraft gasifier, is a highly popular cook stove technology due to its ease of use and flexibility. It offers the same level of adaptability as the updraft gasifier, but with the added advantage of the downdraft gasifier: volatiles, including tar, produced during pyrolysis are partially decomposed and burned as they pass through the hot char bed above. This TLUD, as shown in Figure 4, enhances its flame efficiency by utilizing external fans or blowers. However, the TLUD stove can also be used by natural draft flow (Tryner et al., 2014).

Figure 4. Schematic diagram of a Top-Lit Up Draft (TLUD) gasifier cook stove (Scharler et al., 2021).

Downdraft gasified stove

A downdraft gasified stove is a type of cooking stove that operates by burning wood or other biomass in a closed chamber, which produces a gas that is then burned in a secondary combustion chamber to generate heat. The downdraft design of the stove allows for more efficient and complete combustion, resulting in lower emissions and higher energy efficiency compared to traditional open fire cooking.

The downdraft gasifier involves introducing biomass feedstock into the top of the gasifier, where it undergoes a series of processes including drying, pyrolysis, oxidation, and reduction as it moves downwards through the gasifier, as depicted in Figure 5 (Susastriawan & Saptoadi, 2017). The gasification process produces a gas called producer gas which exits the gasifier through an outlet at the bottom. Producer gas is typically composed of both combustible gases, including CO, H₂, and CH₄, and non-combustible gases like CO₂ and N₂.

Figure 5. Schematic diagram of downdraft gasifier (Susastriawan & Saptoadi, 2017).

Natural draft gasified stove

The gasifier stoves are built from sheet metals using basic mechanical techniques, and they include a fuel chamber for loading biomass residue, air inlets for partial combustion, and a pot stand for holding cooking utensils. This particular gasifier stove is natural, so it does not require any external power source to drive the primary and secondary air into the stove, unlike other gasifier stoves that rely on electricity. Figure 6 illustrates a schematic diagram of natural up draft gasifier stove. This stove is constructed by Hailu (2022) from mild steel sheet metal and can hold a maximum of 0.0005 m³ (500 gm) of fuel for effective gasification. Secondary air enters the stove through the gap between the external cylinder and the internal gasifier chamber. The study suggests that the heat generated by the gasifier chamber's surface plays a crucial role in the combustion process. Specifically, this heat warms up the secondary air by means of conduction and convection, creating optimal conditions for combustion at the top of the gasifier chambers exterior. Due to this efficient process, the gasifier is able to function effectively and produce the desired output.

Figure 6. Natural draft gasified stove (Hailu, 2022).

Forced draft gasified stove

A forced draft gasified stove is a type of cook stove that uses a fan to introduce air into the combustion chamber at a higher pressure than the surrounding air. This results in a more efficient combustion process, with fuel burned more completely and at a higher temperature. Forced draft stoves also often include features such as insulation and preheated air supplies, which further optimize the combustion process and minimize heat loss.

Figure 7 depicts a forced draft gasified stove with two separate fans to supply primary and secondary air (Himanshu et al., 2022). According to their study, the primary air was fed from a grate located below the fuel bed, which facilitated gasification, while the secondary air was introduced from the top of the cook stove and utilized to burn the volatiles released during biomass pellet gasification. The design also included an annulus chamber that preheated the secondary air before it entered the combustion chamber, minimizing heat loss and leading to a more efficient, cleaner combustion process. Overall, the study found that these measures were highly effective in optimizing the cook stove's performance. By providing a steady supply of preheated air and facilitating optimal gasification and combustion processes, the cook stove was able to produce the desired results while minimizing waste and reducing its environmental impact.

Figure 7. A forced draft gasified stove with two separate fans to supply primary and secondary air (Himanshu et al., 2022).

Forced draft gasified stoves have the potential to greatly reduce fuel consumption and minimize indoor air pollution, particularly in developing countries where traditional cooking methods can be both inefficient and harmful to human health. Further research and development in this area may lead to even more effective and sustainable cook stove technologies.

Micro gasified stove

A micro gasified stove is a small and portable stove that converts solid biomass fuel into a clean-burning gas. Figure 8 illustrates an experimental setup of an advanced micro-gasifier cook stove, built by Sakthivadivel and Iniyan (2017). The working principle of a micro gasified stove involves the partial combustion of solid biomass fuel in a low-oxygen environment. As the fuel heats up, it releases volatile gases, which are then burned in a separate combustion chamber to produce a clean-burning gas. This gas can be used to cook food or heat water, providing a convenient and efficient source of energy. The velocity of the air determines the rate of flame propagation of biomass fuel in fixed bed micro-gasifiers. The combustion air velocity, combustion process, and heat transfer all have an impact on the flame propagation, and are influenced by various fuel properties such as size, density, thermal conductivity, moisture content, ash content, and calorific value. Additionally, parameters such as bed porosity, peak temperature of the combustion chamber, and heat losses from the reactor can also affect flame propagation.

Figure 8. Advanced micro-gasifier cook stove (Sakthivadivel & Iniyan, 2017).

Investigation location

Most of the identified articles on different gasified gas stoves are conducted in Asian and African continents as due to energy security and crisis people in these continents for which people of these continents mainly depend on the biomass fuel driven cooking system. Country wise identified published articles from Table 2 are presented in Figure 9. Among the selected articles 71% mentioned their study location. The figure shows 11 different countries from Asian and African continent where the investigation on gasified cooking stoves were conducted. The figure also highlights that 21% published articles performed their studies in India, which is the highest while the lowest study was performed in Thailand, which was only 3%. The design, configuration and burning fuels for any cooking stoves usually develop and investigate based on the geographical locations, climate, environment and materials availability. Therefore, this finding may help researchers, organizations and government to investigate and implement this type of cooking stoves based on the geographical location so that the adoption rate of the research can increase.

Figure 9. Country wise publication percentages.

Materials to fabricate stoves

Cast iron, mild steel, metal, ceramic fiber, steel sheet, carbon steel and stainless steel were mainly used to manufacture the gasified cooking stoves. Among the selected articles for the current review, only 60% articles addressed the materials they used to fabricate their experimental gasified stove. From Table 2 it can be said that various types of steel were the main materials for manufacturing the body of the gasified cooking stoves among those mild steel was applied mostly. The availability of mild steel in the investigated locations and higher thermal properties of stainless steel for cooking devices are the key reasons for applying it in production. In some studies, cast iron was used with steel for manufacturing purposes due to the cost effectiveness of cast iron and better mechanical wear resistance property. Additionally, ceramic fiber and wool were used for insulation purposes for updraft type and Premixed producer gas burner with a swirl vane type gasified cooking stoves.

Cooking fuels

The fuels used in the cooking stoves are categorized in four types from the Table 2 and presented in Figure 10. The categories are wooden fuel, animals manure, cereals, charcoal and others. However, wooden fuels are classified in seven types, which are pellets, cassava peel, coconut shell, sized, shavings, chip and sawdust. Among the fuels wooden pellets fuels were used maximum. Peanut shell, cornstalk and cow animal waste, from pine patula, saw dust pellets, tamarind pellet, wood pellets and rice hull pellets are identified as wooden pellets fuels from selected articles. Moreover, Babul wood (Prosopis Juliflora), mango (magnifera indica), babul (prosopis julifera) and nim (azadirachta indica) wood, eucalyptus, bamboo and pinusroxburgii (Salla) wood are identified as sized wooden fuels. The rice husk, wheat straw and corncobs are categorized as cereal fuels while gas and briquettes are categorized in other types. In briquette fuels rice husk, sawdust-cow animal waste and corn straw are identified. This finding highlights the potential fuels to run a gasified cooking stove through which general people and research will be benefited.

Figure 10. Cooking fuels based on published articles.

Thermal performance of different gasified cooking stoves

The overall thermal performance of different gasified cooking stoves from Table 2 is identified 5.88% to 91% depends on the design and burning fuels. The thermal performances of the cooking stoves usually determine by using three approaches named water-boiling test, control cooking test and kitchen performance test. The overall thermal performance of different gasified cooking stoves obtained from selected studies is presented in Figure 11 and Table 3. Figure 11 shows that natural draft semi gasified cooking stove provide the highest overall thermal performance which was 42% while Mayon rice husk gasified stoves shows the lowest performance which was 11%. This overall thermal performance of the stoves usually varied due to the design and fuels applied in the experimental tests. In the meantime, the overall thermal performance of some gasified stoves was presented as range in the literature therefore those performance is not presented in Figure 11, which can only find in Table 3. Table 3 shows that premixed producer gas burner with a swirl vane stove provided the highest overall thermal performance range which was 84% to 91% and updraft gasified stove provided the lowest performance which was 5.88% to 8.79%. Swirl vanes use in stoves usually a flame retardant device that highlight the recirculation zone formation to improve the mixing of flame stabilization and reactants compared to other stoves. Due to the improve in flame stabilization and reactants mixture, the performance and efficiency of the stoves are increased compared to other stoves.

Figure 11. Overall thermal performance of different gasified cooking stoves.

Thermal performances of cooking fuels for gasified cooking stoves

Due to the different mechanical properties such as fuel consumption rate, calorific value, heating rate and fire point different cooking fuels provided different thermal performance presented in Table 2. To understand the insight of the thermal performance of different stoves for different cooking fuels a summarization table is created. The Table 4 presents the overall thermal performance for some cooking fuels that are directly mentioned in Table 2. From Table 4 it can be seen that wood pellets provided the highest thermal performance and corn straw briquette provided the lowest. The overall thermal performance of wood pellets was 38.5% and corn straw briquette was 10.86%. Due to the thermal, physical and biomass characteristics including burning rate, heat capacity, proximate analysis and energy content, wood pellets provided the better perform compared to corn straw briquette.