**1. Introduction**

Access to clean cooking energy for all, is a major challenge in twenty-first century. In modern cooking practices, people across the globe are using various cookstoves with fuels such as biomass, Liquefied Petroleum Gas (LPG)/ Piped Natural Gas (PNG), kerosene, Charcoal, biogas etc. Other cooking devices such as electric, solar and induction are also being used. About one third of global population does not have access to clean energy mainly due to issue of affordability. The most commonly used cookstoves in the developing nations are the biomass cookstoves. Traditional versions of these cookstoves are highly polluting and very

inefficient which results in severe health issues and millions of premature deaths globally.

According to International Energy Agency, in 2018, the global consumption of energy in residential sector was about 88 EJ (1 EJ = 1018 J) which was about 23.3% of the total energy consumption [1]. The components of residential energy are: 32% combustion of bio-fuels & waste, 24% combustion of gas, 21% combustion of coal, 4% combustion of oil and the remaining 26% energy for generation of residential electricity [1]. Since year 2000 till 2019, there is about 48% rise in global energy consumption [2]. The cost of cooking energy is also rising day by day. For example, in India the price of LPG cylinder has been doubled in last 7 years from Rs. 410.0 in 2014 to Rs. 819.0 in 2021 [3]. These statistics indicate that there is an urgent need for conservation of residential cooking energy by using energy efficient cookstoves.

Primitive humans started cooking with fire nearly 2 million years ago [4, 5]. The first method of cooking was probably roasting of a fish or a bird by holding it over an open fire [6]. The different stages of evolution in cooking process as reported in literature are: Prehistoric cooking, ancient cooking, medieval cooking, renaissance cooking, modern cooking and twentieth century cooking [6]. Since prehistoric era till present days, human beings have continued using open fires for cooking purpose. In present days, commonly used domestic cookstoves in different parts of the world can be broadly classified into two groups *viz.* combustion cookstoves and non-combustion cookstoves. The cookstoves in which direct combustion of solid, liquid or gaseous fuels occur and chemical energy of fuels is converted into thermal energy, are known as combustion cookstoves. The examples of combustion cookstoves are: Biomass cookstove, Gas cookstove, Kerosene cookstove, Charcoal cookstove and their variants. In non-combustion cookstoves, no combustion of fuels occur but solar or electric energy is converted into thermal energy. The examples of these cookstoves are: Solar cooker, Electric cookstove, Induction cook-top and their variants. With reference to the developments occurred in biomass cookstoves over last few decades, they are mainly classified into three categories *viz.* traditional cookstoves, improved cookstoves and advanced cookstoves. Biomass cookstoves are also classified as: stationary (non-metal cookstoves) and portable (metal cookstoves), natural draft (buoyancy induced) and forced draft (fan or blower driven). The advanced biomass cookstoves are of two type *viz*. combustion cookstove and a gasifier cookstove. The gasifier cookstoves are further available in four types: updraft, downdraft, cross draft and top lit up draft (TLUD). The detailed classification of biomass cookstoves can be found in literature [7–11].

According to International Energy Agency (IEA) [12], about 2.6 billion people globally (i.e. about 34% of the global population) do not have access to clean cooking energy. They still rely on solid biomass as the only cooking fuel. According to World Health Organization (WHO) [13], every year about 4 million premature deaths occur from the illnesses resulting from household air pollution due to inefficient cooking practices using solid biomass and kerosene cookstoves.

Over a long period of time, the evolutions in design and operation of cookstoves have occurred. The developments in combustion cookstoves are attributed to increase in their overall efficiencies due to improved thermal and emission performance. Also attention is being provided on user friendly designs of the cookstoves.

The present chapter reports parameters affecting thermal and emission performance of biomass cookstoves. It reports emission norms set by national and international agencies for cookstoves using biomass and fossil fuels. It reports the advancements in technologies of biomass cookstoves. It also reports factors affecting adoption of biomass cookstoves. Recommendations are also given on promotion of clean cooking energy options.
