Motivation for the Proposed Work

Introduction 5 earth elements to porous ceramic led to saving of the fuel consumption by 4.5%, and reduction in CO emission by 40.9%.

6 Introduction

Towards enhancing the existing stove effectiveness, Pantangi et al. [59] proposed highly conducting and radiating PIB instead of perforated metallic burner head in the LPG cooking stove. They investigated the thermal efficiency and emission characteristics of the conventional domestic LPG cooking stoves with various PM such as metal balls, pebbles and metal chips. The maximum thermal efficiency increase of 4% was obtained with metal chips. In another work [21], to improve the flame stabilization and burner effectiveness of the LPG cooking stove, two-layered PIB was used. The combustion was allowed to take place in the combustion zone made of silicon carbide (SiC) PM, and the preheating zone was filled with alumina balls (Al2O3) of 3 mm diameter. The measured CO and NOx emissions were found to be significantly low in PIB than the conventional LPG cooking stoves. The feasibility of burning liquid fuel within a PIB was studied by Sharma et al. [60] for kerosene pressure stove. They investigated the optimum efficiency of the burner through exergy calculation analyses and found higher thermal efficiency for the PIB integrated stove as compared to the traditional pressure cooking burners.

Nevertheless, the above researchers [21, 52, 59, 60] have used numerous experimental trial and error methods to explore the stable combustion of air-fuel mixtures inside the PIB. Thus, numerical modeling of heat transfer in the PIB is required for better assessment of geometric and operating parameters of the burner without the need for extensive experimental trials.

In developing countries like India and China, considering the increase in petroleum product consumption and sudden rise in dependence on imported LPG, there is a need to pay significant attention to alternative fuels. As a promising renewable energy source, dimethyl ether (DME) is one of the excellent alternative fuel with similar physical properties as that of the LPG. DME which can be produced from the renewable resources like coal bed, methane, agriculture waste, syngas and CO2-rich feedstocks, is a low carbon content fuel and is environmentally friendly. As an additive with petroleum-based fuels it can reduce emissions, polycyclic aromatic hydrocarbons (PAH), and soot [61, 62].

To establish the superiority of DME as a substitute fuel, numerous investigations have been conducted in diesel engines [63], homogeneous charge compression ignition engines [64], gas turbines [65], and heating [66] and cooking applications [67]. However, when DME is allowed to combust in conventional burners, problems related to flame

Introduction 7 sustainability, low flammability limit, and low thermal efficiency arise because of its lower calorific value [67-69].

Marchionna et al. [67] investigated the potential of DME as a substitute fuel for household applications and observed that combustion could not be sustained in existing burners for DME concentration above 20% in the LPG-DME mixture. Arya et al. [68]

studied the effect of DME addition on LPG cooking burners and found that the thermal efficiency decreased by 5.26% when DME volume fraction in the DME-LPG mixture increased to 20%. Similar observation of a decrease in thermal efficiency with the increase of DME blend in the conventional cooking stoves was reported by Anggarani et al. [69]. However, to date, only a few studies [67-70] have been performed to establish the viability of DME as a substitute fuel in the domestic LPG cooking stoves and these studies have revealed that to burn DME-LPG blend with DME volume fraction above 20%, the burner requires modification of its components and design. Indeed, reports in the literature suggest that DME and LPG are not completely interchangeable by using the existing conventional LPG stoves. In order to overcome these shortcomings, there is a need to improve the existing burners toward providing better fuel compatibility for both LPG and DME.

Furthermore, it is observed from the relevant literature that although some efforts have been made concerning the applicability of employing the idea of PIB in domestic burners, fundamental studies toward analyzing the complex kinetics and flame dynamics of air- fuel mixture inside the PM have not been reported to date. Therefore, in this work, a detailed and comprehensive modeling of the LPG and DME flames inside the PIB are also investigated through reaction pathways and rate of production analyses.

Combustion-derived soot particulates generated due to the burning of fuel-rich mixtures and liquid fuels pose adverse effects on human health and climate change. Toward understanding the fundamental of complexity in soot formation process, many studies have been performed in laminar premixed FF [71-73] over the last two decades. To explore the thermal dependence of the aerosol dynamics Ciajolo et al. [74] and Böhm et al. [75] studied the effect of flame temperature on the soot production process and observed an inverted bell-shaped profile for the soot volume fraction with a reduced amount of soot formation at low and high temperature. In order to accurately capture the

8 Introduction

soot inception, surface growth and particle oxidation mechanism in FF combustion, various kinetic models, such as two-equation model [76, 77], method of moments model [78-80], stochastic method [81, 82] and sectional model [83-85] have been proposed that can be coupled with different thermal systems to predict the aerosols dynamics. From the literature survey, it is also revealed that, in spite of the negative impact of soot components on public health and environment, no studies have been performed regarding soot particle evolution process in the PIB. Thus, toward addressing these issues, the problem statements for the present research work along with the roadmap are summarized in the following section.