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Combustion hazards
Published in J. F. Griffiths, J. A. Barnard, Flame and Combustion, 2019
J. F. Griffiths, J. A. Barnard
The propagation of a combustion wave within porous or fibrous material combustion, or sometimes at the surface may be manifest as a smouldering process. This is a term used to describe the heterogeneous combustion of a solid without the appearance of flame. It is widely accepted that only materials which are capable of forming a char in the early stages of combustion can exhibit smouldering [250]. The char is expected to be highly porous. The difference between smouldering and flaming combustion then lies in the fate of the volatiles. The volatiles which are liberated by thermal degradation either ignite in the gas phase, the radiation from which promotes further degradation and flame propagation, or the volatiles escape without further oxidation. In the latter, the heat release is confined to the oxidation of the remaining char. Heat transfer is largely by conduction into the solid material. The smouldering propagation rate is an order of magnitude lower than that of firespread by flaming combustion because heat conduction is so much slower than heat transfer by radiation.
Dimethyl Ether
Published in Arumugam S. Ramadhas, Alternative Fuels for Transportation, 2016
Other properties of DME are given in Table 6.1. The overall chemical formula is the same as that of ethanol, so the stoichiometric fuel air ratio is the same and heating values of DME and ethanol are close to each other. While the heating value of DME per kg fuel is about 33% lower than that of diesel fuel, the heating value per kg of air at a stoichiometric mixture of fuel and air is about 10% higher than that of diesel fuel (and most other liquid hydrocarbon fuels). Since air capacity is a limiting factor in combustion devices with air as the oxidizer, one would not expect a lower power output with DME as compared to other fuels. For combustion devices with heterogeneous combustion, operation at stoichiometric conditions is not encountered and power levels for DME and hydrocarbon powered equipment can be expected to be similar. Limitations in devices with heterogeneous combustion are typically due to combustion limits such as excess smoke or carbon monoxide, or thermal loading on mechanical parts.
Performance Optimization of Hybrid Draft Biomass Cookstove Using CFD
Published in Combustion Science and Technology, 2023
Suraj S. Ghiwe, Vilas R. Kalamkar, Pravin D. Sawarkar
Drying, devolatilization, volatile combustion, and char combustion are the four phases of biomass combustion, as shown in Figure 5. Biomass combustion initiates with drying, during which all moisture is evaporated. After drying, gaseous volatiles, which primarily consist of CO, CO2, H2O, CH4, H2, higher hydrocarbons, and tar, are released from solid biomass, a process known as devolatilization (Husain et al. 2020; Porteiro et al. 2009). At high temperatures (573K − 823K), these volatiles react with oxygen, resulting in combustion (Manoj, Kumar, and Tyagi 2013). The combustion is referred as “homogeneous combustion” because the reactants, the volatiles, and the air are in the same phase. Finally, at higher temperatures, the unburned solid carbon from volatile combustion interacts with available oxygen, resulting in heterogeneous combustion due to the mixing of solid and gas (Husain et al. 2019; Li et al. 2016).