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The ash thickness formed above the combustion front of peat, which is affected by the inorganic content and the piled bed height of peat column, plays both positive and negative effects on peat smouldering fires. This work investigated the effects of the inorganic content and the piled bed height (5, 10 and 20 cm) on the natural downward smouldering mechanism of peat, both experimentally and numerically. It was observed that the char formation and char oxidation processes are stable and dominant during the downward smouldering. The spread rate of the pyrolysis front was found to decrease almost linearly with the inorganic content, while the spread rate of the char oxidation front was less dependent on the inorganic content and the piled bed height at higher inorganic content. The spread rate of the char oxidation front levelled off when the ash layer above the char layer was thick enough, which was also well-predicted by a 1-D numerical model. The model also predicted the nonlinearly increasing peak temperature and decreasing downward spread rate with depths in experiments. This work provides a better understanding of the multiple role of inorganic content in peat smouldering fires, especially for the fires in the in-depth peat layer with abundant inorganics in natural peatlands.

Smoldering combustion of natural organic layers like peatlands leads to the largest fires on Earth. The multidimensional smoldering structure of peatlands is observed in the field, but the mechanism is poorly understood. In this work, a 2-D cylindrical axi-symmetric model that considers volume shrinkage is developed for the natural downward smoldering of peat with different inorganic contents. Numerical results show that the model captures the two-dimensional multisubfront structure of the peat smoldering process. For the peat with lower inorganic content, the predicted bidimensionality of wall-attachment is more obvious, the mass loss rate and the spread rate are higher, and the smoldering front is thinner. For the peat with higher inorganic content, smoldering is more sensitive to lateral heat loss. Both the inorganic content and the lateral heat loss have negative effects on the volume shrinkage, peak temperature, and in-depth spread rate. Additionally, two groups of experiments using peat samples with...

An ignition model of reactive material (RM) by a hot particle, taking into account the interface thermal resistance (ITR) and reactant consumption is established. The heat transfer process between RM and the particle was described by a radiation boundary condition at the interface. Five regimes were identified from the ignition model through numerical simulations. The criticality of reaction heat on the ignition regime was determined by the sensitivity analysis technique. It was found that a larger ITR would result in a longer ignition delay time, a smaller burnout area and a higher critical reaction heat of RM, and a higher critical radius and initial temperature of the particle. The effects of particle size, initial particle temperature and particle shape on the ignition delay time were more significant at a larger ITR. This work shows that both ITR and reactant consumption have unusual and significant influences on the ignition process of RM by a hot particle, and may have an instructive significance for the hot-spot ignition theory and RM management.

Reduced-scale mock-ups had been developed to assess and regulate smoldering ignition resistance of residential upholstered furniture (RUF). However, there are limited data available on the effects of the mock-up test configuration and foam thickness on smoldering propensity and how they affect the degree of correlation with full-scale performance. In this work, the smoldering propensity for standard mock-ups (SMs, where the foam is in contact with a support frame) and modified mock-ups (MMs, where a 13 ± 1 mm air gap is introduced between the foam and the frame), were computationally simulated and compared to experimental results. The model results indicated that the buoyant airflow at the bottom of the mock-up was enhanced in the MM, giving rise to a higher foam oxidation rate, a higher peak smoldering temperature and higher mass loss rate as compared to the SM, and; that oxygen supply was dominated by diffusion-driven transport from the boundaries in proximity of the heating source in the SM. Additionally, the effects of foam thickness on smoldering propensity in the SM and MM were studied with foam thicknesses of 51 mm (2 in.) and 76 mm (3 in.). With an increase in the foam thickness, the smoldering propensity is weakened in the MM but enhanced in the SM. The model was able to predict the ranking of smoldering propensity quantified by the mass loss (ML) in experiments: ML(t)SM2

Thermal characteristics and gas compositions during peat pyrolysis under helium atmosphere were investigated using the TG–FTIR-MS coupling technique. The majority of gas products were released during the decomposition temperature of 150–550 °C, resulting in about 60% mass loss of peat. The main gas species detected during 150–400 °C were CO 2 , CO, CH 4 , C 2 H 6 , HCOOH, CH 3 CH 2 COOH, C 4 H 8 and CH 2 CHCHO. From 400 °C to 550 °C, some aromatic hydrocarbons were identified, including benzaldehyde, phenol, benzoic acid and toluene. The release of CO 2 , CO, CH 4 and some aromatic hydrocarbons over 550 °C provided the evidence of char pyrolysis. A five-step pyrolysis scheme including water evaporation, hemicellulose, cellulose and lignin degradation, and char pyrolysis was used to simulate peat decomposition process in inert atmosphere. The well agreement between the calculated and experimental curves indicated that major aliphatic gases were derived from hemicellulose and cellulose pyrolysis, while aromatic hydrocarbons were mainly from lignin and char pyrolysis. This work provides a deep insight into the utilization of peat for gaseous biofuels.

Smoldering combustion of peat receives considerable attention for the substantial destruction of carbon storage and potential health threats from high yields of noxious gaseous products. In this work, the combustion characteristics of peat were investigated by using thermogravimetric analysis coupled with Fourier transform infrared spectrometry (TG-FTIR) at five heating rates (5, 10, 15, 20 and 30 K min−1). The results showed that the combustion process included three stages, corresponding to the processes of dehydration (302–423 K), decomposition of organic matters of peat (423–643 K) and char oxidation (643–873 K). Tiny light organic gas products were generated in a lower temperature range (473–643 K), primarily ascribing to the decomposition of organic matters. Abundant CO2 and slight CO were released in a higher temperature range (643–873 K) during the combustion process, mainly due to char oxidation. A four-step kinetic scheme was developed through Genetic Algorithm and described the combustion kinetics very well. These results provide a better insight into the smoldering combustion characteristics and the gas emission behaviors of peat.