In this study, an extensive set of experiments has been performed to investigate how the emissions of carbon monoxide (CO) and particulate matter (PM) from wood pellet combustion are correlated with the different layout of air inlets in the two burner pots of pellet stoves. In particular, emissions generated using a “traditional” burner pot are compared with those produced with an innovative one. Tests were carried out on four pellet stoves (8–11 kW burning power). Tests show that CO emissions can be reduced close to zero using the innovative burner pot. PM emissions are also reduced, but not as much as those of CO. This phenomenon is explained assuming that CO reduction implies a reduction of the organic part of PM, but not of the inorganic matter. Experiments also show an apparent dependence of PM release on the time from ignition for both burner pot models: PM emissions increase and the color of PM deposited on filters varies over a wide range. It is argued that this effect is due to ash accumulation on the bottom of the burner pot and to its interaction with the primary air stream that flows over it.

In this study, results of an extensive set of experiments on a wood pellet stove model equipped with innovative burning pots are presented. Tests have been performed to investigate the relations between design data and operation parameters of the stove and its emissions. In particular, carbon monoxide (CO) and particulate matter (PM) emissions are correlated to the burning-pot depth. The burning pot A, adopted by AICO S.p.A, allows to obtain near-to-zero CO emissions and low PM emissions: however, PM emissions reduction with respect to standard burning pots is not as enhanced as CO emission reduction. Here it is shown that a further reduction of PM emissions (down to 6-16 mg/Nm3) can be attained increasing the burning pot depth. Experiments show also an increment of PM emissions in subsequent tests in the same day: there is an apparent dependence of PM release on the time from ignition. It is likely that this effect is due to ashes accumulation on the bottom of the burning pot and to their interaction with the primary air stream that flows over them.

Pellet stoves are popular appliances because they are an affordable technology and because the fuel is easy to store and to use. The increasing concern for environmental issues, however, requires a continuous effort to reduce pollutant levels in the atmosphere. This experimental work focuses on flue gas recirculation (FGR) as a possible way to improve combustion and decrease the emissions of carbon monoxide CO, particulate matter PM, and nitrogen oxides NOx in order to fulfill European and Italian emission requirements, for NOx in particular. A pellet stove has been tested in several experimental sessions with and without FGR. Pollutant emissions have been measured and analyzed in terms of statistical summaries and instantaneous trends. With FGR, the average CO and PM emissions were found to be 80% and 45% lower than the corresponding emissions without FGR. Results for PM are significant since FGR reduces emissions well below the most restrictive limits enforced in Italy. The analysis of instantaneous emissions in relation to excess air indicated that FGR can considerably reduce emissions, especially at the extremities of the oxygen O2 content range. Optimal ranges of excess air, in terms of O2 in flue gas, were identified for both the tested configurations, in which CO and PM emissions are minimized. The optimal range is 8–9% without FGR, and it decreases to 5–7% with FGR. Finally, a reduction in NOx emissions by about 11% has been observed in the configuration with FGR. Although this reduction seems modest as compared to CO and PM, it is important in that it lowers the emission level to the most severe limit in Italian regulations and indicates an improved FGR system as the solution for further reduction.

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