CO and NO emissions from pellet stoves: an experimental study

The present work presents a report on an experimental investigation on commercial pellet stoves aimed to fully understand which parameters influence CO and NO emissions (NO2 is present in negligible quantities): tests are performed on different type of pellet stoves varying nominal power, combustion chamber size and combustion grid geometry. After a brief review on the factors which influence the production of these pollutants, we present and discuss the results of the experimental tests aimed to ascertain how the geometry of the combustion chamber and the distribution of primary and secondary air, can modify the quantity of CO and NO in the flue gases. Experimental tests show that production of CO is strongly affected by the excess air and by its distribution: in particular, it is critical an effective control of air distribution. In these devices a low level of CO emissions does require a proper setup to operate in the optimal range of excess air that minimizes CO production. We have observed that the optimal range of operation can be enlarged as a consequence of proper combustion grid design. NO emissions, on the other hand, are not a critical issue, since they are well below threshold enforced by law, are not influenced by the distribution of air in the combustion chamber, and their behavior as a function of air excess is the same for all the geometries that were investigated