A simplified model for understanding natural convection driven biomass cooking stoves—Part 2: With cook piece operation and the dimensionless form

Abstract

In the preceding work of Part 1: Setup and Baseline Validation, a simple model was developed for understanding the simplified, but fundamental operating behavior of natural convection biomass cooking stoves. The model predicts combustion chamber bulk flow parameters—including mass flow rate, temperature, and excess air ratio—from stove design and operation inputs such as geometry and firepower. In the following work of Part 2, this model will be developed further into a dimensionless form. The dimensionless solution reveals generalized natural convection stove behavior common to all such stoves. The experimental implementation of the dimensionless form provides a reduction of independent parameters, and allows for the bulk flow rate, temperature, and even emissions from various stove configurations to be plotted together, for direct comparison, with a single trend for each parameter. Model validation presented in Part 1 is for stove operation without a cook piece in place; in Part 2, model validation is extended to more practical, with cook piece, stove operation. An increased loss coefficient is experimentally determined to account for the added cook piece restriction; with the new coefficient, the model is shown to remain both applicable and accurate. As in Part 1, carbon monoxide and particulate matter emissions are recorded in conjunction with model validation. With the cook piece now in place, an upper limit to both firepower and efficient combustion will be observed. Applying the dimensionless firepower axis to the emission data from this, and the preceding work, trends for both carbon monoxide and particulate matter form a single trend for three stove configurations. With the consolidated data, the two emission criteria trend together, and a region of improved emissions is observed over a medium dimensionless firepower range.