Some critical combustion aspects of reformulated heating fuels

Abstract

The combustion characteristics of six middle distillate oil blends were examined using the controlled combustion testing facilities at the Energy Research Laboratories of the Canada Centre for Minerals and Energy Technologies (CANMET). Test fuels were specifically prepared for a research project to study the impact of changes in commercial heating fuel composition on the combustion performance of a residential heating appliance. Compositional formulation was modified in such a way that the fuel properties still met Canadian national heating fuel specifications. The experimental combustion conditions were set to reflect possible poor operating situations found in the field and to accelerate the emissions data acquisition process. The results from this combustion study indicate that performance deteriorated with a decrease in the fuel hydrogen-carbon ratio, which relates to the decreasing ratio of aliphatic, saturated hydrocarbon to aromatic hydrocarbon concentrations. When concentrations of high boiling, high molecular weight aromatic hydrocarbons are increased, while simultaneously reducing those of low molecular weight hydrocarbons, other fuel properties, such as flash point, distillation range, density and viscosity are altered. These compositional changes resulted in poorer burner performance characteristics and higher pollution emissions. Video recordings of the combustion experiments revealed progressive degradation of transient flame characteristics as the fuel reformulation changed from moderate to severe. Performance degradation was more pronounced at 7°C, significantly colder than the normal operating temperature range of a residential heating appliance. The effects of hydrocarbon compositional changes in distillate heating fuels on combustion performance, especially in terms of increased aromatics concentrations, were discussed.