ADAPTATION OF A 60kW COMMERCIAL NATURAL GAS FIRED MICROTURBINE FOR OPERATION ON DIESEL AND DIESEL-WATER EMULSIONS

摘要

Injection of water into a combustor is a proven method for reducing emissions of particulate and nitrogen oxide emissions beyond what can be achieved by reducing firing temperature through fuel lean operation. However, the added complexity and cost associated with a standalone water injection circuit makes this method less desirable. A method for reducing the complexity of water injection is to premix the fuel with water as an emulsion and injecting this mixture through the existing liquid fuel circuit. In the present study, the gaseous fuel injectors of a commercial micro gas turbine generator were modified to operate on both water-in-oil emulsions and gas fuel. These injectors were installed in an otherwise unmodified engine. The original air-blast injector was modified by adding a central fuel tube and blocking the original gas fuel passages. Dual-fuel operation was achieved by injecting gaseous fuel through the annular passage surrounding the liquid fuel tube. This gas fuel passageway is used for both gas fuel delivery and for introduction of air that is used to assist in the liquid fuel atomization. The atomization behavior of these injectors has been characterized using laser diffraction and high speed video for water mass fractions of between zero and 0.5, and air-to-liquid ratios between zero and one. Additionally, pollutant emissions were measured from an engine equipped with these modified injectors and operated over the same range of water mass fraction and air-to-liquid ratio. The results confirmed viability of the modified injectors for introducing water in form of an emulsion. It was also observed that, while atomization performance was altered in a minor way, the complex interaction between evaporation and subsequent mixing resulted in non-monotonic impact on NOx emissions.