Yuhua Ai

Numerical Simulation of Pollutant Emissions in a Can-Type Low NOx Gas Turbine Combustor

A research program is in development in China in order to realize a demonstrator of combined cooling heating and power system (CCHP) with net electrical output around 100kW by using of a can-type micro gas turbine. In this paper, numerical simulations were completed to investigate the pollutant emissions in a can-type low NOx gas turbine combustor. Based on the analysis of the computational fluid dynamics (CFD) results, a Chemical Reactor Network (CRN) model was set up to simulate the pollutant emissions in the combustor with detailed gas-phase chemical kinetic mechanism of GRI-Mech 3.0. The CRN consists of a number of ideal reactors of the perfectly stirred reactors (PSR) and plug flow reactors (PFR) in series and parallel structures. Two types of CRN models were designed. One is relatively simple, another is more complex. The results show that the complex CRN model corresponds with the actual combustion process better. The trends of nitrogen oxides (NOx) and carbon monoxide (CO) varying with the equivalence ratio were conducted. Effects of the inlet temperature and pressure on NOx and CO emissions were also presented in this paper. At last, the numerical results are compared with the experimental results.Copyright

Effects of Dilution and Nozzle Diameter on Laminar Dimethyl Ether Lifted Flames

This work aimed at studying the effects of nitrogen dilution and nozzle exit inner diameter on the liftoff properties of the dimethyl ether (DME) jet diffusion flames. The liftoff properties including the liftoff position (HL), the critical liftoff velocity (Ulo) and the critical blowout velocity (Ubo) were studied experimentally. In nitrogen dilution experiments, a slowly converging nozzle was used with inner exit diameter of 0.43 mm. When mole fraction of N2 (Z) increased, a) HL increased because the dilution reduced the chemical activity of fuel, in order to achieve stoichiometric conditions, the stabilization point of the lifted flame moved downstream. b) at the critical liftoff condition, the flow rate of DME decreased with the increase of N2, while the total flow rate was almost unchanged, so the jet velocity was almost the same. c) as Z increased, the stabilization zone of the DME liftoff flames became narrow and small. In the experimental study of the effects of the nozzle diameter on the flame liftoff characteristics, six nozzles with i.d. of 0.17mm, 0.25mm, 0.386mm, 0.43mm, 0.693mm and 1.152mm were used. These nozzles had different materials and nozzle exit types. The experimental results showed that the nozzle inner diameter has a significant impact on the flame liftoff characteristics. As the nozzle diameter increased, four types of different liftoff features were observed. The flame was blown out directly with i.d. of 0.17 mm. The DME flame could only be observed liftoff by ignition at a proper position downstream with i.d. of 0.25 mm, 0.386 mm and 0.43 mm. The observations are agreed with that reported in the literatures. While it could be lifted off directly by increasing the mass flow rate of fuel/dilution with i.d. of 0.693 mm. This is the new observation in the present work. It is different from the report in the literatures that the DME flame could not be lifted off directly by increasing the jet velocity except for far field ignition at relatively low mass flow rate. When the nozzle i.d. was increased to 1.152 mm, the DME flames could be lifted off by three different methods: increasing the flow rate of fuel/dilution, decreasing the flow rate of the fuel and ignition the flame downstream. Oscillation lifted DME flames were found with i.d. of 1.152 mm when the fuel was highly diluted by nitrogen. The experimental results also showed that the critical liftoff velocity Ulo and the critical blowout velocity Ubo were strongly dependent on the inner diameter, which decreased with the increase of the nozzle diameter. When the jet velocity was kept constant, the flame liftoff height HL increased with the increase of the nitrogen mole fraction Z for all lifted flames.Copyright

The Liftoff Properties of Dimethyl Ether Jet Diffusion Flames With Preheating

Liftoff properties of DME laminar axisymmetric diffusion flames were investigated experimentally with emphasis on the preheating effects. At room temperature, DME presented a different liftoff phenomenon from the non-oxygenated hydrocarbon fuels. It could not be lifted off directly by increasing the jet velocity except for far field ignition at relatively low mass flow rate. When fuel and dilution were preheated, the DME flame could be lifted off directly by increasing the jet velocity. The range of the mass flow rate of stabilized DME liftoff flames became much narrower and the liftoff height became much smaller at fuel preheating than that at ambient temperature. With the increase of the jet temperature, the DME liftoff flames exhibited as one of the following three types: stationary lifted flames, stable oscillating lifted flames and unstable oscillating lifted flames. Stationary lifted flames existed when the initial temperature was relatively low (less than 350 K). Stable oscillating lifted flames were observed at relatively high preheated temperature (about 350 K ∼ 750 K), and the trajectory of the liftoff flame base was nearly sinusoidal. Both the oscillating frequency and amplitude increased with the preheating temperature. The oscillating lifted flames were caused by thermal buoyancy effect, inertia and the instability in the inner flow. When the jet temperature exceeded 750 K, the oscillating lifted flames became unstable and easily to be blown out. The flame base of the stabilized DME liftoff flame had a tribrachial structure at both ambient temperature and elevated temperature.Copyright