OCR Text |
Show air temperature will alter reaction rates, and even nozzle velocities to a lesser extent. As the inlet air temperature increases, the reaction rate will increase and the nozzle velocity will also slightly increase. Both of these responses to an increasing inlet temperature result in a decrease in the transport time. The change in transport time could possibly move the combustor from a stable to an unstable region, or vice-versa. Figures 16 and 17 show the effect of inlet air temperature as air flow rate and equivalence ratio are respectively changed. A change in inlet air temperature has a varied effect on each of the cases modeled, as would be expected. Figure 10 shows that flow at 29.4 gls is highly stable and that modest changes in temperature will not have an effect. Flow at 9.1 gis, on the other hand, is highly unstable, but inlet air temperature changes can still not alter the transport time significantly enough to move the flow out of the unstable region. As previously alluded to, flow at 19.3 gls experiences a transition at approximately 293 K and 353 K. Conclusions As an alternative to linear analysis or detailed modeling, a simple, nonlinear model for premixed combustion has been developed to help explain experimental observations and to provide guidance for the development of active control schemes. PCOM represents the relevant processes occurring in a fuel nozzle and combustor which are analogous to current LPM turbine combustors. Conservation equations for the fuel nozzle and combustor are developed from control volume analysis, providing a set of ordinary differential equations that can be solved on a personal computer. The model can be used to quickly examine instability trends associated with changes in equivalence ratio, mass flow rate, geometry, ambient conditions, and other relevant parameters. PCOM will have somewhat limited use a design tool due to its simplicity. Given its limitations, the model has nonetheless proven valuable to our understanding of LPM combustion instability. Comparison to experimental data shows that much of the dynamic behavior observed in the lab is also predicted by PCOM, including the effects of inlet air temperature and some open loop control results. PCOM has been a valuable tool to understanding the fundamental mechanisms which drive combustion oscillations. 8 |