4.4. Preheated air and elevated pressure experiments
The combined effect of both preheated inlet air and elevated
combustor pressure is now presented. The focus here was to evaluate
the performance of the combustor under both conditions and
obtain data from which the performance of the combustor at higher
pressures can be extrapolated. It is anticipated that combining
both high temperature and elevated pressure will significantly increase
NO emissions while simultaneously cause a dramatic decrease
of CO emission.
The experimental emissions data obtained from the combustor
were as expected; NO emission increased due to the accelerated
chemical kinetics and increased temperature. However, CO emission
decreased dramatically which is a highly desirable. One very
favorable outcome was the ability to sustain the flame at lower
equivalence ratio as compared to the previously discussed conditions.
Such extension of the lean flammability limit enabled the
combustor to run at an equivalence ratio down to 0.5 without having
incomplete combustion (presenting with significantly increased
emission of CO emission). Fig. 12 shows a comparison for NO and
CO emission under current conditions as compared to the previous
conditions for non-premixed combustion case. A trend similar to
that discussed earlier was demonstrated, wherein NO emission
increased while CO emission decreased. Under preheated air and
elevated temperature conditions, the combustor demonstrated
emissions as low as 10 PPM NO and 8 PPM CO for non premixed
combustion at a heat release intensity of 22.5 MW/m3-atm.
Fig. 13 shows a comparison for NO and CO emission under preheated
air and elevated pressure conditions and compared to the
previously discussed conditions for premixed combustion case.
The trend demonstrated for non-premixed combustion case was
found for the premixed case. The more favorable operational point
was found to be at an equivalence ratio of 0.6 and a heat release
intensity of 27 MW/m3-atm yielding emissions as low as 5 PPM
NO and 8 PPM CO.
The radical intensity distribution of OH chemiluminescence
showed that the reaction zone is again in the shape of a crescent
formed opposite to fuel injection point for the non-premixed combustion
case and found to be near to the region opposite to air/fuel
injection point for premixed combustion. The results showed a decrease
in OH intensity with a decrease in equivalence ratio. Fig. 14
shows the OH chemiluminescence intensity distribution for the
extended axial exit arrangement under the discussed conditions.
Note that the intensity scale is different than that used in Fig. 5
due to the increased OH intensity with preheated combustion air.