The overall goal of this combustion characterization experiment is to develop a model combustion exhaust by mixing the exhaust species of interest in order to test a solid oxide fuel cell in the mixture. This maxsold can help answer key questions in solid oxide fuel cell fields, such as whether fewer rich combustion is forming instead of endothermic fuel reformer. The main advantage of this technique is that we can develop a model combustion exhaust for fuel cell testing without actually developing an entire burner and fuel cell prototype.
Visual demonstration of this method is critical, as the experimental setup procedure, safety precautions and troubleshooting can be difficult to understand by reading a manuscript alone. Construct the characterization apparatus using a prepared combustion chamber at a bench with sources of air and the methane fuel. Select the mass flow controllers based on previously determined flow rates.
For this experiment, use a 40 liter per minute controller for methane. Use a 200 liter per minute controller for air. Next, get copper tubing and connect it to the outlet of the methane source.
From there, connect the tubing to the fuel mass flow controller. Similarly, connect the air mass flow controller to its source. For safety, add a one way valve after the methane flow controller.
Orient the valve to only allow flow away from the controller and connect it to the controller output. Next, use copper tubing to merge the flows from the air and the fuel flow controllers. Have the flows from the controllers enter a T connector.
As added safety measures, place a flame arrestor and another one way valve after the T connector. In this setup, the one way valve is connected first to the T connector, oriented to allow flow away from the T connector. The flame arrestor is next.
At the source tanks for the gases, set the regulators to the appropriate pressures. For this experiment, that is 138 kilopascal. Back at the bench, obtain leak detection solution to test all the tubing for leaks.
With the flow controllers on, apply the leak detection solution with a brush onto the copper tubing. Make sure there are no bubbles which would indicate a leak. At this point, turn attention to the combustion chamber and it's attached burner.
This chamber has K type thermocouples already in place, with their tips at the center of the chamber. Ports along the chamber length accommodate both combustion exhaust analysis and the thermocouples. Mount the thermocouples using compression fittings matched to their diameter.
To add a thermocouple, begin with the stem of the compression fitting that is already in the chamber wall. Place an appropriate high temperature metal feral into the stem. Next, lower the compression nut with a thermocouple probe threaded through it onto the stem.
Push the thermocouple probe through until its end is at the center of the chamber. Then tighten the compression nut to seal the chamber against leaks from this opening. Connect the thermocouples to the computer setup for data acquisition and control.
Return to connect the output of the mass flow controllers to the combustion chamber burner. For this, use copper tubing to send the flow from the one way valve to the combustion chamber. The final addition is the hardware for testing the exhaust, which has already been assembled here.
For this, an exhaust port in the chamber allows gases to flow into the copper tubing. This tubing goes into a three way valve. One output of the valve is tubing leading to a gas chromatograph.
The other output is tubing that goes to a 25 milliliter syringe used for drawing and redirecting exhaust. The setup can now be used for characterization. Before testing, prepare the syringe and three way valve.
First, push the syringe plunger in fully. Then ensure the three way valve is open on the exhaust port side. Move to the computer to start the fuel and air flowing and start data collection.
Initiate the air flow and the methane flow using a rich mixture for ease of ignition. Get a butane lighter and move to the end of the combustion chamber. When it is safe to do so, ignite the mixture.
Before proceeding, perform a visual check to make sure the flame has stabilize at the burner front. This flame is changing as the air flow is slowly adjusted to the desired value to avoid quenching the flame. Meanwhile, monitor the thermocouple temperatures and record the temperature data when the temperatures stabilize.
Now, go to the syringe connected to the three way valve. Pull the plunger back to extract residual gas and exhaust from the exhaust port. Use the three way valve to open the gas chromatograph side and close the exhaust port side.
Continue by pushing the plunger until all of the exhaust has been sent to the gas chromatograph. Return the valve to allow the syringe to extract more residual gas and exhaust. Continue extracting gas and injecting it into the gas chromatograph until all residual gases are removed.
When all the residual gases have bee removed, extract a final exhaust sample for analysis. Turn the three way valve and push the exhaust gas into the gas chromatograph. Perform the gas chromatograph analysis and record the data.
Continue by choosing another air flow rate and repeating the analysis for the new equivalents ratio. These results for chemical equilibrium analysis of methane and air combustion give the thermodynamic equilibrium predictions of the exhaust gas composition at different equivalents ratios. The left vertical axis is for the volume percentage of Nitrogen gas, plotted in black.
The right vertical axis gives the volume percentage scale for the exhaust products and other molecules. This analysis will not necessarily match the experiment data perfectly, but should indicate expected trends and magnitude of the results. Initial experiment data for the combustion chamber did not follow the trends expected from chemical equilibrium analysis.
For example, the molecular oxygen data in red, suggests a high concentration at high equivalence ratios compared to low equivalence ratios. This is a possible indication of incomplete mixing or back flow in the combustion chamber, which other data corroborated. When back flow is identified and prevented, the data were more consistent with the trends expected from chemical equilibrium analysis.
After watching this video, you should have a good understanding of how to characterize a combustion exhaust and to build a model combustion exhauster for fuel cell testing. Don't forget that working with combustion can be extremely hazardous and precautions such as flame arrestor, one way valves and other personal protective equipment should always be used while performing this procedure. Following this procedure, other methods, like integrating a fuel cell and a burner together can help answer additional questions about long term performance stability, Carbon deposition, and total system efficiency of the flame assisted fuel cell.
