A Project for Thermodynamics II. Entitled

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1 A Project for Thermodynamics II Entitled Determination of the Effect of Equivalence Ratio and Pressure on the Adiabatic Flame Temperature and Reaction "Completeness" during 75% Propane and 25% Methane Mixture Combustion Prepared by Brad Schaffer Department of Mechanical Engineering and Mechanics Drexel University August 24, 2004

2 Schaffer 2 Table of Contents: Abstract 3 Introduction..4 Methods 5 Results..7 Discussion/Conclusion.9 Appendix A 10 Appendix B 12 Appendix C 14 Appendix D 15

3 Schaffer 3 Abstract: This report explored the effects of equivalence ratio and pressure on the adiabatic flame temperature and the completeness of combustion for a mixture of twenty-five percent methane and seventy-five percent propane during its combustion with air. Completeness was measured on a percentage scale by comparing actual carbon dioxide produced with that produced during stoichiometric combustion. Any value above ninetyfive percent was considered to be complete. For the given combustion process, it was found that as pressure increased, both completeness and adiabatic flame temperature also increased. It was also found that as the equivalence ratio increased, the completeness of combustion steadily declined. However, the adiabatic flame temperature peaked when the equivalence ratio was at an intermediate value between 1.01 and 1.10 for the tested pressures of 0.01 to 1000 atm. The maximum obtainable adiabatic flame temperature for the tested values was K with a completeness of percent. This occurred at a pressure of 1000 atm and an equivalence ratio of 1.01.

4 Schaffer 4 Introduction: The combustion of hydrocarbons plays a crucial role in many aspects of our lives. Two of the largest industries that utilize the combustion hydrocarbons are the power generation and the automotive industries. Since hydrocarbon fuels are scarce resources, they must be utilized wisely. This creates the need for an understanding of how combustion processes work and a need to optimize combustion processes. The objective for this experiment was to find how equivalence ratio and pressure affect adiabatic flame temperature and completeness of combustion for the burning of a mixture of 25% CH 4 and 75% C 3 H 8 with air at the standard reference state. From these results, the optimized equivalence ratio and pressure were to be determined. The experiment s basis was from the first law of thermodynamics, conservation of energy, and the second law of thermodynamics which deals with the directionality of a reaction. Since the given system did not involve any work or heat transfer, only the change in chemical energy of the system had to be analyzed. This was done using the program STANJAN. Given a chemical equation and its reactant information, STANJAN produces the equilibrium composition and the product temperature.

5 Schaffer 5 Methods: The first step was to produce a balanced chemical equation for a perfect burn: ( ) 0.25CH C H O N 2.5CO + 3.5H O N Evaluating reactants for all equivalence ratios: CH C3H 8 + ( O N2) er er O 2 N This provided all of the necessary reactant information on a molar basis. STANJAN was then used to calculate the enthalpy of the reactants at the standard reference state.

6 Schaffer 6 er h , , , , , , , , , , , , , , , , , ,870 Finally, all reactant data was entered into STANJAN which was then used to calculate adiabatic flame temperature and the equilibrium composition for equivalence ratios ranging from 0.35 to 2.00 and pressures ranging from 0.01 atm to 1000 atm. The output data from STANJAN had two output values of interest. The first was the temperature. This temperature represented the adiabatic flame temperature since the enthalpy of the reactants, calculated in the first step, was used as the enthalpy value for calculating the products. The second output of interest was the equilibrium composition of the product. In particular, the molar amount of CO 2 was of interest because this allowed for the measurement of completeness. Completeness was measured on a percentage scale by comparing actual carbon dioxide produced with that produced during stoichiometric combustion. Any value greater than 95% was considered complete for this experiment

7 Schaffer 7 Results: AFT vs. Equivalence Ratio vs. Pressure K er atm The results showed several important correlations between adiabatic flame temperature, pressure, completeness, and equivalence ratio. The above graph shows how the equivalence ratio and pressure affect the adiabatic flame temperature. As pressure increased, the AFT also increased for all equivalency ratios. It can also be seen that the maximum obtainable AFT increases as pressure increases (please see Appendix D). When analyzing the affects of the equivalency ratio, it is seen that a slightly rich fuel air mixture produces the highest AFT. The lower the pressure the richer the mixture must be to reach the peak AFT (please see appendix C).

8 Schaffer 8 Percent Completeness er atm As the pressure increased, the completeness of combustion also increased in all cases. However, as the equivalence ratio increases, the completeness of combustion fell. This can be seen in the above graph. At equivalence ratios of 0.50 and under, the completeness of combustion was above 99.98% in all cases (pleases see appendix B). However, in these low er ranges, the AFT was only approximately 50% of the maximum AFT.

9 Schaffer 9 Discussion/Conclusion: For a given range of pressures and equivalency ratios, the adiabatic flame temperature and completeness of combustion were successfully calculated for the combustion of a methane and propane mixture. The data provided useful insight to the behavior of this combustion when two major parameters, pressure and equivalency ratio, were adjusted. Further research could include increasing the pressure range and conducting research on optimizing the ratio of methane to propane.

10 Schaffer 10 Appendix A: AFT vs. Equivalence Ratio vs. Pressure Data AFT vs. Equivalence Ratio vs. Pressure K er atm

11 AFT Pressure (atm) er Schaffer 11

12 Schaffer 12 Appendix B: Percent Completeness Data Percent Completeness er Pressure (atm)

13 Percent Completeness Pressure (atm) er Schaffer 13

14 Schaffer 14 Appendix C: Pressure vs. Optimum Equivalency Ratio Pressure vs. Optimum er er atm *Optimum er is the equivalence ratio at which the maximum AFT occurred.

15 Schaffer 15 Appendix D: Pressure vs. Maximum Adiabatic Flame Temperature Pressure vs. Max AFT K atm

Reacting Gas Mixtures

Reacting Gas Mixtures Reading Problems 15-1 15-7 15-21, 15-32, 15-51, 15-61, 15-74 15-83, 15-91, 15-93, 15-98 Introduction thermodynamic analysis of reactive mixtures is primarily an extension of the principles