Combustion Systems and Entropy Generation — Lesson 4

This lesson covers the detailed analysis of combustion systems, focusing on the calculation of entropy generation in the universe due to chemical reactions in a combustor steady flow situation. It explains the concept of blended fuels, their calorific value, and the implications of using fuels like ethanol. The lesson also introduces the concept of adiabatic flame temperature, which represents the theoretical maximum product temperature that can be realized at the combustor exit. It further discusses the application of the second law of thermodynamics to combustion systems, explaining how to calculate the entropy generation in a control volume. The lesson uses the example of a gas turbine combustor to illustrate these concepts.

Video Highlights

00:22 - Explanation of why gasoline is blended with ethanol
06:57 - Calculating the adiabatic flame temperature for methane
13:05 - Calculating the absolute entropy of a substance
18:58 - Second law analysis of combustion systems

Key Takeaways

- Blended fuels like gasoline E10, a blend of 90% n-octane and 10% ethanol, are becoming popular due to their potential to reduce dependence on oil and emissions.
- The lower calorific value of a fuel can be determined using given parameters like enthalpy of formation and specific gravity.
- The adiabatic flame temperature is the maximum product temperature that can be realized at the combustor exit.
- The second law of thermodynamics can be applied to combustion systems to calculate entropy generation.
- The absolute entropy of substances at the reference temperature of 298 Kelvin and reference pressure of one atmosphere can be used to evaluate entropy at any other pressure and temperature.