Summary

In this tutorial you used ANSYS FLUENT to model the transport, mixing, and reaction of chemical species. The reaction system was defined by using and modifying a mixture-material entry in the ANSYS FLUENT database. The procedures used here for simulation of hydrocarbon combustion can be applied to other reacting flow systems.

This exercise illustrated the important role of the mixture heat capacity in the prediction of flame temperature. The combustion modeling results are summarized in the following table.

	Peak Temp.	Exit Temp.	Exit Velocity
	( ${\rm K}$)	( ${\rm K}$)	( ${\rm m/s}$)
Constant $C_p$	3080	2241	4.03
Variable $C_p$	2300	1834	3.29

Note:   Some of the values in the table were not explicitly calculated during the tutorial.

The use of a constant $C_p$ results in a significant overprediction of the peak temperature. The average exit temperature and velocity are also overpredicted.

The variable $C_p$ solution produces dramatic improvements in the predicted results. Further improvements are possible by considering additional models and features available in ANSYS FLUENT, as discussed in the following section.

The NOx production in this case was dominated by the thermal NO mechanism. This mechanism is very sensitive to temperature. Every effort should be made to ensure that the temperature solution is not overpredicted, since this will lead to unrealistically high predicted levels of NO.