Question

Using EES (or other) software, determine the effect of the amount of air on the adiabatic flame temperature of liquid octane \(\left(\mathrm{C}_{8} \mathrm{H}_{18}\right)\). Assume both the air and the octane are initially at \(25^{\circ} \mathrm{C}\). Determine the adiabatic flame temperature for 75,90,100,120,150,200,300 \(500,\) and 800 percent theoretical air. Assume the hydrogen in the fuel always burns \(\mathrm{H}_{2} \mathrm{O}\) and the carbon \(\mathrm{CO}_{2}\), except when there is a deficiency of air. In the latter case, assume that part of the carbon forms CO. Plot the adiabatic flame temperature against the percent theoretical air, and discuss the results.

Short answer

Based on the step-by-step solution provided, here is the short answer: To analyze the adiabatic flame temperature of liquid octane at various percentages of theoretical air, we first calculated the stoichiometric air-fuel ratio using the balanced combustion equation. Then, we used EES (or other software) to compute the adiabatic flame temperatures for the given percentages of theoretical air (75, 90, 100, 120, 150, 200, 300, 500, and 800). After obtaining the adiabatic flame temperatures, we plotted them against the percent theoretical air to visualize the relationship. The results showed that the adiabatic flame temperature varied with the change in percent theoretical air. In cases of air deficiency, the formation of CO instead of CO2 had an impact on the flame temperature.

Step-by-step solution

Understand the problem and gather required data

We want to find the adiabatic flame temperature of liquid octane for various percentages of theoretical air. The given values are: 1. Both air and octane have an initial temperature of 25°C. 2. The hydrogen in the fuel always forms H2O and the carbon forms CO2, except when there is a deficiency of air. In that case, part of the carbon forms CO.

Compute the stoichiometric air-fuel ratio

For determining the theoretical air required, we need to compute the stoichiometric air-fuel ratio. The balanced combustion equation for octane can be written as: \(C_8H_{18} + 12.5 \mathrm{(O}_{2}\mathrm{+}3.76\mathrm{N}_{2}) \rightarrow 8\mathrm{CO}_{2} + 9\mathrm{H}_{2}\mathrm{O} + 47\mathrm{N}_{2}\) The stoichiometric air-fuel ratio can be calculated as follows: \(\frac{12.5 \times (molecular \ weight \ of \ air)}{molecular \ weight \ of \ C_8H_{18}}\)

Determine the percent theoretical air

The percent theoretical air is given in the problem (75, 90, 100, 120, 150, 200, 300, 500, and 800).

Use EES (or other software) to compute the adiabatic flame temperatures

Input the initial conditions, balanced combustion equation, and stoichiometric air-fuel ratio into EES (or other software). Next, input the various percentages of theoretical air to compute the adiabatic flame temperature for each case.

Generate a plot of adiabatic flame temperature versus percent theoretical air

Using the adiabatic flame temperatures obtained in step 4, create a plot of adiabatic flame temperature versus the percent theoretical air. This will help to visualize the relationship between these two variables and make it easier to discuss the results.

Discuss the results

Analyze the plot obtained in Step 5 and discuss the results. Compare the adiabatic flame temperatures at different percentages of theoretical air. Explain how the air affects the adiabatic flame temperature and why the temperature changes with the variation in percent theoretical air. In cases with air deficiency, discuss the formation of CO instead of CO2 and its impact on flame temperature.