Question 13.12: The average power cylinder and compression cylinder pressure...
The average power cylinder and compression cylinder pressures for the early 1878 Brayton cycle engine shown in Figure 13.45 were p_1 = p_{4s} = 0.210 \text{ MPa} and p_{2s} = p_3 = 0.190 \text{ MPa}, respectively. For this engine, determine
a. The isentropic pressure ratio PR.
b. The isentropic compression ratio CR.
c. The Brayton cold ASC thermal efficiency.
Using the Brayton cycle diagram shown in Figure 13.44, we can carry out the following analysis.
a. The isentropic pressure ratio of a Brayton cycle engine is given by
\text{PR} = \frac{p_{4s}}{p_3} = \frac{0.210 \text{MPa}}{0.190 \text{MPa}} = 1.11
b. The isentropic compression ratio of a Brayton cycle engine is given by
\text{CR} = \text{(PR)}^{1/k} = (1.11)^{1/1.40} = 1.07
c. Equation (13.23) gives the Brayton cold ASC thermal efficiency as
(η_T)_{\substack{\text{Brayton}\\\text{cold ASC}\\}} = 1- \frac{T_3}{T_{4s}} =1 −\text{PR}^{(1−k)/k} = 1 – (1.11)^{(1−1.40)/1.40} = 0.0294 = 2.94\%
