# Plotting performance vs inlet temp for jet engine and measuring performance as dh as shown. What am I doing wrong?

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Nick Olibrice on 21 Jul 2022
Answered: Dyuman Joshi on 21 Jul 2022
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P1 = 101 ;%pressure in kpa
T1 = 298;%temperature in kelvin
n = 1.4;
Cp = 1.004;
Cv = 0.717;
R = 0.287 ;%gas constant in kJ/kg*k
v1 = R * T1/P1 ;%specific volume in m^3/kg
IsentConst1 = P1 * v1^n;
P2 = 28 * P1 ;%outlet compressor/inlet combuster pressure
T2 = ((P2 / P1)^((n-1)/n)) * (T1);
v2 = (R * T2) / P2;
Wc = Cp * (T2 - T1);
P3 = P2;
T3 = 2828 ;
v3 = R * T3 / P3;
IsentConst2 = P3 * v3^n;
Wt = Wc;
T4 = (-Wt / Cp) + T3;
v4 = ((P3 * v3^n)/(R * T4))^(1/(n-1));
P4 = R * T4 /v4;
IsentConst3 = P4 * v4^n;
u4 = Cv * T4;
h4 = u4 + P4 * v4;
P5 = P1;
v5 = (P4 *v4^n / P5)^(1/n);
T5 = P5 *v5 / R;
u5 = Cv * T5;
h5 = u5 + P5 * v5;
dh = (h5 - h4)*1000;%performance parameter
Ti = 298:0.001:900
Ti = 1×602001
298.0000 298.0010 298.0020 298.0030 298.0040 298.0050 298.0060 298.0070 298.0080 298.0090 298.0100 298.0110 298.0120 298.0130 298.0140 298.0150 298.0160 298.0170 298.0180 298.0190 298.0200 298.0210 298.0220 298.0230 298.0240 298.0250 298.0260 298.0270 298.0280 298.0290
for i = length(Ti)
result(i) = Cp * Ti(i)
end
result = 1×602001
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Ti = 298:0.001:900
Ti = 1×602001
298.0000 298.0010 298.0020 298.0030 298.0040 298.0050 298.0060 298.0070 298.0080 298.0090 298.0100 298.0110 298.0120 298.0130 298.0140 298.0150 298.0160 298.0170 298.0180 298.0190 298.0200 298.0210 298.0220 298.0230 298.0240 298.0250 298.0260 298.0270 298.0280 298.0290
plot(Ti, result) Dyuman Joshi on 21 Jul 2022
The for loop indexing is incorrect
close all
clear all
P1 = 101 ;%pressure in kpa
T1 = 298;%temperature in kelvin
n = 1.4;
Cp = 1.004;
Cv = 0.717;
R = 0.287 ;%gas constant in kJ/kg*k
v1 = R * T1/P1 ;%specific volume in m^3/kg
IsentConst1 = P1 * v1^n;
P2 = 28 * P1 ;%outlet compressor/inlet combuster pressure
T2 = ((P2 / P1)^((n-1)/n)) * (T1);
v2 = (R * T2) / P2;
Wc = Cp * (T2 - T1);
P3 = P2;
T3 = 2828 ;
v3 = R * T3 / P3;
IsentConst2 = P3 * v3^n;
Wt = Wc;
T4 = (-Wt / Cp) + T3;
v4 = ((P3 * v3^n)/(R * T4))^(1/(n-1));
P4 = R * T4 /v4;
IsentConst3 = P4 * v4^n;
u4 = Cv * T4;
h4 = u4 + P4 * v4;
P5 = P1;
v5 = (P4 *v4^n / P5)^(1/n);
T5 = P5 *v5 / R;
u5 = Cv * T5;
h5 = u5 + P5 * v5;
dh = (h5 - h4)*1000;%performance parameter
Ti = 298:0.001:900;
for i = 1:length(Ti)
result(i) = Cp*Ti(i);
end
plot(Ti, result)
xlim([250 1e3]) Alternatively you can use
plot(Ti,Cp*Ti)