Question

Problem 1 A diesel engine has a compression ratio r = 20 and uses air as the working fluid. The state of air at the beginning of the compression process is P1 = 95 kPa and T = 20°C. However, the isentropic expansion normally occuring between state 3 and state 4 is replaced by a polytropic process along which: Pul.35 = constant. The maximum temperature in the cycle is not to exceed 2200 K. In this analysis, the variation of the specific heats with temperature will be accounted for. Pu1.35 = constant Yout 1- Determine the thermal efficiency of the engine, nu 2- Calculate the mean effective pressure, MEP 3- Using Excel or Matlab, plot the net work output, mean effective pressure, and thermal efficiency as a function of the compression ratio over the range 14<r <24 4- Plot the T-s and P-v diagrams for the cycle when the compression ratio is 20

Answer 1

Ans - 3

p1	t1	v1	p2	t2	v2	p3	t3	v3	p4	v4	qin	win	wout	wnet	efficiency	mep	r
95	293	0.8851	3822.4	842.01	0.0632	3822.403	2200	0.1652	396.42	0.8851	1364.777	393.9331	801.5146	407.5814	29.8643285	495.91	14
95	293	0.8851	4210	865.57	0.059	4210.028	2200	0.15	383.24	0.8851	1341.098	410.838	834.8386	424.0007	31.6159277	513.26	15
95	293	0.8851	4608.1	888.21	0.0553	4608.135	2200	0.137	371.31	0.8851	1318.349	427.0794	865.0077	437.9284	33.217939	527.76	16
95	293	0.8851	5016.3	910.01	0.0521	5016.325	2200	0.1259	360.44	0.8851	1296.438	442.7225	892.4913	449.7688	34.6926638	539.92	17
95	293	0.8851	5434.2	931.06	0.0492	5434.238	2200	0.1162	350.49	0.8851	1275.287	457.8227	917.6663	459.8436	36.0580478	550.1	18
95	293	0.8851	5861.5	951.41	0.0466	5861.547	2200	0.1077	341.32	0.8851	1254.83	472.4275	940.8395	468.412	37.3287217	558.62	19
95	293	0.8851	6297.9	971.14	0.0443	6297.949	2200	0.1003	332.85	0.8851	1235.009	486.5781	962.2636	475.6855	38.5167522	565.72	20
95	293	0.8851	6743.2	990.27	0.0421	6743.171	2200	0.0936	324.99	0.8851	1215.775	500.3103	982.1485	481.8382	39.6321962	571.61	21
95	293	0.8851	7197	1008.9	0.0402	7196.957	2200	0.0877	317.67	0.8851	1197.082	513.6554	1000.671	487.0151	40.6835139	576.44	22
95	293	0.8851	7659.1	1027	0.0385	7659.072	2200	0.0824	310.82	0.8851	1178.893	526.6414	1017.979	491.3376	41.6778831	580.35	23
95	293	0.8851	8129.3	1044.6	0.0369	8129.296	2200	0.0777	304.41	0.8851	1161.172	539.2929	1034.201	494.9082	42.6214415	583.47	24

Net work output vs compression ratio Net work output (kl/Kg) 10 12 14 16 24 26 28 30 18 20 22 Compression ratio

Mean effective pressure vs compression ratio Mean effective pressure (kPa) 13 14 15 16 17 21 22 23 24 25 18 19 20 Compression ratio

Thermal efficieancy vs compression ratio Thermal efficiency (%) 13 14 15 16 17 21 22 23 24 25 18 19 20 Compression ratio

Ans - 4

T - S and P - v diagram for r=20

---P= constant to Wont ---8= constant & Win - Qout . Qin . pr 1:35 to Wort Poleh Mirะ * Dout