Otto cycle analysis worksheet.ppt - University of Alabama

Otto Cycle Calculation

Problem statement:

The compression ratio of an air-standard Otto cycle is 9.5. Prior to the isentropic compression process, the air is at 100kPa, 35oC, and 600 cm3. The temperature at the end of the isentropic expansion process is 800 K. Determine the highest temperature and pressure in the cycle; the amount of heat supplied per cycle (in kJ); the thermal efficiency; and the mean effective pressure. Perform the calculations assuming 1) cold air standard conditions and 2) air standard conditions.

p Given:

Otto cycle, r = 9.5

State1: p1 = 100 kPa; T1 = 35oC; V1 = 600 cc

State 4: T4 = 800 K

State 3 State 2

TDC

State 4

State 1

v BDC

Assumptions: Method 1) cold air standard Method 2) air standard

To find: a) Tmax, Pmax

b) QH (kJ) c) th

d) MEP

Solution: System mass:

p

State 3

State 2

State 4

State 1

v

Method 1) Cold air standard Isentropic process(1 ? 2), ideal gas:

Isentropic process(3 ? 4), ideal gas:

p

State 3

State 2

State 4

State 1

v Note that Tmax = T3 = 1970K ?

pmax = ? kPa

Heat transferred:

p

State 3

First law:

U3 -U 2 = Q2-3 -W2-3

State 2

State 4

State 1

v but,

and,

QH = ?

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