(2) Determine the thermal efficiency and
compression ratio using Dieselcycle model
The Pv and Ts diagrams of the ideal Diesel cycle
are shown on the left. The
previous section, the properties
at the four states of an Otto cycle was determined. They are:
state 1: T_{1} = 15^{o}C,
P_{1} = 100 kPa (given)
State 2: T_{2} = 343.3^{o}C
State 3: T_{3} = 1800^{o}C
(given)
State 4: T_{4} = 695.7^{o}C
The heat input to the cycle is:
q_{in,Otto} = c_{v23} (T_{3} 
T_{2}) = 0.718(1800  343.3)
=
1045.9 kJ
In Diesel cycle, with the temperature limit is the same as In Otto cycle,
temperature at state 1 and state 3 are:
T_{1} = 15^{o}C
T_{3} = 1800^{o}C
Also, heat input is the same as in the ideal Otto cycle. In Diesel cycle,
heat is input from the constant pressure cycle.
q_{in,Diesel} = c_{P23} (T_{3} 
T_{2}) = 1.005 (1800  T_{2})
=
1045.9 kJ
The temperature at state 2 can be determined from the above expression.
That is,
T_{2} = 759.3^{o}C
= 1032.3 K
The thermal efficiency of the ideal Diesel cycle is:
where r is the compression ratio and r_{c} is the cutoff ratio.
r = v_{1}/v_{2}
r_{c} = v_{3}/v_{2}
In Diesel cycle, process 12 is isentropic compression process. It gives,
