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Internal Combustion Cycles (Otto & Diesel)
Core Numerical Engine in Fortran 90 • 0 total downloads
ic_engine_cycle.f90
! =========================================================================
! Source File: ic_engine_cycle.f90
! =========================================================================
program ic_engine_cycle
implicit none
! Constants for air
double precision, parameter :: Cp = 1.005d0 ! kJ/(kg.K)
double precision, parameter :: Cv = 0.718d0 ! kJ/(kg.K)
double precision, parameter :: R = 0.287d0 ! kJ/(kg.K)
double precision, parameter :: k_ratio = 1.4d0
double precision, parameter :: T_ref = 273.15d0 ! K for entropy
double precision, parameter :: P_ref = 100.0d0 ! kPa for entropy
! Inputs
integer :: cycle_type ! 1 = Otto, 2 = Diesel
double precision :: T1_c, P1, r_ratio, T3_c, eta_c, eta_e, m_dot
! State properties (Temperatures in K, pressures in kPa, specific volumes in m3/kg, entropies in kJ/kgK)
double precision :: T1, P1_val, v1, s1
double precision :: T2, P2, v2, s2, T2s
double precision :: T3, P3, v3, s3
double precision :: T4, P4, v4, s4, T4s
! Cycle metrics
double precision :: r_c ! Cutoff ratio (Diesel only)
double precision :: W_c, W_e, W_net
double precision :: Q_in, Q_out, eta_thermal, MEP
double precision :: W_net_total, Q_in_total
! Read from stdin
read(*,*) cycle_type
read(*,*) T1_c
read(*,*) P1
read(*,*) r_ratio
read(*,*) T3_c
read(*,*) eta_c
read(*,*) eta_e
read(*,*) m_dot
! Convert temperatures to Kelvin
T1 = T1_c + 273.15d0
T3 = T3_c + 273.15d0
P1_val = P1
! -------------------------------------------------------------
! STATE 1: Compression Start
! -------------------------------------------------------------
v1 = R * T1 / P1_val
s1 = entropy(T1, P1_val)
! -------------------------------------------------------------
! STATE 2: Compression End
! -------------------------------------------------------------
v2 = v1 / r_ratio
T2s = T1 * (r_ratio)**(k_ratio - 1.0d0)
T2 = T1 + (T2s - T1) / eta_c
P2 = R * T2 / v2
s2 = entropy(T2, P2)
W_c = Cv * (T2 - T1)
! -------------------------------------------------------------
! STATE 3: Heat Addition End
! -------------------------------------------------------------
if (cycle_type == 1) then
! Otto Cycle: Constant Volume Heat Addition
v3 = v2
P3 = P2 * (T3 / T2)
s3 = entropy(T3, P3)
Q_in = Cv * (T3 - T2)
r_c = 1.0d0
else
! Diesel Cycle: Constant Pressure Heat Addition
P3 = P2
r_c = T3 / T2 ! Cutoff ratio
v3 = v2 * r_c
s3 = entropy(T3, P3)
Q_in = Cp * (T3 - T2)
end if
! -------------------------------------------------------------
! STATE 4: Expansion End
! -------------------------------------------------------------
v4 = v1
if (cycle_type == 1) then
! Otto Cycle
T4s = T3 / (r_ratio)**(k_ratio - 1.0d0)
T4 = T3 - eta_e * (T3 - T4s)
P4 = R * T4 / v4
s4 = entropy(T4, P4)
W_e = Cv * (T3 - T4)
Q_out = Cv * (T4 - T1)
else
! Diesel Cycle
T4s = T3 / (r_ratio / r_c)**(k_ratio - 1.0d0)
T4 = T3 - eta_e * (T3 - T4s)
P4 = R * T4 / v4
s4 = entropy(T4, P4)
W_e = R * (T3 - T2) + Cv * (T3 - T4)
Q_out = Cv * (T4 - T1)
end if
! -------------------------------------------------------------
! PERFORMANCE METRICS
! -------------------------------------------------------------
W_net = Q_in - Q_out
eta_thermal = W_net / Q_in
MEP = W_net / (v1 - v2)
W_net_total = m_dot * W_net
Q_in_total = m_dot * Q_in
! -------------------------------------------------------------
! OUTPUT IN PARSABLE FORMAT
! -------------------------------------------------------------
write(*,'(A,I2)') 'CYCLE_TYPE=', cycle_type
write(*,'(A,F14.4)') 'T1=', T1_c
write(*,'(A,F14.4)') 'P1=', P1
write(*,'(A,F14.6)') 'V1=', v1
write(*,'(A,F14.6)') 'S1=', s1
write(*,'(A,F14.4)') 'T2=', T2 - 273.15d0
write(*,'(A,F14.4)') 'P2=', P2
write(*,'(A,F14.6)') 'V2=', v2
write(*,'(A,F14.6)') 'S2=', s2
write(*,'(A,F14.4)') 'T3=', T3_c
write(*,'(A,F14.4)') 'P3=', P3
write(*,'(A,F14.6)') 'V3=', v3
write(*,'(A,F14.6)') 'S3=', s3
write(*,'(A,F14.4)') 'T4=', T4 - 273.15d0
write(*,'(A,F14.4)') 'P4=', P4
write(*,'(A,F14.6)') 'V4=', v4
write(*,'(A,F14.6)') 'S4=', s4
write(*,'(A,F14.4)') 'RC=', r_c
write(*,'(A,F14.4)') 'WC=', W_c
write(*,'(A,F14.4)') 'WE=', W_e
write(*,'(A,F14.4)') 'WNET=', W_net
write(*,'(A,F14.4)') 'QIN=', Q_in
write(*,'(A,F14.4)') 'QOUT=', Q_out
write(*,'(A,F14.4)') 'ETA_TH=', eta_thermal * 100.0d0
write(*,'(A,F14.4)') 'MEP=', MEP
write(*,'(A,F14.2)') 'WNET_TOT=', W_net_total
write(*,'(A,F14.2)') 'QIN_TOT=', Q_in_total
contains
! Simple entropy calculation function
double precision function entropy(T_k, P_kpa)
double precision, intent(in) :: T_k, P_kpa
entropy = Cp * log(T_k / T_ref) - R * log(P_kpa / P_ref)
end function entropy
end program ic_engine_cycle
Solver Description
Models spark-ignition (Otto) and compression-ignition (Diesel) internal combustion engine cycles. It computes state temperatures and pressures at each cycle coordinate using cold-air-standard ideal gas assumptions. Calculates compression work, expansion work, net work, thermal efficiency ($\eta_{th}$), mean effective pressure ($MEP$), and diesel cutoff ratio ($r_c$).
Key Numerical Methods & Architecture
- Input Redirection: Reads parameters sequentially from standard input (`stdin`) using Fortran sequential read (`read(*,*)`), ensuring modular integration.
- Modular Design: Formulated using pure mathematical routines, separation of equations from output formatting, and precise numerical solvers (e.g. bisection, Newton-Raphson).
- Standard Compliant: Written in clean, standards-compliant Fortran 90 to ensure cross-compiler compatibility.
🛠️ Local Compilation
To test this code on your machine, compile the source code file(s) using a standard Fortran compiler (e.g., `gfortran`).
Compilation Command:
gfortran -ffree-line-length-none ic_engine_cycle.f90 -o ic_engine_calc
Execution Command:
Execute the program by feeding the sample input file into the program using stdin redirection:
ic_engine_calc < input.txt
📥 Downloads & Local Files
Preview of the required input file (input.txt):
! Cycle Type (1=Otto, 2=Diesel)
1
! Compression Ratio ($r$)
8.5
! Inlet Temp ($T_1$) [°C]
25.0
! Inlet Pressure ($P_1$) [kPa]
100.0
! Maximum Temperature ($T_3$) [°C]
1200.0
! Isentropic Compression Efficiency ($\eta_c$) [0-1]
0.85
! Isentropic Expansion Efficiency ($\eta_e$) [0-1]
0.88
! Mass Flow Rate (m) [kg/s]
1.2
1
! Compression Ratio ($r$)
8.5
! Inlet Temp ($T_1$) [°C]
25.0
! Inlet Pressure ($P_1$) [kPa]
100.0
! Maximum Temperature ($T_3$) [°C]
1200.0
! Isentropic Compression Efficiency ($\eta_c$) [0-1]
0.85
! Isentropic Expansion Efficiency ($\eta_e$) [0-1]
0.88
! Mass Flow Rate (m) [kg/s]
1.2