-// Module: 10520c.c
-// Author: Phil Schubert
-// Date started: 12/03/99
-// Purpose: Models a Continental IO-520-M Engine
-// Called by: FGSimExec
-//
-// Copyright (C) 1999 Philip L. Schubert (philings@ozemail.com.au)
+// IO360.cxx - a piston engine model currently for the IO360 engine fitted to the C172
+// but with the potential to model other naturally aspirated piston engines
+// given appropriate config input.
+//
+// Written by David Luff, started 2000.
+// Based on code by Phil Schubert, started 1999.
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License as
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
-// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
-// 02111-1307, USA.
-//
-// Further information about the GNU General Public License can also
-// be found on the world wide web at http://www.gnu.org.
-//
-// FUNCTIONAL DESCRIPTION
-// ------------------------------------------------------------------------
-// Models a Continental IO-520-M engine. This engine is used in Cessna
-// 210, 310, Beechcraft Bonaza and Baron C55. The equations used below
-// were determined by a first and second order curve fits using Excel.
-// The data is from the Cessna Aircraft Corporations Engine and Flight
-// Computer for C310. Part Number D3500-13
-//
-// ARGUMENTS
-// ------------------------------------------------------------------------
-//
-//
-// HISTORY
-// ------------------------------------------------------------------------
-// 12/03/99 PLS Created
-// 07/03/99 PLS Added Calculation of Density, and Prop_Torque
-// 07/03/99 PLS Restructered Variables to allow easier implementation
-// of Classes
-// 15/03/99 PLS Added Oil Pressure, Oil Temperature and CH Temp
-// ------------------------------------------------------------------------
-// INCLUDES
-// ------------------------------------------------------------------------
-//
-//
-/////////////////////////////////////////////////////////////////////
-//
-// Modified by Dave Luff (david.luff@nottingham.ac.uk) September 2000
-//
-// Altered manifold pressure range to add a minimum value at idle to simulate the throttle stop / idle bypass valve,
-// and to reduce the maximum value whilst the engine is running to slightly below ambient to account for CdA losses across the throttle
-//
-// Altered it a bit to model an IO360 from C172 - 360 cubic inches, 180 HP max, fixed pitch prop
-// Added a simple fixed pitch prop model by Nev Harbor - this is not intended as a final model but simply a hack to get it running for now
-// I used Phil's ManXRPM correlation for power rather than do a new one for the C172 for now, but altered it a bit to reduce power at the low end
-//
-// Added EGT model based on combustion efficiency and an energy balance with the exhaust gases
-//
-// Added a mixture - power correlation based on a curve in the IO360 operating manual
-//
-// I've tried to match the prop and engine model to give roughly 600 RPM idle and 180 HP at 2700 RPM
-// but it is by no means currently at a completed stage - DCL 15/9/00
-//
-// DCL 28/09/00 - Added estimate of engine and prop inertia and changed engine speed calculation to be calculated from Angular acceleration = Torque / Inertia.
-// Requires a timestep to be passed to FGNewEngine::init and currently assumes this timestep does not change.
-// Could easily be altered to pass a variable timestep to FGNewEngine::update every step instead if required.
-//
-// DCL 27/10/00 - Added first stab at cylinder head temperature model
-// See the comment block in the code for details
-//
-// DCL 02/11/00 - Modified EGT code to reduce values to those more representative of a sensor downstream
-//
-// DCL 02/02/01 - Changed the prop model to one based on efficiency and co-efficient of power curves from McCormick instead of the
-// blade element method we were using previously. This works much better, and is similar to how Jon is doing it in JSBSim.
-//
-// DCL 08/02/01 - Overhauled fuel consumption rate support.
-//
-// DCL 22/03/01 - Added input of actual air pressure and temperature (and hence density) to the model. Hence the power correlation
-// with pressure height and temperature is no longer required since the power is based on the actual manifold pressure.
-//
-// DCL 22/03/01 - based on Riley's post on the list (25 rpm gain at 1000 rpm as lever is pulled out from full rich)
-// I have reduced the sea level full rich mixture to thi = 1.3
-//////////////////////////////////////////////////////////////////////
+// Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
#include <simgear/compiler.h>
-#include <iostream>
-#include <fstream>
#include <math.h>
+#include STL_FSTREAM
+#include STL_IOSTREAM
+
+#if !defined(SG_HAVE_NATIVE_SGI_COMPILERS)
+SG_USING_STD(cout);
+#endif
+
#include "IO360.hxx"
+#include "LaRCsim/ls_constants.h"
-FG_USING_STD(cout);
+#include <Main/fg_props.hxx>
-// Static utility functions
+//*************************************************************************************
+// Initialise the engine model
+void FGNewEngine::init(double dt) {
-// Calculate Density Ratio
-static float Density_Ratio ( float x )
-{
- float y ;
- y = ((3E-10 * x * x) - (3E-05 * x) + 0.9998);
- return(y);
-}
+ // These constants should probably be moved eventually
+ CONVERT_CUBIC_INCHES_TO_METERS_CUBED = 1.638706e-5;
+ CONVERT_HP_TO_WATTS = 745.6999;
+ // Properties of working fluids
+ Cp_air = 1005; // J/KgK
+ Cp_fuel = 1700; // J/KgK
+ calorific_value_fuel = 47.3e6; // W/Kg Note that this is only an approximate value
+ rho_fuel = 800; // kg/m^3 - an estimate for now
+ R_air = 287.3;
-// Calculate Air Density - Rho, using the ideal gas equation
-// Takes and returns SI values
-static float Density ( float temperature, float pressure )
-{
- // rho = P / RT
- // R = 287.3 for air
+ // environment inputs
+ p_amb_sea_level = 101325; // Pascals
+
+ // Control inputs - ARE THESE NEEDED HERE???
+ Throttle_Lever_Pos = 75;
+ Propeller_Lever_Pos = 75;
+ Mixture_Lever_Pos = 100;
+
+ //misc
+ IAS = 0;
+ time_step = dt;
+
+ // Engine Specific Variables that should be read in from a config file
+ MaxHP = 200; //Lycoming IO360 -A-C-D series
+// MaxHP = 180; //Current Lycoming IO360 ?
+// displacement = 520; //Continental IO520-M
+ displacement = 360; //Lycoming IO360
+ displacement_SI = displacement * CONVERT_CUBIC_INCHES_TO_METERS_CUBED;
+ engine_inertia = 0.2; //kgm^2 - value taken from a popular family saloon car engine - need to find an aeroengine value !!!!!
+ prop_inertia = 0.05; //kgm^2 - this value is a total guess - dcl
+ Max_Fuel_Flow = 130; // Units??? Do we need this variable any more??
+
+ // Engine specific variables that maybe should be read in from config but are pretty generic and won't vary much for a naturally aspirated piston engine.
+ Max_Manifold_Pressure = 28.50; //Inches Hg. An approximation - should be able to find it in the engine performance data
+ Min_Manifold_Pressure = 6.5; //Inches Hg. This is a guess corresponding to approx 0.24 bar MAP (7 in Hg) - need to find some proper data for this
+ Max_RPM = 2700;
+ Min_RPM = 600; //Recommended idle from Continental data sheet
+ Mag_Derate_Percent = 5;
+ Gear_Ratio = 1;
+ n_R = 2; // Number of crank revolutions per power cycle - 2 for a 4 stroke engine.
+
+ // Various bits of housekeeping describing the engines initial state.
+ running = false;
+ cranking = false;
+ crank_counter = false;
+ starter = false;
- float R = 287.3;
- float rho = pressure / (R * temperature);
- return(rho);
+ // Initialise Engine Variables used by this instance
+ if(running)
+ RPM = 600;
+ else
+ RPM = 0;
+ Percentage_Power = 0;
+ Manifold_Pressure = 29.96; // Inches
+ Fuel_Flow_gals_hr = 0;
+// Torque = 0;
+ Torque_SI = 0;
+ CHT = 298.0; //deg Kelvin
+ CHT_degF = (CHT_degF * 1.8) - 459.67; //deg Fahrenheit
+ Mixture = 14;
+ Oil_Pressure = 0; // PSI
+ Oil_Temp = 85; // Deg C
+ current_oil_temp = 298.0; //deg Kelvin
+ /**** one of these is superfluous !!!!***/
+ HP = 0;
+ RPS = 0;
+ Torque_Imbalance = 0;
+
+ // Initialise Propellor Variables used by this instance
+ FGProp1_RPS = 0;
+ // Hardcode propellor for now - the following two should be read from config eventually
+ prop_diameter = 1.8; // meters
+ blade_angle = 23.0; // degrees
}
+//*****************************************************************************
+// update the engine model based on current control positions
+void FGNewEngine::update() {
-// Calculate Speed in FPS given Knots CAS
-static float IAS_to_FPS (float x)
-{
- float y;
- y = x * 1.68888888;
- return y;
+/*
+ // Hack for testing - should output every 5 seconds
+ static int count1 = 0;
+ if(count1 == 0) {
+// cout << "P_atmos = " << p_amb << " T_atmos = " << T_amb << '\n';
+// cout << "Manifold pressure = " << Manifold_Pressure << " True_Manifold_Pressure = " << True_Manifold_Pressure << '\n';
+// cout << "p_amb_sea_level = " << p_amb_sea_level << '\n';
+// cout << "equivalence_ratio = " << equivalence_ratio << '\n';
+// cout << "combustion_efficiency = " << combustion_efficiency << '\n';
+// cout << "AFR = " << 14.7 / equivalence_ratio << '\n';
+// cout << "Mixture lever = " << Mixture_Lever_Pos << '\n';
+// cout << "n = " << RPM << " rpm\n";
+// cout << "T_amb = " << T_amb << '\n';
+// cout << "running = " << running << '\n';
+ cout << "fuel = " << fgGetFloat("/consumables/fuel/tank[0]/level-gal_us") << '\n';
+// cout << "Percentage_Power = " << Percentage_Power << '\n';
+// cout << "current_oil_temp = " << current_oil_temp << '\n';
+ cout << "EGT = " << EGT << '\n';
+ }
+ count1++;
+ if(count1 == 100)
+ count1 = 0;
+*/
+
+ // Check parameters that may alter the operating state of the engine.
+ // (spark, fuel, starter motor etc)
+
+ // Check for spark
+ bool Magneto_Left = false;
+ bool Magneto_Right = false;
+ // Magneto positions:
+ // 0 -> off
+ // 1 -> left only
+ // 2 -> right only
+ // 3 -> both
+ if(mag_pos != 0) {
+ spark = true;
+ } else {
+ spark = false;
+ } // neglects battery voltage, master on switch, etc for now.
+ if((mag_pos == 1) || (mag_pos > 2))
+ Magneto_Left = true;
+ if(mag_pos > 1)
+ Magneto_Right = true;
+
+ // crude check for fuel
+ if((fgGetFloat("/consumables/fuel/tank[0]/level-gal_us") > 0) || (fgGetFloat("/consumables/fuel/tank[1]/level-gal_us") > 0)) {
+ fuel = true;
+ } else {
+ fuel = false;
+ } // Need to make this better, eg position of fuel selector switch.
+
+ // Check if we are turning the starter motor
+ if(cranking != starter) {
+ // This check saves .../cranking from getting updated every loop - they only update when changed.
+ cranking = starter;
+ crank_counter = 0;
+ }
+ // Note that although /engines/engine[0]/starter and /engines/engine[0]/cranking might appear to be duplication it is
+ // not since the starter may be engaged with the battery voltage too low for cranking to occur (or perhaps the master
+ // switch just left off) and the sound manager will read .../cranking to determine wether to play a cranking sound.
+ // For now though none of that is implemented so cranking can be set equal to .../starter without further checks.
+
+// int Alternate_Air_Pos =0; // Off = 0. Reduces power by 3 % for same throttle setting
+ // DCL - don't know what this Alternate_Air_Pos is - this is a leftover from the Schubert code.
+
+ //Check mode of engine operation
+ if(cranking) {
+ crank_counter++;
+ if(RPM <= 480) {
+ RPM += 100;
+ if(RPM > 480)
+ RPM = 480;
+ } else {
+ // consider making a horrible noise if the starter is engaged with the engine running
+ }
+ }
+ if((!running) && (spark) && (fuel) && (crank_counter > 120)) {
+ // start the engine if revs high enough
+ if(RPM > 450) {
+ // For now just instantaneously start but later we should maybe crank for a bit
+ running = true;
+// RPM = 600;
+ }
+ }
+ if( (running) && ((!spark)||(!fuel)) ) {
+ // Cut the engine
+ // note that we only cut the power - the engine may continue to spin if the prop is in a moving airstream
+ running = false;
+ }
+
+ // Now we've ascertained whether the engine is running or not we can start to do the engine calculations 'proper'
+
+ // Calculate Sea Level Manifold Pressure
+ Manifold_Pressure = Calc_Manifold_Pressure( Throttle_Lever_Pos, Max_Manifold_Pressure, Min_Manifold_Pressure );
+ // cout << "manifold pressure = " << Manifold_Pressure << endl;
+
+ //Then find the actual manifold pressure (the calculated one is the sea level pressure)
+ True_Manifold_Pressure = Manifold_Pressure * p_amb / p_amb_sea_level;
+
+ //Do the fuel flow calculations
+ Calc_Fuel_Flow_Gals_Hr();
+
+ //Calculate engine power
+ Calc_Percentage_Power(Magneto_Left, Magneto_Right);
+ HP = Percentage_Power * MaxHP / 100.0;
+ Power_SI = HP * CONVERT_HP_TO_WATTS;
+
+ // FMEP calculation. For now we will just use this during motored operation.
+ // Eventually we will calculate IMEP and use the FMEP all the time to give BMEP (maybe!)
+ if(!running) {
+ // This FMEP data is from the Patton paper, assumes fully warm conditions.
+ FMEP = 1e-12*pow(RPM,4) - 1e-8*pow(RPM,3) + 5e-5*pow(RPM,2) - 0.0722*RPM + 154.85;
+ // Gives FMEP in kPa - now convert to Pa
+ FMEP *= 1000;
+ } else {
+ FMEP = 0.0;
+ }
+ // Is this total FMEP or friction FMEP ???
+
+ Torque_FMEP = (FMEP * displacement_SI) / (2.0 * LS_PI * n_R);
+
+ // Calculate Engine Torque. Check for div by zero since percentage power correlation does not guarantee zero power at zero rpm.
+ // However this is problematical since there is a resistance to movement even at rest
+ // Ie this is a dynamics equation not a statics one. This can be solved by going over to MEP based torque calculations.
+ if(RPM == 0) {
+ Torque_SI = 0 - Torque_FMEP;
+ }
+ else {
+ Torque_SI = ((Power_SI * 60.0) / (2.0 * LS_PI * RPM)) - Torque_FMEP; //Torque = power / angular velocity
+ // cout << Torque << " Nm\n";
+ }
+
+ //Calculate Exhaust gas temperature
+ if(running)
+ Calc_EGT();
+ else
+ EGT = 298.0;
+
+ // Calculate Cylinder Head Temperature
+ Calc_CHT();
+
+ // Calculate oil temperature
+ current_oil_temp = Calc_Oil_Temp(current_oil_temp);
+
+ // Calculate Oil Pressure
+ Oil_Pressure = Calc_Oil_Press( Oil_Temp, RPM );
+
+ // Now do the Propeller Calculations
+ Do_Prop_Calcs();
+
+// Now do the engine - prop torque balance to calculate final RPM
+
+ //Calculate new RPM from torque balance and inertia.
+ Torque_Imbalance = Torque_SI - prop_torque; //This gives a +ve value when the engine torque exeeds the prop torque
+ // (Engine torque is +ve when it acts in the direction of engine revolution, prop torque is +ve when it opposes the direction of engine revolution)
+
+ angular_acceleration = Torque_Imbalance / (engine_inertia + prop_inertia);
+ angular_velocity_SI += (angular_acceleration * time_step);
+ // Don't let the engine go into reverse
+ if(angular_velocity_SI < 0)
+ angular_velocity_SI = 0;
+ RPM = (angular_velocity_SI * 60) / (2.0 * LS_PI);
+
+ // And finally a last check on the engine state after doing the torque balance with the prop - have we stalled?
+ if(running) {
+ //Check if we have stalled the engine
+ if (RPM == 0) {
+ running = false;
+ } else if((RPM <= 480) && (cranking)) {
+ //Make sure the engine noise dosn't play if the engine won't start due to eg mixture lever pulled out.
+ running = false;
+ EGT = 298.0;
+ }
+ }
+
+ // And finally, do any unit conversions from internal units to output units
+ EGT_degF = (EGT * 1.8) - 459.67;
+ CHT_degF = (CHT * 1.8) - 459.67;
}
+//*****************************************************************************************************
+
// FGNewEngine member functions
+////////////////////////////////////////////////////////////////////////////////////////////
+// Return the combustion efficiency as a function of equivalence ratio
+//
+// Combustion efficiency values from Heywood,
+// "Internal Combustion Engine Fundamentals", ISBN 0-07-100499-8
+////////////////////////////////////////////////////////////////////////////////////////////
float FGNewEngine::Lookup_Combustion_Efficiency(float thi_actual)
{
const int NUM_ELEMENTS = 11;
float thi[NUM_ELEMENTS] = {0.0, 0.9, 1.0, 1.05, 1.1, 1.15, 1.2, 1.3, 1.4, 1.5, 1.6}; //array of equivalence ratio values
float neta_comb[NUM_ELEMENTS] = {0.98, 0.98, 0.97, 0.95, 0.9, 0.85, 0.79, 0.7, 0.63, 0.57, 0.525}; //corresponding array of combustion efficiency values
- //combustion efficiency values from Heywood, "Internal Combustion Engine Fundamentals", ISBN 0-07-100499-8
- float neta_comb_actual;
+ float neta_comb_actual = 0.0f;
float factor;
int i;
// The lookup table is in AFR because the source data was. I added the two end elements to make sure we are almost always in it.
float AFR[NUM_ELEMENTS] = {(14.7/1.6), 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, (14.7/0.6)}; //array of equivalence ratio values
float mixPerPow[NUM_ELEMENTS] = {78, 86, 93.5, 98, 100, 99, 96.4, 92.5, 88, 83, 78.5, 74, 58}; //corresponding array of combustion efficiency values
- float mixPerPow_actual;
+ float mixPerPow_actual = 0.0f;
float factor;
float dydx;
return mixPerPow_actual;
}
-
-
-// Calculate Manifold Pressure based on Throttle lever Position
-float FGNewEngine::Calc_Manifold_Pressure ( float LeverPosn, float MaxMan, float MinMan)
+// Calculate Cylinder Head Temperature
+// Crudely models the cylinder head as an arbitary lump of arbitary size and area with one third of combustion energy
+// as heat input and heat output as a function of airspeed and temperature. Could be improved!!!
+void FGNewEngine::Calc_CHT()
{
- float Inches;
- // if ( x < = 0 ) {
- // x = 0.00001;
- // }
-
- //Note that setting the manifold pressure as a function of lever position only is not strictly accurate
- //MAP is also a function of engine speed. (and ambient pressure if we are going for an actual MAP model)
- Inches = MinMan + (LeverPosn * (MaxMan - MinMan) / 100);
-
- //allow for idle bypass valve or slightly open throttle stop
- if(Inches < MinMan)
- Inches = MinMan;
-
- return Inches;
-}
-
+ float h1 = -95.0; //co-efficient for free convection
+ float h2 = -3.95; //co-efficient for forced convection
+ float h3 = -0.05; //co-efficient for forced convection due to prop backwash
+ float v_apparent; //air velocity over cylinder head in m/s
+ float v_dot_cooling_air;
+ float m_dot_cooling_air;
+ float temperature_difference;
+ float arbitary_area = 1.0;
+ float dqdt_from_combustion;
+ float dqdt_forced; //Rate of energy transfer to/from cylinder head due to forced convection (Joules) (sign convention: to cylinder head is +ve)
+ float dqdt_free; //Rate of energy transfer to/from cylinder head due to free convection (Joules) (sign convention: to cylinder head is +ve)
+ float dqdt_cylinder_head; //Overall energy change in cylinder head
+ float CpCylinderHead = 800.0; //FIXME - this is a guess - I need to look up the correct value
+ float MassCylinderHead = 8.0; //Kg - this is a guess - it dosn't have to be absolutely accurate but can be varied to alter the warm-up rate
+ float HeatCapacityCylinderHead;
+ float dCHTdt;
+ // The above values are hardwired to give reasonable results for an IO360 (C172 engine)
+ // Now adjust to try to compensate for arbitary sized engines - this is currently untested
+ arbitary_area *= (MaxHP / 180.0);
+ MassCylinderHead *= (MaxHP / 180.0);
+ temperature_difference = CHT - T_amb;
-// Calculate Oil Temperature
-float FGNewEngine::Calc_Oil_Temp (float Fuel_Flow, float Mixture, float IAS)
-{
- float Oil_Temp = 85;
+ v_apparent = IAS * 0.5144444; //convert from knots to m/s
+ v_dot_cooling_air = arbitary_area * v_apparent;
+ m_dot_cooling_air = v_dot_cooling_air * rho_air;
- return (Oil_Temp);
+ //Calculate rate of energy transfer to cylinder head from combustion
+ dqdt_from_combustion = m_dot_fuel * calorific_value_fuel * combustion_efficiency * 0.33;
+
+ //Calculate rate of energy transfer from cylinder head due to cooling NOTE is calculated as rate to but negative
+ dqdt_forced = (h2 * m_dot_cooling_air * temperature_difference) + (h3 * RPM * temperature_difference);
+ dqdt_free = h1 * temperature_difference;
+
+ //Calculate net rate of energy transfer to or from cylinder head
+ dqdt_cylinder_head = dqdt_from_combustion + dqdt_forced + dqdt_free;
+
+ HeatCapacityCylinderHead = CpCylinderHead * MassCylinderHead;
+
+ dCHTdt = dqdt_cylinder_head / HeatCapacityCylinderHead;
+
+ CHT += (dCHTdt * time_step);
}
-// Calculate Oil Pressure
-float FGNewEngine::Calc_Oil_Press (float Oil_Temp, float Engine_RPM)
+// Calculate exhaust gas temperature
+void FGNewEngine::Calc_EGT()
{
- float Oil_Pressure = 0; //PSI
- float Oil_Press_Relief_Valve = 60; //PSI
- float Oil_Press_RPM_Max = 1800;
- float Design_Oil_Temp = 85; //Celsius
- float Oil_Viscosity_Index = 0.25; // PSI/Deg C
- float Temp_Deviation = 0; // Deg C
-
- Oil_Pressure = (Oil_Press_Relief_Valve / Oil_Press_RPM_Max) * Engine_RPM;
+ combustion_efficiency = Lookup_Combustion_Efficiency(equivalence_ratio); //The combustion efficiency basically tells us what proportion of the fuels calorific value is released
- // Pressure relief valve opens at Oil_Press_Relief_Valve PSI setting
- if (Oil_Pressure >= Oil_Press_Relief_Valve)
- {
- Oil_Pressure = Oil_Press_Relief_Valve;
- }
+ //now calculate energy release to exhaust
+ //We will assume a three way split of fuel energy between useful work, the coolant system and the exhaust system
+ //This is a reasonable first suck of the thumb estimate for a water cooled automotive engine - whether it holds for an air cooled aero engine is probably open to question
+ //Regardless - it won't affect the variation of EGT with mixture, and we can always put a multiplier on EGT to get a reasonable peak value.
+ enthalpy_exhaust = m_dot_fuel * calorific_value_fuel * combustion_efficiency * 0.33;
+ heat_capacity_exhaust = (Cp_air * m_dot_air) + (Cp_fuel * m_dot_fuel);
+ delta_T_exhaust = enthalpy_exhaust / heat_capacity_exhaust;
- // Now adjust pressure according to Temp which affects the viscosity
+ EGT = T_amb + delta_T_exhaust;
- Oil_Pressure += (Design_Oil_Temp - Oil_Temp) * Oil_Viscosity_Index;
+ //The above gives the exhaust temperature immediately prior to leaving the combustion chamber
+ //Now derate to give a more realistic figure as measured downstream
+ //For now we will aim for a peak of around 400 degC (750 degF)
- return Oil_Pressure;
+ EGT *= 0.444 + ((0.544 - 0.444) * Percentage_Power / 100.0);
}
-//*************************************************************************************
-// Initialise the engine model
-void FGNewEngine::init(double dt) {
-
- // These constants should probably be moved eventually
- CONVERT_CUBIC_INCHES_TO_METERS_CUBED = 1.638706e-5;
- CONVERT_HP_TO_WATTS = 745.6999;
-
- // Properties of working fluids
- Cp_air = 1005; // J/KgK
- Cp_fuel = 1700; // J/KgK
- calorific_value_fuel = 47.3e6; // W/Kg Note that this is only an approximate value
- rho_fuel = 800; // kg/m^3 - an estimate for now
- R_air = 287.3;
- p_amb_sea_level = 101325;
-
- // Control and environment inputs
- IAS = 0;
- Throttle_Lever_Pos = 75;
- Propeller_Lever_Pos = 75;
- Mixture_Lever_Pos = 100;
-
- time_step = dt;
+// Calculate Manifold Pressure based on Throttle lever Position
+float FGNewEngine::Calc_Manifold_Pressure ( float LeverPosn, float MaxMan, float MinMan)
+{
+ float Inches;
- // Engine Specific Variables.
- // Will be set in a parameter file to be read in to create
- // and instance for each engine.
- Max_Manifold_Pressure = 28.50; //Inches Hg. An approximation - should be able to find it in the engine performance data
- Min_Manifold_Pressure = 6.5; //Inches Hg. This is a guess corresponding to approx 0.24 bar MAP (7 in Hg) - need to find some proper data for this
- Max_RPM = 2700;
- Min_RPM = 600; //Recommended idle from Continental data sheet
- Max_Fuel_Flow = 130;
- Mag_Derate_Percent = 5;
-// MaxHP = 285; //Continental IO520-M
- MaxHP = 180; //Lycoming IO360
-// displacement = 520; //Continental IO520-M
- displacement = 360; //Lycoming IO360
- displacement_SI = displacement * CONVERT_CUBIC_INCHES_TO_METERS_CUBED;
- engine_inertia = 0.2; //kgm^2 - value taken from a popular family saloon car engine - need to find an aeroengine value !!!!!
- prop_inertia = 0.03; //kgm^2 - this value is a total guess - dcl
- Gear_Ratio = 1;
+ //Note that setting the manifold pressure as a function of lever position only is not strictly accurate
+ //MAP is also a function of engine speed. (and ambient pressure if we are going for an actual MAP model)
+ Inches = MinMan + (LeverPosn * (MaxMan - MinMan) / 100);
- started = true;
- cranking = false;
+ //allow for idle bypass valve or slightly open throttle stop
+ if(Inches < MinMan)
+ Inches = MinMan;
+ //Check for stopped engine (crudest way of compensating for engine speed)
+ if(RPM == 0)
+ Inches = 29.92;
- // Initialise Engine Variables used by this instance
- Percentage_Power = 0;
- Manifold_Pressure = 29.00; // Inches
- RPM = 600;
- Fuel_Flow_gals_hr = 0;
- Torque = 0;
- Torque_SI = 0;
- CHT = 298.0; //deg Kelvin
- CHT_degF = (CHT * 1.8) - 459.67; //deg Fahrenheit
- Mixture = 14;
- Oil_Pressure = 0; // PSI
- Oil_Temp = 85; // Deg C
- HP = 0;
- RPS = 0;
- Torque_Imbalance = 0;
-
- // Initialise Propellor Variables used by this instance
- FGProp1_Thrust = 0;
- FGProp1_RPS = 0;
- FGProp1_Blade_Angle = 13.5;
- prop_diameter = 1.8; // meters
- blade_angle = 23.0; // degrees
+ return Inches;
}
-
-//*****************************************************************************
-//*****************************************************************************
-// update the engine model based on current control positions
-void FGNewEngine::update() {
-
-/*
- // Hack for testing - should output every 5 seconds
- static int count1 = 0;
- if(count1 == 0) {
- cout << "P_atmos = " << p_amb << " T_atmos = " << T_amb << '\n';
- cout << "Manifold pressure = " << Manifold_Pressure << " True_Manifold_Pressure = " << True_Manifold_Pressure << '\n';
- cout << "p_amb_sea_level = " << p_amb_sea_level << '\n';
- cout << "equivalence_ratio = " << equivalence_ratio << '\n';
- cout << "combustion_efficiency = " << combustion_efficiency << '\n';
- cout << "AFR = " << 14.7 / equivalence_ratio << '\n';
- cout << "Mixture lever = " << Mixture_Lever_Pos << '\n';
- cout << "n = " << RPM << " rpm\n";
- }
- count1++;
- if(count1 == 600)
- count1 = 0;
-*/
-
- float ManXRPM = 0;
- float Vo = 0;
- float V1 = 0;
-
- // Set up the new variables
- float PI = 3.1428571;
-
- // Parameters that alter the operation of the engine.
- int Fuel_Available = 1; // Yes = 1. Is there Fuel Available. Calculated elsewhere
- int Alternate_Air_Pos =0; // Off = 0. Reduces power by 3 % for same throttle setting
- int Magneto_Left = 1; // 1 = On. Reduces power by 5 % for same power lever settings
- int Magneto_Right = 1; // 1 = On. Ditto, Both of the above though do not alter fuel flow
-
-
- // Calculate Sea Level Manifold Pressure
- Manifold_Pressure = Calc_Manifold_Pressure( Throttle_Lever_Pos, Max_Manifold_Pressure, Min_Manifold_Pressure );
- // cout << "manifold pressure = " << Manifold_Pressure << endl;
-
- //Then find the actual manifold pressure (the calculated one is the sea level pressure)
- True_Manifold_Pressure = Manifold_Pressure * p_amb / p_amb_sea_level;
-
-//*************
-//DCL - next calculate m_dot_air and m_dot_fuel into engine
-
+// Calculate fuel flow in gals/hr
+void FGNewEngine::Calc_Fuel_Flow_Gals_Hr()
+{
//DCL - calculate mass air flow into engine based on speed and load - separate this out into a function eventually
//t_amb is actual temperature calculated from altitude
//calculate density from ideal gas equation
equivalence_ratio = thi_sea_level * p_amb_sea_level / p_amb; //ie as we go higher the mixture gets richer for a given lever position
m_dot_fuel = m_dot_air / 14.7 * equivalence_ratio;
Fuel_Flow_gals_hr = (m_dot_fuel / rho_fuel) * 264.172 * 3600.0; // Note this assumes US gallons
+}
-//***********************************************************************
-//Engine power and torque calculations
-
+// Calculate the percentage of maximum rated power delivered as a function of Manifold pressure multiplied by engine speed (rpm)
+// This is not necessarilly the best approach but seems to work for now.
+// May well need tweaking at the bottom end if the prop model is changed.
+void FGNewEngine::Calc_Percentage_Power(bool mag_left, bool mag_right)
+{
// For a given Manifold Pressure and RPM calculate the % Power
// Multiply Manifold Pressure by RPM
- ManXRPM = True_Manifold_Pressure * RPM;
-// ManXRPM = Manifold_Pressure * RPM;
- // cout << ManXRPM;
- // cout << endl;
+ float ManXRPM = True_Manifold_Pressure * RPM;
/*
// Phil's %power correlation
// on the actual manifold pressure, which takes air pressure into account. However - this fails to
// take the temperature into account - this is TODO.
+ // Adjust power for temperature - this is temporary until the power is done as a function of mass flow rate induced
+ // Adjust for Temperature - Temperature above Standard decrease
+ // power by 7/120 % per degree F increase, and incease power for
+ // temps below at the same ratio
+ float T_amb_degF = (T_amb * 1.8) - 459.67;
+ float T_amb_sea_lev_degF = (288 * 1.8) - 459.67;
+ Percentage_Power = Percentage_Power + ((T_amb_sea_lev_degF - T_amb_degF) * 7 /120);
+
//DCL - now adjust power to compensate for mixture
Percentage_of_best_power_mixture_power = Power_Mixture_Correlation(equivalence_ratio);
Percentage_Power = Percentage_Power * Percentage_of_best_power_mixture_power / 100.0;
// Now Derate engine for the effects of Bad/Switched off magnetos
- if (Magneto_Left == 0 && Magneto_Right == 0) {
+ //if (Magneto_Left == 0 && Magneto_Right == 0) {
+ if(!running) {
// cout << "Both OFF\n";
Percentage_Power = 0;
- } else if (Magneto_Left && Magneto_Right) {
+ } else if (mag_left && mag_right) {
// cout << "Both On ";
- } else if (Magneto_Left == 0 || Magneto_Right== 0) {
+ } else if (mag_left == 0 || mag_right== 0) {
// cout << "1 Magneto Failed ";
Percentage_Power = Percentage_Power * ((100.0 - Mag_Derate_Percent)/100.0);
// cout << FGEng1_Percentage_Power << "%" << "\t";
}
+/*
+ //DCL - stall the engine if RPM drops below 450 - this is possible if mixture lever is pulled right out
+ //This is a kludge that I should eliminate by adding a total fmep estimation.
+ if(RPM < 450)
+ Percentage_Power = 0;
+*/
+ if(Percentage_Power < 0)
+ Percentage_Power = 0;
+}
- HP = Percentage_Power * MaxHP / 100.0;
-
- Power_SI = HP * CONVERT_HP_TO_WATTS;
-
- // Calculate Engine Torque. Check for div by zero since percentage power correlation does not guarantee zero power at zero rpm.
- if(RPM == 0) {
- Torque_SI = 0;
- }
- else {
- Torque_SI = (Power_SI * 60.0) / (2.0 * PI * RPM); //Torque = power / angular velocity
- // cout << Torque << " Nm\n";
+// Calculate Oil Temperature in degrees Kelvin
+float FGNewEngine::Calc_Oil_Temp (float oil_temp)
+{
+ float idle_percentage_power = 2.3; // approximately
+ float target_oil_temp; // Steady state oil temp at the current engine conditions
+ float time_constant; // The time constant for the differential equation
+ if(running) {
+ target_oil_temp = 363;
+ time_constant = 500; // Time constant for engine-on idling.
+ if(Percentage_Power > idle_percentage_power) {
+ time_constant /= ((Percentage_Power / idle_percentage_power) / 10.0); // adjust for power
+ }
+ } else {
+ target_oil_temp = 298;
+ time_constant = 1000; // Time constant for engine-off; reflects the fact that oil is no longer getting circulated
}
-//**********************************************************************
-//Calculate Exhaust gas temperature
-
- // cout << "Thi = " << equivalence_ratio << '\n';
-
- combustion_efficiency = Lookup_Combustion_Efficiency(equivalence_ratio); //The combustion efficiency basically tells us what proportion of the fuels calorific value is released
+ float dOilTempdt = (target_oil_temp - oil_temp) / time_constant;
- // cout << "Combustion efficiency = " << combustion_efficiency << '\n';
+ oil_temp += (dOilTempdt * time_step);
- //now calculate energy release to exhaust
- //We will assume a three way split of fuel energy between useful work, the coolant system and the exhaust system
- //This is a reasonable first suck of the thumb estimate for a water cooled automotive engine - whether it holds for an air cooled aero engine is probably open to question
- //Regardless - it won't affect the variation of EGT with mixture, and we can always put a multiplier on EGT to get a reasonable peak value.
- enthalpy_exhaust = m_dot_fuel * calorific_value_fuel * combustion_efficiency * 0.33;
- heat_capacity_exhaust = (Cp_air * m_dot_air) + (Cp_fuel * m_dot_fuel);
- delta_T_exhaust = enthalpy_exhaust / heat_capacity_exhaust;
-// delta_T_exhaust = Calculate_Delta_T_Exhaust();
-
- // cout << "T_amb " << T_amb;
- // cout << " dT exhaust = " << delta_T_exhaust;
-
- EGT = T_amb + delta_T_exhaust;
-
- //The above gives the exhaust temperature immediately prior to leaving the combustion chamber
- //Now derate to give a more realistic figure as measured downstream
- //For now we will aim for a peak of around 400 degC (750 degF)
-
- EGT *= 0.444 + ((0.544 - 0.444) * Percentage_Power / 100.0);
+ return (oil_temp);
+}
- EGT_degF = (EGT * 1.8) - 459.67;
+// Calculate Oil Pressure
+float FGNewEngine::Calc_Oil_Press (float Oil_Temp, float Engine_RPM)
+{
+ float Oil_Pressure = 0; //PSI
+ float Oil_Press_Relief_Valve = 60; //PSI
+ float Oil_Press_RPM_Max = 1800;
+ float Design_Oil_Temp = 85; //Celsius
+ float Oil_Viscosity_Index = 0.25; // PSI/Deg C
+// float Temp_Deviation = 0; // Deg C
- //cout << " EGT = " << EGT << " degK " << EGT_degF << " degF";// << '\n';
+ Oil_Pressure = (Oil_Press_Relief_Valve / Oil_Press_RPM_Max) * Engine_RPM;
-//***************************************************************************************
-// Calculate Cylinder Head Temperature
+ // Pressure relief valve opens at Oil_Press_Relief_Valve PSI setting
+ if (Oil_Pressure >= Oil_Press_Relief_Valve) {
+ Oil_Pressure = Oil_Press_Relief_Valve;
+ }
-/* DCL 27/10/00
-
-This is a somewhat rough first attempt at modelling cylinder head temperature. The cylinder head
-is assumed to be at uniform temperature. Obviously this is incorrect, but it simplifies things a
-lot, and we're just looking for the behaviour of CHT to be correct. Energy transfer to the cylinder
-head is assumed to be one third of the energy released by combustion at all conditions. This is a
-reasonable estimate, although obviously in real life it varies with different conditions and possibly
-with CHT itself. I've split energy transfer from the cylinder head into 2 terms - free convection -
-ie convection to stationary air, and forced convection, ie convection into flowing air. The basic
-free convection equation is: dqdt = -hAdT Since we don't know A and are going to set h quite arbitarily
-anyway I've knocked A out and just wrapped it up in h - the only real significance is that the units
-of h will be different but that dosn't really matter to us anyway. In addition, we have the problem
-that the prop model I'm currently using dosn't model the backwash from the prop which will add to the
-velocity of the cooling air when the prop is turning, so I've added an extra term to try and cope
-with this.
-
-In real life, forced convection equations are genarally empirically derived, and are quite complicated
-and generally contain such things as the Reynolds and Nusselt numbers to various powers. The best
-course of action would probably to find an empirical correlation from the literature for a similar
-situation and try and get it to fit well. However, for now I am using my own made up very simple
-correlation for the energy transfer from the cylinder head:
-
-dqdt = -(h1.dT) -(h2.m_dot.dT) -(h3.rpm.dT)
-
-where dT is the temperature different between the cylinder head and the surrounding air, m_dot is the
-mass flow rate of cooling air through an arbitary volume, rpm is the engine speed in rpm (this is the
-backwash term), and h1, h2, h3 are co-efficients which we can play with to attempt to get the CHT
-behaviour to match real life.
-
-In order to change the values of CHT that the engine settles down at at various conditions,
-have a play with h1, h2 and h3. In order to change the rate of heating/cooling without affecting
-equilibrium values alter the cylinder head mass, which is really quite arbitary. Bear in mind that
-altering h1, h2 and h3 will also alter the rate of heating or cooling as well as equilibrium values,
-but altering the cylinder head mass will only alter the rate. It would I suppose be better to read
-the values from file to avoid the necessity for re-compilation every time I change them.
+ // Now adjust pressure according to Temp which affects the viscosity
-*/
- //CHT = Calc_CHT( Fuel_Flow, Mixture, IAS);
- // cout << "Cylinder Head Temp (F) = " << CHT << endl;
- float h1 = -95.0; //co-efficient for free convection
- float h2 = -3.95; //co-efficient for forced convection
- float h3 = -0.05; //co-efficient for forced convection due to prop backwash
- float v_apparent; //air velocity over cylinder head in m/s
- float v_dot_cooling_air;
- float m_dot_cooling_air;
- float temperature_difference;
- float arbitary_area = 1.0;
- float dqdt_from_combustion;
- float dqdt_forced; //Rate of energy transfer to/from cylinder head due to forced convection (Joules) (sign convention: to cylinder head is +ve)
- float dqdt_free; //Rate of energy transfer to/from cylinder head due to free convection (Joules) (sign convention: to cylinder head is +ve)
- float dqdt_cylinder_head; //Overall energy change in cylinder head
- float CpCylinderHead = 800.0; //FIXME - this is a guess - I need to look up the correct value
- float MassCylinderHead = 8.0; //Kg - this is a guess - it dosn't have to be absolutely accurate but can be varied to alter the warm-up rate
- float HeatCapacityCylinderHead;
- float dCHTdt;
+ Oil_Pressure += (Design_Oil_Temp - Oil_Temp) * Oil_Viscosity_Index;
- temperature_difference = CHT - T_amb;
+ return Oil_Pressure;
+}
- v_apparent = IAS * 0.5144444; //convert from knots to m/s
- v_dot_cooling_air = arbitary_area * v_apparent;
- m_dot_cooling_air = v_dot_cooling_air * rho_air;
- //Calculate rate of energy transfer to cylinder head from combustion
- dqdt_from_combustion = m_dot_fuel * calorific_value_fuel * combustion_efficiency * 0.33;
-
- //Calculate rate of energy transfer from cylinder head due to cooling NOTE is calculated as rate to but negative
- dqdt_forced = (h2 * m_dot_cooling_air * temperature_difference) + (h3 * RPM * temperature_difference);
- dqdt_free = h1 * temperature_difference;
-
- //Calculate net rate of energy transfer to or from cylinder head
- dqdt_cylinder_head = dqdt_from_combustion + dqdt_forced + dqdt_free;
-
- HeatCapacityCylinderHead = CpCylinderHead * MassCylinderHead;
-
- dCHTdt = dqdt_cylinder_head / HeatCapacityCylinderHead;
-
- CHT += (dCHTdt * time_step);
-
- CHT_degF = (CHT * 1.8) - 459.67;
-
- //cout << " CHT = " << CHT_degF << " degF\n";
-
-
- // End calculate Cylinder Head Temperature
-
-
-//***************************************************************************************
-// Oil pressure calculation
-
- // Calculate Oil Pressure
- Oil_Pressure = Calc_Oil_Press( Oil_Temp, RPM );
- // cout << "Oil Pressure (PSI) = " << Oil_Pressure << endl;
-
-//**************************************************************************************
-// Now do the Propeller Calculations
-
- Gear_Ratio = 1.0;
- FGProp1_RPS = RPM * Gear_Ratio / 60.0; // Borrow this variable from Phils model for now !!
- angular_velocity_SI = 2.0 * PI * RPM / 60.0;
+// Propeller calculations.
+void FGNewEngine::Do_Prop_Calcs()
+{
+ float Gear_Ratio = 1.0;
+ float forward_velocity; // m/s
+ float prop_power_consumed_SI; // Watts
+ double J; // advance ratio - dimensionless
+ double Cp_20; // coefficient of power for 20 degree blade angle
+ double Cp_25; // coefficient of power for 25 degree blade angle
+ double Cp; // Our actual coefficient of power
+ double neta_prop_20;
+ double neta_prop_25;
+ double neta_prop; // prop efficiency
+
+ FGProp1_RPS = RPM * Gear_Ratio / 60.0;
+ angular_velocity_SI = 2.0 * LS_PI * RPM / 60.0;
forward_velocity = IAS * 0.514444444444; // Convert to m/s
- //cout << "Gear_Ratio = " << Gear_Ratio << '\n';
- //cout << "IAS = " << IAS << '\n';
- //cout << "forward_velocity = " << forward_velocity << '\n';
- //cout << "FGProp1_RPS = " << FGProp1_RPS << '\n';
- //cout << "prop_diameter = " << prop_diameter << '\n';
if(FGProp1_RPS == 0)
J = 0;
else
//cout << "RPM = " << RPM << '\n';
//cout << "angular_velocity_SI = " << angular_velocity_SI << '\n';
- prop_power_consumed_SI = Cp * rho_air * pow(FGProp1_RPS,3.0) * pow(prop_diameter,5.0);
+ prop_power_consumed_SI = Cp * rho_air * pow(FGProp1_RPS,3.0f) * pow(float(prop_diameter),5.0f);
//cout << "prop HP consumed = " << prop_power_consumed_SI / 745.699 << '\n';
if(angular_velocity_SI == 0)
prop_torque = 0;
+ // However this can give problems - if rpm == 0 but forward velocity increases the prop should be able to generate a torque to start the engine spinning
+ // Unlikely to happen in practice - but I suppose someone could move the lever of a stopped large piston engine from feathered to windmilling.
+ // This *does* give problems - if the plane is put into a steep climb whilst windmilling the engine friction will eventually stop it spinning.
+ // When put back into a dive it never starts re-spinning again. Although it is unlikely that anyone would do this in real life, they might well do it in a sim!!!
else
prop_torque = prop_power_consumed_SI / angular_velocity_SI;
neta_prop_25 = -0.3121*J*J*J*J + 0.4234*J*J*J - 0.7686*J*J + 1.5237*J - 0.0004;
neta_prop = neta_prop_20 + ( (neta_prop_25 - neta_prop_20) * ((blade_angle - 20)/(25 - 20)) );
- //FIXME - need to check for zero forward velocity to avoid divide by zero
+ // Check for zero forward velocity to avoid divide by zero
if(forward_velocity < 0.0001)
prop_thrust = 0.0;
+ // I don't see how this works - how can the plane possibly start from rest ???
+ // Hmmmm - it works because the forward_velocity at present never drops below about 0.03 even at rest
+ // We can't really rely on this in the future - needs fixing !!!!
+ // The problem is that we're doing this calculation backwards - we're working out the thrust from the power consumed and the velocity, which becomes invalid as velocity goes to zero.
+ // It would be far more natural to work out the power consumed from the thrust - FIXME!!!!!.
else
prop_thrust = neta_prop * prop_power_consumed_SI / forward_velocity; //TODO - rename forward_velocity to IAS_SI
//cout << "prop_thrust = " << prop_thrust << '\n';
-
-//******************************************************************************
-// Now do the engine - prop torque balance to calculate final RPM
-
- //Calculate new RPM from torque balance and inertia.
- Torque_Imbalance = Torque_SI - prop_torque; //This gives a +ve value when the engine torque exeeds the prop torque
-
- angular_acceleration = Torque_Imbalance / (engine_inertia + prop_inertia);
- angular_velocity_SI += (angular_acceleration * time_step);
- RPM = (angular_velocity_SI * 60) / (2.0 * PI);
-
- //DCL - stall the engine if RPM drops below 500 - this is possible if mixture lever is pulled right out
- if(RPM < 500)
- RPM = 0;
-
}
-
projects / flightgear.git / blobdiff