X-Git-Url: https://git.mxchange.org/?a=blobdiff_plain;f=src%2FFDM%2FIO360.cxx;h=c75b9b3f2fea84f37ca9d4ac62a46a1444b9474d;hb=ee98995d30e75cda88c9866f3cb6a761fda7d078;hp=f17b88e8ea2d2814daadb0b481d52b8fbd0f1df8;hpb=646f93e618229c45bc2855c14bde160270bf01a7;p=flightgear.git diff --git a/src/FDM/IO360.cxx b/src/FDM/IO360.cxx index f17b88e8e..c75b9b3f2 100644 --- a/src/FDM/IO360.cxx +++ b/src/FDM/IO360.cxx @@ -1,10 +1,9 @@ -// 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 @@ -18,79 +17,7 @@ // // 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 -// -// DCL 18/9/01 - Got the engine to start and stop in response to the magneto switch. -// Changed all PI to LS_PI (in ls_constants.h). -// Engine now checks for fuel and stops when not available. -// -////////////////////////////////////////////////////////////////////// +// Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. #include @@ -108,188 +35,6 @@ SG_USING_STD(cout); #include
-// Static utility functions - -// Calculate Density Ratio -static float Density_Ratio ( float x ) -{ - float y ; - y = ((3E-10 * x * x) - (3E-05 * x) + 0.9998); - return(y); -} - - -// 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 - - float R = 287.3; - float rho = pressure / (R * temperature); - return(rho); -} - - -// Calculate Speed in FPS given Knots CAS -static float IAS_to_FPS (float x) -{ - float y; - y = x * 1.68888888; - return y; -} - -// FGNewEngine member functions - -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 = 0.0f; - float factor; - - int i; - int j = NUM_ELEMENTS; //This must be equal to the number of elements in the lookup table arrays - - for(i=0;i thi[i]) && (thi_actual < thi[i + 1])) { - //do linear interpolation between the two points - factor = (thi_actual - thi[i]) / (thi[i+1] - thi[i]); - neta_comb_actual = (factor * (neta_comb[i+1] - neta_comb[i])) + neta_comb[i]; - return neta_comb_actual; - } - } - - //if we get here something has gone badly wrong - cout << "ERROR: error in FGNewEngine::Lookup_Combustion_Efficiency\n"; - return neta_comb_actual; -} - -//////////////////////////////////////////////////////////////////////////////////////////// -// Return the percentage of best mixture power available at a given mixture strength -// -// Based on data from "Technical Considerations for Catalysts for the European Market" -// by H S Gandi, published 1988 by IMechE -// -// Note that currently no attempt is made to set a lean limit on stable combustion -//////////////////////////////////////////////////////////////////////////////////////////// -float FGNewEngine::Power_Mixture_Correlation(float thi_actual) -{ - float AFR_actual = 14.7 / thi_actual; - // thi and thi_actual are equivalence ratio - const int NUM_ELEMENTS = 13; - // 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 = 0.0f; - float factor; - float dydx; - - int i; - int j = NUM_ELEMENTS; //This must be equal to the number of elements in the lookup table arrays - - for(i=0;i AFR[i]) && (AFR_actual < AFR[i + 1])) { - //do linear interpolation between the two points - factor = (AFR_actual - AFR[i]) / (AFR[i+1] - AFR[i]); - mixPerPow_actual = (factor * (mixPerPow[i+1] - mixPerPow[i])) + mixPerPow[i]; - return mixPerPow_actual; - } - } - - //if we get here something has gone badly wrong - cout << "ERROR: error in FGNewEngine::Power_Mixture_Correlation\n"; - return mixPerPow_actual; -} - - - -// Calculate Manifold Pressure based on Throttle lever Position -float FGNewEngine::Calc_Manifold_Pressure ( float LeverPosn, float MaxMan, float MinMan) -{ - 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; -} - - - - -// Calculate Oil Temperature -float FGNewEngine::Calc_Oil_Temp (float Fuel_Flow, float Mixture, float IAS) -{ - float Oil_Temp = 85; - - return (Oil_Temp); -} - -// 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 - - Oil_Pressure = (Oil_Press_Relief_Valve / Oil_Press_RPM_Max) * Engine_RPM; - - // 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 adjust pressure according to Temp which affects the viscosity - - Oil_Pressure += (Design_Oil_Temp - Oil_Temp) * Oil_Viscosity_Index; - - return Oil_Pressure; -} - //************************************************************************************* // Initialise the engine model void FGNewEngine::init(double dt) { @@ -304,26 +49,20 @@ void FGNewEngine::init(double dt) { 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; + // 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. - // 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 + // 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 @@ -331,12 +70,22 @@ void FGNewEngine::init(double dt) { 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 cylinder engine. + n_R = 2; // Number of crank revolutions per power cycle - 2 for a 4 stroke engine. - running = fgGetBool("/engines/engine[0]/running"); + // Various bits of housekeeping describing the engines initial state. + running = false; cranking = false; - fgSetBool("/engines/engine[0]/cranking", false); + crank_counter = false; + starter = false; // Initialise Engine Variables used by this instance if(running) @@ -344,29 +93,28 @@ void FGNewEngine::init(double dt) { else RPM = 0; Percentage_Power = 0; - Manifold_Pressure = 29.00; // Inches + Manifold_Pressure = 29.96; // Inches Fuel_Flow_gals_hr = 0; - Torque = 0; +// Torque = 0; Torque_SI = 0; - CHT = 298.0; //deg Kelvin - CHT_degF = (CHT * 1.8) - 459.67; //deg Fahrenheit + 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_Thrust = 0; FGProp1_RPS = 0; - FGProp1_Blade_Angle = 13.5; + // 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() { @@ -384,23 +132,23 @@ void FGNewEngine::update() { // cout << "Mixture lever = " << Mixture_Lever_Pos << '\n'; // cout << "n = " << RPM << " rpm\n"; // cout << "T_amb = " << T_amb << '\n'; - cout << "running = " << running << '\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 == 600) + if(count1 == 100) count1 = 0; */ - float ManXRPM = 0; - float Vo = 0; - float V1 = 0; + // Check parameters that may alter the operating state of the engine. + // (spark, fuel, starter motor etc) - // Parameters that alter the operation of the engine. (spark, fuel, starter motor etc) // Check for spark - int Magneto_Left = 0; - int Magneto_Right = 0; - int mag_pos = fgGetInt("/engines/engine[0]/magneto"); + bool Magneto_Left = false; + bool Magneto_Right = false; // Magneto positions: // 0 -> off // 1 -> left only @@ -412,9 +160,9 @@ void FGNewEngine::update() { spark = false; } // neglects battery voltage, master on switch, etc for now. if((mag_pos == 1) || (mag_pos > 2)) - Magneto_Left = 1; + Magneto_Left = true; if(mag_pos > 1) - Magneto_Right = 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)) { @@ -424,25 +172,22 @@ void FGNewEngine::update() { } // Need to make this better, eg position of fuel selector switch. // Check if we are turning the starter motor - bool temp = fgGetBool("/engines/engine[0]/starter"); - if(cranking != temp) { + if(cranking != starter) { // This check saves .../cranking from getting updated every loop - they only update when changed. - cranking = temp; - if(cranking) - fgSetBool("/engines/engine[0]/cranking", true); - else - fgSetBool("/engines/engine[0]/cranking", false); + 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 +// 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) @@ -451,22 +196,22 @@ void FGNewEngine::update() { // consider making a horrible noise if the starter is engaged with the engine running } } - if((!running) && (spark) && (fuel)) { + 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; - fgSetBool("/engines/engine[0]/running", true); - RPM = 600; +// 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; - fgSetBool("/engines/engine[0]/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; @@ -474,201 +219,192 @@ void FGNewEngine::update() { //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 - - //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 - rho_air = p_amb / ( R_air * T_amb ); - rho_air_manifold = rho_air * Manifold_Pressure / 29.6; //This is a bit of a roundabout way of calculating this but it works !! If we put manifold pressure into SI units we could do it simpler. - //calculate ideal engine volume inducted per second - swept_volume = (displacement_SI * (RPM / 60)) / 2; //This equation is only valid for a four stroke engine - //calculate volumetric efficiency - for now we will just use 0.8, but actually it is a function of engine speed and the exhaust to manifold pressure ratio - //Note that this is cylinder vol eff - the throttle drop is already accounted for in the MAP calculation - volumetric_efficiency = 0.8; - //Now use volumetric efficiency to calculate actual air volume inducted per second - v_dot_air = swept_volume * volumetric_efficiency; - //Now calculate mass flow rate of air into engine - m_dot_air = v_dot_air * rho_air_manifold; - -//************** - - //DCL - now calculate fuel flow into engine based on air flow and mixture lever position - //assume lever runs from no flow at fully out to thi = 1.3 at fully in at sea level - //also assume that the injector linkage is ideal - hence the set mixture is maintained at a given altitude throughout the speed and load range - thi_sea_level = 1.3 * ( Mixture_Lever_Pos / 100.0 ); - 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 + //Do the fuel flow calculations + Calc_Fuel_Flow_Gals_Hr(); - // 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; + //Calculate engine power + Calc_Percentage_Power(Magneto_Left, Magneto_Right); + HP = Percentage_Power * MaxHP / 100.0; + Power_SI = HP * CONVERT_HP_TO_WATTS; -/* -// Phil's %power correlation - // Calculate % Power - Percentage_Power = (+ 7E-09 * ManXRPM * ManXRPM) + ( + 7E-04 * ManXRPM) - 0.1218; - // cout << Percentage_Power << "%" << "\t"; -*/ + // 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 ??? -// DCL %power correlation - basically Phil's correlation modified to give slighty less power at the low end -// might need some adjustment as the prop model is adjusted -// My aim is to match the prop model and engine model at the low end to give the manufacturer's recommended idle speed with the throttle closed - 600rpm for the Continental IO520 - // Calculate % Power for Nev's prop model - //Percentage_Power = (+ 6E-09 * ManXRPM * ManXRPM) + ( + 8E-04 * ManXRPM) - 1.8524; + Torque_FMEP = (FMEP * displacement_SI) / (2.0 * LS_PI * n_R); - // Calculate %power for DCL prop model - Percentage_Power = (7e-9 * ManXRPM * ManXRPM) + (7e-4 * ManXRPM) - 1.0; + // 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"; + } - // Power de-rating for altitude has been removed now that we are basing the power - // on the actual manifold pressure, which takes air pressure into account. However - this fails to - // take the temperature into account - this is TODO. + //Calculate Exhaust gas temperature + if(running) + Calc_EGT(); + else + EGT = 298.0; - // 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; + // 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); - // Now Derate engine for the effects of Bad/Switched off magnetos - //if (Magneto_Left == 0 && Magneto_Right == 0) { - if(!running) { - // cout << "Both OFF\n"; - Percentage_Power = 0; - } else if (Magneto_Left && Magneto_Right) { - // cout << "Both On "; - } else if (Magneto_Left == 0 || Magneto_Right== 0) { - // cout << "1 Magneto Failed "; - Percentage_Power = Percentage_Power * ((100.0 - Mag_Derate_Percent)/100.0); - // cout << FGEng1_Percentage_Power << "%" << "\t"; + // 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; + } } - //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; + // 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; +} - // FMEP calculation. For now we will just use this during motored operation, ie when %Power == 0. - // Eventually we will calculate IMEP and use the FMEP all the time to give BMEP - // - if(Percentage_Power == 0) { - // 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; - } +//***************************************************************************************************** - Torque_FMEP = (FMEP * displacement_SI) / (2.0 * LS_PI * n_R); +// FGNewEngine member functions - HP = Percentage_Power * MaxHP / 100.0; +//////////////////////////////////////////////////////////////////////////////////////////// +// 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 + float neta_comb_actual = 0.0f; + float factor; - Power_SI = HP * CONVERT_HP_TO_WATTS; + int i; + int j = NUM_ELEMENTS; //This must be equal to the number of elements in the lookup table arrays - // 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"; + for(i=0;i thi[i]) && (thi_actual < thi[i + 1])) { + //do linear interpolation between the two points + factor = (thi_actual - thi[i]) / (thi[i+1] - thi[i]); + neta_comb_actual = (factor * (neta_comb[i+1] - neta_comb[i])) + neta_comb[i]; + return neta_comb_actual; + } } -//********************************************************************** -//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 - - // cout << "Combustion efficiency = " << combustion_efficiency << '\n'; - - //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; + //if we get here something has gone badly wrong + cout << "ERROR: error in FGNewEngine::Lookup_Combustion_Efficiency\n"; + return neta_comb_actual; +} - //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 the percentage of best mixture power available at a given mixture strength +// +// Based on data from "Technical Considerations for Catalysts for the European Market" +// by H S Gandi, published 1988 by IMechE +// +// Note that currently no attempt is made to set a lean limit on stable combustion +//////////////////////////////////////////////////////////////////////////////////////////// +float FGNewEngine::Power_Mixture_Correlation(float thi_actual) +{ + float AFR_actual = 14.7 / thi_actual; + // thi and thi_actual are equivalence ratio + const int NUM_ELEMENTS = 13; + // 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 = 0.0f; + float factor; + float dydx; - EGT *= 0.444 + ((0.544 - 0.444) * Percentage_Power / 100.0); + int i; + int j = NUM_ELEMENTS; //This must be equal to the number of elements in the lookup table arrays - EGT_degF = (EGT * 1.8) - 459.67; + for(i=0;i AFR[i]) && (AFR_actual < AFR[i + 1])) { + //do linear interpolation between the two points + factor = (AFR_actual - AFR[i]) / (AFR[i+1] - AFR[i]); + mixPerPow_actual = (factor * (mixPerPow[i+1] - mixPerPow[i])) + mixPerPow[i]; + return mixPerPow_actual; + } + } - //cout << " EGT = " << EGT << " degK " << EGT_degF << " degF";// << '\n'; + //if we get here something has gone badly wrong + cout << "ERROR: error in FGNewEngine::Power_Mixture_Correlation\n"; + return mixPerPow_actual; +} -//*************************************************************************************** // Calculate Cylinder Head Temperature - -/* 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. - -*/ - //CHT = Calc_CHT( Fuel_Flow, Mixture, IAS); - // cout << "Cylinder Head Temp (F) = " << CHT << endl; +// 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 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 @@ -686,6 +422,11 @@ the values from file to avoid the necessity for re-compilation every time I chan 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; v_apparent = IAS * 0.5144444; //convert from knots to m/s @@ -707,35 +448,209 @@ the values from file to avoid the necessity for re-compilation every time I chan 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 !! +} + +// Calculate exhaust gas temperature +void FGNewEngine::Calc_EGT() +{ + combustion_efficiency = Lookup_Combustion_Efficiency(equivalence_ratio); //The combustion efficiency basically tells us what proportion of the fuels calorific value is released + + //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; + + 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); +} + +// Calculate Manifold Pressure based on Throttle lever Position +float FGNewEngine::Calc_Manifold_Pressure ( float LeverPosn, float MaxMan, float MinMan) +{ + float Inches; + + //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; + + //Check for stopped engine (crudest way of compensating for engine speed) + if(RPM == 0) + Inches = 29.92; + + return Inches; +} + +// 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 + rho_air = p_amb / ( R_air * T_amb ); + rho_air_manifold = rho_air * Manifold_Pressure / 29.6; //This is a bit of a roundabout way of calculating this but it works !! If we put manifold pressure into SI units we could do it simpler. + //calculate ideal engine volume inducted per second + swept_volume = (displacement_SI * (RPM / 60)) / 2; //This equation is only valid for a four stroke engine + //calculate volumetric efficiency - for now we will just use 0.8, but actually it is a function of engine speed and the exhaust to manifold pressure ratio + //Note that this is cylinder vol eff - the throttle drop is already accounted for in the MAP calculation + volumetric_efficiency = 0.8; + //Now use volumetric efficiency to calculate actual air volume inducted per second + v_dot_air = swept_volume * volumetric_efficiency; + //Now calculate mass flow rate of air into engine + m_dot_air = v_dot_air * rho_air_manifold; + +//************** + + //DCL - now calculate fuel flow into engine based on air flow and mixture lever position + //assume lever runs from no flow at fully out to thi = 1.3 at fully in at sea level + //also assume that the injector linkage is ideal - hence the set mixture is maintained at a given altitude throughout the speed and load range + thi_sea_level = 1.3 * ( Mixture_Lever_Pos / 100.0 ); + 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 +} + +// 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 + float ManXRPM = True_Manifold_Pressure * RPM; + +/* +// Phil's %power correlation + // Calculate % Power + Percentage_Power = (+ 7E-09 * ManXRPM * ManXRPM) + ( + 7E-04 * ManXRPM) - 0.1218; + // cout << Percentage_Power << "%" << "\t"; +*/ + +// DCL %power correlation - basically Phil's correlation modified to give slighty less power at the low end +// might need some adjustment as the prop model is adjusted +// My aim is to match the prop model and engine model at the low end to give the manufacturer's recommended idle speed with the throttle closed - 600rpm for the Continental IO520 + // Calculate % Power for Nev's prop model + //Percentage_Power = (+ 6E-09 * ManXRPM * ManXRPM) + ( + 8E-04 * ManXRPM) - 1.8524; + + // Calculate %power for DCL prop model + Percentage_Power = (7e-9 * ManXRPM * ManXRPM) + (7e-4 * ManXRPM) - 1.0; + + // Power de-rating for altitude has been removed now that we are basing the power + // 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(!running) { + // cout << "Both OFF\n"; + Percentage_Power = 0; + } else if (mag_left && mag_right) { + // cout << "Both On "; + } 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; +} + +// 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 + } + + float dOilTempdt = (target_oil_temp - oil_temp) / time_constant; + + oil_temp += (dOilTempdt * time_step); + + return (oil_temp); +} + +// 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 + + Oil_Pressure = (Oil_Press_Relief_Valve / Oil_Press_RPM_Max) * Engine_RPM; + + // 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 adjust pressure according to Temp which affects the viscosity + + Oil_Pressure += (Design_Oil_Temp - Oil_Temp) * Oil_Viscosity_Index; + + return Oil_Pressure; +} + + +// 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 @@ -755,7 +670,7 @@ the values from file to avoid the necessity for re-compilation every time I chan //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; @@ -782,26 +697,4 @@ the values from file to avoid the necessity for re-compilation every time I chan 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 - // (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); - -// if(RPM < 0) -// RPM = 0; - - //DCL - stall the engine if RPM drops below 500 - this is possible if mixture lever is pulled right out -// if(RPM < 500) -// RPM = 0; - }