/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Module: FGPiston.cpp Author: Jon S. Berndt, JSBSim framework Dave Luff, Piston engine model Date started: 09/12/2000 Purpose: This module models a Piston engine ------------- Copyright (C) 2000 Jon S. Berndt (jsb@hal-pc.org) -------------- This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. 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 -------------------------------------------------------------------------------- This class descends from the FGEngine class and models a Piston engine based on parameters given in the engine config file for this class HISTORY -------------------------------------------------------------------------------- 09/12/2000 JSB Created %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% INCLUDES %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/ #include "FGPiston.h" #include "FGPropulsion.h" static const char *IdSrc = "$Id$"; static const char *IdHdr = ID_PISTON; /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% CLASS IMPLEMENTATION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/ FGPiston::FGPiston(FGFDMExec* exec, FGConfigFile* Eng_cfg) : FGEngine(exec), CONVERT_CUBIC_INCHES_TO_METERS_CUBED(1.638706e-5), R_air(287.3), rho_fuel(800), // estimate calorific_value_fuel(47.3e6), Cp_air(1005), Cp_fuel(1700) { string token; MinManifoldPressure_inHg = 6.5; MaxManifoldPressure_inHg = 28.5; Displacement = 360; MaxHP = 200; Cycles = 2; IdleRPM = 600; Name = Eng_cfg->GetValue("NAME"); Eng_cfg->GetNextConfigLine(); while (Eng_cfg->GetValue() != string("/FG_PISTON")) { *Eng_cfg >> token; if (token == "MINMP") *Eng_cfg >> MinManifoldPressure_inHg; else if (token == "MAXMP") *Eng_cfg >> MaxManifoldPressure_inHg; else if (token == "DISPLACEMENT") *Eng_cfg >> Displacement; else if (token == "MAXHP") *Eng_cfg >> MaxHP; else if (token == "CYCLES") *Eng_cfg >> Cycles; else if (token == "IDLERPM") *Eng_cfg >> IdleRPM; else if (token == "MAXTHROTTLE") *Eng_cfg >> MaxThrottle; else if (token == "MINTHROTTLE") *Eng_cfg >> MinThrottle; else cerr << "Unhandled token in Engine config file: " << token << endl; } Type = etPiston; crank_counter = 0; EngineNumber = 0; OilTemp_degK = 298; ManifoldPressure_inHg = Atmosphere->GetPressure() * 0.014138; // psf to in Hg dt = State->Getdt(); // Initialisation volumetric_efficiency = 0.8; // Actually f(speed, load) but this will get us running // First column is thi, second is neta (combustion efficiency) Lookup_Combustion_Efficiency = new FGTable(12); *Lookup_Combustion_Efficiency << 0.00 << 0.980; *Lookup_Combustion_Efficiency << 0.90 << 0.980; *Lookup_Combustion_Efficiency << 1.00 << 0.970; *Lookup_Combustion_Efficiency << 1.05 << 0.950; *Lookup_Combustion_Efficiency << 1.10 << 0.900; *Lookup_Combustion_Efficiency << 1.15 << 0.850; *Lookup_Combustion_Efficiency << 1.20 << 0.790; *Lookup_Combustion_Efficiency << 1.30 << 0.700; *Lookup_Combustion_Efficiency << 1.40 << 0.630; *Lookup_Combustion_Efficiency << 1.50 << 0.570; *Lookup_Combustion_Efficiency << 1.60 << 0.525; *Lookup_Combustion_Efficiency << 2.00 << 0.345; Power_Mixture_Correlation = new FGTable(13); *Power_Mixture_Correlation << (14.7/1.6) << 78.0; *Power_Mixture_Correlation << 10 << 86.0; *Power_Mixture_Correlation << 11 << 93.5; *Power_Mixture_Correlation << 12 << 98.0; *Power_Mixture_Correlation << 13 << 100.0; *Power_Mixture_Correlation << 14 << 99.0; *Power_Mixture_Correlation << 15 << 96.4; *Power_Mixture_Correlation << 16 << 92.5; *Power_Mixture_Correlation << 17 << 88.0; *Power_Mixture_Correlation << 18 << 83.0; *Power_Mixture_Correlation << 19 << 78.5; *Power_Mixture_Correlation << 20 << 74.0; *Power_Mixture_Correlation << (14.7/0.6) << 58; Debug(0); // Call Debug() routine from constructor if needed } //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% FGPiston::~FGPiston() { Debug(1); // Call Debug() routine from constructor if needed } //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% double FGPiston::Calculate(double PowerRequired) { ConsumeFuel(); Throttle = FCS->GetThrottlePos(EngineNumber); Mixture = FCS->GetMixturePos(EngineNumber); // // Input values. // p_amb = Atmosphere->GetPressure() * 48; // convert from lbs/ft2 to Pa p_amb_sea_level = Atmosphere->GetPressureSL() * 48; T_amb = Atmosphere->GetTemperature() * (5.0 / 9.0); // convert from Rankine to Kelvin RPM = Propulsion->GetThruster(EngineNumber)->GetRPM(); //if (RPM < IdleRPM) RPM = IdleRPM; // kludge IAS = Auxiliary->GetVcalibratedKTS(); doEngineStartup(); doManifoldPressure(); doAirFlow(); doFuelFlow(); //Now that the fuel flow is done check if the mixture is too lean to run the engine //Assume lean limit at 22 AFR for now - thats a thi of 0.668 //This might be a bit generous, but since there's currently no audiable warning of impending //cutout in the form of misfiring and/or rough running its probably reasonable for now. if (equivalence_ratio < 0.668) Running = false; doEnginePower(); doEGT(); doCHT(); doOilTemperature(); doOilPressure(); PowerAvailable = (HP * hptoftlbssec) - PowerRequired; return PowerAvailable; } //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% /** * Start or stop the engine. */ void FGPiston::doEngineStartup(void) { // Check parameters that may alter the operating state of the engine. // (spark, fuel, starter motor etc) bool spark; bool fuel; // Check for spark Magneto_Left = false; Magneto_Right = false; // Magneto positions: // 0 -> off // 1 -> left only // 2 -> right only // 3 -> both if (Magnetos != 0) { spark = true; } else { spark = false; } // neglects battery voltage, master on switch, etc for now. if ((Magnetos == 1) || (Magnetos > 2)) Magneto_Left = true; if (Magnetos > 1) Magneto_Right = true; // Assume we have fuel for now fuel = !Starved; // 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; } //Check mode of engine operation if (Cranking) { crank_counter++; if (RPM <= 480) { // Do nothing !! - cranking power output is now handled in the doPower section } else { // consider making a horrible noise if the starter is engaged with // the engine running } } // if ((!Running) && (spark) && (fuel) && (crank_counter > 120)) { if ((!Running) && (spark) && (fuel)) { // start the engine if revs high enough if (Cranking) { if ((RPM > 450) && (crank_counter > 175)) { //Add a little delay to startup on the starter Running = true; } } else { if (RPM > 450) { Running = true; //This allows us to in-air start when windmilling } } } 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; } // And finally a last check for stalling 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; } } } //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% /** * Calculate the nominal manifold pressure in inches hg * * This function calculates nominal manifold pressure directly * from the throttle position, and does not adjust it for the * difference between the pressure at sea level and the pressure * at the current altitude (that adjustment takes place in * {@link #doEnginePower}). * * TODO: changes in MP should not be instantaneous -- introduce * a lag between throttle changes and MP changes, to allow pressure * to build up or disperse. * * Inputs: MinManifoldPressure_inHg, MaxManifoldPressure_inHg, Throttle * * Outputs: ManifoldPressure_inHg */ void FGPiston::doManifoldPressure(void) { if (Running || Cranking) { ManifoldPressure_inHg = MinManifoldPressure_inHg + (Throttle * (MaxManifoldPressure_inHg - MinManifoldPressure_inHg)); } else { ManifoldPressure_inHg = Atmosphere->GetPressure() * 0.014138; // psf to in Hg } } //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% /** * Calculate the air flow through the engine. * * At this point, ManifoldPressure_inHg still represents the sea-level * MP, not adjusted for altitude. * * Inputs: p_amb, R_air, T_amb, ManifoldPressure_inHg, Displacement, * RPM, volumetric_efficiency * * Outputs: rho_air, m_dot_air */ void FGPiston::doAirFlow(void) { rho_air = p_amb / (R_air * T_amb); double rho_air_manifold = rho_air * ManifoldPressure_inHg / 29.6; double displacement_SI = Displacement * CONVERT_CUBIC_INCHES_TO_METERS_CUBED; double swept_volume = (displacement_SI * (RPM/60)) / 2; double v_dot_air = swept_volume * volumetric_efficiency; m_dot_air = v_dot_air * rho_air_manifold; } //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% /** * Calculate the fuel flow into the engine. * * Inputs: Mixture, thi_sea_level, p_amb_sea_level, p_amb, m_dot_air * * Outputs: equivalence_ratio, m_dot_fuel */ void FGPiston::doFuelFlow(void) { double thi_sea_level = 1.3 * Mixture; equivalence_ratio = thi_sea_level * p_amb_sea_level / p_amb; m_dot_fuel = m_dot_air / 14.7 * equivalence_ratio; FuelFlow_gph = m_dot_fuel * 3600 // seconds to hours * 2.2046 // kg to lb / 6.6; // lb to gal_us of kerosene } //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% /** * Calculate the power produced by the engine. * * Currently, the JSBSim propellor model does not allow the * engine to produce enough RPMs to get up to a high horsepower. * When tested with sufficient RPM, it has no trouble reaching * 200HP. * * Inputs: ManifoldPressure_inHg, p_amb, p_amb_sea_level, RPM, T_amb, * equivalence_ratio, Cycles, MaxHP * * Outputs: Percentage_Power, HP */ void FGPiston::doEnginePower(void) { ManifoldPressure_inHg *= p_amb / p_amb_sea_level; if (Running) { double ManXRPM = ManifoldPressure_inHg * RPM; // FIXME: this needs to be generalized Percentage_Power = (6e-9 * ManXRPM * ManXRPM) + (8e-4 * ManXRPM) - 1.0; double T_amb_degF = (T_amb * 1.8) - 459.67; double T_amb_sea_lev_degF = (288 * 1.8) - 459.67; Percentage_Power = Percentage_Power + ((T_amb_sea_lev_degF - T_amb_degF) * 7 /120); double Percentage_of_best_power_mixture_power = Power_Mixture_Correlation->GetValue(14.7 / equivalence_ratio); Percentage_Power = Percentage_Power * Percentage_of_best_power_mixture_power / 100.0; if (Percentage_Power < 0.0) Percentage_Power = 0.0; else if (Percentage_Power > 100.0) Percentage_Power = 100.0; HP = Percentage_Power * MaxHP / 100.0; } else { // Power output when the engine is not running if (Cranking) { if (RPM < 10) { HP = 3.0; // This is a hack to prevent overshooting the idle rpm in the first time step // It may possibly need to be changed if the prop model is changed. } else if (RPM < 480) { HP = 3.0 + ((480 - RPM) / 10.0); // This is a guess - would be nice to find a proper starter moter torque curve } else { HP = 3.0; } } else { // Quick hack until we port the FMEP stuff if (RPM > 0.0) HP = -1.5; else HP = 0.0; } } } //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% /** * Calculate the exhaust gas temperature. * * Inputs: equivalence_ratio, m_dot_fuel, calorific_value_fuel, * Cp_air, m_dot_air, Cp_fuel, m_dot_fuel, T_amb, Percentage_Power * * Outputs: combustion_efficiency, ExhaustGasTemp_degK */ void FGPiston::doEGT(void) { double delta_T_exhaust; double enthalpy_exhaust; double heat_capacity_exhaust; double dEGTdt; if ((Running) && (m_dot_air > 0.0)) { // do the energy balance combustion_efficiency = Lookup_Combustion_Efficiency->GetValue(equivalence_ratio); 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; ExhaustGasTemp_degK = T_amb + delta_T_exhaust; ExhaustGasTemp_degK *= 0.444 + ((0.544 - 0.444) * Percentage_Power / 100.0); } else { // Drop towards ambient - guess an appropriate time constant for now dEGTdt = (298.0 - ExhaustGasTemp_degK) / 100.0; delta_T_exhaust = dEGTdt * dt; ExhaustGasTemp_degK += delta_T_exhaust; } } //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% /** * Calculate the cylinder head temperature. * * Inputs: T_amb, IAS, rho_air, m_dot_fuel, calorific_value_fuel, * combustion_efficiency, RPM * * Outputs: CylinderHeadTemp_degK */ void FGPiston::doCHT(void) { double h1 = -95.0; double h2 = -3.95; double h3 = -0.05; double arbitary_area = 1.0; double CpCylinderHead = 800.0; double MassCylinderHead = 8.0; double temperature_difference = CylinderHeadTemp_degK - T_amb; double v_apparent = IAS * 0.5144444; double v_dot_cooling_air = arbitary_area * v_apparent; double m_dot_cooling_air = v_dot_cooling_air * rho_air; double dqdt_from_combustion = m_dot_fuel * calorific_value_fuel * combustion_efficiency * 0.33; double dqdt_forced = (h2 * m_dot_cooling_air * temperature_difference) + (h3 * RPM * temperature_difference); double dqdt_free = h1 * temperature_difference; double dqdt_cylinder_head = dqdt_from_combustion + dqdt_forced + dqdt_free; double HeatCapacityCylinderHead = CpCylinderHead * MassCylinderHead; CylinderHeadTemp_degK += (dqdt_cylinder_head / HeatCapacityCylinderHead) * dt; } //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% /** * Calculate the oil temperature. * * Inputs: Percentage_Power, running flag. * * Outputs: OilTemp_degK */ void FGPiston::doOilTemperature(void) { double idle_percentage_power = 2.3; // approximately double target_oil_temp; // Steady state oil temp at the current engine conditions double 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 } double dOilTempdt = (target_oil_temp - OilTemp_degK) / time_constant; OilTemp_degK += (dOilTempdt * dt); } //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% /** * Calculate the oil pressure. * * Inputs: RPM * * Outputs: OilPressure_psi */ void FGPiston::doOilPressure(void) { double Oil_Press_Relief_Valve = 60; // FIXME: may vary by engine double Oil_Press_RPM_Max = 1800; // FIXME: may vary by engine double Design_Oil_Temp = 358; // degK; FIXME: may vary by engine double Oil_Viscosity_Index = 0.25; OilPressure_psi = (Oil_Press_Relief_Valve / Oil_Press_RPM_Max) * RPM; if (OilPressure_psi >= Oil_Press_Relief_Valve) { OilPressure_psi = Oil_Press_Relief_Valve; } OilPressure_psi += (Design_Oil_Temp - OilTemp_degK) * Oil_Viscosity_Index; } //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% // // The bitmasked value choices are as follows: // unset: In this case (the default) JSBSim would only print // out the normally expected messages, essentially echoing // the config files as they are read. If the environment // variable is not set, debug_lvl is set to 1 internally // 0: This requests JSBSim not to output any messages // whatsoever. // 1: This value explicity requests the normal JSBSim // startup messages // 2: This value asks for a message to be printed out when // a class is instantiated // 4: When this value is set, a message is displayed when a // FGModel object executes its Run() method // 8: When this value is set, various runtime state variables // are printed out periodically // 16: When set various parameters are sanity checked and // a message is printed out when they go out of bounds void FGPiston::Debug(int from) { if (debug_lvl <= 0) return; if (debug_lvl & 1) { // Standard console startup message output if (from == 0) { // Constructor cout << "\n Engine Name: " << Name << endl; cout << " MinManifoldPressure: " << MinManifoldPressure_inHg << endl; cout << " MaxManifoldPressure: " << MaxManifoldPressure_inHg << endl; cout << " Displacement: " << Displacement << endl; cout << " MaxHP: " << MaxHP << endl; cout << " Cycles: " << Cycles << endl; cout << " IdleRPM: " << IdleRPM << endl; cout << " MaxThrottle: " << MaxThrottle << endl; cout << " MinThrottle: " << MinThrottle << endl; cout << endl; cout << " Combustion Efficiency table:" << endl; Lookup_Combustion_Efficiency->Print(); cout << endl; cout << endl; cout << " Power Mixture Correlation table:" << endl; Power_Mixture_Correlation->Print(); cout << endl; } } if (debug_lvl & 2 ) { // Instantiation/Destruction notification if (from == 0) cout << "Instantiated: FGPiston" << endl; if (from == 1) cout << "Destroyed: FGPiston" << endl; } if (debug_lvl & 4 ) { // Run() method entry print for FGModel-derived objects } if (debug_lvl & 8 ) { // Runtime state variables } if (debug_lvl & 16) { // Sanity checking } if (debug_lvl & 64) { if (from == 0) { // Constructor cout << IdSrc << endl; cout << IdHdr << endl; } } } double FGPiston::CalcFuelNeed(void) { return FuelFlow_gph / 3600 * State->Getdt() * Propulsion->GetRate(); }