/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Module: FGPiston.cpp Author: Jon S. Berndt 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 "FGDefs.h" #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), MinManifoldPressure_inHg(6.5), MaxManifoldPressure_inHg(28.5), Displacement(360), MaxHP(200), Cycles(2), IdleRPM(900), // Set constants 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), running(true), // FIXME: FGEngine already has 'Running' cranking(false) { string token; Name = Eng_cfg->GetValue("NAME"); Eng_cfg->GetNextConfigLine(); while (Eng_cfg->GetValue() != "/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 if (token == "SLFUELFLOWMAX") *Eng_cfg >> SLFuelFlowMax; else cerr << "Unhandled token in Engine config file: " << token << endl; } if (debug_lvl > 0) { 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 << " SLFuelFlowMax: " << SLFuelFlowMax << endl; } Type = etPiston; EngineNumber = 0; // FIXME: this should be the actual number OilTemp_degK = 298; // FIXME: should be initialized in FGEngine dt = State->Getdt(); // Initialisation volumetric_efficiency = 0.8; // Actually f(speed, load) but this will get us running if (debug_lvl & 2) cout << "Instantiated: FGPiston" << endl; } //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% FGPiston::~FGPiston() { if (debug_lvl & 2) cout << "Destroyed: FGPiston" << endl; } //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% float FGPiston::Calculate(float PowerRequired) { float h,EngineMaxPower; // FIXME: calculate from actual fuel flow ConsumeFuel(); Throttle = FCS->GetThrottlePos(EngineNumber); Mixture = FCS->GetMixturePos(EngineNumber); // // Input values. // // convert from lbs/ft2 to Pa p_amb = Atmosphere->GetPressure() * 48; p_amb_sea_level = Atmosphere->GetPressureSL() * 48; // convert from Rankine to Kelvin T_amb = Atmosphere->GetTemperature() * (5.0 / 9.0); RPM = Propulsion->GetThruster(EngineNumber)->GetRPM(); if (RPM < IdleRPM) // kludge RPM = IdleRPM; IAS = Auxiliary->GetVcalibratedKTS(); if (Mixture >= 0.5) { doEngineStartup(); doManifoldPressure(); doAirFlow(); doFuelFlow(); doEnginePower(); doEGT(); doCHT(); doOilTemperature(); doOilPressure(); } else { HP = 0; } PowerAvailable = (HP * HPTOFTLBSSEC) - PowerRequired; return PowerAvailable; } //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% /** * Look up the power/mixture correlation. * * FIXME: this should use JSBSim's interpolation support. */ static float Power_Mixture_Correlation(float thi_actual) { float AFR_actual = 14.7 / thi_actual; const int NUM_ELEMENTS = 13; float AFR[NUM_ELEMENTS] = {(14.7/1.6), 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, (14.7/0.6)}; float mixPerPow[NUM_ELEMENTS] = {78, 86, 93.5, 98, 100, 99, 96.4, 92.5, 88, 83, 78.5, 74, 58}; float mixPerPow_actual = 0.0f; float factor; float dydx; int i; int j = NUM_ELEMENTS; for (i=0;i AFR[i]) && (AFR_actual < AFR[i + 1])) { factor = (AFR_actual - AFR[i]) / (AFR[i+1] - AFR[i]); mixPerPow_actual = (factor * (mixPerPow[i+1] - mixPerPow[i])) + mixPerPow[i]; return mixPerPow_actual; } } cerr << "ERROR: error in FGNewEngine::Power_Mixture_Correlation\n"; return mixPerPow_actual; } //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% /** * Look up the combustion efficiency. * * * FIXME: this should use JSBSim's interpolation support. */ static float 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 cerr << "ERROR: error in FGNewEngine::Lookup_Combustion_Efficiency\n"; return neta_comb_actual; } //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% /** * Start or stop the engine. */ void FGPiston::doEngineStartup(void) { // TODO: check magnetos, spark, starter, etc. and decide whether // engine is running } //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% /** * 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) { ManifoldPressure_inHg = MinManifoldPressure_inHg + (Throttle * (MaxManifoldPressure_inHg - MinManifoldPressure_inHg)); } //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% /** * Calculate the air flow through the engine. * * 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); float rho_air_manifold = rho_air * ManifoldPressure_inHg / 29.6; float displacement_SI = Displacement * CONVERT_CUBIC_INCHES_TO_METERS_CUBED; float swept_volume = (displacement_SI * (RPM/60)) / 2; float 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) { float 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; } //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% /** * 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) { float True_ManifoldPressure_inHg = ManifoldPressure_inHg * p_amb / p_amb_sea_level; float ManXRPM = True_ManifoldPressure_inHg * RPM; // FIXME: this needs to be generalized Percentage_Power = (6e-9 * ManXRPM * ManXRPM) + (8e-4 * ManXRPM) - 1.0; 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); float Percentage_of_best_power_mixture_power = Power_Mixture_Correlation(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; } //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% /** * 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) { combustion_efficiency = Lookup_Combustion_Efficiency(equivalence_ratio); float enthalpy_exhaust = m_dot_fuel * calorific_value_fuel * combustion_efficiency * 0.33; float heat_capacity_exhaust = (Cp_air * m_dot_air) + (Cp_fuel * m_dot_fuel); float 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); } //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% /** * 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) { float h1 = -95.0; float h2 = -3.95; float h3 = -0.05; float arbitary_area = 1.0; float CpCylinderHead = 800.0; float MassCylinderHead = 8.0; float temperature_difference = CylinderHeadTemp_degK - T_amb; float v_apparent = IAS * 0.5144444; float v_dot_cooling_air = arbitary_area * v_apparent; float m_dot_cooling_air = v_dot_cooling_air * rho_air; float dqdt_from_combustion = m_dot_fuel * calorific_value_fuel * combustion_efficiency * 0.33; float dqdt_forced = (h2 * m_dot_cooling_air * temperature_difference) + (h3 * RPM * temperature_difference); float dqdt_free = h1 * temperature_difference; float dqdt_cylinder_head = dqdt_from_combustion + dqdt_forced + dqdt_free; float HeatCapacityCylinderHead = CpCylinderHead * MassCylinderHead; CylinderHeadTemp_degK = dqdt_cylinder_head / HeatCapacityCylinderHead; } //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% /** * Calculate the oil temperature. * * Inputs: Percentage_Power, running flag. * * Outputs: OilTemp_degK */ void FGPiston::doOilTemperature(void) { 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 - OilTemp_degK) / time_constant; OilTemp_degK += (dOilTempdt * dt); } //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% /** * Calculate the oil pressure. * * Inputs: RPM * * Outputs: OilPressure_psi */ void FGPiston::doOilPressure(void) { float Oil_Press_Relief_Valve = 60; // FIXME: may vary by engine float Oil_Press_RPM_Max = 1800; // FIXME: may vary by engine float Design_Oil_Temp = 85; // FIXME: may vary by engine // FIXME: WRONG!!! (85 degK???) float 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; } //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% void FGPiston::Debug(void) { //TODO: Add your source code here }