1 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
5 Date started: 09/12/2000
6 Purpose: This module models a Piston engine
8 ------------- Copyright (C) 2000 Jon S. Berndt (jsb@hal-pc.org) --------------
10 This program is free software; you can redistribute it and/or modify it under
11 the terms of the GNU General Public License as published by the Free Software
12 Foundation; either version 2 of the License, or (at your option) any later
15 This program is distributed in the hope that it will be useful, but WITHOUT
16 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
17 FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
20 You should have received a copy of the GNU General Public License along with
21 this program; if not, write to the Free Software Foundation, Inc., 59 Temple
22 Place - Suite 330, Boston, MA 02111-1307, USA.
24 Further information about the GNU General Public License can also be found on
25 the world wide web at http://www.gnu.org.
27 FUNCTIONAL DESCRIPTION
28 --------------------------------------------------------------------------------
30 This class descends from the FGEngine class and models a Piston engine based on
31 parameters given in the engine config file for this class
34 --------------------------------------------------------------------------------
35 09/12/2000 JSB Created
37 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
39 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
42 #include "FGPropulsion.h"
44 static const char *IdSrc = "$Id$";
45 static const char *IdHdr = ID_PISTON;
47 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
49 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
51 FGPiston::FGPiston(FGFDMExec* exec, FGConfigFile* Eng_cfg)
53 MinManifoldPressure_inHg(6.5),
54 MaxManifoldPressure_inHg(28.5),
60 CONVERT_CUBIC_INCHES_TO_METERS_CUBED(1.638706e-5),
62 rho_fuel(800), // estimate
63 calorific_value_fuel(47.3e6),
69 Name = Eng_cfg->GetValue("NAME");
70 Eng_cfg->GetNextConfigLine();
71 while (Eng_cfg->GetValue() != string("/FG_PISTON")) {
73 if (token == "MINMP") *Eng_cfg >> MinManifoldPressure_inHg;
74 else if (token == "MAXMP") *Eng_cfg >> MaxManifoldPressure_inHg;
75 else if (token == "DISPLACEMENT") *Eng_cfg >> Displacement;
76 else if (token == "MAXHP") *Eng_cfg >> MaxHP;
77 else if (token == "CYCLES") *Eng_cfg >> Cycles;
78 else if (token == "IDLERPM") *Eng_cfg >> IdleRPM;
79 else if (token == "MAXTHROTTLE") *Eng_cfg >> MaxThrottle;
80 else if (token == "MINTHROTTLE") *Eng_cfg >> MinThrottle;
81 else if (token == "SLFUELFLOWMAX") *Eng_cfg >> SLFuelFlowMax;
82 else cerr << "Unhandled token in Engine config file: " << token << endl;
86 cout << "\n Engine Name: " << Name << endl;
87 cout << " MinManifoldPressure: " << MinManifoldPressure_inHg << endl;
88 cout << " MaxManifoldPressure: " << MaxManifoldPressure_inHg << endl;
89 cout << " Displacement: " << Displacement << endl;
90 cout << " MaxHP: " << MaxHP << endl;
91 cout << " Cycles: " << Cycles << endl;
92 cout << " IdleRPM: " << IdleRPM << endl;
93 cout << " MaxThrottle: " << MaxThrottle << endl;
94 cout << " MinThrottle: " << MinThrottle << endl;
95 cout << " SLFuelFlowMax: " << SLFuelFlowMax << endl;
100 EngineNumber = 0; // FIXME: this should be the actual number
101 OilTemp_degK = 298; // FIXME: should be initialized in FGEngine
106 volumetric_efficiency = 0.8; // Actually f(speed, load) but this will get us running
108 // First column is thi, second is neta (combustion efficiency)
109 Lookup_Combustion_Efficiency = new FGTable(12);
110 *Lookup_Combustion_Efficiency << 0.00 << 0.980;
111 *Lookup_Combustion_Efficiency << 0.90 << 0.980;
112 *Lookup_Combustion_Efficiency << 1.00 << 0.970;
113 *Lookup_Combustion_Efficiency << 1.05 << 0.950;
114 *Lookup_Combustion_Efficiency << 1.10 << 0.900;
115 *Lookup_Combustion_Efficiency << 1.15 << 0.850;
116 *Lookup_Combustion_Efficiency << 1.20 << 0.790;
117 *Lookup_Combustion_Efficiency << 1.30 << 0.700;
118 *Lookup_Combustion_Efficiency << 1.40 << 0.630;
119 *Lookup_Combustion_Efficiency << 1.50 << 0.570;
120 *Lookup_Combustion_Efficiency << 1.60 << 0.525;
121 *Lookup_Combustion_Efficiency << 2.00 << 0.345;
124 cout << " Combustion Efficiency table:" << endl;
125 Lookup_Combustion_Efficiency->Print();
128 Power_Mixture_Correlation = new FGTable(13);
129 *Power_Mixture_Correlation << (14.7/1.6) << 78.0;
130 *Power_Mixture_Correlation << 10 << 86.0;
131 *Power_Mixture_Correlation << 11 << 93.5;
132 *Power_Mixture_Correlation << 12 << 98.0;
133 *Power_Mixture_Correlation << 13 << 100.0;
134 *Power_Mixture_Correlation << 14 << 99.0;
135 *Power_Mixture_Correlation << 15 << 96.4;
136 *Power_Mixture_Correlation << 16 << 92.5;
137 *Power_Mixture_Correlation << 17 << 88.0;
138 *Power_Mixture_Correlation << 18 << 83.0;
139 *Power_Mixture_Correlation << 19 << 78.5;
140 *Power_Mixture_Correlation << 20 << 74.0;
141 *Power_Mixture_Correlation << (14.7/0.6) << 58;
144 cout << " Power Mixture Correlation table:" << endl;
145 Power_Mixture_Correlation->Print();
148 if (debug_lvl & 2) cout << "Instantiated: FGPiston" << endl;
151 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
153 FGPiston::~FGPiston()
155 if (debug_lvl & 2) cout << "Destroyed: FGPiston" << endl;
158 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
160 double FGPiston::Calculate(double PowerRequired)
162 double h,EngineMaxPower;
164 // FIXME: calculate from actual fuel flow
167 Throttle = FCS->GetThrottlePos(EngineNumber);
168 Mixture = FCS->GetMixturePos(EngineNumber);
174 p_amb = Atmosphere->GetPressure() * 48; // convert from lbs/ft2 to Pa
175 p_amb_sea_level = Atmosphere->GetPressureSL() * 48;
176 T_amb = Atmosphere->GetTemperature() * (5.0 / 9.0); // convert from Rankine to Kelvin
178 RPM = Propulsion->GetThruster(EngineNumber)->GetRPM();
179 //if (RPM < IdleRPM) RPM = IdleRPM; // kludge
181 IAS = Auxiliary->GetVcalibratedKTS();
183 if (Mixture >= 0.5) {
185 doManifoldPressure();
197 PowerAvailable = (HP * hptoftlbssec) - PowerRequired;
198 return PowerAvailable;
201 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
203 * Start or stop the engine.
206 void FGPiston::doEngineStartup(void)
208 // TODO: check magnetos, spark, starter, etc. and decide whether
211 // Check parameters that may alter the operating state of the engine.
212 // (spark, fuel, starter motor etc)
217 Magneto_Left = false;
218 Magneto_Right = false;
219 // Magneto positions:
228 } // neglects battery voltage, master on switch, etc for now.
230 if ((Magnetos == 1) || (Magnetos > 2)) Magneto_Left = true;
231 if (Magnetos > 1) Magneto_Right = true;
233 // Assume we have fuel for now
236 // Check if we are turning the starter motor
237 if (Cranking != Starter) {
238 // This check saves .../cranking from getting updated every loop - they
239 // only update when changed.
244 //Check mode of engine operation
245 // ACK - unfortunately this hack doesn't work in JSBSim since the RPM is reset
246 // each iteration by the propeller :-(
254 // consider making a horrible noise if the starter is engaged with
255 // the engine running
257 // TODO - find a better guess at cranking speed
260 // if ((!Running) && (spark) && (fuel) && (crank_counter > 120)) {
262 if ((!Running) && (spark) && (fuel)) {
263 // start the engine if revs high enough
265 // For now just instantaneously start but later we should maybe crank for
272 if ( (Running) && ((!spark)||(!fuel)) ) {
274 // note that we only cut the power - the engine may continue to
275 // spin if the prop is in a moving airstream
279 // And finally a last check for stalling
281 //Check if we have stalled the engine
284 } else if ((RPM <= 480) && (Cranking)) {
285 // Make sure the engine noise dosn't play if the engine won't
286 // start due to eg mixture lever pulled out.
292 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
295 * Calculate the nominal manifold pressure in inches hg
297 * This function calculates nominal manifold pressure directly
298 * from the throttle position, and does not adjust it for the
299 * difference between the pressure at sea level and the pressure
300 * at the current altitude (that adjustment takes place in
301 * {@link #doEnginePower}).
303 * TODO: changes in MP should not be instantaneous -- introduce
304 * a lag between throttle changes and MP changes, to allow pressure
305 * to build up or disperse.
307 * Inputs: MinManifoldPressure_inHg, MaxManifoldPressure_inHg, Throttle
309 * Outputs: ManifoldPressure_inHg
312 void FGPiston::doManifoldPressure(void)
314 ManifoldPressure_inHg = MinManifoldPressure_inHg +
315 (Throttle * (MaxManifoldPressure_inHg - MinManifoldPressure_inHg));
318 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
320 * Calculate the air flow through the engine.
322 * Inputs: p_amb, R_air, T_amb, ManifoldPressure_inHg, Displacement,
323 * RPM, volumetric_efficiency
325 * Outputs: rho_air, m_dot_air
328 void FGPiston::doAirFlow(void)
330 rho_air = p_amb / (R_air * T_amb);
331 double rho_air_manifold = rho_air * ManifoldPressure_inHg / 29.6;
332 double displacement_SI = Displacement * CONVERT_CUBIC_INCHES_TO_METERS_CUBED;
333 double swept_volume = (displacement_SI * (RPM/60)) / 2;
334 double v_dot_air = swept_volume * volumetric_efficiency;
335 m_dot_air = v_dot_air * rho_air_manifold;
338 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
340 * Calculate the fuel flow into the engine.
342 * Inputs: Mixture, thi_sea_level, p_amb_sea_level, p_amb, m_dot_air
344 * Outputs: equivalence_ratio, m_dot_fuel
347 void FGPiston::doFuelFlow(void)
349 double thi_sea_level = 1.3 * Mixture;
350 equivalence_ratio = thi_sea_level * p_amb_sea_level / p_amb;
351 m_dot_fuel = m_dot_air / 14.7 * equivalence_ratio;
354 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
356 * Calculate the power produced by the engine.
358 * <p>Currently, the JSBSim propellor model does not allow the
359 * engine to produce enough RPMs to get up to a high horsepower.
360 * When tested with sufficient RPM, it has no trouble reaching
363 * Inputs: ManifoldPressure_inHg, p_amb, p_amb_sea_level, RPM, T_amb,
364 * equivalence_ratio, Cycles, MaxHP
366 * Outputs: Percentage_Power, HP
369 void FGPiston::doEnginePower(void)
371 double True_ManifoldPressure_inHg = ManifoldPressure_inHg * p_amb / p_amb_sea_level;
372 double ManXRPM = True_ManifoldPressure_inHg * RPM;
373 // FIXME: this needs to be generalized
374 Percentage_Power = (6e-9 * ManXRPM * ManXRPM) + (8e-4 * ManXRPM) - 1.0;
375 double T_amb_degF = (T_amb * 1.8) - 459.67;
376 double T_amb_sea_lev_degF = (288 * 1.8) - 459.67;
378 Percentage_Power + ((T_amb_sea_lev_degF - T_amb_degF) * 7 /120);
379 double Percentage_of_best_power_mixture_power =
380 Power_Mixture_Correlation->GetValue(14.7 / equivalence_ratio);
382 Percentage_Power * Percentage_of_best_power_mixture_power / 100.0;
383 if (Percentage_Power < 0.0)
384 Percentage_Power = 0.0;
385 else if (Percentage_Power > 100.0)
386 Percentage_Power = 100.0;
387 HP = Percentage_Power * MaxHP / 100.0;
393 HP = 3.0 + ((480 - RPM) / 10.0);
398 // Quick hack until we port the FMEP stuff
407 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
409 * Calculate the exhaust gas temperature.
411 * Inputs: equivalence_ratio, m_dot_fuel, calorific_value_fuel,
412 * Cp_air, m_dot_air, Cp_fuel, m_dot_fuel, T_amb, Percentage_Power
414 * Outputs: combustion_efficiency, ExhaustGasTemp_degK
417 void FGPiston::doEGT(void)
419 combustion_efficiency = Lookup_Combustion_Efficiency->GetValue(equivalence_ratio);
420 double enthalpy_exhaust = m_dot_fuel * calorific_value_fuel *
421 combustion_efficiency * 0.33;
422 double heat_capacity_exhaust = (Cp_air * m_dot_air) + (Cp_fuel * m_dot_fuel);
423 double delta_T_exhaust = enthalpy_exhaust / heat_capacity_exhaust;
424 ExhaustGasTemp_degK = T_amb + delta_T_exhaust;
425 ExhaustGasTemp_degK *= 0.444 + ((0.544 - 0.444) * Percentage_Power / 100.0);
428 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
430 * Calculate the cylinder head temperature.
432 * Inputs: T_amb, IAS, rho_air, m_dot_fuel, calorific_value_fuel,
433 * combustion_efficiency, RPM
435 * Outputs: CylinderHeadTemp_degK
438 void FGPiston::doCHT(void)
444 double arbitary_area = 1.0;
445 double CpCylinderHead = 800.0;
446 double MassCylinderHead = 8.0;
448 double temperature_difference = CylinderHeadTemp_degK - T_amb;
449 double v_apparent = IAS * 0.5144444;
450 double v_dot_cooling_air = arbitary_area * v_apparent;
451 double m_dot_cooling_air = v_dot_cooling_air * rho_air;
452 double dqdt_from_combustion =
453 m_dot_fuel * calorific_value_fuel * combustion_efficiency * 0.33;
454 double dqdt_forced = (h2 * m_dot_cooling_air * temperature_difference) +
455 (h3 * RPM * temperature_difference);
456 double dqdt_free = h1 * temperature_difference;
457 double dqdt_cylinder_head = dqdt_from_combustion + dqdt_forced + dqdt_free;
459 double HeatCapacityCylinderHead = CpCylinderHead * MassCylinderHead;
461 CylinderHeadTemp_degK = dqdt_cylinder_head / HeatCapacityCylinderHead;
464 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
466 * Calculate the oil temperature.
468 * Inputs: Percentage_Power, running flag.
470 * Outputs: OilTemp_degK
473 void FGPiston::doOilTemperature(void)
475 double idle_percentage_power = 2.3; // approximately
476 double target_oil_temp; // Steady state oil temp at the current engine conditions
477 double time_constant; // The time constant for the differential equation
480 target_oil_temp = 363;
481 time_constant = 500; // Time constant for engine-on idling.
482 if (Percentage_Power > idle_percentage_power) {
483 time_constant /= ((Percentage_Power / idle_percentage_power) / 10.0); // adjust for power
486 target_oil_temp = 298;
487 time_constant = 1000; // Time constant for engine-off; reflects the fact
488 // that oil is no longer getting circulated
491 double dOilTempdt = (target_oil_temp - OilTemp_degK) / time_constant;
493 OilTemp_degK += (dOilTempdt * dt);
496 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
498 * Calculate the oil pressure.
502 * Outputs: OilPressure_psi
505 void FGPiston::doOilPressure(void)
507 double Oil_Press_Relief_Valve = 60; // FIXME: may vary by engine
508 double Oil_Press_RPM_Max = 1800; // FIXME: may vary by engine
509 double Design_Oil_Temp = 85; // FIXME: may vary by engine
510 // FIXME: WRONG!!! (85 degK???)
511 double Oil_Viscosity_Index = 0.25;
513 OilPressure_psi = (Oil_Press_Relief_Valve / Oil_Press_RPM_Max) * RPM;
515 if (OilPressure_psi >= Oil_Press_Relief_Valve) {
516 OilPressure_psi = Oil_Press_Relief_Valve;
519 OilPressure_psi += (Design_Oil_Temp - OilTemp_degK) * Oil_Viscosity_Index;
522 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
524 void FGPiston::Debug(void)
526 //TODO: Add your source code here