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 //these must be initialized this way as they are declared const
54 CONVERT_CUBIC_INCHES_TO_METERS_CUBED(1.638706e-5),
56 rho_fuel(800), // estimate
57 calorific_value_fuel(47.3e6),
64 MinManifoldPressure_inHg=6.5;
65 MaxManifoldPressure_inHg=28.5;
72 Name = Eng_cfg->GetValue("NAME");
73 Eng_cfg->GetNextConfigLine();
74 while (Eng_cfg->GetValue() != string("/FG_PISTON")) {
76 if (token == "MINMP") *Eng_cfg >> MinManifoldPressure_inHg;
77 else if (token == "MAXMP") *Eng_cfg >> MaxManifoldPressure_inHg;
78 else if (token == "DISPLACEMENT") *Eng_cfg >> Displacement;
79 else if (token == "MAXHP") *Eng_cfg >> MaxHP;
80 else if (token == "CYCLES") *Eng_cfg >> Cycles;
81 else if (token == "IDLERPM") *Eng_cfg >> IdleRPM;
82 else if (token == "MAXTHROTTLE") *Eng_cfg >> MaxThrottle;
83 else if (token == "MINTHROTTLE") *Eng_cfg >> MinThrottle;
84 else if (token == "SLFUELFLOWMAX") *Eng_cfg >> SLFuelFlowMax;
85 else cerr << "Unhandled token in Engine config file: " << token << endl;
89 cout << "\n Engine Name: " << Name << endl;
90 cout << " MinManifoldPressure: " << MinManifoldPressure_inHg << endl;
91 cout << " MaxManifoldPressure: " << MaxManifoldPressure_inHg << endl;
92 cout << " Displacement: " << Displacement << endl;
93 cout << " MaxHP: " << MaxHP << endl;
94 cout << " Cycles: " << Cycles << endl;
95 cout << " IdleRPM: " << IdleRPM << endl;
96 cout << " MaxThrottle: " << MaxThrottle << endl;
97 cout << " MinThrottle: " << MinThrottle << endl;
98 cout << " SLFuelFlowMax: " << SLFuelFlowMax << endl;
103 EngineNumber = 0; // FIXME: this should be the actual number
104 OilTemp_degK = 298; // FIXME: should be initialized in FGEngine
109 volumetric_efficiency = 0.8; // Actually f(speed, load) but this will get us running
111 // First column is thi, second is neta (combustion efficiency)
112 Lookup_Combustion_Efficiency = new FGTable(12);
113 *Lookup_Combustion_Efficiency << 0.00 << 0.980;
114 *Lookup_Combustion_Efficiency << 0.90 << 0.980;
115 *Lookup_Combustion_Efficiency << 1.00 << 0.970;
116 *Lookup_Combustion_Efficiency << 1.05 << 0.950;
117 *Lookup_Combustion_Efficiency << 1.10 << 0.900;
118 *Lookup_Combustion_Efficiency << 1.15 << 0.850;
119 *Lookup_Combustion_Efficiency << 1.20 << 0.790;
120 *Lookup_Combustion_Efficiency << 1.30 << 0.700;
121 *Lookup_Combustion_Efficiency << 1.40 << 0.630;
122 *Lookup_Combustion_Efficiency << 1.50 << 0.570;
123 *Lookup_Combustion_Efficiency << 1.60 << 0.525;
124 *Lookup_Combustion_Efficiency << 2.00 << 0.345;
127 cout << " Combustion Efficiency table:" << endl;
128 Lookup_Combustion_Efficiency->Print();
131 Power_Mixture_Correlation = new FGTable(13);
132 *Power_Mixture_Correlation << (14.7/1.6) << 78.0;
133 *Power_Mixture_Correlation << 10 << 86.0;
134 *Power_Mixture_Correlation << 11 << 93.5;
135 *Power_Mixture_Correlation << 12 << 98.0;
136 *Power_Mixture_Correlation << 13 << 100.0;
137 *Power_Mixture_Correlation << 14 << 99.0;
138 *Power_Mixture_Correlation << 15 << 96.4;
139 *Power_Mixture_Correlation << 16 << 92.5;
140 *Power_Mixture_Correlation << 17 << 88.0;
141 *Power_Mixture_Correlation << 18 << 83.0;
142 *Power_Mixture_Correlation << 19 << 78.5;
143 *Power_Mixture_Correlation << 20 << 74.0;
144 *Power_Mixture_Correlation << (14.7/0.6) << 58;
147 cout << " Power Mixture Correlation table:" << endl;
148 Power_Mixture_Correlation->Print();
151 if (debug_lvl & 2) cout << "Instantiated: FGPiston" << endl;
154 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
156 FGPiston::~FGPiston()
158 if (debug_lvl & 2) cout << "Destroyed: FGPiston" << endl;
161 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
163 double FGPiston::Calculate(double PowerRequired)
166 // FIXME: calculate from actual fuel flow
169 Throttle = FCS->GetThrottlePos(EngineNumber);
170 Mixture = FCS->GetMixturePos(EngineNumber);
176 p_amb = Atmosphere->GetPressure() * 48; // convert from lbs/ft2 to Pa
177 p_amb_sea_level = Atmosphere->GetPressureSL() * 48;
178 T_amb = Atmosphere->GetTemperature() * (5.0 / 9.0); // convert from Rankine to Kelvin
180 RPM = Propulsion->GetThruster(EngineNumber)->GetRPM();
181 //if (RPM < IdleRPM) RPM = IdleRPM; // kludge
183 IAS = Auxiliary->GetVcalibratedKTS();
185 if (Mixture >= 0.5) {
187 doManifoldPressure();
199 PowerAvailable = (HP * hptoftlbssec) - PowerRequired;
200 return PowerAvailable;
203 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
205 * Start or stop the engine.
208 void FGPiston::doEngineStartup(void)
210 // TODO: check magnetos, spark, starter, etc. and decide whether
213 // Check parameters that may alter the operating state of the engine.
214 // (spark, fuel, starter motor etc)
219 Magneto_Left = false;
220 Magneto_Right = false;
221 // Magneto positions:
230 } // neglects battery voltage, master on switch, etc for now.
232 if ((Magnetos == 1) || (Magnetos > 2)) Magneto_Left = true;
233 if (Magnetos > 1) Magneto_Right = true;
235 // Assume we have fuel for now
238 // Check if we are turning the starter motor
239 if (Cranking != Starter) {
240 // This check saves .../cranking from getting updated every loop - they
241 // only update when changed.
246 //Check mode of engine operation
247 // ACK - unfortunately this hack doesn't work in JSBSim since the RPM is reset
248 // each iteration by the propeller :-(
256 // consider making a horrible noise if the starter is engaged with
257 // the engine running
259 // TODO - find a better guess at cranking speed
262 // if ((!Running) && (spark) && (fuel) && (crank_counter > 120)) {
264 if ((!Running) && (spark) && (fuel)) {
265 // start the engine if revs high enough
267 // For now just instantaneously start but later we should maybe crank for
274 if ( (Running) && ((!spark)||(!fuel)) ) {
276 // note that we only cut the power - the engine may continue to
277 // spin if the prop is in a moving airstream
281 // And finally a last check for stalling
283 //Check if we have stalled the engine
286 } else if ((RPM <= 480) && (Cranking)) {
287 // Make sure the engine noise dosn't play if the engine won't
288 // start due to eg mixture lever pulled out.
294 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
297 * Calculate the nominal manifold pressure in inches hg
299 * This function calculates nominal manifold pressure directly
300 * from the throttle position, and does not adjust it for the
301 * difference between the pressure at sea level and the pressure
302 * at the current altitude (that adjustment takes place in
303 * {@link #doEnginePower}).
305 * TODO: changes in MP should not be instantaneous -- introduce
306 * a lag between throttle changes and MP changes, to allow pressure
307 * to build up or disperse.
309 * Inputs: MinManifoldPressure_inHg, MaxManifoldPressure_inHg, Throttle
311 * Outputs: ManifoldPressure_inHg
314 void FGPiston::doManifoldPressure(void)
316 ManifoldPressure_inHg = MinManifoldPressure_inHg +
317 (Throttle * (MaxManifoldPressure_inHg - MinManifoldPressure_inHg));
320 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
322 * Calculate the air flow through the engine.
324 * Inputs: p_amb, R_air, T_amb, ManifoldPressure_inHg, Displacement,
325 * RPM, volumetric_efficiency
327 * Outputs: rho_air, m_dot_air
330 void FGPiston::doAirFlow(void)
332 rho_air = p_amb / (R_air * T_amb);
333 double rho_air_manifold = rho_air * ManifoldPressure_inHg / 29.6;
334 double displacement_SI = Displacement * CONVERT_CUBIC_INCHES_TO_METERS_CUBED;
335 double swept_volume = (displacement_SI * (RPM/60)) / 2;
336 double v_dot_air = swept_volume * volumetric_efficiency;
337 m_dot_air = v_dot_air * rho_air_manifold;
340 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
342 * Calculate the fuel flow into the engine.
344 * Inputs: Mixture, thi_sea_level, p_amb_sea_level, p_amb, m_dot_air
346 * Outputs: equivalence_ratio, m_dot_fuel
349 void FGPiston::doFuelFlow(void)
351 double thi_sea_level = 1.3 * Mixture;
352 equivalence_ratio = thi_sea_level * p_amb_sea_level / p_amb;
353 m_dot_fuel = m_dot_air / 14.7 * equivalence_ratio;
356 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
358 * Calculate the power produced by the engine.
360 * <p>Currently, the JSBSim propellor model does not allow the
361 * engine to produce enough RPMs to get up to a high horsepower.
362 * When tested with sufficient RPM, it has no trouble reaching
365 * Inputs: ManifoldPressure_inHg, p_amb, p_amb_sea_level, RPM, T_amb,
366 * equivalence_ratio, Cycles, MaxHP
368 * Outputs: Percentage_Power, HP
371 void FGPiston::doEnginePower(void)
373 double True_ManifoldPressure_inHg = ManifoldPressure_inHg * p_amb / p_amb_sea_level;
374 double ManXRPM = True_ManifoldPressure_inHg * RPM;
375 // FIXME: this needs to be generalized
376 Percentage_Power = (6e-9 * ManXRPM * ManXRPM) + (8e-4 * ManXRPM) - 1.0;
377 double T_amb_degF = (T_amb * 1.8) - 459.67;
378 double T_amb_sea_lev_degF = (288 * 1.8) - 459.67;
380 Percentage_Power + ((T_amb_sea_lev_degF - T_amb_degF) * 7 /120);
381 double Percentage_of_best_power_mixture_power =
382 Power_Mixture_Correlation->GetValue(14.7 / equivalence_ratio);
384 Percentage_Power * Percentage_of_best_power_mixture_power / 100.0;
385 if (Percentage_Power < 0.0)
386 Percentage_Power = 0.0;
387 else if (Percentage_Power > 100.0)
388 Percentage_Power = 100.0;
389 HP = Percentage_Power * MaxHP / 100.0;
395 HP = 3.0 + ((480 - RPM) / 10.0);
400 // Quick hack until we port the FMEP stuff
409 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
411 * Calculate the exhaust gas temperature.
413 * Inputs: equivalence_ratio, m_dot_fuel, calorific_value_fuel,
414 * Cp_air, m_dot_air, Cp_fuel, m_dot_fuel, T_amb, Percentage_Power
416 * Outputs: combustion_efficiency, ExhaustGasTemp_degK
419 void FGPiston::doEGT(void)
421 combustion_efficiency = Lookup_Combustion_Efficiency->GetValue(equivalence_ratio);
422 double enthalpy_exhaust = m_dot_fuel * calorific_value_fuel *
423 combustion_efficiency * 0.33;
424 double heat_capacity_exhaust = (Cp_air * m_dot_air) + (Cp_fuel * m_dot_fuel);
425 double delta_T_exhaust = enthalpy_exhaust / heat_capacity_exhaust;
426 ExhaustGasTemp_degK = T_amb + delta_T_exhaust;
427 ExhaustGasTemp_degK *= 0.444 + ((0.544 - 0.444) * Percentage_Power / 100.0);
430 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
432 * Calculate the cylinder head temperature.
434 * Inputs: T_amb, IAS, rho_air, m_dot_fuel, calorific_value_fuel,
435 * combustion_efficiency, RPM
437 * Outputs: CylinderHeadTemp_degK
440 void FGPiston::doCHT(void)
446 double arbitary_area = 1.0;
447 double CpCylinderHead = 800.0;
448 double MassCylinderHead = 8.0;
450 double temperature_difference = CylinderHeadTemp_degK - T_amb;
451 double v_apparent = IAS * 0.5144444;
452 double v_dot_cooling_air = arbitary_area * v_apparent;
453 double m_dot_cooling_air = v_dot_cooling_air * rho_air;
454 double dqdt_from_combustion =
455 m_dot_fuel * calorific_value_fuel * combustion_efficiency * 0.33;
456 double dqdt_forced = (h2 * m_dot_cooling_air * temperature_difference) +
457 (h3 * RPM * temperature_difference);
458 double dqdt_free = h1 * temperature_difference;
459 double dqdt_cylinder_head = dqdt_from_combustion + dqdt_forced + dqdt_free;
461 double HeatCapacityCylinderHead = CpCylinderHead * MassCylinderHead;
463 CylinderHeadTemp_degK = dqdt_cylinder_head / HeatCapacityCylinderHead;
466 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
468 * Calculate the oil temperature.
470 * Inputs: Percentage_Power, running flag.
472 * Outputs: OilTemp_degK
475 void FGPiston::doOilTemperature(void)
477 double idle_percentage_power = 2.3; // approximately
478 double target_oil_temp; // Steady state oil temp at the current engine conditions
479 double time_constant; // The time constant for the differential equation
482 target_oil_temp = 363;
483 time_constant = 500; // Time constant for engine-on idling.
484 if (Percentage_Power > idle_percentage_power) {
485 time_constant /= ((Percentage_Power / idle_percentage_power) / 10.0); // adjust for power
488 target_oil_temp = 298;
489 time_constant = 1000; // Time constant for engine-off; reflects the fact
490 // that oil is no longer getting circulated
493 double dOilTempdt = (target_oil_temp - OilTemp_degK) / time_constant;
495 OilTemp_degK += (dOilTempdt * dt);
498 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
500 * Calculate the oil pressure.
504 * Outputs: OilPressure_psi
507 void FGPiston::doOilPressure(void)
509 double Oil_Press_Relief_Valve = 60; // FIXME: may vary by engine
510 double Oil_Press_RPM_Max = 1800; // FIXME: may vary by engine
511 double Design_Oil_Temp = 85; // FIXME: may vary by engine
512 // FIXME: WRONG!!! (85 degK???)
513 double Oil_Viscosity_Index = 0.25;
515 OilPressure_psi = (Oil_Press_Relief_Valve / Oil_Press_RPM_Max) * RPM;
517 if (OilPressure_psi >= Oil_Press_Relief_Valve) {
518 OilPressure_psi = Oil_Press_Relief_Valve;
521 OilPressure_psi += (Design_Oil_Temp - OilTemp_degK) * Oil_Viscosity_Index;
524 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
526 void FGPiston::Debug(void)
528 //TODO: Add your source code here