Module: FGPiston.cpp
Author: Jon S. Berndt, JSBSim framework
Dave Luff, Piston engine model
+ Ronald Jensen, Piston engine model
Date started: 09/12/2000
Purpose: This module models a Piston engine
Cycles = 2;
IdleRPM = 600;
+ MaxRPM = 2800;
Displacement = 360;
SparkFailDrop = 1.0;
MaxHP = 200;
MinManifoldPressure_inHg = 6.5;
MaxManifoldPressure_inHg = 28.5;
+ BSFC = 0.45;
// These are internal program variables
*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;
+ *Power_Mixture_Correlation << (14.7/1.6) << 0.780;
+ *Power_Mixture_Correlation << 10 << 0.860;
+ *Power_Mixture_Correlation << 11 << 0.935;
+ *Power_Mixture_Correlation << 12 << 0.980;
+ *Power_Mixture_Correlation << 13 << 1.000;
+ *Power_Mixture_Correlation << 14 << 0.990;
+ *Power_Mixture_Correlation << 15 << 0.964;
+ *Power_Mixture_Correlation << 16 << 0.925;
+ *Power_Mixture_Correlation << 17 << 0.880;
+ *Power_Mixture_Correlation << 18 << 0.830;
+ *Power_Mixture_Correlation << 19 << 0.785;
+ *Power_Mixture_Correlation << 20 << 0.740;
+ *Power_Mixture_Correlation << (14.7/0.6) << 0.58;
+
+ Mixture_Efficiency_Correlation = new FGTable(15);
+ *Mixture_Efficiency_Correlation << 0.05000 << 0.00000;
+ *Mixture_Efficiency_Correlation << 0.05137 << 0.00862;
+ *Mixture_Efficiency_Correlation << 0.05179 << 0.21552;
+ *Mixture_Efficiency_Correlation << 0.05430 << 0.48276;
+ *Mixture_Efficiency_Correlation << 0.05842 << 0.70690;
+ *Mixture_Efficiency_Correlation << 0.06312 << 0.83621;
+ *Mixture_Efficiency_Correlation << 0.06942 << 0.93103;
+ *Mixture_Efficiency_Correlation << 0.07786 << 1.00000;
+ *Mixture_Efficiency_Correlation << 0.08845 << 1.00000;
+ *Mixture_Efficiency_Correlation << 0.09270 << 0.98276;
+ *Mixture_Efficiency_Correlation << 0.10120 << 0.93103;
+ *Mixture_Efficiency_Correlation << 0.11455 << 0.72414;
+ *Mixture_Efficiency_Correlation << 0.12158 << 0.45690;
+ *Mixture_Efficiency_Correlation << 0.12435 << 0.23276;
+ *Mixture_Efficiency_Correlation << 0.12500 << 0.00000;
+
+
+/*
+Manifold_Pressure_Lookup = new
+
+ 0 0.2 0.4 0.6 0.8 1
+0 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000
+1000 0.7778 0.8212 0.8647 0.9081 0.9516 0.9950
+2000 0.5556 0.6424 0.7293 0.8162 0.9031 0.9900
+3000 0.3333 0.4637 0.5940 0.7243 0.8547 0.9850
+4000 0.2000 0.2849 0.4587 0.6324 0.8062 0.9800
+5000 0.2000 0.2000 0.3233 0.5406 0.7578 0.9750
+6000 0.2000 0.2000 0.2000 0.4487 0.7093 0.9700
+7000 0.2000 0.2000 0.2000 0.2000 0.4570 0.7611
+8000 0.2000 0.2000 0.2000 0.2000 0.2047 0.5522
+*/
// Read inputs from engine data file where present.
Cycles = el->FindElementValueAsNumber("cycles");
if (el->FindElement("idlerpm"))
IdleRPM = el->FindElementValueAsNumber("idlerpm");
+ if (el->FindElement("maxrpm"))
+ MaxRPM = el->FindElementValueAsNumber("maxrpm");
if (el->FindElement("maxthrottle"))
MaxThrottle = el->FindElementValueAsNumber("maxthrottle");
if (el->FindElement("minthrottle"))
MinThrottle = el->FindElementValueAsNumber("minthrottle");
+ if (el->FindElement("bsfc"))
+ BSFC = el->FindElementValueAsNumber("bsfc");
if (el->FindElement("numboostspeeds")) { // Turbo- and super-charging parameters
BoostSpeeds = (int)el->FindElementValueAsNumber("numboostspeeds");
if (el->FindElement("boostoverride"))
if (el->FindElement("ratedaltitude3"))
RatedAltitude[2] = el->FindElementValueAsNumberConvertTo("ratedaltitude3", "FT");
}
+ char property_name[80];
+ snprintf(property_name, 80, "/engines/engine[%d]/power_hp", engine_number);
+ PropertyManager->Tie(property_name, &HP);
+ snprintf(property_name, 80, "/engines/engine[%d]/bsfc", engine_number);
+ PropertyManager->Tie(property_name, &BSFC);
+
minMAP = MinManifoldPressure_inHg * inhgtopa; // inHg to Pa
maxMAP = MaxManifoldPressure_inHg * inhgtopa;
StarterHP = sqrt(MaxHP) * 0.4;
BoostSpeed = 0;
}
bBoostOverride = (BoostOverride == 1 ? true : false);
-
+ if (MinThrottle < 0.001) MinThrottle = 0.001; //MinThrottle is a denominator in a power equation so it can't be zero
Debug(0); // Call Debug() routine from constructor if needed
}
FGPiston::~FGPiston()
{
+ char property_name[80];
+ snprintf(property_name, 80, "/engines/engine[%d]/power_hp", EngineNumber);
+ PropertyManager->Untie(property_name);
+ snprintf(property_name, 80, "/engines/engine[%d]/bsfc", EngineNumber);
+ PropertyManager->Untie(property_name);
+
delete Lookup_Combustion_Efficiency;
delete Power_Mixture_Correlation;
+ delete Mixture_Efficiency_Correlation;
Debug(1); // Call Debug() routine from constructor if needed
}
if (FuelFlow_gph > 0.0) ConsumeFuel();
Throttle = FCS->GetThrottlePos(EngineNumber);
+ ThrottlePos = MinThrottle+((MaxThrottle-MinThrottle)*Throttle );
Mixture = FCS->GetMixturePos(EngineNumber);
//
//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;
+// if (equivalence_ratio < 0.668)
+// Running = false;
doEnginePower();
+if(HP<0.1250)
+ Running = false;
+
doEGT();
doCHT();
doOilTemperature();
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
+ if ((RPM > IdleRPM*0.8) && (crank_counter > 175)) // Add a little delay to startup
Running = true; // on the starter
} else {
- if (RPM > 450) // This allows us to in-air start
+ if (RPM > IdleRPM*0.8) // This allows us to in-air start
Running = true; // when windmilling
}
}
if (Running) {
if (RPM == 0) {
Running = false;
- } else if ((RPM <= 480) && (Cranking)) {
+ } else if ((RPM <= IdleRPM *0.8 ) && (Cranking)) {
Running = false;
}
}
void FGPiston::doMAP(void)
{
- if(RPM > 10) {
- // Naturally aspirated
- MAP = minMAP + (Throttle * (maxMAP - minMAP));
- MAP *= p_amb / p_amb_sea_level;
+ suction_loss = pow( ThrottlePos*0.98, RPM/MaxRPM );
+ MAP = p_amb * suction_loss;
+
if(Boosted) {
// If takeoff boost is fitted, we currently assume the following throttle map:
// (In throttle % - actual input is 0 -> 1)
}
}
// Boost the manifold pressure.
- MAP *= BoostMul[BoostSpeed];
+ MAP += MAP * BoostMul[BoostSpeed] * RPM/MaxRPM;
// Now clip the manifold pressure to BCV or Wastegate setting.
if(bTakeoffPos) {
if(MAP > TakeoffMAP[BoostSpeed]) {
}
}
}
- } else {
- // rpm < 10 - effectively stopped.
- // TODO - add a better variation of MAP with engine speed
- MAP = Atmosphere->GetPressure() * psftopa;
- }
// And set the value in American units as well
ManifoldPressure_inHg = MAP / inhgtopa;
* (used in CHT calculation for air-cooled engines).
*
* Inputs: p_amb, R_air, T_amb, MAP, Displacement,
- * RPM, volumetric_efficiency
+ * RPM, volumetric_efficiency, ThrottlePos
*
* TODO: Model inlet manifold air temperature.
*
void FGPiston::doAirFlow(void)
{
- rho_air = p_amb / (R_air * T_amb);
- double rho_air_manifold = MAP / (R_air * T_amb);
+
+rho_air = p_amb / (R_air * T_amb);
double displacement_SI = Displacement * in3tom3;
double swept_volume = (displacement_SI * (RPM/60)) / 2;
double v_dot_air = swept_volume * volumetric_efficiency;
+
+ double rho_air_manifold = MAP / (R_air * T_amb);
m_dot_air = v_dot_air * rho_air_manifold;
}
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;
+ double thi_sea_level = 1.3 * Mixture; // Allows an AFR of infinity:1 to 11.3075:1
+ equivalence_ratio = thi_sea_level; // * p_amb_sea_level / p_amb;
+ double AFR = 10+(12*(1-Mixture));// mixture 10:1 to 22:1
+ m_dot_fuel = m_dot_air / AFR;
FuelFlow_gph = m_dot_fuel
* 3600 // seconds to hours
* 2.2046 // kg to lb
- / 6.6; // lb to gal_us of kerosene
+ / 6.0; // lb to gal_us of gasoline
+// / 6.6; // lb to gal_us of kerosene
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
* 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
+ * Inputs: ManifoldPressure_inHg, p_amb, RPM, T_amb,
+ * Mixture_Efficiency_Correlation, Cycles, MaxHP
*
* Outputs: Percentage_Power, HP
*/
double T_amb_sea_lev_degF = KelvinToFahrenheit(288);
// FIXME: this needs to be generalized
- double ManXRPM; // Convienience term for use in the calculations
- if(Boosted) {
- // Currently a simple linear fit.
- // The zero crossing is moved up the speed-load range to reduce the idling power.
- // This will change!
- double zeroOffset = (minMAP / 2.0) * (IdleRPM / 2.0);
- ManXRPM = MAP * (RPM > RatedRPM[BoostSpeed] ? RatedRPM[BoostSpeed] : RPM);
- // The speed clip in the line above is deliberate.
- Percentage_Power = ((ManXRPM - zeroOffset) / ((RatedMAP[BoostSpeed] * RatedRPM[BoostSpeed]) - zeroOffset)) * 107.0;
- Percentage_Power -= 7.0; // Another idle power reduction offset - see line above with 107.
- if (Percentage_Power < 0.0) Percentage_Power = 0.0;
- // Note that %power is allowed to go over 100 for boosted powerplants
- // such as for the BCV-override or takeoff power settings.
- // TODO - currently no altitude effect (temperature & exhaust back-pressure) modelled
- // for boosted engines.
- } else {
- ManXRPM = ManifoldPressure_inHg * RPM; // Note that inHg must be used for the following correlation.
- Percentage_Power = (6e-9 * ManXRPM * ManXRPM) + (8e-4 * ManXRPM) - 1.0;
-// Percentage_Power += ((T_amb_sea_lev_degF - T_amb_degF) * 7 /120);
- Percentage_Power += ((T_amb_sea_lev_degF - T_amb_degF) * 7 * dt);
- if (Percentage_Power < 0.0) Percentage_Power = 0.0;
- else if (Percentage_Power > 100.0) Percentage_Power = 100.0;
- }
-
- double Percentage_of_best_power_mixture_power =
- Power_Mixture_Correlation->GetValue(14.7 / equivalence_ratio);
-
- Percentage_Power *= Percentage_of_best_power_mixture_power / 100.0;
+ double ManXRPM, ME, Adjusted_BSFC; // Convienience term for use in the calculations
+ ME = Mixture_Efficiency_Correlation->GetValue(m_dot_fuel/m_dot_air);
+ Adjusted_BSFC = (1/ThrottlePos) * BSFC;
+ Percentage_Power = 1.000;
if( Magnetos != 3 )
Percentage_Power *= SparkFailDrop;
- if (Boosted) {
- HP = Percentage_Power * RatedPower[BoostSpeed] / 100.0;
- } else {
- HP = Percentage_Power * MaxHP / 100.0;
- }
+ HP = (FuelFlow_gph * 6.0 / Adjusted_BSFC )* ME * suction_loss * Percentage_Power;
} else {
if (Cranking) {
if (RPM < 10) {
HP = StarterHP;
- } else if (RPM < 480) {
- HP = StarterHP + ((480 - RPM) / 8.0);
+ } else if (RPM < IdleRPM*0.8) {
+ HP = StarterHP + ((IdleRPM*0.8 - RPM) / 8.0);
// This is a guess - would be nice to find a proper starter moter torque curve
} else {
HP = StarterHP;
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);
+ ExhaustGasTemp_degK *= 0.444 + ((0.544 - 0.444) * Percentage_Power);
} else { // Drop towards ambient - guess an appropriate time constant for now
combustion_efficiency = 0;
dEGTdt = (RankineToKelvin(Atmosphere->GetTemperature()) - ExhaustGasTemp_degK) / 100.0;
void FGPiston::doOilTemperature(void)
{
- double idle_percentage_power = 2.3; // approximately
+ double idle_percentage_power = 0.023; // approximately
double target_oil_temp; // Steady state oil temp at the current engine conditions
double time_constant; // The time constant for the differential equation
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 Oil_Press_RPM_Max = MaxRPM * 0.75; // 75% of max rpm FIXME: may vary by engine
double Design_Oil_Temp = 358; // degK; FIXME: may vary by engine
double Oil_Viscosity_Index = 0.25;
Power_Mixture_Correlation->Print();
cout << endl;
+ cout << endl;
+ cout << " Mixture Efficiency Correlation table:" << endl;
+ Mixture_Efficiency_Correlation->Print();
+ cout << endl;
+
}
}
if (debug_lvl & 2 ) { // Instantiation/Destruction notification
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