{
_boost = 1;
_running = false;
- _cranking = false;
+ _fuel = true;
+ _boostPressure = 0;
+ _hasSuper = false;
+
+ _oilTemp = Atmosphere::getStdTemperature(0);
+ _oilTempTarget = _oilTemp;
+ _dOilTempdt = 0;
// Presume a BSFC (in lb/hour per HP) of 0.45. In SI that becomes
// (2.2 lb/kg, 745.7 W/hp, 3600 sec/hour) 7.62e-08 kg/Ws.
_mixCoeff = realFlow * 1.1f / _omega0;
_turbo = 1;
+ _minthrottle = 0.1;
_maxMP = 1e6; // No waste gate on non-turbo engines.
+ _wastegate = 1;
+ _charge = 1;
+ _chargeTarget = 1;
+ _turboLag = 2;
// Guess at reasonable values for these guys. Displacements run
// at about 2 cubic inches per horsepower or so, at least for
_compression = c;
}
-float PistonEngine::getMaxPower()
-{
- return _power0;
-}
-
-void PistonEngine::setThrottle(float t)
-{
- _throttle = t;
-}
-
-void PistonEngine::setRunning(bool r)
+void PistonEngine::setMinThrottle(float m)
{
- _running = r;
+ _minthrottle = m;
}
-void PistonEngine::setStarter(bool s)
-{
- _cranking = s;
-}
-
-void PistonEngine::setMagnetos(int m)
-{
- _magnetos = m;
-}
-
-void PistonEngine::setMixture(float m)
-{
- _mixture = m;
-}
-
-void PistonEngine::setBoost(float boost)
-{
- _boost = boost;
-}
-
-bool PistonEngine::isRunning()
+float PistonEngine::getMaxPower()
{
- return _running;
+ return _power0;
}
bool PistonEngine::isCranking()
{
- return _cranking;
+ return _starter;
}
float PistonEngine::getTorque()
return _egt;
}
+void PistonEngine::stabilize()
+{
+ _oilTemp = _oilTempTarget;
+ _charge = _chargeTarget;
+}
+
+void PistonEngine::integrate(float dt)
+{
+ _oilTemp += (_dOilTempdt * dt);
+
+ // See comments in Jet.cpp for how this decay constant works
+ float decay = 2.3f / _turboLag;
+ _charge = (_charge + dt*decay * _chargeTarget) / (1 + dt*decay);
+}
+
void PistonEngine::calc(float pressure, float temp, float speed)
{
- if(_magnetos == 0 || speed < 200*RPM2RADPS)
- _running = false;
- else
- _running = true;
-
- // Calculate manifold pressure as ambient pressure modified for
- // turbocharging and reduced by the throttle setting. According
- // to Dave Luff, minimum throttle at sea level corresponds to 6"
- // manifold pressure. Assume that this means that minimum MP is
- // always 20% of ambient pressure. (But that's too much idle
- // power, so use 10% instead!) But we need to produce _zero_
- // thrust at that setting, so hold onto the "output" value
- // separately. Ick.
- _mp = pressure * (1 + _boost*(_turbo-1)); // turbocharger
- float mp = _mp * (0.1f + 0.9f * _throttle); // throttle
- _mp *= _throttle;
- if(mp > _maxMP) mp = _maxMP; // wastegate
+ _running = _magnetos && _fuel && (speed > 60*RPM2RADPS);
+
+ // Calculate the factor required to modify supercharger output for
+ // rpm. Assume that the normalized supercharger output ~= 1 when
+ // the engine is at the nominal peak-power rpm. A power equation
+ // of the form (A * B^x * x^C) has been derived empirically from
+ // some representative supercharger data. This provides
+ // near-linear output over the normal operating range, with
+ // fall-off in the over-speed situation.
+ float rpm_norm = (speed / _omega0);
+ float A = 1.795206541;
+ float B = 0.55620178;
+ float C = 1.246708471;
+ float rpm_factor = A * Math::pow(B, rpm_norm) * Math::pow(rpm_norm, C);
+ _chargeTarget = 1 + (_boost * (_turbo-1) * rpm_factor);
+
+ if(_hasSuper) {
+ // Superchargers have no lag
+ _charge = _chargeTarget;
+ } else if(!_running) {
+ // Turbochargers only work well when the engine is actually
+ // running. The 25% number is a guesstimate from Vivian.
+ _chargeTarget = 1 + (_chargeTarget - 1) * 0.25;
+ }
+
+ // We need to adjust the minimum manifold pressure to get a
+ // reasonable idle speed (a "closed" throttle doesn't suck a total
+ // vacuum in real manifolds). This is a hack.
+ float _minMP = (-0.008 * _turbo ) + _minthrottle;
+
+ _mp = pressure * _charge;
+
+ // Scale to throttle setting, clamp to wastegate
+ if(_running)
+ _mp *= _minMP + (1 -_minMP) * _throttle;
+
+ // Scale the max MP according to the WASTEGATE control input. Use
+ // the un-supercharged MP as the bottom limit.
+ float max = _wastegate * _maxMP;
+ if(max < _mp/_charge) max = _mp/_charge;
+ if(_mp > max) _mp = max;
+
+
+ // The "boost" is the delta above ambient
+ _boostPressure = _mp - pressure;
// Air entering the manifold does so rapidly, and thus the
// pressure change can be assumed to be adiabatic. Calculate a
// temperature change, and use that to get the density.
- float T = temp * Math::pow(mp/pressure, 2.0/7.0);
- float rho = mp / (287.1f * T);
+ // Note: need to model intercoolers here...
+ float T = temp * Math::pow((_mp*_mp)/(pressure*pressure), 1.0/7.0);
+ float rho = _mp / (287.1f * T);
// The actual fuel flow is determined only by engine RPM and the
// mixture setting. Not all of this will burn with the same
// efficiency.
_fuelFlow = _mixture * speed * _mixCoeff;
+ if(_fuel == false) _fuelFlow = 0;
// How much fuel could be burned with ideal (i.e. uncorrected!)
// combustion.
float power = _power0 * burned/_f0;
_torque = power/speed;
- // Figure that the starter motor produces 20% of the engine's
- // cruise torque.
- if(_cranking && !_running)
- _torque += 0.20f * _power0/_omega0;
+ // Figure that the starter motor produces 15% of the engine's
+ // cruise torque. Assuming 60RPM starter speed vs. 1800RPM cruise
+ // speed on a 160HP engine, that comes out to about 160*.15/30 ==
+ // 0.8 HP starter motor. Which sounds about right to me. I think
+ // I've finally got this tuned. :)
+ if(_starter && !_running)
+ _torque += 0.15f * _power0/_omega0;
- // Also, add a negative torque of 10% of cruise, to represent
+ // Also, add a negative torque of 8% of cruise, to represent
// internal friction. Propeller aerodynamic friction is too low
// at low RPMs to provide a good deceleration. Interpolate it
- // away as we approach cruise RPMs, though, to prevent interaction
- // with the power computations. Ugly.
- if(speed > 0 && speed < _omega0)
- _torque -= 0.05f * (_power0/_omega0) * (1 - speed/_omega0);
+ // away as we approach cruise RPMs (full at 50%, zero at 100%),
+ // though, to prevent interaction with the power computations.
+ // Ugly.
+ if(speed > 0 && speed < _omega0) {
+ float interp = 2 - 2*speed/_omega0;
+ interp = (interp > 1) ? 1 : interp;
+ _torque -= 0.08f * (_power0/_omega0) * interp;
+ }
// Now EGT. This one gets a little goofy. We can calculate the
// work done by an isentropically expanding exhaust gas as the
// what we'd expect. And diddle the work done by the gas a bit to
// account for non-thermodynamic losses like internal friction;
// 10% should do it.
-
float massFlow = _fuelFlow + (rho * 0.5f * _displacement * speed);
float specHeat = 1300;
float corr = 1.0f/(Math::pow(_compression, 0.4f) - 1.0f);
_egt = corr * (power * 1.1f) / (massFlow * specHeat);
if(_egt < temp) _egt = temp;
+
+
+ // Oil temperature.
+ // Assume a linear variation between ~90degC at idle and ~120degC
+ // at full power. No attempt to correct for airflow over the
+ // engine is made. Make the time constant to attain target steady-
+ // state oil temp greater at engine off than on to reflect no
+ // circulation. Nothing fancy, but populates the guage with a
+ // plausible value.
+ float tau; // secs
+ if(_running) {
+ _oilTempTarget = 363.0f + (30.0f * (power/_power0));
+ tau = 600;
+ // Reduce tau linearly to 300 at max power
+ tau -= (power/_power0) * 300.0f;
+ } else {
+ _oilTempTarget = temp;
+ tau = 1500;
+ }
+ _dOilTempdt = (_oilTempTarget - _oilTemp) / tau;
}
}; // namespace yasim
projects / flightgear.git / blobdiff