328 lines
13 KiB
C#
328 lines
13 KiB
C#
using System;
|
||
using System.Collections.Generic;
|
||
using FluidSim.Interfaces;
|
||
|
||
namespace FluidSim.Components
|
||
{
|
||
public class Cylinder : IComponent
|
||
{
|
||
public Port IntakePort { get; }
|
||
public Port ExhaustPort { get; }
|
||
public Crankshaft Crankshaft { get; }
|
||
|
||
private readonly Port[] _ports;
|
||
IReadOnlyList<Port> IComponent.Ports => _ports;
|
||
|
||
// Geometry
|
||
public double Bore { get; }
|
||
public double Stroke { get; }
|
||
public double ConRodLength { get; }
|
||
public double CompressionRatio { get; }
|
||
|
||
// Valve timings (degrees, 0 = TDC compression, 720° full cycle)
|
||
public double IVO { get; }
|
||
public double IVC { get; }
|
||
public double EVO { get; }
|
||
public double EVC { get; }
|
||
|
||
// Valve geometry
|
||
public double IntakeValveDiameter { get; set; } = 0.030;
|
||
public double ExhaustValveDiameter { get; set; } = 0.028;
|
||
public double IntakeValveLift { get; set; } = 0.005;
|
||
public double ExhaustValveLift { get; set; } = 0.005;
|
||
|
||
public double IntakeValveMaxArea => Math.PI * IntakeValveDiameter * IntakeValveLift;
|
||
public double ExhaustValveMaxArea => Math.PI * ExhaustValveDiameter * ExhaustValveLift;
|
||
|
||
// Ignition and combustion
|
||
public double SparkAdvance { get; set; } = 20.0;
|
||
public double WiebeA { get; set; } = 5.0;
|
||
public double WiebeM { get; set; } = 2.0;
|
||
public double WiebeDuration { get; set; } = 60.0;
|
||
public double WiebeStart { get; set; } = 5.0;
|
||
|
||
// Fuel
|
||
public double StoichiometricAFR { get; set; } = 14.7;
|
||
public double FuelLowerHeatingValue { get; set; } = 44e6;
|
||
|
||
// Cycle‑to‑cycle randomness
|
||
/// <summary>Fractional variation in fuel energy (±). 0.05 = ±5%.</summary>
|
||
public double EnergyVariationFraction { get; set; } = 0.05;
|
||
/// <summary>Probability of a misfire (0‑1).</summary>
|
||
public double MisfireProbability { get; set; } = 0.01;
|
||
|
||
// Heat loss
|
||
public double CylinderWallArea { get; set; } = 0.02;
|
||
public double HeatTransferCoefficient { get; set; } = 100.0;
|
||
public double AmbientTemperature { get; set; } = 300.0;
|
||
|
||
// State
|
||
public double Volume => cylinderVolume;
|
||
public double Pressure => (Gamma - 1.0) * cylinderEnergy / Math.Max(cylinderVolume, 1e-12);
|
||
public double Temperature => Pressure / Math.Max(Density * GasConstant, 1e-12);
|
||
public double Density => Mass / Math.Max(cylinderVolume, 1e-12);
|
||
public double Mass => _airMass + _exhaustMass;
|
||
public double AirFraction => _airMass / Math.Max(Mass, 1e-12);
|
||
public double PistonFraction => (cylinderVolume - clearanceVolume) / SweptVolume;
|
||
|
||
private double cylinderVolume;
|
||
private double cylinderEnergy;
|
||
private double _airMass;
|
||
private double _exhaustMass;
|
||
private double trappedAirMass;
|
||
private double fuelMass;
|
||
private double burnFraction;
|
||
private bool combustionActive;
|
||
private bool fuelInjected;
|
||
|
||
// per‑cycle randomness
|
||
private double _energyFactor = 1.0; // applied to FuelLowerHeatingValue this cycle
|
||
private readonly Random _random = new Random();
|
||
|
||
private const double Gamma = 1.4;
|
||
private const double GasConstant = 287.0;
|
||
|
||
private const double MaxPressurePa = 200e5;
|
||
private const double MaxTemperatureK = 3500.0;
|
||
|
||
public Cylinder(double bore, double stroke, double conRodLength, double compressionRatio,
|
||
double ivo, double ivc, double evo, double evc, Crankshaft crankshaft)
|
||
{
|
||
Bore = bore;
|
||
Stroke = stroke;
|
||
ConRodLength = conRodLength;
|
||
CompressionRatio = compressionRatio;
|
||
IVO = ivo;
|
||
IVC = ivc;
|
||
EVO = evo;
|
||
EVC = evc;
|
||
|
||
Crankshaft = crankshaft ?? throw new ArgumentNullException(nameof(crankshaft));
|
||
|
||
cylinderVolume = clearanceVolume;
|
||
double initRho = 1.225;
|
||
_airMass = initRho * clearanceVolume;
|
||
_exhaustMass = 0.0;
|
||
cylinderEnergy = 101325.0 * clearanceVolume / (Gamma - 1.0);
|
||
|
||
IntakePort = new Port { Owner = this };
|
||
ExhaustPort = new Port { Owner = this };
|
||
_ports = new[] { IntakePort, ExhaustPort };
|
||
}
|
||
|
||
// Derived volumes
|
||
private double SweptVolume => Math.PI * 0.25 * Bore * Bore * Stroke;
|
||
private double clearanceVolume => SweptVolume / (CompressionRatio - 1.0);
|
||
private double CrankRadius => Stroke / 2.0;
|
||
private double Obliquity => CrankRadius / ConRodLength;
|
||
private double CrankDeg => (Crankshaft.CrankAngle % (4.0 * Math.PI)) * 180.0 / Math.PI % 720.0;
|
||
|
||
public double ComputeVolume(double thetaRad)
|
||
{
|
||
double r = CrankRadius;
|
||
double l = ConRodLength;
|
||
double cosTh = Math.Cos(thetaRad);
|
||
double sinTh = Math.Sin(thetaRad);
|
||
double term = Math.Sqrt(1.0 - Obliquity * Obliquity * sinTh * sinTh);
|
||
double x = r * (1.0 - cosTh) + l * (1.0 - term);
|
||
double area = Math.PI * 0.25 * Bore * Bore;
|
||
return clearanceVolume + area * x;
|
||
}
|
||
|
||
private double ValveLift(double thetaDeg, double opens, double closes, double peakLift)
|
||
{
|
||
double deg = thetaDeg % 720.0;
|
||
if (deg < 0) deg += 720.0;
|
||
|
||
double duration = closes - opens;
|
||
if (duration <= 0) return 0.0;
|
||
|
||
double rampDur = duration * 0.25;
|
||
double holdDur = duration - 2.0 * rampDur;
|
||
|
||
if (deg >= opens && deg < opens + rampDur)
|
||
{
|
||
double t = (deg - opens) / rampDur;
|
||
return peakLift * t * t * (3.0 - 2.0 * t);
|
||
}
|
||
else if (deg >= opens + rampDur && deg < opens + rampDur + holdDur)
|
||
{
|
||
return peakLift;
|
||
}
|
||
else if (deg >= opens + rampDur + holdDur && deg <= closes)
|
||
{
|
||
double t = (deg - (opens + rampDur + holdDur)) / rampDur;
|
||
return peakLift * (1.0 - t) * (1.0 - t) * (1.0 + 2.0 * t);
|
||
}
|
||
return 0.0;
|
||
}
|
||
|
||
public double IntakeValveArea =>
|
||
Math.PI * IntakeValveDiameter * ValveLift(CrankDeg, IVO, IVC, IntakeValveLift);
|
||
|
||
public double ExhaustValveArea =>
|
||
Math.PI * ExhaustValveDiameter * ValveLift(CrankDeg, EVO, EVC, ExhaustValveLift);
|
||
|
||
private double Wiebe(double angleSinceSpark)
|
||
{
|
||
if (angleSinceSpark < WiebeStart) return 0.0;
|
||
double phi = (angleSinceSpark - WiebeStart) / WiebeDuration;
|
||
if (phi <= 0) return 0.0;
|
||
return 1.0 - Math.Exp(-WiebeA * Math.Pow(phi, WiebeM + 1));
|
||
}
|
||
|
||
public void PreStep(double dt)
|
||
{
|
||
double prevVolume = cylinderVolume;
|
||
double crankAngleRad = Crankshaft.CrankAngle;
|
||
cylinderVolume = ComputeVolume(crankAngleRad);
|
||
|
||
double dV = cylinderVolume - prevVolume;
|
||
|
||
// Piston torque
|
||
double pRel = Pressure - 101325.0;
|
||
double sinTh = Math.Sin(crankAngleRad);
|
||
double cosTh = Math.Cos(crankAngleRad);
|
||
double term = Math.Sqrt(1.0 - Obliquity * Obliquity * sinTh * sinTh);
|
||
double dxdtheta = CrankRadius * sinTh * (1.0 + Obliquity * cosTh / term);
|
||
double pistonArea = Math.PI * 0.25 * Bore * Bore;
|
||
double torque = pRel * pistonArea * dxdtheta;
|
||
Crankshaft.AddTorque(torque);
|
||
|
||
cylinderEnergy -= Pressure * dV;
|
||
|
||
double prevDeg = Crankshaft.PreviousAngle * 180.0 / Math.PI % 720.0;
|
||
double currDeg = crankAngleRad * 180.0 / Math.PI % 720.0;
|
||
|
||
// ----- Intake closing: capture trapped air mass and compute fuel -----
|
||
if (prevDeg >= IVO && prevDeg < IVC && currDeg >= IVC)
|
||
{
|
||
trappedAirMass = _airMass;
|
||
fuelMass = trappedAirMass / StoichiometricAFR;
|
||
fuelInjected = true;
|
||
}
|
||
|
||
// ----- Spark ignition (once per cycle, with misfire chance) -----
|
||
double sparkAngle = 0.0 - SparkAdvance;
|
||
if (sparkAngle < 0) sparkAngle += 720.0;
|
||
|
||
bool crossedSpark = (prevDeg < sparkAngle && currDeg >= sparkAngle) ||
|
||
(prevDeg > sparkAngle + 360.0 && currDeg < sparkAngle);
|
||
if (crossedSpark && !combustionActive && fuelInjected)
|
||
{
|
||
// Decide misfire
|
||
bool misfire = _random.NextDouble() < MisfireProbability;
|
||
if (misfire)
|
||
{
|
||
combustionActive = false; // no combustion this cycle
|
||
// fuel is not burned – will remain in cylinder and eventually exit as unburned mixture
|
||
}
|
||
else
|
||
{
|
||
combustionActive = true;
|
||
burnFraction = 0.0;
|
||
|
||
// Energy variation factor for this cycle
|
||
double range = EnergyVariationFraction;
|
||
_energyFactor = 1.0 + range * (2.0 * _random.NextDouble() - 1.0);
|
||
}
|
||
}
|
||
|
||
// ----- Combustion progress -----
|
||
if (combustionActive)
|
||
{
|
||
double angleSinceSpark = currDeg - sparkAngle;
|
||
if (angleSinceSpark < 0) angleSinceSpark += 720.0;
|
||
double newFraction = Wiebe(angleSinceSpark);
|
||
|
||
if (newFraction >= 1.0 || angleSinceSpark > (WiebeDuration + WiebeStart + SparkAdvance))
|
||
{
|
||
newFraction = 1.0;
|
||
combustionActive = false;
|
||
// All gas becomes exhaust
|
||
double totalMass = _airMass + _exhaustMass;
|
||
_airMass = 0.0;
|
||
_exhaustMass = totalMass;
|
||
}
|
||
|
||
double dFraction = newFraction - burnFraction;
|
||
if (dFraction > 0)
|
||
{
|
||
double dQ = fuelMass * FuelLowerHeatingValue * _energyFactor * dFraction;
|
||
cylinderEnergy += dQ;
|
||
_exhaustMass += fuelMass * dFraction;
|
||
burnFraction = newFraction;
|
||
}
|
||
}
|
||
|
||
// ----- Heat loss to cylinder walls -----
|
||
double dQ_loss = HeatTransferCoefficient * CylinderWallArea *
|
||
(Temperature - AmbientTemperature) * dt;
|
||
cylinderEnergy -= dQ_loss;
|
||
|
||
// Update port states
|
||
double p = Pressure, rho = Density, T = Temperature;
|
||
double h = Gamma / (Gamma - 1.0) * p / Math.Max(rho, 1e-12);
|
||
double af = AirFraction;
|
||
|
||
IntakePort.Pressure = p;
|
||
IntakePort.Density = rho;
|
||
IntakePort.Temperature = T;
|
||
IntakePort.SpecificEnthalpy = h;
|
||
IntakePort.AirFraction = af;
|
||
|
||
ExhaustPort.Pressure = p;
|
||
ExhaustPort.Density = rho;
|
||
ExhaustPort.Temperature = T;
|
||
ExhaustPort.SpecificEnthalpy = h;
|
||
ExhaustPort.AirFraction = af;
|
||
}
|
||
|
||
public void UpdateState(double dt)
|
||
{
|
||
double dmAir = 0.0, dmExhaust = 0.0, dE = 0.0;
|
||
|
||
foreach (var port in _ports)
|
||
{
|
||
double mdot = port.MassFlowRate;
|
||
double af = mdot >= 0 ? port.AirFraction : AirFraction;
|
||
dmAir += mdot * af * dt;
|
||
dmExhaust += mdot * (1.0 - af) * dt;
|
||
dE += mdot * port.SpecificEnthalpy * dt;
|
||
}
|
||
|
||
_airMass += dmAir;
|
||
_exhaustMass += dmExhaust;
|
||
cylinderEnergy += dE;
|
||
|
||
double V = Math.Max(cylinderVolume, 1e-12);
|
||
|
||
double currentP = (Gamma - 1.0) * cylinderEnergy / V;
|
||
if (currentP > MaxPressurePa)
|
||
cylinderEnergy = MaxPressurePa * V / (Gamma - 1.0);
|
||
|
||
double currentRho = (_airMass + _exhaustMass) / V;
|
||
double currentT = currentP / Math.Max(currentRho * GasConstant, 1e-12);
|
||
if (currentT > MaxTemperatureK)
|
||
{
|
||
double pAtTlimit = currentRho * GasConstant * MaxTemperatureK;
|
||
cylinderEnergy = pAtTlimit * V / (Gamma - 1.0);
|
||
}
|
||
|
||
double totalMass = _airMass + _exhaustMass;
|
||
if (totalMass < 1e-9)
|
||
{
|
||
_airMass = 1e-9;
|
||
_exhaustMass = 0.0;
|
||
cylinderEnergy = 101325.0 * V / (Gamma - 1.0);
|
||
}
|
||
else if (cylinderEnergy < 0.0)
|
||
{
|
||
cylinderEnergy = 101325.0 * V / (Gamma - 1.0);
|
||
}
|
||
|
||
if (_airMass < 0.0) _airMass = 0.0;
|
||
if (_exhaustMass < 0.0) _exhaustMass = 0.0;
|
||
}
|
||
}
|
||
} |