265 lines
11 KiB
C#
265 lines
11 KiB
C#
using System;
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using System.Collections.Generic;
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using FluidSim.Interfaces;
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namespace FluidSim.Components
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{
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public class Cylinder : IComponent
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{
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public Port IntakePort { get; }
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public Port ExhaustPort { get; }
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public Crankshaft Crankshaft { get; }
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private readonly Port[] _ports;
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IReadOnlyList<Port> IComponent.Ports => _ports;
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public float Bore { get; }
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public float Stroke { get; }
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public float ConRodLength { get; }
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public float CompressionRatio { get; }
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public float IVO, IVC, EVO, EVC; // degrees
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public float IntakeValveDiameter = 0.03f;
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public float ExhaustValveDiameter = 0.028f;
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public float IntakeValveLift = 0.005f;
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public float ExhaustValveLift = 0.005f;
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public float IntakeValveMaxArea => MathF.PI * IntakeValveDiameter * IntakeValveLift;
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public float ExhaustValveMaxArea => MathF.PI * ExhaustValveDiameter * ExhaustValveLift;
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public float SparkAdvance = 20f;
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public float WiebeA = 5f, WiebeM = 2f, WiebeDuration = 60f, WiebeStart = 5f;
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public float StoichiometricAFR = 14.7f;
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public float FuelLowerHeatingValue = 44e6f;
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public float EnergyVariationFraction = 0.05f;
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public float MisfireProbability = 0.01f;
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public float CylinderWallArea = 0.02f;
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public float HeatTransferCoefficient = 100f;
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public float AmbientTemperature = 300f;
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public float PhaseOffset; // rad
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public float Volume => cylinderVolume;
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public float Pressure => (Gamma - 1f) * cylinderEnergy / MathF.Max(cylinderVolume, 1e-12f);
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public float Temperature => Pressure / MathF.Max(Density * GasConstant, 1e-12f);
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public float Density => Mass / MathF.Max(cylinderVolume, 1e-12f);
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public float Mass => _airMass + _exhaustMass;
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public float AirFraction => _airMass / MathF.Max(Mass, 1e-12f);
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public float PistonFraction => (cylinderVolume - clearanceVolume) / SweptVolume;
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private float cylinderVolume, cylinderEnergy;
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private float _airMass, _exhaustMass;
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private float trappedAirMass, fuelMass, burnFraction;
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private bool combustionActive, fuelInjected;
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private float _energyFactor = 1f;
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private readonly Random _random = new Random();
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private const float Gamma = 1.4f;
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private const float GasConstant = 287f;
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private const float MaxPressurePa = 200e5f;
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private const float MaxTemperatureK = 3500f;
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public Cylinder(float bore, float stroke, float conRodLength, float compressionRatio,
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float ivo, float ivc, float evo, float evc, Crankshaft crankshaft)
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{
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Bore = bore; Stroke = stroke; ConRodLength = conRodLength;
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CompressionRatio = compressionRatio;
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IVO = ivo; IVC = ivc; EVO = evo; EVC = evc;
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Crankshaft = crankshaft ?? throw new ArgumentNullException(nameof(crankshaft));
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cylinderVolume = clearanceVolume;
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float initRho = 1.225f;
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_airMass = initRho * clearanceVolume;
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_exhaustMass = 0f;
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cylinderEnergy = 101325f * clearanceVolume / (Gamma - 1f);
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IntakePort = new Port { Owner = this };
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ExhaustPort = new Port { Owner = this };
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_ports = new[] { IntakePort, ExhaustPort };
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}
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private float SweptVolume => MathF.PI * 0.25f * Bore * Bore * Stroke;
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private float clearanceVolume => SweptVolume / (CompressionRatio - 1f);
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private float CrankRadius => Stroke * 0.5f;
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private float Obliquity => CrankRadius / ConRodLength;
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private float CrankDeg =>
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((Crankshaft.CrankAngle + PhaseOffset) % (4f * MathF.PI)) * 180f / MathF.PI % 720f;
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public float ComputeVolume(float thetaRad)
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{
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float r = CrankRadius, l = ConRodLength;
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float cosTh = MathF.Cos(thetaRad), sinTh = MathF.Sin(thetaRad);
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float term = MathF.Sqrt(1f - Obliquity * Obliquity * sinTh * sinTh);
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float x = r * (1f - cosTh) + l * (1f - term);
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float area = MathF.PI * 0.25f * Bore * Bore;
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return clearanceVolume + area * x;
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}
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private float ValveLift(float thetaDeg, float opens, float closes, float peakLift)
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{
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float deg = thetaDeg % 720f;
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if (deg < 0f) deg += 720f;
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float duration = closes - opens;
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if (duration <= 0f) return 0f;
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float rampDur = duration * 0.25f;
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float holdDur = duration - 2f * rampDur;
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if (deg >= opens && deg < opens + rampDur)
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{
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float t = (deg - opens) / rampDur;
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return peakLift * t * t * (3f - 2f * t);
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}
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else if (deg >= opens + rampDur && deg < opens + rampDur + holdDur)
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{
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return peakLift;
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}
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else if (deg >= opens + rampDur + holdDur && deg <= closes)
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{
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float t = (deg - (opens + rampDur + holdDur)) / rampDur;
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return peakLift * (1f - t) * (1f - t) * (1f + 2f * t);
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}
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return 0f;
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}
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public float IntakeValveArea =>
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MathF.PI * IntakeValveDiameter * ValveLift(CrankDeg, IVO, IVC, IntakeValveLift);
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public float ExhaustValveArea =>
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MathF.PI * ExhaustValveDiameter * ValveLift(CrankDeg, EVO, EVC, ExhaustValveLift);
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private float Wiebe(float angleSinceSpark)
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{
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if (angleSinceSpark < WiebeStart) return 0f;
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float phi = (angleSinceSpark - WiebeStart) / WiebeDuration;
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if (phi <= 0f) return 0f;
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return 1f - MathF.Exp(-WiebeA * MathF.Pow(phi, WiebeM + 1f));
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}
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public void PreStep(float dt)
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{
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float prevVolume = cylinderVolume;
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float crankAngleRad = Crankshaft.CrankAngle + PhaseOffset;
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cylinderVolume = ComputeVolume(crankAngleRad);
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float dV = cylinderVolume - prevVolume;
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float pRel = Pressure - 101325f;
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float sinTh = MathF.Sin(crankAngleRad), cosTh = MathF.Cos(crankAngleRad);
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float term = MathF.Sqrt(1f - Obliquity * Obliquity * sinTh * sinTh);
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float dxdtheta = CrankRadius * sinTh * (1f + Obliquity * cosTh / term);
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float pistonArea = MathF.PI * 0.25f * Bore * Bore;
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Crankshaft.AddTorque(pRel * pistonArea * dxdtheta);
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cylinderEnergy -= Pressure * dV;
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float prevDeg = (Crankshaft.PreviousAngle + PhaseOffset) * 180f / MathF.PI % 720f;
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float currDeg = crankAngleRad * 180f / MathF.PI % 720f;
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// Intake closing
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if (prevDeg >= IVO && prevDeg < IVC && currDeg >= IVC)
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{
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trappedAirMass = _airMass;
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fuelMass = trappedAirMass / StoichiometricAFR;
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fuelInjected = true;
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}
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// Spark
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float sparkAngle = 0f - SparkAdvance;
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if (sparkAngle < 0f) sparkAngle += 720f;
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bool crossedSpark = (prevDeg < sparkAngle && currDeg >= sparkAngle) ||
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(prevDeg > sparkAngle + 360f && currDeg < sparkAngle);
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if (crossedSpark && !combustionActive && fuelInjected)
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{
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if (_random.NextDouble() < MisfireProbability)
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{
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combustionActive = false;
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}
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else
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{
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combustionActive = true; burnFraction = 0f;
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float range = EnergyVariationFraction;
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_energyFactor = 1f + range * (2f * (float)_random.NextDouble() - 1f);
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}
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}
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// Combustion
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if (combustionActive)
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{
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float angleSinceSpark = currDeg - sparkAngle;
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if (angleSinceSpark < 0f) angleSinceSpark += 720f;
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float newFraction = Wiebe(angleSinceSpark);
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if (newFraction >= 1f || angleSinceSpark > (WiebeDuration + WiebeStart + SparkAdvance))
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{
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newFraction = 1f; combustionActive = false;
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float totalMass = _airMass + _exhaustMass;
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_airMass = 0f; _exhaustMass = totalMass;
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}
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float dFraction = newFraction - burnFraction;
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if (dFraction > 0f)
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{
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float dQ = fuelMass * FuelLowerHeatingValue * _energyFactor * dFraction;
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cylinderEnergy += dQ;
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_exhaustMass += fuelMass * dFraction;
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burnFraction = newFraction;
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}
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}
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// Heat loss
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float dQ_loss = HeatTransferCoefficient * CylinderWallArea *
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(Temperature - AmbientTemperature) * dt;
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cylinderEnergy -= dQ_loss;
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// Update port states
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float p = Pressure, rho = Density, T = Temperature;
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float h = Gamma / (Gamma - 1f) * p / MathF.Max(rho, 1e-12f);
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float af = AirFraction;
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IntakePort.Pressure = p; IntakePort.Density = rho;
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IntakePort.Temperature = T; IntakePort.SpecificEnthalpy = h; IntakePort.AirFraction = af;
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ExhaustPort.Pressure = p; ExhaustPort.Density = rho;
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ExhaustPort.Temperature = T; ExhaustPort.SpecificEnthalpy = h; ExhaustPort.AirFraction = af;
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}
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public void UpdateState(float dt)
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{
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float dmAir = 0f, dmExhaust = 0f, dE = 0f;
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foreach (var port in _ports)
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{
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float mdot = port.MassFlowRate;
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float af = mdot >= 0f ? port.AirFraction : AirFraction;
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dmAir += mdot * af * dt;
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dmExhaust += mdot * (1f - af) * dt;
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dE += mdot * port.SpecificEnthalpy * dt;
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}
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_airMass += dmAir; _exhaustMass += dmExhaust;
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cylinderEnergy += dE;
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float V = MathF.Max(cylinderVolume, 1e-12f);
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float currentP = (Gamma - 1f) * cylinderEnergy / V;
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if (currentP > MaxPressurePa) cylinderEnergy = MaxPressurePa * V / (Gamma - 1f);
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float currentRho = (_airMass + _exhaustMass) / V;
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float currentT = currentP / MathF.Max(currentRho * GasConstant, 1e-12f);
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if (currentT > MaxTemperatureK)
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{
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float pAtTlimit = currentRho * GasConstant * MaxTemperatureK;
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cylinderEnergy = pAtTlimit * V / (Gamma - 1f);
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}
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float totalMass = _airMass + _exhaustMass;
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if (totalMass < 1e-9f)
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{
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_airMass = 1e-9f; _exhaustMass = 0f;
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cylinderEnergy = 101325f * V / (Gamma - 1f);
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}
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else if (cylinderEnergy < 0f)
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{
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cylinderEnergy = 101325f * V / (Gamma - 1f);
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}
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if (_airMass < 0f) _airMass = 0f;
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if (_exhaustMass < 0f) _exhaustMass = 0f;
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}
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}
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} |