crank case based two stroke testing

2026-06-10 00:13:14 +02:00
parent 56e9c2867a
commit 16498f8041
4 changed files with 406 additions and 308 deletions
--- a/Components/Crankcase.cs
+++ b/Components/Crankcase.cs
@@ -0,0 +1,150 @@
+// ============================================================
+// File: Crankcase.cs
+// ============================================================
+using System.Collections.Generic;
+using FluidSim.Interfaces;
+
+namespace FluidSim.Components
+{
+    public class Crankcase : IComponent
+    {
+        private readonly Crankshaft _crankshaft;
+        private readonly float _crankRadius, _conrodLength, _pistonArea;
+        private readonly float _clearanceVolume, _obliquity;
+
+        private float _mass, _internalEnergy, _airFraction;
+        public float Pressure { get; private set; }
+        public float Temperature { get; private set; }
+        public float Density => _mass / MathF.Max(Volume, 1e-12f);
+        public float Volume { get; private set; }
+
+        public Port IntakePort { get; }
+        public Port TransferPort { get; }
+        private readonly List<Port> _ports;
+        public IReadOnlyList<Port> Ports => _ports;
+
+        // FIX: store previous volume to calculate PdV work
+        private float _prevVolume;
+
+        private const float Rgas = 287.0f;
+        private const float Gamma = 1.4f;
+        private const float Cv = Rgas / (Gamma - 1.0f);
+
+        public Crankcase(Crankshaft crankshaft,
+                         float crankRadius, float conrodLength, float bore,
+                         float clearanceVolume,
+                         float initialPressure, float initialTemperature)
+        {
+            _crankshaft = crankshaft;
+            _crankRadius = crankRadius;
+            _conrodLength = conrodLength;
+            _pistonArea = MathF.PI * 0.25f * bore * bore;
+            _clearanceVolume = clearanceVolume;
+            _obliquity = crankRadius / conrodLength;
+
+            Pressure = initialPressure;
+            Temperature = initialTemperature;
+            float rho = initialPressure / (Rgas * initialTemperature);
+            _mass = rho * clearanceVolume;
+            _internalEnergy = _mass * Cv * initialTemperature;
+            _airFraction = 1.0f;
+            Volume = clearanceVolume;
+            _prevVolume = Volume;
+
+            IntakePort = new Port { Owner = this };
+            TransferPort = new Port { Owner = this };
+            _ports = new List<Port> { IntakePort, TransferPort };
+        }
+
+        public void PreStep(float dt)
+        {
+            // Save previous volume before updating
+            _prevVolume = Volume;
+
+            float theta = _crankshaft.CrankAngleRad % (2f * MathF.PI);
+            float cosTh = MathF.Cos(theta);
+            float sinTh = MathF.Sin(theta);
+            float term = MathF.Sqrt(1f - _obliquity * _obliquity * sinTh * sinTh);
+
+            // FIX: correct piston displacement: downstroke reduces crankcase volume
+            float x = _crankRadius * (1f - cosTh) + _conrodLength * (1f - term);
+            // Maximum volume at TDC (x = 0), minimum at BDC (x = stroke)
+            float maxVolume = _clearanceVolume + _pistonArea * 2f * _crankRadius; // stroke = 2 * crankRadius
+            Volume = maxVolume - _pistonArea * x;
+
+            // Update thermodynamic state using the new volume (before mass transfer)
+            if (_mass > 1e-12f && Volume > 1e-12f)
+            {
+                Temperature = _internalEnergy / (_mass * Cv);
+                Pressure = _mass * Rgas * Temperature / Volume;
+            }
+        }
+
+        public void UpdateState(float dt)
+        {
+            // ---- Mass and energy transport (identical to original) ----
+            float mdotIn = IntakePort.MassFlowRate;
+            float mdotOut = TransferPort.MassFlowRate;
+
+            float dm = (mdotIn - mdotOut) * dt;
+            float dE = (mdotIn * IntakePort.SpecificEnthalpy
+                      - mdotOut * (Cv * Temperature + Pressure / MathF.Max(Density, 1e-12f))) * dt;
+            float dY = (mdotIn * IntakePort.AirFraction - mdotOut * _airFraction) * dt;
+
+            _mass += dm;
+            _internalEnergy += dE;
+            if (_mass > 1e-12f)
+                _airFraction = Math.Clamp((_airFraction * (_mass - dm) + dY) / _mass, 0f, 1f);
+
+            // ---- FIX: add mechanical work done BY the gas ON the piston ----
+            // During a step, volume changed from _prevVolume to current Volume.
+            // Work done BY gas = P * dV (if dV > 0, gas expands and does work, losing energy)
+            float dV = Volume - _prevVolume;
+            // Use average pressure during the step (approximate with current pressure)
+            _internalEnergy -= Pressure * dV;   // removes energy when volume increases
+
+            // Safety floors
+            if (_mass < 1e-9f)
+            {
+                _mass = 1e-9f;
+                _internalEnergy = _mass * Cv * 300f;
+                _airFraction = 1f;
+            }
+            if (_internalEnergy < 0f)
+                _internalEnergy = _mass * Cv * 300f;
+
+            // Final state update
+            if (_mass > 1e-12f && Volume > 1e-12f)
+            {
+                Temperature = _internalEnergy / (_mass * Cv);
+                Pressure = _mass * Rgas * Temperature / Volume;
+            }
+            else
+            {
+                Temperature = 300f;
+                Pressure = 101325f;
+            }
+
+            // Safety limits (unchanged, but now rarely triggered)
+            const float safetyPressure = 1.0f;
+            if (Pressure < safetyPressure && _mass > 1e-12f && Volume > 1e-12f)
+            {
+                Temperature = safetyPressure * Volume / (_mass * Rgas);
+                _internalEnergy = _mass * Cv * Temperature;
+                Pressure = safetyPressure;
+            }
+
+            const float maxPressure = 5e5f;
+            if (Pressure > maxPressure && _mass > 1e-12f && Volume > 1e-12f)
+            {
+                float targetMass = maxPressure * Volume / (Rgas * Temperature);
+                if (_mass > targetMass)
+                {
+                    _mass = targetMass;
+                    _internalEnergy = _mass * Cv * Temperature;
+                    Pressure = maxPressure;
+                }
+            }
+        }
+    }
+}