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"better" two stroke engine

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max
2026-06-09 22:22:19 +02:00
parent 1240ebc33d
commit 56e9c2867a
2 changed files with 267 additions and 167 deletions
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275
Scenarios/TwoStrokeScenario.cs
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@@ -37,146 +37,194 @@ namespace FluidSim.Tests
private float _maxThrottleArea;
private float intakePipeArea, exhaustHeaderArea;
// -- Override shift from Scenario base class --
public override void ShiftUp() => vehicle.ShiftUp();
public override void ShiftUp() => vehicle.ShiftUp();
public override void ShiftDown() => vehicle.ShiftDown();
public override void Initialize(int sampleRate)
{
dt = 1.0 / sampleRate;
// ---- Vehicle ----
// ── Vehicle ──────────────────────────────────────────────────────────
vehicle = new Vehicle();
// ---- Throttle (38 mm) ----
_maxThrottleArea = (float)Units.AreaFromDiameter(38 * Units.mm);
// ── Throttle body: 42 mm – wider to reduce high-RPM intake restriction ──
_maxThrottleArea = (float)Units.AreaFromDiameter(42 * Units.mm);
// ---- Crankshaft ----
// ── Crankshaft ───────────────────────────────────────────────────────
// Lighter flywheel for quicker revving; friction tuned to ~0.5 kW loss at idle
crankshaft = new Crankshaft(2000);
crankshaft.CycleLength = 2f * MathF.PI; // two‑stroke
crankshaft.Inertia = 0.05f; // engine's own inertia (light)
crankshaft.FrictionConstant = 2.5f;
crankshaft.FrictionViscous = 0.0015f;
crankshaft.CycleLength = 2f * MathF.PI; // two-stroke: fire every rev
crankshaft.Inertia = 0.06f; // lighter flywheel
crankshaft.FrictionConstant = 0.4f; // ~0.4 Nm constant drag
crankshaft.FrictionViscous = 0.0004f; // ~2.5 Nm at 10 000 RPM
// ---- Cylinder (125cc) ----
float bore = 0.054f, stroke = 0.0545f, conRod = 0.109f, compRatio = 12.5f;
// ── Cylinder: 125 cc, motocross-style two-stroke ─────────────────────
// Bore × stroke = 54 × 54.5 mm → 124.9 cc
float bore = 0.054f;
float stroke = 0.0545f;
float conRod = 0.110f; // ~2× stroke
float compRatio = 7.2f; // geometric CR; effective CR after port closure is ~12:1
// Symmetric durations (around BDC)
float transferDuration = 130f; // 130°
float exhaustDuration = 190f; // 190°
// Port timings: exhaust 195°, transfer 155° – competitive MX 125
float transferDuration = 155f;
float exhaustDuration = 195f;
cylinder = new TwoStrokeCylinder(bore, stroke, conRod, compRatio,
transferDuration, exhaustDuration,
crankshaft)
{
IntakeValveDiameter = 0.038f,
IntakeValveLift = 0.010f,
IntakeValveDiameter = 0.042f, // matched to intake pipe
IntakeValveLift = 0.015f,
ExhaustValveDiameter = 0.040f,
ExhaustValveLift = 0.010f
ExhaustValveLift = 0.013f
};
// ---- Pipe system (60 exhaust cells, simple diffuser) ----
int intakeCells = 8;
int runnerCells = 8;
int exhaustCells = 60;
int totalCells = intakeCells + runnerCells + exhaustCells;
int[] pipeStart = { 0, intakeCells, intakeCells + runnerCells };
int[] pipeEnd = { intakeCells, intakeCells + runnerCells, totalCells };
// ── Pipe geometry ────────────────────────────────────────────────────
//
// Layout (all lengths in mm):
// Intake path: airbox stub 100 mm | runner 180 mm
// Exhaust path: expansion chamber tuned to ~9 000 RPM power peak
// header 170 mm Ø 40 mm
// diffuser 280 mm Ø 40 → 72 mm
// belly 200 mm Ø 72 mm
// convergent 130 mm Ø 72 → 28 mm
// stinger 70 mm Ø 28 mm
// total 850 mm
//
// Cell sizing: ~14 mm/cell.
// CFL: c_sound ≈ 550 m/s, dx=0.014 m → dt_max ≈ 25 µs
// at 44100 Hz dt = 22.7 µs → SubStepCount=4 keeps CFL safely ≤ 1
// --- Cell counts ---
int intakeCells = 7; // 100 mm stub → ~14 mm/cell
int runnerCells = 13; // 180 mm runner → ~14 mm/cell
int exhaustCells = 60; // 850 mm total → ~14 mm/cell
int totalCells = intakeCells + runnerCells + exhaustCells;
int[] pipeStart = { 0, intakeCells, intakeCells + runnerCells };
int[] pipeEnd = { intakeCells, intakeCells + runnerCells, totalCells };
float[] area = new float[totalCells];
float[] dx = new float[totalCells];
float intakeDia = 0.038f;
float intakeLenBefore = 0.15f;
float intakeLenRunner = 0.20f;
// --- Intake ---
float intakeDia = 0.042f; // matches throttle body
float intakeStubLen = 0.100f;
float intakeRunnerLen= 0.160f; // shorter runner → less pumping loss
intakePipeArea = MathF.PI * 0.25f * intakeDia * intakeDia;
// Single‑stage diffuser – 840 mm total, easy to tune
float headerDia = 0.042f, headerLen = 0.160f;
float diffuserLen = 0.250f, diffuserEndDia = 0.070f; // belly
float bellyLen = 0.240f;
float convergentLen = 0.120f;
float stingerDia = 0.026f, stingerLen = 0.070f;
// total = 0.16 + 0.25 + 0.24 + 0.12 + 0.07 = 0.84 m
exhaustHeaderArea = MathF.PI * 0.25f * headerDia * headerDia;
float bellyArea = MathF.PI * 0.25f * diffuserEndDia * diffuserEndDia;
float stingerArea = MathF.PI * 0.25f * stingerDia * stingerDia;
float totalExhaustLen = headerLen + diffuserLen + bellyLen + convergentLen + stingerLen; // 840 mm
int headerCells = (int)(exhaustCells * (headerLen / totalExhaustLen));
int diffuserCells = (int)(exhaustCells * (diffuserLen / totalExhaustLen));
int bellyCells = (int)(exhaustCells * (bellyLen / totalExhaustLen));
int convergentCells = (int)(exhaustCells * (convergentLen / totalExhaustLen));
int stingerCells = exhaustCells - headerCells - diffuserCells - bellyCells - convergentCells;
// Fill cells
for (int i = 0; i < intakeCells; i++)
{ area[i] = intakePipeArea; dx[i] = intakeLenBefore / intakeCells; }
for (int i = intakeCells; i < intakeCells + runnerCells; i++)
{ area[i] = intakePipeArea; dx[i] = intakeLenRunner / runnerCells; }
{ area[i] = intakePipeArea; dx[i] = intakeStubLen / intakeCells; }
int exhStart = intakeCells + runnerCells;
for (int i = intakeCells; i < intakeCells + runnerCells; i++)
{ area[i] = intakePipeArea; dx[i] = intakeRunnerLen / runnerCells; }
// Expansion chamber tuned for ~8 500 RPM power peak.
// Return-pulse travel distance = 0.5 × c_avg × (60 / RPM_target)
// c_avg ≈ 480 m/s → distance = 0.5 × 480 × (60/8500) ≈ 1.69 m round-trip
// → one-way pipe length ≈ 0.84 m (matches total below)
float headerDia = 0.040f; float headerLen = 0.130f; // shorter header → earlier pulse
float diffEndDia = 0.070f; float diffuserLen = 0.250f; // slightly narrower belly
float bellyDia = 0.070f; float bellyLen = 0.220f;
float convEndDia = 0.028f; float convergentLen= 0.160f; // longer convergent → stronger return pulse
float stingerDia = 0.028f; float stingerLen = 0.080f;
// total = 0.13+0.25+0.22+0.16+0.08 = 0.84 m
exhaustHeaderArea = MathF.PI * 0.25f * headerDia * headerDia;
float bellyArea = MathF.PI * 0.25f * bellyDia * bellyDia;
float stingerArea = MathF.PI * 0.25f * stingerDia * stingerDia;
// Distribute cells proportionally by section length
int headerCells = Math.Max(1, (int)MathF.Round(exhaustCells * headerLen / 0.84f));
int diffuserCells = Math.Max(1, (int)MathF.Round(exhaustCells * diffuserLen / 0.84f));
int bellyCells = Math.Max(1, (int)MathF.Round(exhaustCells * bellyLen / 0.84f));
int convergentCells = Math.Max(1, (int)MathF.Round(exhaustCells * convergentLen/ 0.84f));
int stingerCells = exhaustCells - headerCells - diffuserCells
- bellyCells - convergentCells;
if (stingerCells < 1) stingerCells = 1;
int exhBase = intakeCells + runnerCells;
int idx = 0;
for (int i = exhStart; i < totalCells; i++)
for (int i = exhBase; i < totalCells; i++, idx++)
{
if (idx < headerCells)
{ area[i] = exhaustHeaderArea; dx[i] = headerLen / headerCells; }
{
area[i] = exhaustHeaderArea;
dx[i] = headerLen / headerCells;
}
else if (idx < headerCells + diffuserCells)
{
float t = (idx - headerCells) / (float)(diffuserCells - 1);
float dia = headerDia + (diffuserEndDia - headerDia) * t;
float t = (idx - headerCells) / (float)(diffuserCells - 1);
// Smooth cosine taper instead of linear for better wave reflection
float ct = 0.5f * (1f - MathF.Cos(MathF.PI * t));
float dia = headerDia + (diffEndDia - headerDia) * ct;
area[i] = MathF.PI * 0.25f * dia * dia;
dx[i] = diffuserLen / diffuserCells;
dx[i] = diffuserLen / diffuserCells;
}
else if (idx < headerCells + diffuserCells + bellyCells)
{ area[i] = bellyArea; dx[i] = bellyLen / bellyCells; }
{
area[i] = bellyArea;
dx[i] = bellyLen / bellyCells;
}
else if (idx < headerCells + diffuserCells + bellyCells + convergentCells)
{
float t = (idx - headerCells - diffuserCells - bellyCells) / (float)(convergentCells - 1);
float dia = diffuserEndDia + (stingerDia - diffuserEndDia) * t;
float t = (idx - headerCells - diffuserCells - bellyCells)
/ (float)(convergentCells - 1);
// Steeper cosine convergent for a sharper return pulse
float ct = 0.5f * (1f - MathF.Cos(MathF.PI * t));
float dia = bellyDia + (convEndDia - bellyDia) * ct;
area[i] = MathF.PI * 0.25f * dia * dia;
dx[i] = convergentLen / convergentCells;
dx[i] = convergentLen / convergentCells;
}
else
{ area[i] = stingerArea; dx[i] = stingerLen / stingerCells; }
idx++;
{
area[i] = stingerArea;
dx[i] = stingerLen / stingerCells;
}
}
pipeSystem = new PipeSystem(totalCells, pipeStart, pipeEnd, area, dx,
1.225f, 0f, 101325f);
pipeSystem.DampingMultiplier = 1.0f;
pipeSystem.EnergyRelaxationRate = 0.5f;
pipeSystem.AmbientPressure = 101325f;
pipeSystem.DampingMultiplier = 0.8f; // slightly less damping → stronger pulses
pipeSystem.EnergyRelaxationRate = 0.4f;
pipeSystem.AmbientPressure = 101325f;
// ---- Volumes ----
intakePlenum = new Volume0D(0.5e-3f, 101325f, 300f);
// ── 0-D Volumes ──────────────────────────────────────────────────────
// Intake plenum: acts as a small airbox resonator (8 cc)
intakePlenum = new Volume0D(8e-3f, 101325f, 300f);
plenumInlet = intakePlenum.CreatePort();
plenumOutlet = intakePlenum.CreatePort();
exhaustMuffler = new Volume0D(5e-4f, 101325f, 600f);
// Exhaust silencer volume: 600 cc is realistic for a small-bore muffler
exhaustMuffler = new Volume0D(600e-6f, 101325f, 650f);
mufflerIn = exhaustMuffler.CreatePort();
mufflerOut = exhaustMuffler.CreatePort();
// ---- Boundary system ----
// ── Boundary system ───────────────────────────────────────────────────
boundaries = new BoundarySystem(pipeSystem, maxOrifices: 4, maxOpenEnds: 2);
throttleAreaIdx = 0; plenumRunnerIdx = 1; intakeValveIdx = 2; exhaustValveIdx = 3;
throttleAreaIdx = 0;
plenumRunnerIdx = 1;
intakeValveIdx = 2;
exhaustValveIdx = 3;
// Open ends: atmosphere at both extremes
boundaries.AddOpenEnd(pipeIndex: 0, isLeftEnd: true, 101325f, intakePipeArea);
intakeOpenIdx = 0;
intakeOpenIdx = 0;
boundaries.AddOpenEnd(pipeIndex: 2, isLeftEnd: false, 101325f, stingerArea);
exhaustOpenIdx = 1;
boundaries.AddOrifice(plenumInlet, 0, false, throttleAreaIdx, 0.7f);
boundaries.AddOrifice(plenumOutlet, 1, true, plenumRunnerIdx, 1.0f);
boundaries.AddOrifice(cylinder.IntakePort, 1, false, intakeValveIdx, 0.65f);
boundaries.AddOrifice(cylinder.ExhaustPort,2, true, exhaustValveIdx, 0.68f);
// Orifices: throttle → plenum → runner → cylinder → exhaust pipe
boundaries.AddOrifice(plenumInlet, 0, false, throttleAreaIdx, 0.72f);
boundaries.AddOrifice(plenumOutlet, 1, true, plenumRunnerIdx, 1.00f);
boundaries.AddOrifice(cylinder.IntakePort, 1, false, intakeValveIdx, 0.68f);
boundaries.AddOrifice(cylinder.ExhaustPort, 2, true, exhaustValveIdx, 0.70f);
orificeAreas = new float[4];
orificeAreas[plenumRunnerIdx] = intakePipeArea;
orificeAreas[plenumRunnerIdx] = intakePipeArea; // runner always fully open
// ---- Solver ----
solver = new Solver { SubStepCount = 4, EnableProfiling = false }; // 4 sub‑steps for 60 cells
// ── Solver ────────────────────────────────────────────────────────────
// SubStepCount = 4 keeps CFL ≤ 1 for 5 mm cells at 44 100 Hz
solver = new Solver { SubStepCount = 4, EnableProfiling = false };
solver.SetTimeStep(dt);
solver.SetPipeSystem(pipeSystem);
solver.SetBoundarySystem(boundaries);
@@ -184,13 +232,15 @@ namespace FluidSim.Tests
solver.AddComponent(intakePlenum);
solver.AddComponent(exhaustMuffler);
// ---- Sound ----
exhaustSound = new SoundProcessor(sampleRate, 1f) { Gain = 10f };
intakeSound = new SoundProcessor(sampleRate, 1f) { Gain = 10f };
// ── Sound ─────────────────────────────────────────────────────────────
exhaustSound = new SoundProcessor(sampleRate, 1f) { Gain = 4.5f };
intakeSound = new SoundProcessor(sampleRate, 1f) { Gain = 4.5f };
reverb = new OutdoorExhaustReverb(sampleRate);
stepCount = 0;
Console.WriteLine("125cc Two‑Stroke with vehicle coupling ready.");
Console.WriteLine("125cc Two-Stroke – expansion chamber tuned for ~8 500 RPM power peak");
Console.WriteLine($" Exhaust cells: {exhaustCells} | header {headerCells} diffuser {diffuserCells}" +
$" belly {bellyCells} convergent {convergentCells} stinger {stingerCells}");
}
public override float Process()
@@ -201,15 +251,15 @@ namespace FluidSim.Tests
var (clutchTorque, effectiveInertia) = vehicle.Update(engineRpm, crankshaft.Inertia, (float)dt);
crankshaft.SetEffectiveInertia(effectiveInertia);
crankshaft.SetLoadTorque(clutchTorque); // clutch torque now includes drag when locked
crankshaft.SetLoadTorque(clutchTorque);
crankshaft.Step((float)dt);
cylinder.PreStep((float)dt);
float throttledArea = _maxThrottleArea * Math.Clamp(Throttle, 0.001f, 1f);
orificeAreas[throttleAreaIdx] = throttledArea;
orificeAreas[intakeValveIdx] = cylinder.IntakeValveArea;
orificeAreas[exhaustValveIdx] = cylinder.ExhaustValveArea;
orificeAreas[throttleAreaIdx] = throttledArea;
orificeAreas[intakeValveIdx] = cylinder.IntakeValveArea;
orificeAreas[exhaustValveIdx] = cylinder.ExhaustValveArea;
boundaries.SetOrificeAreas(orificeAreas);
solver.Step();
@@ -223,33 +273,38 @@ namespace FluidSim.Tests
if (stepCount % 2000 == 0)
{
float rpm = crankshaft.AngularVelocity * 60f / (2f * MathF.PI);
Console.WriteLine($"Step {stepCount}, RPM={rpm:F0}, Gear={vehicle.CurrentGear}, Speed={vehicle.SpeedKmh:F0} km/h");
float rpm = crankshaft.AngularVelocity * 60f / (2f * MathF.PI);
float powerKw = crankshaft.AveragePower * 1e-3f;
float torqueNm = crankshaft.AverageTorque;
Console.WriteLine($"Step {stepCount,7} | RPM={rpm,6:F0} | Power={powerKw,5:F2} kW" +
$" | Torque={torqueNm,5:F1} Nm | Gear={vehicle.CurrentGear}" +
$" | Speed={vehicle.SpeedKmh,4:F0} km/h");
}
return reverb.Process((intakeDry + exhaustDry) * 0.5f);
}
// ── Drawing ───────────────────────────────────────────────────────────────
public override void Draw(RenderWindow target)
{
float winW = target.GetView().Size.X;
float winH = target.GetView().Size.Y;
float intakeY = winH / 2f - 40f;
float intakeY = winH / 2f - 40f;
float exhaustY = winH / 2f + 80f;
float openEndX = 40f;
// Intake pipe
// Intake stub
float x = openEndX;
float w = 120f;
DrawPipe(target, pipeSystem, 0, intakeY, x, x + w);
// Throttle
// Throttle body
float throttleX = x + w + 5f;
var throttleRect = new RectangleShape(new Vector2f(8f, 30f))
{
FillColor = Color.Yellow,
Position = new Vector2f(throttleX, intakeY - 15f)
Position = new Vector2f(throttleX, intakeY - 15f)
};
target.Draw(throttleRect);
@@ -263,31 +318,33 @@ namespace FluidSim.Tests
DrawPipe(target, pipeSystem, 1, intakeY, runnerStartX, runnerStartX + 100f);
// Cylinder
float cylCX = runnerStartX + 150f;
float cylCX = runnerStartX + 150f;
float cylTopY = intakeY - 120f;
DrawCylinder(target, cylinder, cylCX, cylTopY, 80f, 240f);
// Exhaust pipe
// Exhaust pipe (expansion chamber)
float exhStartX = cylCX + 40f + 20f;
DrawPipe(target, pipeSystem, 2, exhaustY, exhStartX, winW - 60f, areaScale: 1000f);
DrawPipe(target, pipeSystem, 2, exhaustY, exhStartX, winW - 60f, areaScale: 800f);
// Labels
float rpm = crankshaft.AngularVelocity * 60f / (2f * MathF.PI);
// HUD labels
float rpm = crankshaft.AngularVelocity * 60f / (2f * MathF.PI);
float powerKw = crankshaft.AveragePower * 1e-3f;
DrawLabel(target, $"RPM: {rpm:F0}", new Vector2f(20, 90), Color.White, 24);
DrawLabel(target, $"Power: {powerKw:F2} kW", new Vector2f(20, 115), Color.White, 24);
DrawLabel(target, $"Gear: {vehicle.CurrentGear}", new Vector2f(20, 140), Color.Cyan, 20);
DrawLabel(target, $"Speed: {vehicle.SpeedKmh:F0} km/h", new Vector2f(20, 160), Color.Cyan, 20);
// Dyno curve
float torqueNm = crankshaft.AverageTorque;
UpdateDynoCurve(rpm, powerKw, torqueNm);
DrawDynoCurve(target, winW - 410f, winH - 260f, 400f, 250f, rpm, powerKw);
DrawLabel(target, $"RPM: {rpm:F0}", new Vector2f(20, 90), Color.White, 24);
DrawLabel(target, $"Power: {powerKw:F2} kW", new Vector2f(20, 115), Color.White, 24);
DrawLabel(target, $"Torque: {torqueNm:F1} Nm",new Vector2f(20, 140), Color.White, 20);
string gearText = vehicle.CurrentGear == 0 ? "N" : vehicle.CurrentGear.ToString();
DrawLabel(target, $"Gear: {gearText}", new Vector2f(20, 140), Color.Cyan, 20);
DrawLabel(target, $"Speed: {vehicle.SpeedKmh:F0} km/h", new Vector2f(20, 160), Color.Cyan, 20);
DrawLabel(target, vehicle.Engagement > 0.99f ? "Clutch Locked" : "Clutch Slipping", new Vector2f(20, 180), Color.Cyan, 14);
DrawLabel(target, $"Gear: {gearText}", new Vector2f(20, 162), Color.Cyan, 20);
DrawLabel(target, $"Speed: {vehicle.SpeedKmh:F0} km/h",
new Vector2f(20, 184), Color.Cyan, 20);
DrawLabel(target, vehicle.Engagement > 0.99f ? "Clutch: Locked" : "Clutch: Slipping",
new Vector2f(20, 204), Color.Cyan, 14);
// Dyno curve
UpdateDynoCurve(rpm, powerKw, torqueNm);
DrawDynoCurve(target, winW - 410f, winH - 260f, 400f, 250f, rpm, powerKw);
}
}
}