Remove particle speed limit, reduce steam effect volume more realistically

Author: SteelFill

Source/Documentation/Manual/physics.rst

@@ -2474,7 +2474,6 @@ the one shown below::
         
         Comment ( Advanced optional parameters. )
         ORTSMaxParticles ( 2500 )
-        ORTSEmissionSpeedLimit ( 150m/s )
         ORTSGraphic ( "smokemain.ace" )
         ORTSGraphicAtlasLayout ( 4 4 )
     )
@@ -2485,7 +2484,6 @@ the one shown below::
    single: ORTSParticleDiameter
    single: ORTSPositionVariation
    single: ORTSInitialVelocityVariation
-   single: ORTSEmissionSpeedLimit
    single: ORTSFinalVelocity
    single: ORTSFinalVelocityVariation
    single: ORTSLifespanMultiplier
@@ -2624,13 +2622,6 @@ and poor framerates:
   the particle limit. Do NOT increase the limit if particles are already overlapping; it is often
   better to simply reduce the number of particles emitted using ORTSRateMultiplier and/or other
   parameters listed here.
-- ``ORTSEmissionSpeedLimit ( v )`` -- Some particle emitters are driven by the simulated flow
-  rate of exhaust, which has to make some assumptions about the pressure and volume of exhaust.
-  This can lead to unrealistically high speed particles being emitted, so a speed limit can be
-  set (default units are meters per second) to keep particle speed reasonable. This is not a hard
-  limit, it is gradually enforced as the simulation calculates higher and higher exhaust speed.
-  The limit is also applied before considering the emitter velocity factor, so actual exhaust speed
-  will vary depending on other settings.
   By default, the limit is 150 meters per second, which will be suitable in most cases.
 - ``ORTSGraphic ( "tex" )`` -- Gives the name and path to the texture that should be used to render
   particles from this emitter. The default texture is "smokemain.ace" for steam-type emitters and

Source/Orts.Simulation/Simulation/RollingStocks/MSTSSteamLocomotive.cs

@@ -396,7 +396,9 @@ public class MSTSSteamLocomotive : MSTSLocomotive
 
         #region Additional steam properties
         const float SpecificHeatCoalKJpKGpK = 1.26f; // specific heat of coal - kJ/kg/K
-        const float SteamVaporSpecVolumeAt100DegC1BarM3pKG = 1.696f;
+        const float SaturatedSteam1BarSpecificVolM3pKG = 1.694f;  // specific volume of saturated steam at 1 bar (100 degC) in m^3 / kg
+        const float SaturatedSteam5BarSpecificVolM3pKG = 0.375f;  // specific volume of saturated steam at 5 bar (152 degC) in m^3 / kg
+        const float SaturatedSteam10BarSpecificVolM3pKG = 0.194f; // specific volume of saturated steam at 10 bar (180 degC) in m^3 / kg
         float WaterHeatBTUpFT3;             // Water heat in btu/ft3
         bool FusiblePlugIsBlown = false;    // Fusible plug blown, due to lack of water in the boiler
         bool LocoIsOilBurner = false;       // Used to identify if loco is oil burner
@@ -3260,35 +3262,35 @@ private void UpdateFX(float elapsedClockSeconds)
             SanderSteamExhaustReverseVelocityMpS = Sander && SandingSystemType == SandingSystemTypes.Steam && Direction == Direction.Reverse ? (1.0f * SteamEffectsFactor) : 0.0f;
             SanderSteamExhaustParticleDurationS = 1.0f;
 
-            Cylinders1SteamVolumeM3pS = CylinderCock1On && CylinderCocksAreOpen && throttle > 0.0 && CylCockSteamUsageDisplayLBpS > 0.0 ? (1.00f * SteamEffectsFactor) : 0.0f;
-            Cylinders2SteamVolumeM3pS = CylinderCock2On && CylinderCocksAreOpen && throttle > 0.0 && CylCockSteamUsageDisplayLBpS > 0.0 ? (1.00f * SteamEffectsFactor) : 0.0f;
+            Cylinders1SteamVolumeM3pS = CylinderCock1On && CylinderCocksAreOpen && throttle > 0.0 && CylCockSteamUsageDisplayLBpS > 0.0 ? (1.0f * SteamEffectsFactor) : 0.0f;
+            Cylinders2SteamVolumeM3pS = CylinderCock2On && CylinderCocksAreOpen && throttle > 0.0 && CylCockSteamUsageDisplayLBpS > 0.0 ? (1.0f * SteamEffectsFactor) : 0.0f;
 
-            Cylinders11SteamVolumeM3pS = CylinderCock11On && CylinderCocksAreOpen && throttle > 0.0 && CylCockSteamUsageDisplayLBpS > 0.0 ? (1.00f * SteamEffectsFactor) : 0.0f;
-            Cylinders12SteamVolumeM3pS = CylinderCock12On && CylinderCocksAreOpen && throttle > 0.0 && CylCockSteamUsageDisplayLBpS > 0.0 ? (1.00f * SteamEffectsFactor) : 0.0f;
-            Cylinders21SteamVolumeM3pS = CylinderCock21On && CylinderCocksAreOpen && throttle > 0.0 && CylCockSteamUsageDisplayLBpS > 0.0 ? (1.00f * SteamEffectsFactor) : 0.0f;
-            Cylinders22SteamVolumeM3pS = CylinderCock22On && CylinderCocksAreOpen && throttle > 0.0 && CylCockSteamUsageDisplayLBpS > 0.0 ? (1.00f * SteamEffectsFactor) : 0.0f;
-            Cylinders31SteamVolumeM3pS = CylinderCock31On && CylinderCocksAreOpen && throttle > 0.0 && CylCockSteamUsageDisplayLBpS > 0.0 ? (1.00f * SteamEffectsFactor) : 0.0f;
-            Cylinders32SteamVolumeM3pS = CylinderCock32On && CylinderCocksAreOpen && throttle > 0.0 && CylCockSteamUsageDisplayLBpS > 0.0 ? (1.00f * SteamEffectsFactor) : 0.0f;
-            Cylinders41SteamVolumeM3pS = CylinderCock41On && CylinderCocksAreOpen && throttle > 0.0 && CylCockSteamUsageDisplayLBpS > 0.0 ? (1.00f * SteamEffectsFactor) : 0.0f;
-            Cylinders42SteamVolumeM3pS = CylinderCock42On && CylinderCocksAreOpen && throttle > 0.0 && CylCockSteamUsageDisplayLBpS > 0.0 ? (1.00f * SteamEffectsFactor) : 0.0f;
+            Cylinders11SteamVolumeM3pS = CylinderCock11On && CylinderCocksAreOpen && throttle > 0.0 && CylCockSteamUsageDisplayLBpS > 0.0 ? (1.0f * SteamEffectsFactor) : 0.0f;
+            Cylinders12SteamVolumeM3pS = CylinderCock12On && CylinderCocksAreOpen && throttle > 0.0 && CylCockSteamUsageDisplayLBpS > 0.0 ? (1.0f * SteamEffectsFactor) : 0.0f;
+            Cylinders21SteamVolumeM3pS = CylinderCock21On && CylinderCocksAreOpen && throttle > 0.0 && CylCockSteamUsageDisplayLBpS > 0.0 ? (1.0f * SteamEffectsFactor) : 0.0f;
+            Cylinders22SteamVolumeM3pS = CylinderCock22On && CylinderCocksAreOpen && throttle > 0.0 && CylCockSteamUsageDisplayLBpS > 0.0 ? (1.0f * SteamEffectsFactor) : 0.0f;
+            Cylinders31SteamVolumeM3pS = CylinderCock31On && CylinderCocksAreOpen && throttle > 0.0 && CylCockSteamUsageDisplayLBpS > 0.0 ? (1.0f * SteamEffectsFactor) : 0.0f;
+            Cylinders32SteamVolumeM3pS = CylinderCock32On && CylinderCocksAreOpen && throttle > 0.0 && CylCockSteamUsageDisplayLBpS > 0.0 ? (1.0f * SteamEffectsFactor) : 0.0f;
+            Cylinders41SteamVolumeM3pS = CylinderCock41On && CylinderCocksAreOpen && throttle > 0.0 && CylCockSteamUsageDisplayLBpS > 0.0 ? (1.0f * SteamEffectsFactor) : 0.0f;
+            Cylinders42SteamVolumeM3pS = CylinderCock42On && CylinderCocksAreOpen && throttle > 0.0 && CylCockSteamUsageDisplayLBpS > 0.0 ? (1.0f * SteamEffectsFactor) : 0.0f;
 
             Cylinder1ParticleDurationS = 1.0f;
             Cylinder2ParticleDurationS = 1.0f;
 
 
-            CylinderSteamExhaust1SteamVolumeM3pS = throttle > 0.0 && CylinderSteamExhaust1On ? (cutoff * 10.0f * SteamEffectsFactor) : 0.0f;
-            CylinderSteamExhaust2SteamVolumeM3pS = throttle > 0.0 && CylinderSteamExhaust2On ? (cutoff * 10.0f * SteamEffectsFactor) : 0.0f;
-            CylinderSteamExhaust3SteamVolumeM3pS = throttle > 0.0 && CylinderSteamExhaust3On ? (cutoff * 10.0f * SteamEffectsFactor) : 0.0f;
-            CylinderSteamExhaust4SteamVolumeM3pS = throttle > 0.0 && CylinderSteamExhaust4On ? (cutoff * 10.0f * SteamEffectsFactor) : 0.0f;
+            CylinderSteamExhaust1SteamVolumeM3pS = throttle > 0.0 && CylinderSteamExhaust1On ? (cutoff * 2.5f * SteamEffectsFactor) : 0.0f;
+            CylinderSteamExhaust2SteamVolumeM3pS = throttle > 0.0 && CylinderSteamExhaust2On ? (cutoff * 2.5f * SteamEffectsFactor) : 0.0f;
+            CylinderSteamExhaust3SteamVolumeM3pS = throttle > 0.0 && CylinderSteamExhaust3On ? (cutoff * 2.5f * SteamEffectsFactor) : 0.0f;
+            CylinderSteamExhaust4SteamVolumeM3pS = throttle > 0.0 && CylinderSteamExhaust4On ? (cutoff * 2.5f * SteamEffectsFactor) : 0.0f;
             CylinderSteamExhaustParticleDurationS = 1.0f;
 
-            CylinderSteamExhaust2_1SteamVolumeM3pS = throttle > 0.0 && CylinderSteamExhaust2_1On ? (cutoff * 10.0f * SteamEffectsFactor) : 0.0f;
-            CylinderSteamExhaust2_2SteamVolumeM3pS = throttle > 0.0 && CylinderSteamExhaust2_2On ? (cutoff * 10.0f * SteamEffectsFactor) : 0.0f;
+            CylinderSteamExhaust2_1SteamVolumeM3pS = throttle > 0.0 && CylinderSteamExhaust2_1On ? (cutoff * 2.5f * SteamEffectsFactor) : 0.0f;
+            CylinderSteamExhaust2_2SteamVolumeM3pS = throttle > 0.0 && CylinderSteamExhaust2_2On ? (cutoff * 2.5f * SteamEffectsFactor) : 0.0f;
 
-            Cylinders2_11SteamVolumeM3pS = CylinderCock2_11On && CylinderCocksAreOpen && throttle > 0.0 && CylCockSteamUsageDisplayLBpS > 0.0 ? (1.00f * SteamEffectsFactor) : 0.0f;
-            Cylinders2_12SteamVolumeM3pS = CylinderCock2_12On && CylinderCocksAreOpen && throttle > 0.0 && CylCockSteamUsageDisplayLBpS > 0.0 ? (1.00f * SteamEffectsFactor) : 0.0f;
-            Cylinders2_21SteamVolumeM3pS = CylinderCock2_21On && CylinderCocksAreOpen && throttle > 0.0 && CylCockSteamUsageDisplayLBpS > 0.0 ? (1.00f * SteamEffectsFactor) : 0.0f;
-            Cylinders2_22SteamVolumeM3pS = CylinderCock2_22On && CylinderCocksAreOpen && throttle > 0.0 && CylCockSteamUsageDisplayLBpS > 0.0 ? (1.00f * SteamEffectsFactor) : 0.0f;
+            Cylinders2_11SteamVolumeM3pS = CylinderCock2_11On && CylinderCocksAreOpen && throttle > 0.0 && CylCockSteamUsageDisplayLBpS > 0.0 ? (1.0f * SteamEffectsFactor) : 0.0f;
+            Cylinders2_12SteamVolumeM3pS = CylinderCock2_12On && CylinderCocksAreOpen && throttle > 0.0 && CylCockSteamUsageDisplayLBpS > 0.0 ? (1.0f * SteamEffectsFactor) : 0.0f;
+            Cylinders2_21SteamVolumeM3pS = CylinderCock2_21On && CylinderCocksAreOpen && throttle > 0.0 && CylCockSteamUsageDisplayLBpS > 0.0 ? (1.0f * SteamEffectsFactor) : 0.0f;
+            Cylinders2_22SteamVolumeM3pS = CylinderCock2_22On && CylinderCocksAreOpen && throttle > 0.0 && CylCockSteamUsageDisplayLBpS > 0.0 ? (1.0f * SteamEffectsFactor) : 0.0f;
 
             // Booster Cylinder Steam Exhausts (automatic)
             BoosterCylinderSteamExhaust01SteamVolumeM3pS = BoosterCylinderSteamExhaustOn && BoosterCylinderSteamExhaust01On ? (1.0f * BoosterSteamFraction) : 0.0f;
@@ -3337,7 +3339,7 @@ private void UpdateFX(float elapsedClockSeconds)
 
 
             // Blowdown Steam Effects
-            BlowdownSteamVolumeM3pS = (BlowdownValveOpen && BlowdownSteamUsageLBpS > 0.0) ? Kg.FromLb(BlowdownSteamUsageLBpS) * SteamVaporSpecVolumeAt100DegC1BarM3pKG : 0;
+            BlowdownSteamVolumeM3pS = (BlowdownValveOpen && BlowdownSteamUsageLBpS > 0.0) ? Kg.FromLb(BlowdownSteamUsageLBpS) * SaturatedSteam10BarSpecificVolM3pKG : 0;
             BlowdownParticleDurationS = 2.0f;
 
             // Drainpipe Steam Effects
@@ -3376,7 +3378,7 @@ private void UpdateFX(float elapsedClockSeconds)
 
             // Safety Valves Steam Effects
 
-            SafetyValvesSteamVolumeM3pS = SafetyIsOn ? Kg.FromLb(SafetyValveUsageLBpS) * SteamVaporSpecVolumeAt100DegC1BarM3pKG : 0;
+            SafetyValvesSteamVolumeM3pS = SafetyIsOn ? Kg.FromLb(SafetyValveUsageLBpS) * SaturatedSteam10BarSpecificVolM3pKG : 0;
             SafetyValvesParticleDurationS = MathHelper.Clamp(3.0f / (AbsSpeedMpS / 4.0f), 0.1f, 3.0f);
 
             // Smoke Stack Smoke Effects
@@ -3409,8 +3411,8 @@ private void UpdateFX(float elapsedClockSeconds)
                 {
                     float smokeVolumeVariationFactor = 1.0f * cutoff; // adjust smoke volume based upon throttle and cutoff settings
 
-                    StackSteamVolumeM3pS = Kg.FromLb(CylinderSteamUsageLBpS + BlowerSteamUsageLBpS + RadiationSteamLossLBpS + CompSteamUsageLBpS + GeneratorSteamUsageLBpS) * smokeVolumeVariationFactor * SteamVaporSpecVolumeAt100DegC1BarM3pKG;
-                    StackSteamVolumeM3pS = (StackSteamVolumeM3pS) / StackCount;
+                    StackSteamVolumeM3pS = Kg.FromLb(CylinderSteamUsageLBpS + BlowerSteamUsageLBpS + RadiationSteamLossLBpS + CompSteamUsageLBpS + GeneratorSteamUsageLBpS) *
+                        smokeVolumeVariationFactor * SaturatedSteam5BarSpecificVolM3pKG;
                     StackParticleDurationS = Throttlepercent + FireRatio;
                 }
                 else // when not exhausting
@@ -3419,8 +3421,8 @@ private void UpdateFX(float elapsedClockSeconds)
                     {
                         float smokeRestVolumeVariationFactor = 1.0f * cutoff; // adjust smoke volume based upon throttle and cutoff settings
 
-                        StackSteamVolumeM3pS = Kg.FromLb(BlowerSteamUsageLBpS + RadiationSteamLossLBpS + CompSteamUsageLBpS + GeneratorSteamUsageLBpS) * smokeRestVolumeVariationFactor * SteamVaporSpecVolumeAt100DegC1BarM3pKG;
-                        StackSteamVolumeM3pS = (StackSteamVolumeM3pS) / StackCount;
+                        StackSteamVolumeM3pS = Kg.FromLb(BlowerSteamUsageLBpS + RadiationSteamLossLBpS + CompSteamUsageLBpS + GeneratorSteamUsageLBpS) *
+                            smokeRestVolumeVariationFactor * SaturatedSteam5BarSpecificVolM3pKG;
                         StackParticleDurationS = Throttlepercent + FireRatio;
                     }
                 }
@@ -3429,8 +3431,8 @@ private void UpdateFX(float elapsedClockSeconds)
             else // Legacy smoke implementation
             {
                 float velocityRate = (float)Math.Sqrt(KPa.FromPSI(SteamReleasePressure_AtmPSI) * 1000 * 2 / WaterDensityAt100DegC1BarKGpM3);
-                StackSteamVolumeM3pS = Kg.FromLb(CylinderSteamUsageLBpS + BlowerSteamUsageLBpS + RadiationSteamLossLBpS + CompSteamUsageLBpS + GeneratorSteamUsageLBpS) * SteamVaporSpecVolumeAt100DegC1BarM3pKG;
-                StackSteamVolumeM3pS = (StackSteamVolumeM3pS) / StackCount;
+                StackSteamVolumeM3pS = Kg.FromLb(CylinderSteamUsageLBpS + BlowerSteamUsageLBpS + RadiationSteamLossLBpS + CompSteamUsageLBpS + GeneratorSteamUsageLBpS) *
+                    SaturatedSteam5BarSpecificVolM3pKG;
                 StackParticleDurationS = Throttlepercent + FireRatio;
             }
 

Source/Orts.Simulation/Simulation/RollingStocks/MSTSWagon.cs

@@ -4608,8 +4608,6 @@ public class ParticleEmitterData
         public Vector3 FinalVelocityMpS = Vector3.Up; // Default final velocity is 1 m/s upward
         public Vector3 FinalVelocityVariationMpS = new Vector3(0.75f);
 
-        public float SpeedLimitMpS = 150.0f;
-
         public float NozzleDiameterM = 0.1f;
         public float NozzleAreaM2 = -1; // If left at -1, will be initialized later
 
@@ -4704,7 +4702,6 @@ public ParticleEmitterData(STFReader stf)
                         FinalVelocityVariationMpS.Z = FinalVelocityVariationMpS.Y = FinalVelocityVariationMpS.X;
                     }
                 }),
-                new STFReader.TokenProcessor("ortsemissionspeedlimit", ()=>{ SpeedLimitMpS = stf.ReadFloatBlock(STFReader.UNITS.Speed, null); }),
                 new STFReader.TokenProcessor("ortsparticlediameter", ()=>{ NozzleDiameterM = stf.ReadFloatBlock(STFReader.UNITS.Distance, null); }),
                 new STFReader.TokenProcessor("ortslifespanmultiplier", ()=>{ LifetimeFactor = stf.ReadFloatBlock(STFReader.UNITS.None, null); }),
                 new STFReader.TokenProcessor("ortslifespanvariation", ()=>{ LifetimeVariationFactor = stf.ReadFloatBlock(STFReader.UNITS.None, null); }),

Source/RunActivity/Viewer3D/ParticleEmitter.cs

@@ -136,14 +136,6 @@ public void SetOutputRate(float particlespS)
         /// <param name="volumeM3pS">The cubic meter volume of particles to emit every second.</param>
         public void SetOutputVolumetric(float volumeM3pS)
         {
-            // Volumetric flow rate is assumed to be at atmospheric pressure, but this can give unrealistically fast-moving exhaust
-            // Limit exhaust speed to the 'speed limit' and calculate how 'compressed' the exhaust still is when emitter
-            // This calculation gradually increases the 'compression' as calculated speed increases
-            float factor = (volumeM3pS / EmissionHoleM2 + Emitter.EmitterData.SpeedLimitMpS) / Emitter.EmitterData.SpeedLimitMpS;
-
-            Emitter.CompressionFactor = factor;
-            volumeM3pS /= factor;
-
             Emitter.XNAInitialVelocity = Emitter.EmitterData.InitialVelocityFactor * volumeM3pS / EmissionHoleM2;
             Emitter.ParticlesPerSecond = EmitterData.RateFactor * volumeM3pS / ParticleVolumeM3;
 
@@ -377,8 +369,6 @@ struct ParticleVertex
 
         internal int SpriteCount;
 
-        internal float CompressionFactor = 1.0f;
-
         internal WorldPosition WorldPosition;
 
         internal MSTSWagonViewer CarViewer;
@@ -666,11 +656,11 @@ public void Update(float currentTime, ElapsedTime elapsedTime)
                         finalVelocity.X += ParticleViewer.Viewer.Simulator.Weather.WindInstantaneousSpeedMpS * ParticleViewer.Viewer.Simulator.Weather.WindInstantaneousDirection.X * EmitterData.WindEffect;
                         finalVelocity.Z += ParticleViewer.Viewer.Simulator.Weather.WindInstantaneousSpeedMpS * ParticleViewer.Viewer.Simulator.Weather.WindInstantaneousDirection.Y * EmitterData.WindEffect;
 
-                        // Amount by which particles initially expand depends on change in particle speed; faster particles expand more due to 'high pressure' at exhaust
-                        float speedDeltaRatio = (float)Math.Sqrt(initialSpeed * CompressionFactor);
-                        float initialExpansion = speedDeltaRatio * EmitterData.InitialExpansionFactor;
+                        // Amount by which particles initially expand depends on particle speed; faster particles expand more due to 'high pressure' at exhaust
+                        float speedIntensity = (float)Math.Sqrt(initialSpeed);
+                        float initialExpansion = speedIntensity * EmitterData.InitialExpansionFactor;
                         // Speed at which particles slow down depends on change in particle speed; faster particles slow down faster due to 'drag' from speed difference
-                        settling /= speedDeltaRatio / 5.0f + 1.0f; // Note: The / 5 is largely arbitrary, chosen to give results that look good
+                        settling /= speedIntensity / 5.0f + 1.0f; // Note: The / 5 is largely arbitrary, chosen to give results that look good
 
                         for (var j = 0; j < VerticesPerParticle; j++)
                         {

Source/RunActivity/Viewer3D/RollingStock/MSTSSteamLocomotiveViewer.cs

@@ -428,7 +428,7 @@ public override void PrepareFrame(RenderFrame frame, ElapsedTime elapsedTime)
             foreach (var drawer in Stack)
             {
                 Color_Value = car.SmokeColor.SmoothedValue;
-                drawer.SetOutputVolumetric(car.StackSteamVolumeM3pS, car.StackParticleDurationS, new Color(Color_Value, Color_Value, Color_Value));
+                drawer.SetOutputVolumetric(car.StackSteamVolumeM3pS / car.StackCount, car.StackParticleDurationS, new Color(Color_Value, Color_Value, Color_Value));
             }
 
             foreach (var drawer in Whistle)