Fixes N2O not decomposing above 100000 Kelvin (ParadiseSS13#26817)

* Replaces the N2O decomposition function with one that is slightly above 0 at 1400 Kelvin and approaches 1 as temp increases.

* adds a min check to the calculation of the amount to decompose

code/__DEFINES/atmospherics_defines.dm

@@ -151,7 +151,12 @@
 // Reactions
 #define N2O_DECOMPOSITION_MIN_ENERGY		1400
 #define N2O_DECOMPOSITION_ENERGY_RELEASED	200000
-
+/// The coefficient a for a function of the form: 1 - (a / (x + c)^2) which gives a decomposition rate of 0.5 at 50000 Kelvin
+/// And a decomposition close to 0 at 1400 Kelvin
+#define N2O_DECOMPOSITION_COEFFICIENT_A 1.376651173e10
+/// The coefficient c for a function of the form: 1 - (a / (x + c)^2) which gives a decomposition rate of 0.5 at 50000 Kelvin
+/// And a decomposition rate close to 0 at 1400 Kelvin
+#define N2O_DECOMPOSITION_COEFFICIENT_C 115930.77913
 // From milla/src/model.rs, line 126
 #define ATMOS_MODE_SPACE 0						//! Tile is exposed to space and loses air every second
 #define ATMOS_MODE_SEALED 1						//! Tile has no special behaviour

code/modules/atmospherics/gasmixtures/gas_mixture.dm

@@ -574,21 +574,19 @@ What are the archived variables for?
 		var/energy_released = 0
 		var/old_heat_capacity = heat_capacity()
 		var/burned_fuel = 0
+		burned_fuel = min((1 - (N2O_DECOMPOSITION_COEFFICIENT_A  / ((private_temperature + N2O_DECOMPOSITION_COEFFICIENT_C) ** 2))) * private_sleeping_agent, private_sleeping_agent)
+		private_sleeping_agent -= burned_fuel
 
-		burned_fuel = max(0, 0.00002 * (private_temperature - (0.00001 * (private_temperature ** 2)))) * private_sleeping_agent
-		if(private_sleeping_agent - burned_fuel > 0)
-			private_sleeping_agent -= burned_fuel
+		if(burned_fuel)
+			energy_released += (N2O_DECOMPOSITION_ENERGY_RELEASED * burned_fuel)
 
-			if(burned_fuel)
-				energy_released += (N2O_DECOMPOSITION_ENERGY_RELEASED * burned_fuel)
+			private_oxygen += burned_fuel * 0.5
+			private_nitrogen += burned_fuel
 
-				private_oxygen += burned_fuel * 0.5
-				private_nitrogen += burned_fuel
-
-				var/new_heat_capacity = heat_capacity()
-				if(new_heat_capacity > MINIMUM_HEAT_CAPACITY)
-					private_temperature = (private_temperature * old_heat_capacity + energy_released) / new_heat_capacity
-				reacting = TRUE
+			var/new_heat_capacity = heat_capacity()
+			if(new_heat_capacity > MINIMUM_HEAT_CAPACITY)
+				private_temperature = (private_temperature * old_heat_capacity + energy_released) / new_heat_capacity
+			reacting = TRUE
 
 	fuel_burnt = 0
 	//Handle plasma burning