diff --git a/src/thermophysicalModels/specie/specie/specie.H b/src/thermophysicalModels/specie/specie/specie.H
index a5855cfd..cb113e0f 100644
--- a/src/thermophysicalModels/specie/specie/specie.H
+++ b/src/thermophysicalModels/specie/specie/specie.H
@@ -149,6 +149,9 @@ public:
             //- Gas constant [J/(kg K)]
             inline scalar R() const;
 
+            //- Charge number
+            inline scalar z() const;
+
 
         // I-O
 
diff --git a/src/thermophysicalModels/specie/specie/specieI.H b/src/thermophysicalModels/specie/specie/specieI.H
index c0efbe62..66a4dd6b 100644
--- a/src/thermophysicalModels/specie/specie/specieI.H
+++ b/src/thermophysicalModels/specie/specie/specieI.H
@@ -132,6 +132,12 @@ inline scalar specie::R() const
 }
 
 
+inline scalar specie::z() const
+{
+    return nCharges_;
+}
+
+
 // * * * * * * * * * * * * * * * Member Operators  * * * * * * * * * * * * * //
 
 inline void specie::operator=(const specie& st)