[Test] Test low-T range of ion--neutral collision integral

test/data/ET_test.yaml

@@ -6,9 +6,6 @@ units: {length: cm, quantity: mole, activation-energy: K}
 phases:
 - name: gas
   thermo: ideal-gas
-  elements: [O, N, E]
-  species:
-  - species: [O2, E, O2^-]
   skip-undeclared-third-bodies: true
   kinetics: gas
   reactions:
@@ -69,6 +66,23 @@ species:
     well-depth: 136.5
     polarizability: 1.424
   note: L4/89
+- name: C10H8
+  composition: {C: 10, H: 8}
+  thermo:
+    model: NASA7
+    temperature-ranges: [300.0, 1370.0, 3500.0]
+    data:
+    - [-8.71832426, 0.108564074, -9.40254318e-05, 4.10014902e-08, -7.10574258e-12,
+      1.66434413e+04, 61.5987877]
+    - [15.1184828, 0.0389675576, -1.78248658e-05, 3.92092279e-09, -3.39215689e-13,
+      1.01121562e+04, -60.9041102]
+  transport:
+    model: gas
+    geometry: nonlinear
+    well-depth: 630.4
+    diameter: 6.18
+    polarizability: 16.5
+    rotational-relaxation: 1.0
 
 reactions:
 - equation: E + O2 + O2 => O2^- + O2  # Kossyi (1992) Eq.45

test/python/test_transport.py

@@ -94,7 +94,7 @@ def test_CK_mode(self, phase):
         for key in err_ct:
             assert err_ct[key] < err_ck[key]
 
-    def test_ionGas(self, phase):
+    def test_ionized_gas_with_no_ions(self, phase):
         # IonGasTransport gives the same result for a mixture
         # without ionized species
         phase.transport_model = 'ionized-gas'
@@ -107,6 +107,19 @@ def test_ionGas(self, phase):
         assert Dkm1 == approx(Dkm2)
         assert Dbin1 == approx(Dbin2)
 
+    def test_ionized_low_T(self):
+        """ (C10H8, O2-) interaction exercises low T* range of Stockmayer potential """
+        phase = ct.Solution('ET_test.yaml')
+        kO2m = phase.species_index("O2^-")
+        kNaphthalene = phase.species_index("C10H8")
+        # Regression test values
+        phase.TP = 300, ct.one_atm
+        Dbin = phase.binary_diff_coeffs
+        assert Dbin[kO2m, kNaphthalene] == approx(2.18902175e-06)
+        phase.TP = 350, ct.one_atm
+        Dbin = phase.binary_diff_coeffs
+        assert Dbin[kO2m, kNaphthalene] == approx(2.92899733e-06)
+
     def test_multiComponent(self, phase):
         with pytest.raises(NotImplementedError):
             phase.multi_diff_coeffs