[CTI/CTML] Add 'nonreactant_orders' option to allow non-reactant orders

The flag 'allow_nonreactant_orders' in class Reaction is set to 'true' when
using this option in cti/ctml.

Resolves #317
Resolves #321

doc/sphinx/cti/reactions.rst

@@ -483,6 +483,8 @@ This reaction could be defined as::
 Special care is required in this case since the units of the pre-exponential
 factor depend on the sum of the reaction orders, which may not be an integer.
 
+Note that you can change reaction orders only for irreversible reactions.
+
 Normally, reaction orders are required to be positive. However, in some cases
 negative reaction orders are found to be better fits for experimental data. In
 these cases, the default behavior may be overridden by adding
@@ -491,6 +493,13 @@ these cases, the default behavior may be overridden by adding
     reaction("C8H18 + 12.5 O2 => 8 CO2 + 9 H2O", [4.6e11, 0.0, 30.0],
              order="C8H18:-0.25 O2:1.75", options=['negative_orders'])
 
+Some global reactions could have reactions orders for non-reactant species. One
+should add ``nonreactant_orders`` to the reaction options to use this feature::
+
+    reaction("C8H18 + 12.5 O2 => 8 CO2 + 9 H2O", [4.6e11, 0.0, 30.0],
+             order="C8H18:-0.25 CO:0.15",
+             options=['negative_orders', 'nonreactant_orders'])
+
 
 .. rubric:: References
 

interfaces/cython/cantera/ctml_writer.py

@@ -1110,7 +1110,8 @@ def __init__(self,
             e.g. ``"CH4:0.25 O2:1.5"``.
         :param options: Processing options, as described in
             :ref:`sec-reaction-options`. May be one or more (as a list) of the
-            following: 'skip', 'duplicate', 'negative_A', 'negative_orders'.
+            following: 'skip', 'duplicate', 'negative_A', 'negative_orders',
+            'nonreactant_orders'.
         """
         self._id = id
         self._e = equation
@@ -1137,10 +1138,12 @@ def __init__(self,
         if self._order:
             order = getPairs(self._order)
             for o in order.keys():
-                if o in self._rxnorder:
-                    self._rxnorder[o] = order[o]
+                if (o not in self._rxnorder and
+                    'nonreactant_orders' not in self._options):
+                    raise CTI_Error("order specified for non-reactant: " + o +
+                                    " and no 'nonreactant_orders' option given")
                 else:
-                    raise CTI_Error("order specified for non-reactant: "+o)
+                    self._rxnorder[o] = order[o]
 
         self._kf = kf
         self._igspecies = []
@@ -1211,6 +1214,8 @@ def build(self, p):
             r['negative_A'] = 'yes'
         if 'negative_orders' in self._options:
             r['negative_orders'] = 'yes'
+        if 'nonreactant_orders' in self._options:
+            r['nonreactant_orders'] = 'yes'
 
         ee = self._e.replace('<','[').replace('>',']')
         r.addChild('equation',ee)

src/kinetics/Reaction.cpp

@@ -360,6 +360,9 @@ void setupElementaryReaction(ElementaryReaction& R, const XML_Node& rxn_node)
     if (rxn_node["negative_orders"] == "yes") {
         R.allow_negative_orders = true;
     }
+    if (rxn_node["nonreactant_orders"] == "yes") {
+        R.allow_nonreactant_orders = true;
+    }
     setupReaction(R, rxn_node);
 }