  Computational feasibility of turbulent reacting flows hinges on the reduction
of large chemical kinetics systems to smaller more manageable reaction sets.
Recently, several sophisticated reduction techniques have been developed but
they continue to be computationally prohibitive for practical three-dimensional
unsteady computations. For such applications, the classical quasi-steady state
assumption (QSSA), despite serious shortcomings, continues to be popular due to
its conceptual clarity and computational simplicity. Starting from invariant
manifold description, we develop an advanced quasi-steady state assumption
which (i) is independent of the choice of the retained (slow) species; (ii)
possesses much improved physical and mathematical characteristics; and (iii)
can be specialized for any objective function.
