Simulation of quasi one-dimensional reacting flow is a standard in many combustion studies. Here Ember, a new open-source code for efficiently performing these calculations using large, detailed chemical kinetic models is presented. Ember outperforms other standard software, such as Chemkin, in computation time by leveraging rebalanced Strang operator splitting which does not suffer the steady-state inaccuracies of most splitting methods. The splitting approach and implementation used in Ember are described. Ember is validated for computation of flame extinction through imposed strain, extinction strain rate (ESR), and shown to be capable of modeling three typical experimental strained flame configurations: premixed twin flames, premixed single flames opposing inert, and diffusion flames. As further demonstration, Ember is used to investigate Lewis number effects on ESR using a detailed chemical kinetic model with 500 species for simulation of strained extinction of lean (Le > 1) and rich (Le < 1) propane/air flames. Primary trends predicted by Law (2006) using asymptotic theories of strained flames are accurately reproduced with the large, detailed chemical kinetic model. However, the complicated chemistry introduces some subtle phenomena not seen with single-step models. The Ember software is open-source and freely available to any user online. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.