To prepare a reaction mechanism for engine simulations, it is important to ensure that the mechanism is valid over the range of local conditions that exists inside the combustion chamber, especially at the start of combustion phasing. It is equally important to make sure the reduced mechanism is also valid under the range of conditions that might exist in the engine prior to autoignition or initiation of flame or production of emissions species. To cover these ranges of conditions, use the Parameter Study Facility in Chemkin after setting up the baseline reactor model. (See the Chemkin Advanced Analysis Guide.)