A short mechanism for the low-temperature ignition of n-heptane at high pressures

• The San Diego mechanism is enhanced to obtain low-temperature ignition of n-heptane.
• We added few elementary steps and rate parameters from chemical-kinetic literature.
• The chemical mechanism capture both the NTC phenomena and the two-stage ignition.
• The short mechanism produces agreement with experimental ignition-time data.

The low-temperature ignition of mixtures of n-heptane and air at elevated pressures (13–40 bar) is addressed. A base mechanism of 272 elementary reactions among 45 species, which models the ignition time of this fuel under a wide range of conditions for initial temperatures above about 1000 K is revised and augmented to produce the two-stage ignition and negative-temperature-coefficient (NTC) behavior seen experimentally for this fuel below 1000 K. By using available kinetic data, it is shown that by adding only 4 additional species to the original chemical mechanism, removing 8 of the original steps and replacing them by 14 new steps, the low-temperature ignition phenomena are modeled well. The numerical ignition-time predictions of this mechanism are compared with results of experimental shock-tube measurements in which NTC behavior and two-stage ignition are observed, showing reasonably good agreement. These results thus extend the range of applicability of the original mechanism to lower temperatures that are of interest in various applications, such as those for HCCI engines.