Ignition in diesel engines, HCCI or other compression-ignition controlled engines: Combustion in compression ignition engines is governed by autoignition of fuels. Autoignition can be simulated using the Closed Homogeneous Batch reactor model in Chemkin.
Note: Batch reactor template: For ease of mechanism reduction setup, a batch reactor template has been created that can be used for mechanism reduction. While setting up a reactor model as part of mechanism reduction, the option to use the batch reactor template is presented. This template has pre-defined most of the reactor settings so that you only need to define the operating conditions (temperature, pressure, and species composition of the reactor). The batch reactor template is usually the most convenient way to set up a mechanism reduction operation. On the other hand, if more flexibility is needed to set up the model, the template option can be declined and a Chemkin model can be set up in its entirety.
Knock in spark-ignited engines: Knocking occurs due to autoignition of end gases after spark initiation. Autoignition can be simulated using the Closed Homogeneous Batch reactor template in Chemkin.
Flame propagation in spark-ignited engines: Turbulent flame speeds in CFD are typically computed from laminar flame speeds of the unburned fuel-air mixture. Laminar flame speeds could be simulated using the Flame Speed Calculator model in Chemkin. Although the Flame Speed Calculator could be used, the run times may be too long for the iterative mechanism reduction process when the full mechanism contains 1000 or more species. We therefore recommend the alternative of using the Closed Homogeneous reactor template for mechanism reductions for flame-speed applications. There is no loss in accuracy, because the underlying kinetics that govern flame speeds are captured accurately using the Closed Homogeneous reactor as long as a parameter study is used that includes the range of high temperatures expected in the flames. Section Chemkin Project With Parameter Study for Basis of Reduction discusses the appropriate range of conditions to employ in the Closed Homogeneous reactor when it is used for flame-speed calculations.
Emissions: In any engine, all emissions, including NOx, CO, UHC, and soot, are the result of combustion. High temperatures during post-combustion typically produce NOx. Low temperatures and improper mixing lead to incomplete combustion and emissions of CO and UHC. High temperatures with fuel-rich zones lead to soot production. Using an appropriate parameter study in Chemkin, all emissions can therefore be included in a mechanism reduction. They can be included as targets with either the Closed Homogeneous reactor or the Laminar Flame Speed Calculator. As discussed above, we recommend use of the Closed Homogeneous Reactor to allow a more complete parameter study with many iterations during the mechanism reduction.