### 9.12.2. Customize Knock Reaction Rate

When autoignition is detected for the Knock model, the fuel burns locally according to the Knock Reaction Rate. If unspecified the solver assumes a first-order Arrhenius rate with default coefficients. You may customize the coefficients by enabling the Customize Knock Reaction Rate option. The following options are available:

- Arrhenius: first-order reaction rate proportional to fuel available

- Value: specify custom reaction rate (to be applied locally when knock occurs).

The Solution Change Factor may be specified in order to limit the fraction of fuel consumed per time step (default=0.6 or 60%). Using this setting ensures that the fuel combustion is resolved by at least few timesteps; this can improve robustness significantly.

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