Date of Completion


Embargo Period



Tianfeng Lu; Baki M. Cetegen

Field of Study

Mechanical Engineering


Master of Science

Open Access

Open Access


The Relative Importance Index (RII) method for determination of appropriate target species for dynamic adaptive chemistry (DAC) simulations using the directed relation graph with error propagation (DRGEP) method was developed and validated for two fuels. The conventional method of DRGEP target species selection involves picking an static set of target species based on the expected major combustion processes; however, these static target species may not remain important throughout a combustion simulation. The RII method determines appropriate DRGEP target species solely from the local thermochemical state of the simulation, enabling DAC simulations to better respond to changing combustion conditions while ensuring that accuracy is maintained. Further, the RII method reduces the expertise required of users to select DRGEP target species sets. The RII method was tested on constant volume ignition delay studies as well as single-cell engine simulations under homogenous charge compression ignition (HCCI) conditions for n-heptane and isopentanol reaction mechanisms. It is illustrated that the RII is capable of accurate predictions of constant volume ignition delays over a wide range of starting conditions. Further, for a similar maximum error in ignition delay predictions, under certain autoignition conditions the RII method produced considerably smaller local skeletal mechanisms compared to those of conventional DRGEP target species selections; however, both methods generated similarly sized local skeletal mechanisms outside these regions. In addition, the RII method was capable of accurately predicting ignition crank angles for single cell engine simulations under HCCI conditions with significantly smaller local skeletal mechanisms than conventional DRGEP target species selections.

Major Advisor

Chih-Jen Sung