Predictive combustion trajectory visualization model for study of conventional and advanced direct injection compression ignition combustion modes

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University of Alabama Libraries

There are many diagnostic approaches for determine in-cylinder quantities in an internal combustion engine. Of primary importance in this work are equivalence ratio and flame temperature. These parameters can be measured using expensive and highly modified optical engines or calculated using time consuming computational fluid dynamics and chemical kinetic models. These approaches work well in a lab but become less feasible when trying to implement diagnostics for real world on-board consumer use. With the decreasing cost of in-cylinder pressure transducers, the question arises of the whether or not it is feasible to create a diagnostic model based on in-cylinder pressure data and known engine parameter based on existing engine sensors. Using this model, it may be possible to actively modulate engine parameters to change combustion behavior in order to decrease harmful emissions without penalty to efficiency. In this context, combustion behavior (or a trajectory) is meant to describe the local temperatures and equivalence ratios that exist during burning in a direct injection compression ignition engine’s combustion chamber. This work builds on earlier attempts to model combustion trajectories on the equivalence ratio – temperature plane (Φ-T plane), as calculated from cylinder pressure. This work uses a 1-D non-vaporizing spray model with assumed radial profile. The proposed model accounts for the change in cylinder pressure throughout the combustion process by using a time step based on the resolution of the cylinder pressure data. Based on the predicted equivalence ratio, local flame temperature, calculated heat release, and amount of fuel burned at each portion (control volume) of the spray, a plot of the combustion trajectory can be developed. The temperature and equivalence ratio at which the fuel burns can be tracked to give a full mass weighted history of the combustion event with respect to both the ignition conditions and post-mixing heating and cooling on the Φ-T plane. The model was tested over multiple operating conditions including conventional and late timing diesel combustion, with and without EGR, lower and higher injection pressure. The encouraging results obtained from this study suggest engine control strategies could use this simple approach to reduce harmful emissions in the future.

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Mechanical engineering