Date of Award


Document Type

Master's Thesis

Degree Name

Master of Science in Mechanical Engineering (MS)

College, School or Department Name

Department of Mechanical Engineering-Engineering Mechanics


Mahdi Shahbakhti


Homogeneous Charge Compression Ignition (HCCI) and Premixed Charge Compression Ignition (PCCI) combustion strategies are promising methods for achieving low engine-out NOx and soot emissions as well as high indicated efficiency. However, these combustion strategies have difficulties with controlling the rate of heat release and lack of an adequate combustion phasing control mechanism. A dual-fuel Reactivity Controlled Compression Ignition (RCCI) combustion strategy will address these issues due to the existence of precise means for controlling the heat release rate and combustion phasing. In the RCCI strategy two fuels with different reactivity (auto-ignition characteristics, e.g., gasoline and diesel) are blended inside the combustion chamber. Combustion phasing is controlled by the relative ratios of these two fuels and the combustion duration is controlled by the local equivalence ratio gradient between the two fuels. This thesis focuses on development of RCCI engine combustion model and understanding the effects of key parameters controlling RCCI engine combustion. This thesis includes three major modeling and analysis contributions.

In the first part, a computationally efficient modeling platform is developed and validated against the experimental data. The model is able to predict start of combustion (SOC) with average error around 1 Crank Angle Degree (CAD). However, due to premixed nature of air-fuel mixture and considering the whole combustion chamber as one uniform zone, the model over predicts peak in-cylinder pressure and therefore is not capable of predicting crank angle for 50 percent mass of fuel burned (CA50) and Burn Duration (BD). Proper operation of RCCI engines requires an in-depth understanding of the interactions between fluid flows, turbulent mixing and chemical kinetics. In the second part of this thesis, a detailed 3D/Computational Fluid Dynamics (CFD) combustion model in commercial CFD code called CONVERGE is developed and validated against experimental data. In-cylinder pressure trace, combustion phasing and emissions (e.g., NOx, HC and CO) are shown to be in good agreement with experimental data for different operating conditions.

In the last part, the effects of fuel injection system parameters on the performance and emissions characteristics of an RCCI engine are discussed. The injection system parameters include Premixed Ratio (PR), injection pressure, Start of Injection (SOI) timing and spray angle. The CFD model is then used to suggest an injection strategy capable of achieving optimized RCCI engine operation.