Semester

Fall

Date of Graduation

2023

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Hailin Li

Committee Member

Cosmin Dumitrescu

Committee Member

Harold Sun

Committee Member

Kenneth Means

Committee Member

Scott Wayne

Committee Member

V'yacheslav Akkerman

Abstract

Advanced combustion strategies have been proposed to improve fuel efficiency while minimizing exhaust emissions. Gasoline compression ignition (GCI) combustion featuring partially premixed compression ignition (PPCI) and diffusion combustion has been recognized as an attractive, viable combustion strategy for its potential and advantages over conventional diesel and gasoline engines. The optimization of the GCI engine system requires the development of a quasi-dimensional GCI combustion model capable of simulating GCI combustion while requesting less computational burden than CFD simulation, which is very critical in engine system simulation. This study developed a quasi-dimension, phenomenological combustion model for PPCI and diffusion combustion to facilitate the early development of GCI combustion strategy. Due to the limited GCI engine test results, additional parametric CFD studies were conducted and served as a reference to develop the GCI combustion model and investigate the effect on GCI combustion of thermal conditions typically considered during early strategy development. A reduced toluene primary reference fuel and ethanol (TPRFE) mechanism with 65 species and 283 reactions was used to simulate GCI combustion in CFD and quasi-dimension models. Additionally, the behavior of high-pressure gasoline spray was investigated using CFD to support the development of the phenomenological spray dynamics model. The traditional phenomenological SI and CI combustion model frameworks were improved to simulate gasoline PPCI-diffusion combustion accurately with the spray dynamics, air entrainment, ignition delay, and heat release sub-models. The traditional spray model was improved and validated using CFD simulation results as a reference. The CFD result identified a high level of fuel concentration at the spray tip due to the drag and pushing momentum by the following fuel packets. This observation was accounted for in the development of the spray model. The ignition delay was calculated by solving the chemistry kinetics and curve fitting using the identical chemistry mechanism employed in CFD analysis. This research demonstrated that the phenomenological combustion model developed in this study could simulate fuel spray, fuel atomization, ignition delay, and heat release process. The GCI model has been integrated into GT-Suite and successfully applied to improve the combustion process with the valvetrain system. Various variable valve actuation (VVA) strategies were investigated at low-load operating conditions, including early exhaust valve open (EEVO), late exhaust valve open (LEVO), negative valve overlap (NVO), positive valve overlap (PVO), and exhaust gas rebreathing (RB). The RB strategies were identified as the most effective in promoting in-cylinder gas temperature by increasing the hot internal residual gas fraction. This research also numerically investigated the potential of a close coupled-selective catalytic reduction (CC-SCR) system in further NOx emissions of a heavy-duty diesel engine using GT-suite. Diesel engine transient test results were utilized to evaluate CC-SCR instead of GCI results due to limited GCI testing data available. The effects of volume and geometry of the CC-SCR on NOx reduction were numerically investigated under the HD FTP transient cycle. The simulation results revealed that CC-SCR was a very effective strategy, showing that nearly 80 % of the total reduction was realized at the CC-SCR under the transient cycle. This study examined the necessity of accounting for the non-uniform distribution of exhaust gas and urea in the SCR model based on the observation of inhomogeneity at the inlet of CC-SCR in CFD simulation.

Download

Share

COinS