Access Type

Open Access Dissertation

Date of Award

January 2013

Degree Type


Degree Name



Mechanical Engineering

First Advisor

Ming-Chia Lai


Direct Injection (DI) has been known for its improved performance and efficiency in gasoline spark-ignition engines. In order to take all the advantages of the GDI technology, it is important to investigate in detail the interactions of fuel spray and combustion system, such as air-fuel mixing, in-cylinder flow development, surface wetting, and turbulence intensity. The characterizations of the internal nozzle flow of DI injector are first studied using the multidimensional computational fluid dynamic (CFD) simulation. In the meanwhile the numerical and experimental studies are carried out to observe the external spray and wall impingements in an optical constant volume vessel. The fuel film deposit characteristics were derived using the Refractive Index Matching (RIM) technique. Finally, the interactions of sprays with the charge motion are investigated in an optical accessible engine using CFD simulation and high-speed imaging of sprays inside engines.

The numerical results DI injector nozzle show that the complicated unsteady flow features dominate the near-nozzle breakup mechanisms which are quite unlike those of diesel. The spray impingement, wetted area, fuel film thickness, and the resultant footprint mass were investigated experimentally. The CFD simulation with selected models of spray validated first for its transport in the air is used to compare the impingement models with the experimental measurements. The spray cone, tip penetration and fuel film shapes were in very good agreement. The effects of spray patterns, injection timing and flexible valve-train on the bulk flow motion and fuel-air mixing in an optical accessible engine, in terms of tumble and swirl ratios, turbulence level, and fuel wall film behaviors are discussed. Using integral analyses of the simulation results, the mechanisms in reducing fuel consumption and emissions in a variable valve-actuation engine, fueled by side-mounted multi-hole DI injectors are illustrated. The implications to the engine mixing and the resultant combustion in a metal engine are also demonstrated.