Air/fuel mixing enhancement and emission reduction through intake port design and various fuel emulsions for diesel combustion

Upcoming environmental constraints require the next generation internal combustion engine (ICE) to yield lower pollutant emissions and higher fuel efficiency. The air/fuel mixture inside the ICE, which has a pivotal impact on the subsequent combustion and emission performance, is a key aspect to achieve those requirements. The work done in this dissertation aims at exploring different strategies to enhance the air/fuel mixing rates and thus to improve the combustion and reduce emission in the modern ICE. The air/fuel mixing enhancement can be approached from both sides of the mixture. For air, different intake port designs were considered to generate a strong in-cylinder tangential velocity, known as swirl flow, to promote air/fuel mixing. The mean and turbulent characteristics of the swirl flow were explored under various valve lifts using particle image velocimetry (PIV). This information is of significant value for advanced combustion strategies such as reactivity controlled compression ignition (RCCI) in which the fuel stratification before autoigntion is critical for combustion efficiency. Furthermore, the correlation between the PIV and conventional bench flow measurement using paddle wheel swirl meter, which is of particular importance in guiding the future industrial bench flow tests, was also demonstrated. For fuel, although the spray and atomization process could be improved through complicated hardware design, the atomization enhancement due to inherent fuel properties is more attractive due to its low cost and easy implementation. In this study, water as an additive was mainly considered for enhancing spray atomization and air/fuel mixing through a unique behavior known as micro-explosion. Although the micro-explosion phenomena in fuel droplets have been extensively studied, their presence in the fuel spray and the corresponding impact on the combustion and emissions has rarely been reported. In this work, various laser diagnostic methods were applied to capture the spray and combustion characteristics of fuels with additives and as such, the observed phenomena were correlated with other combustion features. The findings will be important towards the fundamental understanding of the spray and combustion of these multi-component fuels under diesel-engine-like conditions and valuable for future computational model validation. Through this work, a) Swirl flow generated through different intake ports were demonstrated using PIV measurement and the potential mixing enhancement using certain port design was shown; b) The impacts of in-cylinder velocity flow field, piston geometry and injection timing on fuel stratification were demonstrated through a simulation study. c) High speed imaging was carried out in a constant volume chamber to reveal the spray and combustion processes of diesel fuel with various additives under various ambient conditions. Quantitative analysis of spray penetration, soot lift-off length, broadband natural flame luminosity and soot distribution were performed. d) It is revealed how the improved atomization, through the unique micro-explosion phenomena, leads to better air/fuel mixing and lower emissions. e) Quantitative measurement and analysis of spray penetration and droplets size using a micro-variable circular orifice (MVCO) injector were performed