Term of Award

Fall 2015

Degree Name

Master of Science in Applied Engineering (M.S.A.E.)

Document Type and Release Option

Thesis (open access)

Copyright Statement / License for Reuse

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.

Department

Department of Mechanical Engineering

Committee Chair

Cheng Zhang

Committee Member 1

Aniruddha Mitra

Committee Member 2

Mosfequr Rahman

Abstract

Water injection has been used in internal combustion engines for many years. It has been used to cool combustion temperatures, reduce emissions, and in some instances clean carbon buildup from the cylinder. Research has shown that the water to fuel mass ratio is most effective between 20-30%, so the upper and lower limit were used for simulations in Converge CFD. To validate the CFD model, a case without water injection was compared to experimental data from Sandia National Laboratory. The predicted in-cylinder pressure and heat release rate showed good agreement with the experimental data. Cases were run with the injection of the water at 65 and 95 degrees BTDC to increase vaporization and reduce wall film. The water droplet size injected was the principal focus of the study as its effects on emissions had not been investigated. The water droplet sizes used were 0.196, 0.210, 0.240, 0.286 μm. The 0.196 μm droplet was chosen because it was equivalent to the fuel droplet diameter. The others were from literature research for tests done on the effect injected water droplet sizes had on the flame length and speed. It was found that the highest reduction in temperature and pressure was observed with the water injected closer to TDC; however, this commonly resulted in larger emissions reductions. Also, increasing the water mass ratio generally reduced the temperature, pressure, and heat release rate more, which often further reduced the emissions. Maximum NOx reductions of 5.61% using the 0.210 μm droplet size with 20% water and 7.66% using the 0.240 μm droplet size with 30% water were observed. Droplet size comparison showed up to a 9.67% variation in the NOx formation. Simulations were then run by changing the temperature of the water being injected ±20K from the original temperature of 368K. The decreased water temperature cases showed a larger variation between the results for the NOx formation in water injected at 65 and 95 degrees BTDC. Water was then injected at TDC which showed a 48.3% reduction of NOx. However, all other emissions and combustion properties were negatively affected with the TDC injection timing.

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