On-Board Ultrasonic Water-in-Diesel Emulsion (WiDE) Fuel System for Low-Emission Diesel Engine Combustion

Water-in-diesel emulsion (WiDE) fuel is a promising alternative fuel capable of reducing nitrogen oxides (NOX) and particulate matter (PM) in diesel engine exhaust while simultaneously preserving combustion efficiency of the engine. However, the instability of WiDE fuel—and the high costs of production and transportation—hinder its commercialization and widespread use. An on-board ultrasonic WiDE fuel supply system is proposed as a solution to this challenge. This system allows diesel fuel and water to be continuously emulsified on-board a diesel vehicle. Diesel fuel and water, stored in individual reservoirs, are conveyed in specific ratios to an in-line mixing chamber and are rapidly homogenized by ultrasonic cavitation before entering the fuel injectors. The produced emulsion fuel is then supplied to the engine. A proof-of-concept study was conducted to compare exhaust emissions between emulsion fuels and conventional fuels. Open-flame combustion experiments were conducted using a lab-scale burner to test the system with both diesel and biodiesel fuels. Unique optical diagnostics and image-processing techniques were used to estimate PM emission levels. Results showed a reduction of PM with the use of the on-board WiDE system compared to traditional diesel fuels. PM emissions from biodiesel fuel were reduced by 58% when water-in-biodiesel emulsion was combusted with 2% water. Additionally, a PM emission reduction of 35% was achieved through emulsification of diesel fuel with 2% water. This prototype demonstrates the potential for the on-board WiDE fuel supply concept to both overcome the traditional barriers hindering the commercialization of WiDE fuel and preserve its low-emission and superior combustion efficiency characteristics.