An Experimental Investigation of Flame Lift-Off Length and Soot Luminosity of the Emulsified Diesel Under Various Ambient Temperatures

The emulsified fuel remains attractive due to its potential capability of reducing the NO_x and particular matter (PM) at the same time. In this work, the emulsified diesel, with the amount of water quantities ranged between 10% and 20% by volume, was injected and combusted in an optical constant volume chamber. With controlled combustion of acetylene mixture prior to the fuel injection, the chamber is able to provide high ambient temperature and pressure to mimic the real engine operation. In this study, ambient temperatures ranging from 800K to 1200K were investigated. Mie scattering images, at 15000 fps, were first taken to record the evolution of the spray using a Phantom 7.1 high speed camera coupled with a copper vapor laser as the light source. The spray images revealed longer liquid penetration and wider cone angle at the beginning stage of the injection event for emulsified fuel, supporting the occurrence of micro-explosion. Ambient temperature played an important role in the dynamic behavior of soot lift-off length as low ambient temperature features a long initial soot lift-off length and sharp decrease afterwards for both fuels while high ambient temperature enables the soot lift-off to achieve quasi-steady state immediately after the onset of the fuel injection. The broadband luminosity results indicate the advantage of using emulsified fuel to suppress soot formation, and this benefit can be maximized if coupled with a low temperature combustion strategy.