Combustion and Sooting Behavior of Spark-Ignited Ethanol–Isooctane Sprays under Stratified Charge Conditions

Abstract

A spray combustion investigation within an optically accessible high-temperature/high-pressure chamber with ignition was conducted to study soot formation of ethanol blended fuels at cold start conditions. The fuels ethanol, isooctane, and its blends E85 (85 vol% of ethanol in isooctane) and E20 were studied at different temperatures under direct injection spark ignition engine stratified charge conditions. A high-speed camera in combination with an image stereoscope was used in order to visualize the combustion in two different wavelength regions simultaneously to distinguish between premixed and sooting combustion. Additionally, a spectroscopic setup was applied for detailed flame emission analysis on high time-resolved scale. Furthermore, a spray formation investigation was carried out in order to evaluate the fuel evaporation process. The study reveals that depending on the operation conditions either the chemical or the physical processes dominate the combustion and sooting behavior. At low ambient temperature (473 K at 0.8 MPa air pressure) fuel blends with high ethanol content show reduced soot luminosity despite of the delayed evaporation and mixture formation. For E20 stronger soot radiation intensities than for isooctane were found, indicating that the physical fuel properties are governing the soot formation. An increase of gas temperature (673 K) reduces the intensity of soot luminosity for all fuels due to faster evaporation and lower probability of droplet combustion. The soot radiation decreases with increasing ethanol content. The results show that at the high gas temperature condition the physical fuel properties, especially the enthalpy of evaporation, are less important, but chemical effects dominate soot formation.

Analysis of ethanol and butanol direct-injection spark-ignition sprays using two-phase structured laser illumination planar imaging droplet sizing

“…where d is the nozzle diameter, u is the jet velocity, L is the liquid kinematic viscosity, L is the liquid fuel density, and L is the surface tension of the liquid fuel. With a nozzle diameter of 168 mm and an estimated jet velocity of u ¼ 120 m/s (determined in Storch et al 2 at similar conditions), the We and corresponding Re can be deduced (see Table 2). An increase of the temperature leads to an increase in We of about 11-16%.…”

Characterization of Nile Red as a Tracer for Laser-Induced Fluorescence Spectroscopy of Gasoline and Kerosene and Their Mixture with Biofuels

“…This article reports on fluorescence and absorption measurements of the dye nile red in a gasoline surrogate and in aviation fuels blended with bio-components, which was conducted to evaluate its applicability for LIF/Mie droplet sizing. For the investigations, the gasoline surrogate fuel “Toliso”, consisting of isooctane and toluene (65 vol%/35 vol%; see also Section 3 for further explanation) [1,39,40,41] mixed with ethanol (20 vol% in E20 and 40 vol% in E40), as well as four aviation fuel mixtures were analyzed. The aviation fuels studied are the base fuel Jet A-1 and blends with HEFA (30 vol% and 50 vol%) and with farnesane (10 vol%), which are approved by the ASTM for aviation applications.…”

A Novel Approach for Measurement of Composition and Temperature of N-Decane/Butanol Blends Using Two-Color Laser-Induced Fluorescence of Nile Red

“…This effect is also known for some iso-octane/ethanol-mixtures [ 35 ]. For example, for E20, it is found that ethanol evaporates faster than iso-octane at certain conditions, while for E85, the sequence can be in inverse [ 35 , 36 , 37 ]. Similar behavior is expected for butanol admixture.…”