Location: Bio-oils Research Unit
Title: Liquid-phase penetration under unsteady in-cylinder conditions: Soy- and Cuphea-derived biodiesel fuels vs. conventional diesel Authors
|Fisher, Brian -|
|Mueller, Charles -|
Submitted to: Energy and Fuels
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 21, 2010
Publication Date: August 24, 2010
Citation: Fisher, B.T., Knothe, G.H., Mueller, C.J. 2010. Liquid-phase penetration under unsteady in-cylinder conditions: Soy- and Cuphea-derived biodiesel fuels vs. conventional diesel. Energy and Fuels. 24:5163-5180. Interpretive Summary: Biodiesel is an alternative to petroleum-derived diesel fuel derived from vegetable oils, animal fats, waste cooking oils, and potential sources such as algal oils. Improving biodiesel properties will facilitate its market acceptance and ultimately enhance production. Besides well-known issues such as stability during storage and behavior at cold temperatures, performance in diesel engines is a major issue. In this work, biodiesel derived from a plant known as cuphea was compared to biodiesel derived from soybean oil. The major components in cuphea biodiesel differ significantly from those in soy biodiesel. It is shown that under certain circumstances of injecting fuel into the engine, cuphea biodiesel has advantages compared to soy biodiesel while under other circumstances no advantage was detected. Cuphea biodiesel likely has advantages compared to soy biodiesel when in contact with the lubrication oil in an engine. Besides these results, this work shows that changing the major components of biodiesel is a promising route to improving its properties.
Technical Abstract: Accelerated dilution of engine-lubrication oil is a significant potential issue when fueling with biodiesel. Biodiesel produced from some feedstocks is less volatile than conventional diesel, which makes wall-impingement of liquid fuel more likely, a problem that could be exacerbated by advanced injection strategies such as early direct-injection and late-cycle post-injection. In addition, the low volatility of biodiesel makes it less likely to evaporate out of engine oil. A quantitative understanding of liquid penetration length for biodiesel fuels is needed to mitigate these potential issues. This work reports liquid penetration lengths measured in an optical engine under time-varying conditions for two types of biodiesel, using a commercial diesel as a baseline for comparison. Diagnostics included laser light scattering for measurement of the liquid length and cylinder-pressure data acquisition for heat-release analysis. Unsteady liquid penetration was characterized for different injection pressures, intake-manifold pressures, and a wide range of injection timings for soy- and cuphea-derived biodiesel fuels (soy methyl esters = SME and cuphea methyl esters = CuME, respectively), and a commercial ultra-low-sulfur diesel (ULSD). SME and CuME both were found to have ~20-30% longer liquid lengths than the diesel fuel, despite a large concentration of higher-volatility components in CuME. Measured liquid lengths suggest that the thermodynamic history during injection is an important factor for multi-component fuels. In addition, CuME displayed complex liquid-length behavior that was highly dependent on injection timing compared to ULSD and SME. Results suggest that early direct-injection strategies may benefit from the use of CuME while late-cycle post-injection strategies may be hindered.