Liquid-Phase Penetration under Unsteady In-Cylinder Conditions: Soy- and Cuphea-Derived Biodiesel Fuels Versus Conventional Diesel

Abstract

Accelerated dilution of engine lubrication oil with unburned fuel is a significant potential issue when utilizing fuels that contain biodiesel. Biodiesel produced from some feedstocks is less volatile than conventional diesel, which makes wall impingement of liquid fuel more likely and reduces the ability of the fuel to evaporate out of engine oil once dilution has occurred. These are growing concerns, particularly with the emergence of strategies that involve injection of fuel into relatively cool, low-density, in-cylinder gases. Examples of these strategies include early direct-injection and late-cycle post-injection, which facilitate partially premixed low-temperature combustion and aftertreatment system regeneration, respectively. A quantitative understanding of liquid-phase penetration for biodiesel fuels is needed to help mitigate these potential issues. This work reports liquid penetration lengths measured in an optical engine under timevarying in-cylinder conditions for soy-and cuphea-derived biodiesel fuels (soy methyl esters=SME and cuphea methyl esters = CuME, respectively) and a commercial ultralow-sulfur diesel (ULSD). Experiments included laser light scattering for measurement of the liquid length and cylinder-pressure data acquisition for heat-release analysis. Data were acquired for multiple injection pressures, intake-manifold pressures, and injection timings for each fuel. SME and CuME both were found to have ∼20-30% longer liquid lengths than ULSD, despite a large concentration of higher-volatility components in CuME. Compared to ULSD and SME, however, CuME liquid lengths were more dependent on injection timing. Results suggest that early direct-injection and late-cycle post-injection strategies may benefit from the use of CuME vs SME.

Diesel Surrogate Fuels for Engine Testing and Chemical-Kinetic Modeling: Compositions and Properties

“…This mismatch is likely to result in shorter in-cylinder liquid-phase fuel penetration lengths (i.e., liquid lengths) for V0a relative to those of CF, because liquid lengths have been shown to correlate well with the heavy end of the fuel distillation range. 77,78 …”

Fundamental spray and combustion measurements of soy methyl-ester biodiesel

“…Recent studies performed under high-temperature, but non-reactive, unsteady conditions showed that biodiesel can increases LL by up to 20% [5,6] or 100% [7] with respect to conventional diesel fuels. This behavior has been related to its higher density and lower volatility [7,8].…”

Observed Differences in Low-Temperature Heat Release and Their Possible Effect on Efficiency between Petroleum Diesel and Soybean Biodiesel Operating in Low-Temperature Combustion Mode

“…It is also noted that liquid length is likely longer with the studied biodiesel due to its higher volatility (i.e., the studied soy biodiesel has an initial boiling point that is higher than petroleum diesel's final boiling point, as shown in Table 2). 21 The analysis of Figure 8, however, relies on flame lift-off length information as it is believed that the same parameters affecting liquid and flame liftoff lengths will influence the transient mixing of the jet during ignition delay and thus create an opportunity to temporally separate LTHR from HTHR even if a standing flame does not develop. That is, the reaction zone where HTHR occurs is lifted further from the nozzle, causing a temporal separation between LTHR and HTHR.…”