Optical Measurements of In-Flame Soot in Compression-Ignited Methyl Ester Flames

Abstract

This study investigates in-ame sooting characteristics of biodiesel surrogates in compressionignited spray ames. The aim of the study is to produce reliable experimental data on in-ame soot for validation of kinetic mechanisms and soot models. A rapeseed oil biodiesel (RME) was compared to neat methyl oleate (MO) and methyl decanoate (MD). In addition, neat nheptane was chosen as a baseline fuel and the eect of blending n-heptane and MD on soot production was investigated. The study was performed in a single cylinder research engine with optical access to a single spray for varying ambient gas temperatures (825 K to 990 K).The in-ame soot was measured by a high speed diuse back-illuminated extinction imaging system, and the ame lift-o length (FLOL) and the corresponding estimated equivalence ratio at FLOL was measured from high speed OH* chemiluminescence imaging. Results show that RME has the highest tendency to soot, closely followed by MO, independent of the FLOL equivalence ratio. Having almost identical fuel properties, this is likely due to the higher degree of unsaturation in RME compared to MO.When comparing MD to n-heptane, a much lower in-ame soot production rate is observed despite the fact that MD has a higher number of carbon-carbon bonds, concluding that the high fuel oxygen ratio in MD is eectively reducing in-ame soot production. Generally, for FLOL equivalence ratio leaner than ∼2, no in-ame soot was produced for all ambient gas temperatures. The in-ame soot production rate also showed a clear ambient gas temperature dependence for constant FLOL equivalence ratios, where the soot production rate increased with increased gas temperatures.

New Renewable Hydrothermal Liquefaction (HTL) Biofuel: A Combustion and Emissions Study in an Optical Engine

“…The intake air is compressed by a root compressor, and an electric flow heater is located near the intake manifold. Further details of the engine can be found in Table 1, and a more comprehensive description of the OACIC is available in a previous publication [24]. For the zero-dimensional analysis of the chamber's thermodynamic conditions, the first law approach was employed [25].…”

“…The iterative calculation of the in-cylinder temperature utilized the energy conservation equation and the ideal gas law. The specific thermodynamic conditions considered in this study were the intake pressure of 1.25 bar and the intake temperature of 55.3 • C. The ambient gas density at top dead center (TDC) was set at 16.5 kg/m 3 , while the ambient gas temperature at TDC was established at 827.4 K. More detailed information regarding the acquisition system, sensor precision, and uncertainty calculation can be found in our previous work [24]. The in-cylinder pressure data were recorded over 100 consecutive cycles with a sampling interval of approximately 0.15 crank angle degrees (CAD), and the mean value was used for calculations.…”

“…This reaction triggers the release of energy and the rapid formation of radicals, which can be captured by the OH* signal. The ID serves as a valuable benchmark for understanding the combustion characteristics and performance of fuels in combustion systems [24]. To capture the regions of high release rate within the flame, imaging was conducted using a narrow bandwidth in the ultraviolet (UV) spectrum centered at 310 nm with a bandwidth of 10 nm (full width at half maximum).…”

Mini Review of Current Combustion Research Progress of Biodiesel and Model Compounds for Gas Turbine Application

“…In the numerical investigation of Lin et al, 30 remarkable production of CO and CO 2 was predicted in methyl butanoate oxidation due to the fuel-bound oxygen in the methyl ester moiety. 30,33,34 Compared to n-butane oxidation, the formation of oxygenated species preferred in methyl butanoate oxidation simultaneously reduces the production of acetylene and ethylene which can be deemed as soot precursors. 30 Therefore, the existence of the ester group can lead to the reduction of soot precursors, which is consistent with the observed difference in the yield sooting index (YSI) between methyl esters (e.g., methyl pentanoate with a YSI value of −12.6) and n-alkanes (e.g., n-pentane and n-hexane with YSI values of −8.9 and 0.0, respectively) measured by McEnally and Pfefferle.…”