Analysis of the relation between thermal decomposition and PM reduction of bio-diesel mixed fuels in diesel combustion atmosphere

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1 Analysis of the relation between thermal decomposition and M reduction of bio-diesel mixed fuels in diesel combustion atmosphere H. Noge *1 and Y. Kidoguchi 1 H. Noge Department of Mechanical Engineering, Maizuru National College of Technology Y. Kidoguchi, Institute of Technology and Science, The University of Tokushima Abstract To investigate particulate matter (M) reduction mechanism by blending bio-diesel fuel (BDF) with diesel fuel, thermal decomposition during diesel combustion was analyzed using a plug flow reactor and a co-flow diffusion burner. Ethanol ( H OH) and Methyl Decanoate (C 11 H O ) were mixed with n-saturated fuel Solvent (C 1, C 13, C 1 ) by 1 vol.% respectively. Both ethanol (E1) and methyl decanoate (MD1) blending fuel reduce M by ~ 3 % at fuel rich condition. Ester bond in methyl decanoate contributes oxidation of H or another hydrocarbons. Fluorescence intensity for AHs in the burner exhaust follows Solvent > E1 ³ MD1. This trend is similar to M concentration at same experimental condition. Introduction Demand for bio-fuels such as bio-diesel fuel (BDF) and bio-ethanol rises rapidly all over the world to prevent global warming and to use the energy effectively. BDF reduces particulate matter (M) in diesel combustion because the fuel includes oxygen in its molecular structure that is origin of M reduction, but there is a little knowledge about M reduction mechanism during diesel combustion. In Japan, most of BDFs are originated from waste cooking oils with different chemical and physical components. The differences of the constitutions make it difficult to evaluate M reduction mechanism. However, BDF has ester bond (-COO-) via transesterification. As BDF blending fuel will popularize in the near future, present work studies M reduction mechanism by BDF blending fuel. Methyl decanoate (C 11 H O ), which has ester bond and the carbon number is similar to diesel fuel, were used as BDF blending fuel. Ethanol ( H OH) blending fuel and ethanol were examined to gain a further understanding of M reduction mechanism. M is produced when fuel is exposed to high temperature and inadequate oxygen vapor phase [1]. Fuel decomposition might affect M reduction. To investigate the relation between thermal decomposition and M reduction in diesel combustion atmosphere, a plug flow reactor and a co-flow diffusion burner were used. Four kinds of fuels thermally decomposed in a plug flow reactor were analyzed. Those fuels are as follows. (1) -Solvent (Normal saturated paraffin, C 1 H : 7wt.%, C 13 H 8 : 7wt.%, C 1 H 3 : wt.%) () -Solvent+Ethanol1vol.% (E1) (3) -Solvent+Methyl Decanote1vol.% (MD1) () Ethanol 1vol.% (E1) Thermally decomposed fuels were burned using the coflow diffusion burner and M was produced. lug flow reactor Fuel was injected into an evaporator kept at 3 by a fuel injector. The fuel soon vaporized and formed mixture with nitrogen that introduced into an infrared gold image furnace (ULVAC RHL-E1) where the temperatures were controlled by temperature program controller (ULVAC TC-1) with K type thermocouple (OKAZAKI). Residence time (tr) in the reactor was a relatively long ms and controlled furnace temperatures (Tr) of 13K and 1K were high enough to decompose high molecular liquefied fuel in nitrogen atmosphere. GC GC/MS NDIR(CO,CO ) C,H,N corder Fluorescence Spectrophotometer Cooled Experimental Method The experimental setup (Fig.1) consisted of a plug flow reactor and a co-flow diffusion burner. Immediately after fuel was thermally decomposed in the flow reactor, the fuel was fed to the co-flow diffusion burner directly. Fuel injector Carrier gas Heater Temp. controller Heater GC O /N,GC/MS * Corresponding author: noge@maizuru-ct.ac.jp roceedings of the European Combustion Meeting 9 Infrared reflex furnace Fig.1 Schematic diagram of experimental setup

2 Examined fuel/carrier gas ratio (=.7,.1,.13) in the flow reactor corresponds to equivalence ratio (φ b=1., 1.,.) in the combustion vessel at burner outlet. A high temperature gas sampler (Yanaco GHS-) was used to inject thermally decomposed fuels into a gas chromatograph (GC: Yanaco G38) equipped with FID and TCD. Low molecule hydrocarbons were analyzed by Squalane % packed column (Length=3m, mm i.d.). CO and CO were detected by Shincarbon-T column (Length=m, mm i.d.). Thermally decomposed hydrocarbons were sampled on a teflon filter (MILLIORE FHL7 Diameter=7mm hole=.mm). Soluble organic fraction () was eluted into dichloromethane (DCM) by a soxhlet extractor. olycyclic aromatic hydrocarbons (AHs) in the DCM concentrated to 1 times using gentle stream of nitrogen were injected by 1ml into a gas chromatography / mass spectrometry device (Shimazu GC/MS-Q1 lus). Separation was performed in a RTX-MS capillary column (Restek: Length=3m,.mm i.d.,.mm film thickness). The injection port temperature was kept at 8 and the program started from 9 for 1 min. The oven temperature rose to 1 at 1 /min, followed by /min to. Helium was used as the carrier gas at ml/min flow rate. The total ion chromatograms were analyzed qualitatively in aid of NIST 3. On the chromatographic peak, 9% mass spectral match or greater was considered as possible AHs. Fluorescence spectra of AHs in were measured on a Solvent 13K E1 13K MD1 13K M mg/m 3 8 1K 1K 1K Fig. M produced by diffusion combustion fueled by thermally decomposed blending fuels 8 Fuel:Solvent 13K E1 13K MD1 13K LHC vol.%, H 1K C H C 1K, C H 1 C H C 1K.7 H,.1 C.13.7 H CH C 1, H.1 Fig.3 LHCs production at 13K and 1K thermal decomposition in the plug flow reactor C.13

3 fluorescence spectrophotometer (Hitachi F-7) in the - nm wavelength region by using quartz vessel. Excited wavelength (l ex ) was 337nm. Co-flow diffusion burner In an atmospheric pressure, axial co-flow diffusion flame was generated using the burner in which fuel and nitrogen mixture flowed from a centerline tube (.mm i.d.). Oxygen and nitrogen supplied through the outer tube (38mm i.d.) as oxidizer. The oxidizer velocity was controlled same as the mixture by an adjust ring. A cylindrical quartz tube surrounded the burner outlet to prevent excess air inflow. M was sampled at l/min with a diaphragm pump on the teflon filter, which was dried at least 1 hours before and after collection. M concentration was determined by weight. was extracted from M using the soxhlet extractions for 3 hours. Results and Discussion M formation M are produced by a co-flow diffusion burner using thermally decomposed fuels. Figure shows quantity of M that are separated into and SOLID. Blending of ethanol (E1) or methyl decanoate (MD1) with Solvent reduces M by ~ 3 % at fuel rich condition. M reduction tendency by E1 and MD1 is almost same. The reason will be discussed in LHCs formation paragraph. In E1 and MD1, the compositions of and SOLID are almost same. Blending ethanol and methyl decanoate can reduce both and. Only at 13K, =. with MD1, increases compared with Solvent. BDF produces greater amount of in comparison with diesel fuel at low load combustion in a diesel engine []. The difference of fuel properties such as kinematic viscosity or original fuel composition between BDF and diesel might be a reason [], [3]. On the other hand, a high engine speed reduces by means of high turbulence in the cylinder []. Formation of a mixture in which fuel and oxidizer mixed well may reduce. The experimental condition at 13K with MD1 is similar to low load diesel combustion. MD 1 may reduce at low load diesel combustion by forming well mixture with equivalence ratio under 1., because the at 13K, =1. and 1. with MD1 is lower than Solvent s at same experimental condition. LHCs formation Light hydrocarbons (LHCs) produced in plug flow reactor were qualified and quantified to analyze the relation between M reduction and thermal decomposition. LHCs composition was reported in Fig.3. The total amount of LHCs in E1 and MD1 is less than Solvent a little. Blending of E1 and MD1 reduces total molecular weight more than pure Solvent. And also OH and COO radicals produced by thermal decomposition react with hydrocarbons, which may produce CO, CO and H O. Measurement concerning CO and CO will be discussed below. As the molecular weight of methyl decanoate (18g/mol) is larger than ethanol (g/mol), M concentrations of MD1 are expected to be more than E1. However the M concentrations in MD1 are almost as same as E1. For this reasons, at 13K, MD1 produces C less than E1, and C H 1 generation perhaps have a relation to more M reduction. At 1K, H concentration changes remarkably and it follows Solvent > E1 > MD1. In addition, C H 1 appears definitely at 1K, MD1. LHC vol.% M mg/m 3 Intensity.7 1. Fuel:E1 1K 1K n-c H 1 C Fig. M concentration and LHCs production by pure ethanol N CO N CO E1 Tr=1K, =.13 MD1 Tr=1K, =.13 CO Retantion time [min] Fig. CO and CO separation corresponding to E1 and MD1 thermal decomposition 3

4 The ester bond (-COO-) in methyl decanoate contributes oxidation of H or another hydrocarbons, which probably leads to M reduction. Appearance of C H 1, which is a stable chemical species, may contribute to chemical equilibrium in the decomposed system and control M. Additional insights into the relation between M concentration and LHCs at 1K, E1 (pure ethanol) were provided in Fig.. E1 decreases total LHCs more than the other fuels but C H 1 is appeared specifically and there is less H, which reduce a lot of M. C H 1 and H produced during thermal decomposition can be a judgment species in relation to M reduction. Figure provides a chromatograph regarding CO, CO production in E1 and MD1. CO appears before min in both E1 and MD1. CO peak appears before 1 min only at 1K, MD1. Molecular structure of methyl decanoate contributes to CO production that maybe has relation to prevention of soot precursor growth. AHs formation olycyclic aromatic hydrocarbons (AHs) produced in the flow reactor were qualified by GC/MS. The chromatographs of detectable AHs in Fig. are ➀:- methylnaphthalene, ➁ :biphenyl, ➂ :biphenylene, ➃:fluorene, ➄:phenanthrene, ➅: anthracene, ➆: H-cyclopenta[def]phenanthrene, ➇ : fluoranthene, ➈ : pyrene. Quantity of the AHs is uncertain, however, most of areas in the chromatographs at E1 and MD 1 are smaller than Solvent, and total AHs areas are in the order Solvent > E1 MD1. This is due to oxidation of LHCs and AHs. - methylnaphthalene appears remarkably in MD1 than the others. Approximate outline of oxidation pathways by E1 and MD1 are shown in Fig.7. OH radical divided from ethanol will oxidize thermal decomposed Solvent molecules and the residual H. The ester bond included in methyl decanoate is strong oxidizer but this fuel has more hydrocarbons than ethanol. Therefore, this ester bond has a lot of candidates for oxidation and it is inadequate to oxidize, which may produce much - methylnaphthalene. However, as there are CO and CO in thermally decomposed MD1, conversion from small AHs to large AHs is prevented. AHs fluorescenc e spectra analysis AHs such as ~ member rings are detected by GC/MS during 1K thermal decomposition but the growth for more than member rings is unknown. Our previous work reported that UV-VIS measurement could identify pyrene peaks[]. Based on UV-VIS results, AHs having wavelength peaks higher than pyrene were excited using fluorescence spectrophotometer (FL). Absolute intensity [ 1 ] Fig. AHs production during 1K, =.13 thermal decomposition of Solvent, E1 and MD1 in the flow reactor Solvent C1, C13, C1 CH OH Ethanol Tr=1K, =.13 Fuel:solvent Tr=1K, =.13 Fuel:E1 Tr=1K, =.13 Fuel:MD R.time min C1, C13, C1 CH3-(CH)8 -C-O- CH3 O Methyl Decanoate Fig.7 Supposed oxidation path diagram by OH and COO radicals in ethanol and methyl decanoate respectively 7 8 9

5 Fluorescense intensity Tr=1K, =.13 Burner Fuel:Solvent Burner Fuel:E1 Fuel:MD1 [] In MD 1, there is a possibility to reduce at low load diesel combustion by forming a mixture where the equivalence ratio is less than 1.. [3] H concentration at 1K follows Solvent > E1 > MD1. C H 1 appears definitely at 1K, MD1. [] Both E1 and MD1 produce CO during 1K thermal decomposition and MD1 produces CO as well. [] In thermal decomposition, fluorescence emission spectrum of AHs is weak and the fluorescence intensity of every fuel is all the same. However, the fluorescence intensity in the burner exhaust follows Solvent > E1 MD1. [] MD1 can prevent conversion from small AHs to large AHs. Burner 3 wavelength [nm] Fig.8 Fluorescence spectra of AHs sampled at the reactor exit and the burner exhaust Strong peaks detected in high wavelength regions might be a signal for high molecular weight AHs. Figure 8 shows fluorescence wavelength excited at λ ex =337nm. Samples are collected at the reactor exit or at the burner exhaust and, which are extracted from the samples by soxhlet method, are analyzed. In all samples at burner exhaust, both 37nm and 39nm wavelength corresponds to pyrene peaks appear sharply. There is a nm wavelength peak with strong fluorescence intensity. The nm peak is probably caused by larger molecules of AHs than pyrene. Fluorescence intensity in AHs at the reactor exit is weak and the intensity level of every fuel is all the same. However, the fluorescence intensity in the burner exhaust follows Solvent > E1 MD1. This trend is similar to M concentration order at same experimental condition. LHCs concentrations in E1 and MD1 are less than Solvent. roduction of CO, CO during thermal decomposition controls AHs development, thus M are reduced. Acknowledgements The authors wish to thank Mr. H. Iyama and Mr. N. Hosomi for their contributions to the experiment, and also thank Kyoto prefectural technology center for small and medium enterprises, for helpful support of experimental equipments. References [1] Glassman, I., Combustion nd edition, Academic ress, Inc., pp.3-37, (1987). [] Jazair W., et al., Improvement of Emission in a DI Diesel Engine Fuelled by Bio-diesel Fuel and Waste Cooking Oil, SAE paper No [3] Radu R., et al, Fuel and Injection Characteristics for a Biodiesel Type Fuel From Waste Cooking Oil, SAE paper No [] Yamane K., et al., Influence of hysical and Chemical roperties of Biodiesel Fuels on Injection, Combustion and Emission Characteristics in a Direct Injection Compression Ignition Engine, Int. J. Engine Research, Vol., No., pp.9-1. [] Noge, H., et al., Formation of M and Soot recursor in Diffusion Flame Generated by Thermally Decomposed Diesel Fuel, 3rd European Combustion Meeting ECM7, pp.1-, Crete, Greece, April, (7). [] Noge, H., et al., A Study on Soot Formation of Iso- araffin Fuel using Diffusion Burner, JSAE paper Vol.38, No. pp.9-1, (7). (in Japanese) Conclusions The relation between M reduction mechanism and thermal decomposition in diesel combustion atmosphere was investigated using blending BDF with diesel fuel. The following conclusions have been drawn. [1] Blending of E1 or MD1 to Solvent reduces M by ~ 3 % at fuel rich condition.