- Email: [email protected]
Performance and emission characteristics of diesel engine powered with diesel–glycerol derivatives blends
Fuel Processing Technology 126 (2014) 460–468
Contents lists available at ScienceDirect
Fuel Processing Technology journal homepage: www.elsevier.com/locate/fuproc
Performance and emission characteristics of diesel engine powered with diesel–glycerol derivatives blends Elena-Emilia Oprescu a, Raluca Elena Dragomir a,⁎, Elena Radu b, Adrian Radu b, Sanda Velea b, Ion Bolocan a, Emil Stepan b, Paul Rosca a a b
Faculty of Petroleum Refining and Petrochemistry, Petroleum-Gas University of Ploiesti, 39 Bucuresti Avenue, 100680 Ploiesti, Romania National Research & Development Institute for Chemistry and Petrochemistry ICECHIM, 202 Splaiul Independentei St., P.O. Box 194, 060021 Bucharest, Romania
a r t i c l e
i n f o
Article history: Received 3 February 2014 Received in revised form 14 April 2014 Accepted 27 May 2014 Available online xxxx Keywords: Diesel Glycerol ketal ester Solid superacid catalyst Emissions Diesel engine
a b s t r a c t The present work investigates the possibility of using two glycerol derivatives as additives for diesel fuel. The first additive was obtained by catalytic condensation of glycerol with butane-2-one over solid superacid SO2− 4 /TiO2-La2O3, while the second additive was synthesized from the first one by transesterification with methyl hexanoate. In order to investigate the chain length influence of the glycerol ketal ester over diesel properties, we studied the influence of ratio of oxygenated compound on the quality parameters of diesel fuel like viscosity, pour point, flash point and cetane index. To evaluate the effects of (2-ethyl-2-methyl-1,3-dioxolan-4-yl) methanol and (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methyl hexanoate diesel blends on engine performance and emission characteristics, the following parameters were studied: engine power, engine torque, specific fuel consumption (sfc), nitrogen oxide (NOx), hydrocarbon (HC), carbon monoxide (CO), carbon dioxide (CO2) and smoke emission. All tests were carried out on a four cylinder diesel engine, without any modifications, working at full load and engine speeds between 1200 and 3700 rpm. The experimental data indicates (2-ethyl-2methyl-1,3-dioxolan-4-yl)methyl hexanoate as a promising additive for emission reduction (reduces HC, CO and respective smoke emission by 26.04%, 18.93% and 19.20%, respectively, and slightly increases NOx emission). © 2014 Elsevier B.V. All rights reserved.
1. Introduction The environment is heavily polluted by road transport. In order to reduce the emission of pollutants from the public transport sector, the UE implemented Directive 2009/28/EC of the European Parliament of the council of 23 April 2009 on the promotion of the use of energy from renewable sources published on 23 April 2009 which sets the objective of reaching 20% of the EU's energy consumption through renewable energy sources by 2020 [1]. In this context, global production of biodiesel dramatically increased. As a result, a large surplus of glycerin was formed as a byproduct (10% in weight), which has a significant impact on the glycerol market, resulting in a decline of glycerin's price. Glycerol valorification not only revalorizes this byproduct but also increases the fuel yield in the overall biodiesel process. Therefore, many research groups have been devoted to develop glycerol derivatives with industrial interest [2]. An interesting alternative is the production of oxygenate additives based on glycerol.
Oxygenate compounds could improve combustion quality that reduces particulate emission and carbon monoxide production [3]. The molecular structure, local oxygen concentration and content of fuel could influence the reduction amount of particulate emissions [4,5]. The first class of glycerol derivatives added to diesel fuels to improve low-temperature properties and engine efficiency and to reduce harmful emissions were glycerin ethers [6,7]. A recent patent [8] reports that addition of glycerol acetals to diesel blends reduces viscosity and particle emission, and also met the established requirements for flash point and oxidation stability. This study has three main objectives: (i) synthesis of glycerol ketal by catalytic condensation of glycerol with butane-2-one over solid superacid catalyst SO2− 4 /TiO2-La2O3; (ii) transesterification of glycerol ketal with methyl hexanoate and (iii) study of the performance and emission characteristics of diesel engine fueled with diesel blends containing 1 and 2 wt.% of (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methanol and (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methyl hexanoate, respectively. 2. Material and methods
⁎ Corresponding author at: Department of Petroleum Processing Engineering and Environmental Protection, Petroleum-Gas University of Ploiesti, 39 Bucuresti Avenue, 100680 Ploiesti, Romania. Tel.: +40 244 573171; fax: +40 244 575847. E-mail address: [email protected] (R.E. Dragomir).
http://dx.doi.org/10.1016/j.fuproc.2014.05.027 0378-3820/© 2014 Elsevier B.V. All rights reserved.
2.1. Chemicals Anhydrous glycerol (99.9% w/w), sulfuric acid (98.0% w/w), titanium chloride, lanthanum chloride and sodium hydroxide (N98.0% w/w)
E.-E. Oprescu et al. / Fuel Processing Technology 126 (2014) 460–468
were purchased from Sigma-Aldrich (Germany); methanol, butan-2one (99.9% w/w), methyl hexanoate (99.9% w/w) and ammonia, solution 25% w/w, were supplied by Scharlau (Spain).
461
The main reaction for transesterification of butan-2-one glycerol ketal with methyl hexanoate is:
2.2. Catalyst preparation The solid superacid SO2− 4 /TiO2-La2O3 was obtained by co-precipitation method and characterized by X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy and elemental analysis. The acid properties of the sample were evaluated by TG/DTG thermal analysis of chemisorbed n-butylamine. All data are presented into a previous paper [9]. 2.3. Glycerol condensation with butan-2-one The method used to synthesize (2-ethyl-2-methyl-1,3-dioxolan4-yl)methanol is described into a previous paper [10]. The reaction was carried out in a three-neck round-bottom flask equipped with a mechanical stirrer, thermometer and Dean-Stark apparatus. In a typical experiment, glycerol (0.1 mol) and catalyst (3 wt.% with respect to glycerol) were placed under reaction conditions for 10 min before carbonyl compound (0.10 mol) was added dropwise. After the ketone dosing, an amount of 4.5 g solvent (e.g. benzene) was introduced to form a heterogeneous azeotropic system with water. The reaction mixture was mechanically stirred at atmospheric pressure and heated to reflux (80–110 °C). The water, formed along the reaction process, was removed in a Dean-Stark apparatus. The catalyst was filtered after completion of reaction, and solvent and carbonyl compound in excess were removed by distillation. Crude products were purified by vacuum distillation. The GC/MS/MS analysis of glycerol ketals indicated a chromatographic purity of 99%. To determine the optimal parameters for glycerol condensation with butan-2-one in the presence of superacid catalyst SO24 −/TiO2-La2O3, three impact factors were investigated: molar ratio of glycerol to butan-2-one, reaction time and catalyst amount. The experimental results show that the maximum yield in butan-2-one glycerol ketal (96.5%) was reached at a molar ratio of ketone to glycerol of 1.1:1, mass ratio of the catalyst of 3 wt.% with respect to glycerol, and a reaction time of 4 h. The reaction for glycerol condensation with butan-2-one is:
The GC/MS/MS analysis of (2-methyl-2-ethyl-1,3-dioxolan-4-yl) methanol indicated a chromatographic purity of 99% (Fig. 1). 2.4. Transesterification of butan-2-one glycerol ketal with methyl hexanoate Transesterification of butan-2-one glycerol ketal with methyl propionate was performed by using the method proposed by Oprescu et al. [10]. Using the same method we transesterificated butan-2-one glycerol ketal with methyl hexanoate. The reaction was effectuated in a three-neck round-bottom flask equipped with a magnetic stirrer, thermometer, rectifying column, condenser and reflux splitter. A roundbottom flask was loaded with butan-2-one glycerol ketal (0.1 mol) and sodium methoxide 30%, (1.5 wt.% with respect to butan-2-one glycerol ketal). The mixture was heated at 90 °C and methanol condensate was collected. Methyl hexanoate in a molar ratio of glycerol ketal:methyl hexanoate of 1:1.1 was added. The reaction mixture was stirred for 6 h in a temperature range of 120–150 °C and methanol condensate was collected. The catalyst was filtered after completion of reaction and the methyl propionate and methyl hexanoate in excess were removed by distillation. The crude product was purified by vacuum distillation.
The secondary reaction is:
Similar reactions occur for transesterification of butan-2-one glycerol ketal with methyl propionate. The GC/MS/MS analysis of (2-methyl-2-ethyl-1,3-dioxolan-4-yl) methyl hexanoate and (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl propionate indicated a chromatographic purity of 99% and 98%, respectively (Figs. 2 and 3, respectively). 2.5. Product identification The reaction products were analyzed by a GC-MS/MS TRIPLE QUAD (Agilent 7890 A) with DB-WAX capillary column (30 m length, 0.25 mm internal diameter, 0.25 μm film thickness) and helium as carrier gas at 1 mL/min. The temperature program was as follows: 70 °C, 5 °C/min up to 220 °C, hold time of 5 min. The GC injector and MS ion source temperatures were 250 °C and 150 °C, respectively. The transfer line temperature was 280 °C. The MS detector was operated in EI mode at 70 eV, with a m/z scanning range of 50–450 [10]. 2.6. Diesel blend characterization Diesel blend characterization was made using the following European standards: EN ISO 3104 (kinematic viscosity at 40 °C), EN ISO 3016 (pour point), EN ISO 2719 (flash point), EN ISO 4264 (cetane index) and D2015 (heating value). 2.7. Experimental and test procedure One of the objectives of this study is to test the performance and emission characteristics of diesel engine fueled with diesel blends containing 1 and 2 wt.% of (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methanol and (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methyl hexanoate, respectively. For the comparison under the same condition, the running parameters of the engine were kept the same. Engine experiments were performed on a Renault diesel engine K9K P 732, mounted on a Horiba Titan 250 stand test. The main characteristics of the diesel engine are shown in Table 1. The schematic diagram of the experimental setup is shown in Fig. 4. The engine was operated at full load and engine speeds between 1200 and 3700 rpm (1200, 1700, 2200, 2700, 3200 and 3700 rpm). The engine was firstly conducted with diesel fuel and then with diesel blends. The fuel consumption was measured with an AVL Fuel Consumption Measurement System PLU 401/116. The composition of pollutant compounds was determined by gas analyzer Pierburg Hermann, type HGA 400 5G. The smoke was measured by an AVL 415 smoke-meter. The technical properties of the gas analyzing device are presented in Table 2. 3. Results and discussion 3.1. Fuel blend properties The presence of hydroxyl groups in the structure of glycerol acetals/ketals decreases their solubility in hydrocarbons. To eliminate
462
E.-E. Oprescu et al. / Fuel Processing Technology 126 (2014) 460–468
Fig. 1. GC-MS/MS analysis of (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methanol.
this disadvantage and to improve other features, we continued the previous study [10] in which the free hydroxyl group of (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methanol (K) was blocked by transesterification with methyl propionate, obtaining (2-ethyl-2-methyl-1,3-dioxolan-4-yl) methyl propionate (C). Using the same method, we synthesized a longer glycerol ketal ester: (2-ethyl-2-methyl-1,3-dioxolan-4-yl) methyl hexanoate (E). The influence of ratio of oxygenated compounds on the diesel fuel characteristics like viscosity, pour point, flash point and cetane index was studied. The notation used is Diesel for pure diesel, Ki for mixture between diesel and glycerol ketal, Ci for diesel blended with (2-ethyl-2-methyl1,3-dioxolan-4-yl)methyl propionate and Ei for diesel mixed with (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methyl hexanoate. The value of index i corresponds to glycerol ketal and glycerol ketal esters percent in diesel blends (i.e. 1, 2, 5 and 7 wt.%). The experimental results are presented in Table 3. The data presented in Table 3 show an increase of density with the increasing of the chain length of the glycerol ketal ester. As result of OH group blocking, the viscosity increases slightly from 2.56 mm2/s for 1 wt.% of (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methyl propionate to 2.68 mm2/s for 1 wt.% of (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methyl hexanoate. This behavior is in accordance with literature data [11,12]. The value obtained for diesel blends are well within the range of EN 590 standard specification: 2–4.5 mm2/s. The flash point depends on the volatility and inflammability of the added compounds in diesel. The obtained experimental data show
that the increasing of the aliphatic chain of glycerol ketal ester causes an increase in flash point, from 63.4 °C for 7 wt.% glycerol ketal to 70.4 °C for 7 wt.% (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methyl hexanoate. Crystallization phenomena involve a high level of organization to promote nucleation. Branching interferes with the crystal packing, hence decreasing the crystallization temperature [13]. Chain length was found to have a significant influence on the pour point. The best performance of −24 °C was achieved when 7 wt.% of (2-ethyl-2methyl-1,3-dioxolan-4-yl)methyl hexanoate was added to diesel. To note, all tested glycerol derivatives improve the pour point of diesel blends. Another parameter analyzed was the cetane index. Given that the measuring of the cetane number requires an expensive cetane number engine and a large amount of fuel to test, there was developed a method to calculate cetan index based on density and distillation curve temperatures (EN ISO 4264). Because the calculations involve bulk fuel properties, this index is not affected by the presence of diesel ignition improvers. Also, by comparing them to each other, it provides a qualitative measure on the effect of glycerol derivatives in ignition delay of diesel fuel. Looking at the values of cetane index presented in Table 3, a slight improvement is observed with increasing esteric chain, from 57.07 for glycerol ketal to 58.49 and 59.41 for 1 wt.% of (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methyl propionate and 1 wt.% of (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methyl hexanoate, respectively. By increasing the aditive ratio, the cetane index decreases, but for the
E.-E. Oprescu et al. / Fuel Processing Technology 126 (2014) 460–468
463
Fig. 2. GC-MS/MS analysis of (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl hexanoate.
most of mixtures, the values are higher than diesel fuel. This decrease is supposed to be determined by the formula used to calculate the cetane index, which shows a decrease with density, whose value increases with additive/diesel ratio (Table 3). Analyzing the data presented in Table 3, (2-ethyl-2-methyl-1,3dioxolan-4-yl)methyl hexanoate was selected to be tested as diesel additive in diesel engine, because compared with (2-ethyl-2-methyl1,3-dioxolan-4-yl)methyl propionate, it improves the main properties which influence the engine performance and emission characteristics. For economic reasons and for the fact that the cetane index decreases with the additive concentration, the weight percent of the added compound in diesel fuel was not more than 2%. The experimental studies of exhaust emissions were conducted on the following fuel compositions: pure diesel (Diesel), diesel blend with (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methanol 1 wt.% (K1), diesel blend with (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methanol 2 wt.% (K2), diesel blend with (2-ethyl-2-methyl-1,3-dioxolan-4yl)methyl hexanoate 1 wt.% (E1), and diesel blend with (2-ethyl-2methyl-1,3-dioxolan-4-yl)methyl hexanoate 2 wt.% (E2). 3.2. Engine performance characteristics 3.2.1. Engine torque The effect of (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methanol and (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methyl hexanoate on the engine torque with respect to the engine speed is shown in Fig. 5. Torque
initially enhances with increasing of engine speed until it reaches a maximum value and then decreases with further increasing engine speed. The engine torque reduction after certain speed is caused by the lowered volumetric efficiency of the engine due to the increase in the corresponding engine speed [14]. The maximum engine torque was obtained at 2700 rpm, for all test fuel samples. Although, the differences in torque values measured for the Diesel fuel, K1, K2, E1 and E2 blends were not significant, it can be observed in Fig. 5 a slow increase by adding glycerol derivatives in diesel. The differences in torque values measured for the Diesel fuel, K1, K2, E1 and E2 blends were not significant. The engine torque is influenced by the viscosity of the fuel. When the viscosity of the fuel increases the amount of the fuel that should be filled into the oil pump decreases and the volumetric efficiency of engine remains lower, consequently resulting in the decrease of torque [15]. Also, the small viscosity increases atomization and fuel delivery rate, and reduces the droplet diameter and breakup time [16]. To note is that engine torque variation corresponds to the variation of the viscosity of the five fuels (Table 3). 3.2.2. Engine power The variation of engine power versus engine speed is presented in Fig. 6. The results show that there are no noticeable differences in the measured engine power output between the five fuels tested. It can be seen that engine power rises with the increasing of engine speed. Maximum power values were obtained at 3200 rpm. Normally, due to the lower heating value of oxygenate diesel blends engine power should
464
E.-E. Oprescu et al. / Fuel Processing Technology 126 (2014) 460–468
Fig. 3. GC-MS/MS analysis of (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl propionate.
decrease. However, as an average, the engine power increases with the addition of additive content in diesel and reaches a maximum average value for E2 blend. A slight increase in engine power by adding glycerol derivatives in diesel fuel, especially for (2-ethyl-2-methyl-1,3-dioxolan4-yl)methyl hexanoate at high engine speed can be explained by the increase in the fuel consumption (Fig. 7). Because of the greater densities of E1 and E2 blends compared with diesel and K1 and K2 blends (Table 3), for the same volume of combustion chambers a larger fuel mass flow rate was injected resulting an increase in power. At the same time, the decrease of blends viscosities means the less internal leakage in the fuel pump and results an increase in the power [17]. The presence of oxygen in the molecular structure of the additives
Table 1 Technical specification of the diesel engine. Particulars
Specifications
Model Cylinder number Cubic capacity, [cm3] Combustion system Cooling system Bore/Stroke, mm Compression ratio Power, [kW] Maximum torque, [Nm] Maximum speed, [rpm]
Renault K9K P 732 4 cylinder, inline 1461 Common rail direct injection Siemens Water cooled 76/80.5 15.3:1 78 kW at 3700 rpm 240 Nm at 2700 rpm 4000
improves combustion of diesel blends, thus compensating additive lower heating values. 3.2.3. Specific fuel consumption (sfc) Fig. 7 presents the specific fuel consumption (sfc) for the five fuels, as a function of engine speed. The highest sfc was observed for E2 blend with all speeds of the engine, while the lowest sfc's were obtained for diesel fuel. The properties of the fuel tested such as viscosity, density, and heating value influence the relationship between engine performance (the fuel injection system, mainly the spray formation) and combustion [18,19]. Therefore, the greater values of specific fuel consumption (sfc) obtained for glycerol ketal ester blends are explained by the lower heating value, higher viscosity and density (Table 3). For the same volume, due to the greater density of glycerol ketal ester blends, more fuel by mass was injected into the combustion chamber compared with the amount of diesel injected. 3.2.4. Exhaust gas temperature In analyzing of the emission characteristics of the exhaust gas temperature it is an important indicator of the heat of the fuels tested at the combustion period. The variation of exhaust gas temperature with respect to engine speed for the tested fuels is shown in Fig. 8. The exhaust gas temperature values increased with the increase of the engine speed for all five test fuels and an increase in the additive blend ratio resulted in a decrease in the exhaust temperature. The exhaust temperatures for the K1, K2, E1 and E2 blends are lower
E.-E. Oprescu et al. / Fuel Processing Technology 126 (2014) 460–468
465
Fig. 4. Schematic diagram of the experimental setup.
the injected molecules. As can be seen in Fig. 9, the glycerol ketal ester blends produced less NOx during their combustion than glycerol ketal blends, because E1 and E2 blends have a higher cetane index which leads to shorter ignition delay and decreased maximum heat release rate which results in lower cylinder temperature, and this reduces the formation of NOx. These findings are in agreement with those of Graboski et al. [26,27]. Also, in accordance with Graboski et al. [26,27], NOx emission increases for glycerol derivative blends compared with classic diesel, caused by the formation of prompt NOx due to high concentrations of oxygenated derived radicals [28].
Table 2 Technical properties of the gas analyzing device. Measured variable
Measuring range
Precision
CO CO2 HC NOx Smoke
0–10% 0–20% 0–20,000 ppm 0–5000 ppm 0–100%
0.001% 0.1% 1 ppm 1 ppm 1%
compared with Diesel fuel [20]. These results are due to the higher heating value of Diesel fuel compared to diesel blends (Table 3). 3.3. Exhaust emissions 3.3.1. Nitrogen oxide (Nox) emission The engine NOx emission for the tested fuels at different speed engines is given in Fig. 9. The NOx concentration increases with the rise of engine speed for all the fuels. The NOx emission for diesel blends with 2% additive is slightly higher than diesel blends with 1% additive. This behavior is explained by a few researchers, which reported that the high oxygen levels increase the maximum local temperature during the combustion, resulting in high NOx formation [18–20]. It is also agreed that in the production of NOx, the fuel borne oxygen is more effective than the external oxygen supplied with the air [18]. The same trend was observed by M.N. Nabi et al. [21], Bielaczyc et al. [22], Jeong et al. [23], and Schmidt et al. [24] for diesel blends with different biodiesel percents. A way to reduce NOx emission by changing the injection timing was reported by Banapurmatha et al. [25]. The increased NOx emission obtained by glycerol ketal diesel blends compared to glycerol ketal ester diesel blends may be explained by the fact that the alkyl chain strongly influenced the ignition delay periods of
3.3.2. Hydrocarbon (HC) emission Fig. 10 shows the variation of hydrocarbon (HC) emission. At a lower adding ratio, the HC emissions resulted from diesel fuel and diesel blends with additives were lower than that of diesel fuel. The reason for lower HC emissions can be the higher oxygen content in additive, which helps to complete oxidations in rich air–fuel mixture zones by increasing the oxidation reaction ratio. The decrease in HC emissions compared to diesel was about 10.42%, 6.25%, 26.04% and 20.14% for K1, K2, E1 and E2 blends, respectively. For 2% addition ratio it can be observed from Fig. 10 that the HC emission grows. An explanation could be sustained by the cetane number influence which decreases with the increasing of additive content in diesel. A lower cetane index determines the rising of the ignition delay period and increases in this way the unburned HC level from the exhaust gases [29]. The same argument may be used to understand the lower HC emissions obtained for E blends (E1—cetane index: 49.41; E2—cetane index: 48.30) compared to K blends (K1—cetane index: 46.28 and K2—cetane index: 46.07). 3.3.3. Carbon monoxide (CO) emision The characteristics of CO emission for the five fuels are presented in Fig. 11. CO is an intermediate combustion product and is formed
Table 3 Characteristics of the fuel blend components. Blends
Density at 15 °C (kg/m3)
Viscosity at 40 °C (mm2/s)
Flash point (°C)
Pour point (°C)
Cetane index
Heating value (MJ/kg)
Diesel K1 K2 K5 K7 C1 C2 C5 C7 E1 E2 E5 E7
844 843 848 853 855 845 847 851 854 848 850 853 856
2.70 2.65 2.66 2.69 2.71 2.56 2.58 2.60 2.61 2.68 2.69 2.70 2.71
61.1 54.4 56.4 61.4 63.4 55.80 57.40 62.40 67.40 64.4 67.4 67.4 70.4
–10 –13 –15 –18 –19 –13 –15 –18 –20 –16 –18 –22 –24
45.60 46.28 46.05 43.07 42.83 48.49 47.88 44,61 43.84 49.41 48.30 44.69 43.85
42.61 42.65 42.54 42.32 42.24 42.57 42.48 42.31 42.18 42.46 42.35 42.25 42.09
466
E.-E. Oprescu et al. / Fuel Processing Technology 126 (2014) 460–468
Fig. 5. Effect of (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methanol and (2-ethyl-2-methyl-1,3dioxolan-4-yl)methyl hexanoate on the engine torque with respect to the engine speed.
mainly due to incomplete combustion of fuel. If combustion is complete, CO is converted to CO2. If the combustion is incomplete due to shortage of air or due to low gas temperature, CO will be formed [17]. As shown in Fig. 11, the CO emissions generally decrease with the increase in engine speed. It is interesting to note that the engine emits lower CO using diesel blends when compared to diesel fuel. As compared to diesel the average reduction in CO emissions was about 10.19%, 7.77%, 18.93% and 13.11% for K1, K2, E1 and E2 diesel blends, respectively. For E1 and E2 diesel blends the CO emissions were lower because they have a higher cetane index compared to K1 and K2 diesel blends, which reduces the possibility of formation of rich fuel zone and thus reduces CO emissions. This explanation is supported by the studies made by Xue J. et al. and A.M. Liaquata et al. [27,30].
Fig. 7. Specific fuel consumption (sfc) for the five fuels, as a function of engine speed.
4.33% for K1, K2, E1 and E2 diesel blends, respectively. A possible explanation of the increase in the CO2 emissions when fuelling with diesel blends is attributed to the lower exhaust temperature (Fig. 8) of diesel blends compared to diesel, which indicates an earlier combustion allowing more time and crank angle for the expansion process. Therefore, there is more time for converting the formed CO to CO2 [31].
3.3.4. Carbon dioxide (CO2) emisions The characteristics of CO2 emissions are shown in Fig. 12. The CO2 emission decreases with the increase of engine speed. It can be noted that the CO2 emissions generally increase with the addition of additive because of the high oxygen level that ensures necessary oxygen to convert CO to CO2. Compared to diesel more amount of CO2 in exhaust emission was inregistrated for diesel blends. In average, the maximum increase of CO2 emissions was: 1.18%, 2.10%, 3.15% and
3.3.5. Smoke emission The smoke formation is caused by the pyrolysis of higher molecule hydrocarbon and subsequent cyclization to create an aromatic ring and to grow into a polynuclear aromatic hydrocarbon (PAH) structure. Simultaneous to this polymerisation process, the oxidative decomposition of these soot precursor molecules occurs.The variation of smoke emission with engine speed is shown in Fig. 13. Smoke emissions show decreased trends for all fuel tested with the increase in engine speed. The lowest smoke emissions have been obtained at 2700 rpm engine speed, for all test fuel. It can be observed that the production of smoke for diesel blends is lesser compared to diesel. The average smoke reduction in comparation with diesel, is about 11.01%, 13.11%, 14.88% and 19.20% for K1, K2, E1 and E2 diesel blends, respectively. The reduction of smoke emission with the increase of additive ratio can be attributed to the decrease in the aromatic
Fig. 6. Variation of engine power versus engine speed.
Fig. 8. Variation of exhaust gas temperature with respect to engine speed for the tested fuels.
E.-E. Oprescu et al. / Fuel Processing Technology 126 (2014) 460–468
467
Fig. 12. Characteristics of CO2 emissions.
Fig. 9. Engine NOx emission for the tested fuels at different speed engines.
hydrocarbon content and the increase of oxygen content, in the blended fuel [32]. 4. Conclusions
Fig. 10. Variation of hydrocarbon (HC) emission.
Fig. 11. Characteristics of CO emission for the five fuels.
In this work, the performance and exhaust emission of diesel engine fuelled with diesel, diesel–glycerol ketal blends and diesel–glycerol ketal ester blends were investigated. The first additive, glycerol ketal, was obtained by catalytic condensation of glycerol with butane-2-one over solid superacid catalyst SO24 −/TiO2 -La 2 O 3 while the second additive, glycerol ketal ester, was synthesized from the first one by transesterification with methyl hexanoate. In order to test the influence of the glycerol ketal ester chain length and concentration over diesel properties, we studied the following quality parameters of additivated diesel fuel: viscosity, pour point, flash point and cetane index. Experimental results indicated that the transesterification of glycerol ketal with methyl esters having 3 and 6 carbon atoms leads to an increase of flash point, density and cetane index, and a decrease of pour point. The performance and emission characteristics of the diesel engine powered with diesel, diesel–glycerol ketal blends and diesel–glycerol ketal ester blends at full load and variable engine speed were studied. From the experimental results, it can be summarized that compared to diesel and (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methanol diesel
Fig. 13. Variation of smoke emission with engine speed.
468
E.-E. Oprescu et al. / Fuel Processing Technology 126 (2014) 460–468
blends, (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methyl hexanoate diesel blends slightly improve engine performance but influence emission characteristic as follows: reduce HC, CO and smoke emission by 26.04%, 18.93% and 19.20%, respectively, and slightly increase NOx emission.
[15] [16]
[17]
Acknowledgement This research work was supported by the UEFISCDI, Romania, in the framework of the National Partnership Program, financing contract no. 44/2012.
[18]
[19]
[20]
Reference [1] Directive 2009/28/EC of the european parliament and of the council of 23 April 2009 on the promotion of the use of energy from renewable sources and amending and subsequently repealing Directives 2001/77/EC and 2003/30/EC, 2009. [2] E. Garcia, M. Laca, E. Perez, A. Garrido, J. Peinado, New class of acetal derived from glycerin as a biodiesel fuel component, Energy and Fuels 22 (2008) 4274–4280. [3] R. Norhasyimi, A.Z. Abdullah, A.R. Mohamed, Recent progress on innovative and potential technologies for glycerol transformation into fuel additives: a critical review, Renewable and Sustainable Energy Reviews 14 (2010) 987–1000. [4] N.M. Ribeiro, A.C. Pinto, C.M. Quintella, The role of additives for diesel and diesel blended (ethanol or biodiesel) fuels: a review, Energy and Fuels 21 (2007) 2433–2445. [5] A.A. Marchetti, M.G. Knize, M.L. Chiarappa-Zucca, R.J. Pletcher, D.W. Layton, Biodegradation of potential diesel oxygenate additives: dibutyl maleate (DBM), and tripropylene glycol methyl ether (TGME), Chemosphere 25 (2003) 861–868. [6] H.S. Kesling, L.J. Karas, F.J. Liotta, U.S. Patent 5,308,365 (1994). [7] Olah, G. A. U.S. Patent 5,520,710 (1996). [8] J. Delgado, Procedure to obtain biodiesel fuel with improved properties al low temperatures, EP Patent 1331260 (2002). [9] E.-E. Oprescu, E. Stepan, P. Rosca, R. Adrian, C.E. Enăşcuţă, Green synthesis of cyclohexanone glycerol ketal catalyzed by a solid superacid, Ovidius University Annals of Chemistry 23 (2012) 72–76. [10] E.-E. Oprescu, E. Stepan, R.-E. Dragomir, A. Radu, P. Rosca, Synthesis and testing of glycerol ketals as components for diesel fuel, Fuel Processing Technology 110 (2013) 214–217. [11] A.A. Refaat, I Correlation between the chemical structure of biodiesel and its physical properties, International Journal of Environmental Science and Technology 6 (2009) 677–694. [12] K. Gerhard, K.R. Steidley, Kinematic viscosity of biodiesel fuel components and related compounds. Influence of compound structure and comparison to petrodiesel fuel components, Fuel 84 (2005) 1059–1065. [13] J.A. Rodrigues, F.P. Cardoso, E.R. Lachter, L.R.M. Estevao, E. Lima, R.S.V. Nascimento, Correlating chemical structure and physical properties of vegetable oil esters, Journal of the American Oil Chemists' Society 83 (2006) 353–357. [14] A.M. Liaquat, H.H. Masjuki, M.A. Kalam, I.M. Rizwanul Fattah, M.A. Hazrat, M. Varman, M. Mofijur, M. Shahabuddin, Effect of coconut biodiesel blended fuels on
[21]
[22]
[23]
[24] [25] [26]
[27]
[28]
[29]
[30]
[31]
[32]
engine performance and emission characteristics, Procedia Engineering 56 (2013) 583–590. H. Aydin, H. Bayindir, Performance and emission analysis of cottonseed oil methyl ester in a diesel engine, Renewable Energy 35 (2010) 588–592. M. Shahabuddin, A.M. Liaquat, H.H. Masjuki, M.A. Kalam, M. Mofijur, Ignition delay, combustion and emission characteristics of diesel engine fueled with biodiesel, Renewable and Sustainable Energy Reviews 21 (2013) 623–632. M.W. Adaileh, K.S. AlQdah, Performance of diesel engine fuelled by a biodiesel extracted from a waste cocking oil, Energy Procedia 18 (2012) 1317–1334. C. Beatrice, C. Bertoli, J. D'Alessio, N. Del Giacomo, M. Lazzaro, P. Massoli, Experimental characterization of combustion behaviour of new diesel fuels for low emission engines, Combustion Science and Technology 120 (1996) 335–355. J. Song, K. Cheenkachorn, J. Wang, J. Perez, A.L. Boehman, P.J. Young, Effect of oxygenated fuel on combustion and emissions in a light-duty turbo diesel engine, Energy and Fuels 16 (2002) 294–301. A.B. Koc, M. Abdullah, Performance and NOx emissions of a diesel engine fueled with biodiesel–diesel–water nanoemulsions, Fuel Processing Technology 109 (2013) 70–77. A. Shirneshan, HC, CO, CO2 and NOx emission evaluation of a diesel engine fueled with waste frying oil methyl ester, Procedia - Social and Behavioral Sciences 75 (2013) 292–297. N.M. Nurun, S.M.N. Hoque, Md.S Akhter, K. Pongamia, Pinnata biodiesel production in Bangladesh, characterization of karanja biodiesel and its effect on diesel emissions, Fuel Processing Technology 90 (2009) 1080–1086. P. Bielaczyc, A. Szczotka, A study of RME-based biodiesel blend influence on performance, reliability and emissions from modern light-duty diesel engines, SAE proceedings 2008; SAE paper no. 2008-01-1938, 2008. G.T. Jeong, Y.T. Oh, D.H. Park, Emission profile of rapeseed methyl ester and its blend in a diesel engine, Applied Biochemistry and Biotechnology 129 (2006) 165–178. K. Schmidt, J.H. Van Gerpen, The effect of biodiesel fuel composition on diesel combustion and emissions, SAE proceedings 1996; SAE paper no. 961086, 1996. N.R. Banapurmatha, P.G. Tewaria, R.S. Hosmath, Experimental investigations of a four-stroke single cylinder direct injection diesel engine operated on dual fuel mode with producer gas as inducted fuel and honge oil and its methyl ester (HOME) as injected fuels, Renewable Energy 33 (2008) 2007–2018. A. Schönborn, N. Ladommatos, J. Williams, R. Allan, J. Rogerson, The influence of molecular structure of fatty acid monoalkyl esters on diesel combustion, Combustion and Flame 156 (2009) 1396–1412. C.P. Fenimore, Formation of nitric oxide in premixed hydrocarbon flames, 13th Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, PA, USA, 1971, pp. 373–379. M.S. Graboski, R.L. McCormick, T.L. Alleman, A.M. Herring, The effect of biodiesel composition on emissions from a DDC series 60 diesel engine, Report No. NREL/SR-510-31461, National Renewable Energy Laboratory, 2003. A.M. Liaquata, H.H. Masjukia, M.A. Kalama, M. Varmana, M.A. Hazrata, M. Shahabuddin, M. Mofijur, Application of blend fuels in a diesel engine, Energy Procedia 14 (2012) 1124–1133. O. Özener, L. Yüksek, A.T. Ergenç, M. Özkan, Effects of soybean biodiesel on a DI diesel engine performance, emission and combustion characteristics, Fuel 115 (2014) 875–883. A. Sarvia, C.-J. Fogelholmb, R. Zevenhovena, Emissions from large-scale mediumspeed diesel engines: influence of fuel type and operating model, Fuel Processing Technology 89 (2008) 520–527.
Contents lists available at ScienceDirect
Fuel Processing Technology journal homepage: www.elsevier.com/locate/fuproc
Performance and emission characteristics of diesel engine powered with diesel–glycerol derivatives blends Elena-Emilia Oprescu a, Raluca Elena Dragomir a,⁎, Elena Radu b, Adrian Radu b, Sanda Velea b, Ion Bolocan a, Emil Stepan b, Paul Rosca a a b
Faculty of Petroleum Refining and Petrochemistry, Petroleum-Gas University of Ploiesti, 39 Bucuresti Avenue, 100680 Ploiesti, Romania National Research & Development Institute for Chemistry and Petrochemistry ICECHIM, 202 Splaiul Independentei St., P.O. Box 194, 060021 Bucharest, Romania
a r t i c l e
i n f o
Article history: Received 3 February 2014 Received in revised form 14 April 2014 Accepted 27 May 2014 Available online xxxx Keywords: Diesel Glycerol ketal ester Solid superacid catalyst Emissions Diesel engine
a b s t r a c t The present work investigates the possibility of using two glycerol derivatives as additives for diesel fuel. The first additive was obtained by catalytic condensation of glycerol with butane-2-one over solid superacid SO2− 4 /TiO2-La2O3, while the second additive was synthesized from the first one by transesterification with methyl hexanoate. In order to investigate the chain length influence of the glycerol ketal ester over diesel properties, we studied the influence of ratio of oxygenated compound on the quality parameters of diesel fuel like viscosity, pour point, flash point and cetane index. To evaluate the effects of (2-ethyl-2-methyl-1,3-dioxolan-4-yl) methanol and (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methyl hexanoate diesel blends on engine performance and emission characteristics, the following parameters were studied: engine power, engine torque, specific fuel consumption (sfc), nitrogen oxide (NOx), hydrocarbon (HC), carbon monoxide (CO), carbon dioxide (CO2) and smoke emission. All tests were carried out on a four cylinder diesel engine, without any modifications, working at full load and engine speeds between 1200 and 3700 rpm. The experimental data indicates (2-ethyl-2methyl-1,3-dioxolan-4-yl)methyl hexanoate as a promising additive for emission reduction (reduces HC, CO and respective smoke emission by 26.04%, 18.93% and 19.20%, respectively, and slightly increases NOx emission). © 2014 Elsevier B.V. All rights reserved.
1. Introduction The environment is heavily polluted by road transport. In order to reduce the emission of pollutants from the public transport sector, the UE implemented Directive 2009/28/EC of the European Parliament of the council of 23 April 2009 on the promotion of the use of energy from renewable sources published on 23 April 2009 which sets the objective of reaching 20% of the EU's energy consumption through renewable energy sources by 2020 [1]. In this context, global production of biodiesel dramatically increased. As a result, a large surplus of glycerin was formed as a byproduct (10% in weight), which has a significant impact on the glycerol market, resulting in a decline of glycerin's price. Glycerol valorification not only revalorizes this byproduct but also increases the fuel yield in the overall biodiesel process. Therefore, many research groups have been devoted to develop glycerol derivatives with industrial interest [2]. An interesting alternative is the production of oxygenate additives based on glycerol.
Oxygenate compounds could improve combustion quality that reduces particulate emission and carbon monoxide production [3]. The molecular structure, local oxygen concentration and content of fuel could influence the reduction amount of particulate emissions [4,5]. The first class of glycerol derivatives added to diesel fuels to improve low-temperature properties and engine efficiency and to reduce harmful emissions were glycerin ethers [6,7]. A recent patent [8] reports that addition of glycerol acetals to diesel blends reduces viscosity and particle emission, and also met the established requirements for flash point and oxidation stability. This study has three main objectives: (i) synthesis of glycerol ketal by catalytic condensation of glycerol with butane-2-one over solid superacid catalyst SO2− 4 /TiO2-La2O3; (ii) transesterification of glycerol ketal with methyl hexanoate and (iii) study of the performance and emission characteristics of diesel engine fueled with diesel blends containing 1 and 2 wt.% of (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methanol and (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methyl hexanoate, respectively. 2. Material and methods
⁎ Corresponding author at: Department of Petroleum Processing Engineering and Environmental Protection, Petroleum-Gas University of Ploiesti, 39 Bucuresti Avenue, 100680 Ploiesti, Romania. Tel.: +40 244 573171; fax: +40 244 575847. E-mail address: [email protected] (R.E. Dragomir).
http://dx.doi.org/10.1016/j.fuproc.2014.05.027 0378-3820/© 2014 Elsevier B.V. All rights reserved.
2.1. Chemicals Anhydrous glycerol (99.9% w/w), sulfuric acid (98.0% w/w), titanium chloride, lanthanum chloride and sodium hydroxide (N98.0% w/w)
E.-E. Oprescu et al. / Fuel Processing Technology 126 (2014) 460–468
were purchased from Sigma-Aldrich (Germany); methanol, butan-2one (99.9% w/w), methyl hexanoate (99.9% w/w) and ammonia, solution 25% w/w, were supplied by Scharlau (Spain).
461
The main reaction for transesterification of butan-2-one glycerol ketal with methyl hexanoate is:
2.2. Catalyst preparation The solid superacid SO2− 4 /TiO2-La2O3 was obtained by co-precipitation method and characterized by X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy and elemental analysis. The acid properties of the sample were evaluated by TG/DTG thermal analysis of chemisorbed n-butylamine. All data are presented into a previous paper [9]. 2.3. Glycerol condensation with butan-2-one The method used to synthesize (2-ethyl-2-methyl-1,3-dioxolan4-yl)methanol is described into a previous paper [10]. The reaction was carried out in a three-neck round-bottom flask equipped with a mechanical stirrer, thermometer and Dean-Stark apparatus. In a typical experiment, glycerol (0.1 mol) and catalyst (3 wt.% with respect to glycerol) were placed under reaction conditions for 10 min before carbonyl compound (0.10 mol) was added dropwise. After the ketone dosing, an amount of 4.5 g solvent (e.g. benzene) was introduced to form a heterogeneous azeotropic system with water. The reaction mixture was mechanically stirred at atmospheric pressure and heated to reflux (80–110 °C). The water, formed along the reaction process, was removed in a Dean-Stark apparatus. The catalyst was filtered after completion of reaction, and solvent and carbonyl compound in excess were removed by distillation. Crude products were purified by vacuum distillation. The GC/MS/MS analysis of glycerol ketals indicated a chromatographic purity of 99%. To determine the optimal parameters for glycerol condensation with butan-2-one in the presence of superacid catalyst SO24 −/TiO2-La2O3, three impact factors were investigated: molar ratio of glycerol to butan-2-one, reaction time and catalyst amount. The experimental results show that the maximum yield in butan-2-one glycerol ketal (96.5%) was reached at a molar ratio of ketone to glycerol of 1.1:1, mass ratio of the catalyst of 3 wt.% with respect to glycerol, and a reaction time of 4 h. The reaction for glycerol condensation with butan-2-one is:
The GC/MS/MS analysis of (2-methyl-2-ethyl-1,3-dioxolan-4-yl) methanol indicated a chromatographic purity of 99% (Fig. 1). 2.4. Transesterification of butan-2-one glycerol ketal with methyl hexanoate Transesterification of butan-2-one glycerol ketal with methyl propionate was performed by using the method proposed by Oprescu et al. [10]. Using the same method we transesterificated butan-2-one glycerol ketal with methyl hexanoate. The reaction was effectuated in a three-neck round-bottom flask equipped with a magnetic stirrer, thermometer, rectifying column, condenser and reflux splitter. A roundbottom flask was loaded with butan-2-one glycerol ketal (0.1 mol) and sodium methoxide 30%, (1.5 wt.% with respect to butan-2-one glycerol ketal). The mixture was heated at 90 °C and methanol condensate was collected. Methyl hexanoate in a molar ratio of glycerol ketal:methyl hexanoate of 1:1.1 was added. The reaction mixture was stirred for 6 h in a temperature range of 120–150 °C and methanol condensate was collected. The catalyst was filtered after completion of reaction and the methyl propionate and methyl hexanoate in excess were removed by distillation. The crude product was purified by vacuum distillation.
The secondary reaction is:
Similar reactions occur for transesterification of butan-2-one glycerol ketal with methyl propionate. The GC/MS/MS analysis of (2-methyl-2-ethyl-1,3-dioxolan-4-yl) methyl hexanoate and (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl propionate indicated a chromatographic purity of 99% and 98%, respectively (Figs. 2 and 3, respectively). 2.5. Product identification The reaction products were analyzed by a GC-MS/MS TRIPLE QUAD (Agilent 7890 A) with DB-WAX capillary column (30 m length, 0.25 mm internal diameter, 0.25 μm film thickness) and helium as carrier gas at 1 mL/min. The temperature program was as follows: 70 °C, 5 °C/min up to 220 °C, hold time of 5 min. The GC injector and MS ion source temperatures were 250 °C and 150 °C, respectively. The transfer line temperature was 280 °C. The MS detector was operated in EI mode at 70 eV, with a m/z scanning range of 50–450 [10]. 2.6. Diesel blend characterization Diesel blend characterization was made using the following European standards: EN ISO 3104 (kinematic viscosity at 40 °C), EN ISO 3016 (pour point), EN ISO 2719 (flash point), EN ISO 4264 (cetane index) and D2015 (heating value). 2.7. Experimental and test procedure One of the objectives of this study is to test the performance and emission characteristics of diesel engine fueled with diesel blends containing 1 and 2 wt.% of (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methanol and (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methyl hexanoate, respectively. For the comparison under the same condition, the running parameters of the engine were kept the same. Engine experiments were performed on a Renault diesel engine K9K P 732, mounted on a Horiba Titan 250 stand test. The main characteristics of the diesel engine are shown in Table 1. The schematic diagram of the experimental setup is shown in Fig. 4. The engine was operated at full load and engine speeds between 1200 and 3700 rpm (1200, 1700, 2200, 2700, 3200 and 3700 rpm). The engine was firstly conducted with diesel fuel and then with diesel blends. The fuel consumption was measured with an AVL Fuel Consumption Measurement System PLU 401/116. The composition of pollutant compounds was determined by gas analyzer Pierburg Hermann, type HGA 400 5G. The smoke was measured by an AVL 415 smoke-meter. The technical properties of the gas analyzing device are presented in Table 2. 3. Results and discussion 3.1. Fuel blend properties The presence of hydroxyl groups in the structure of glycerol acetals/ketals decreases their solubility in hydrocarbons. To eliminate
462
E.-E. Oprescu et al. / Fuel Processing Technology 126 (2014) 460–468
Fig. 1. GC-MS/MS analysis of (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methanol.
this disadvantage and to improve other features, we continued the previous study [10] in which the free hydroxyl group of (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methanol (K) was blocked by transesterification with methyl propionate, obtaining (2-ethyl-2-methyl-1,3-dioxolan-4-yl) methyl propionate (C). Using the same method, we synthesized a longer glycerol ketal ester: (2-ethyl-2-methyl-1,3-dioxolan-4-yl) methyl hexanoate (E). The influence of ratio of oxygenated compounds on the diesel fuel characteristics like viscosity, pour point, flash point and cetane index was studied. The notation used is Diesel for pure diesel, Ki for mixture between diesel and glycerol ketal, Ci for diesel blended with (2-ethyl-2-methyl1,3-dioxolan-4-yl)methyl propionate and Ei for diesel mixed with (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methyl hexanoate. The value of index i corresponds to glycerol ketal and glycerol ketal esters percent in diesel blends (i.e. 1, 2, 5 and 7 wt.%). The experimental results are presented in Table 3. The data presented in Table 3 show an increase of density with the increasing of the chain length of the glycerol ketal ester. As result of OH group blocking, the viscosity increases slightly from 2.56 mm2/s for 1 wt.% of (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methyl propionate to 2.68 mm2/s for 1 wt.% of (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methyl hexanoate. This behavior is in accordance with literature data [11,12]. The value obtained for diesel blends are well within the range of EN 590 standard specification: 2–4.5 mm2/s. The flash point depends on the volatility and inflammability of the added compounds in diesel. The obtained experimental data show
that the increasing of the aliphatic chain of glycerol ketal ester causes an increase in flash point, from 63.4 °C for 7 wt.% glycerol ketal to 70.4 °C for 7 wt.% (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methyl hexanoate. Crystallization phenomena involve a high level of organization to promote nucleation. Branching interferes with the crystal packing, hence decreasing the crystallization temperature [13]. Chain length was found to have a significant influence on the pour point. The best performance of −24 °C was achieved when 7 wt.% of (2-ethyl-2methyl-1,3-dioxolan-4-yl)methyl hexanoate was added to diesel. To note, all tested glycerol derivatives improve the pour point of diesel blends. Another parameter analyzed was the cetane index. Given that the measuring of the cetane number requires an expensive cetane number engine and a large amount of fuel to test, there was developed a method to calculate cetan index based on density and distillation curve temperatures (EN ISO 4264). Because the calculations involve bulk fuel properties, this index is not affected by the presence of diesel ignition improvers. Also, by comparing them to each other, it provides a qualitative measure on the effect of glycerol derivatives in ignition delay of diesel fuel. Looking at the values of cetane index presented in Table 3, a slight improvement is observed with increasing esteric chain, from 57.07 for glycerol ketal to 58.49 and 59.41 for 1 wt.% of (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methyl propionate and 1 wt.% of (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methyl hexanoate, respectively. By increasing the aditive ratio, the cetane index decreases, but for the
E.-E. Oprescu et al. / Fuel Processing Technology 126 (2014) 460–468
463
Fig. 2. GC-MS/MS analysis of (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl hexanoate.
most of mixtures, the values are higher than diesel fuel. This decrease is supposed to be determined by the formula used to calculate the cetane index, which shows a decrease with density, whose value increases with additive/diesel ratio (Table 3). Analyzing the data presented in Table 3, (2-ethyl-2-methyl-1,3dioxolan-4-yl)methyl hexanoate was selected to be tested as diesel additive in diesel engine, because compared with (2-ethyl-2-methyl1,3-dioxolan-4-yl)methyl propionate, it improves the main properties which influence the engine performance and emission characteristics. For economic reasons and for the fact that the cetane index decreases with the additive concentration, the weight percent of the added compound in diesel fuel was not more than 2%. The experimental studies of exhaust emissions were conducted on the following fuel compositions: pure diesel (Diesel), diesel blend with (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methanol 1 wt.% (K1), diesel blend with (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methanol 2 wt.% (K2), diesel blend with (2-ethyl-2-methyl-1,3-dioxolan-4yl)methyl hexanoate 1 wt.% (E1), and diesel blend with (2-ethyl-2methyl-1,3-dioxolan-4-yl)methyl hexanoate 2 wt.% (E2). 3.2. Engine performance characteristics 3.2.1. Engine torque The effect of (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methanol and (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methyl hexanoate on the engine torque with respect to the engine speed is shown in Fig. 5. Torque
initially enhances with increasing of engine speed until it reaches a maximum value and then decreases with further increasing engine speed. The engine torque reduction after certain speed is caused by the lowered volumetric efficiency of the engine due to the increase in the corresponding engine speed [14]. The maximum engine torque was obtained at 2700 rpm, for all test fuel samples. Although, the differences in torque values measured for the Diesel fuel, K1, K2, E1 and E2 blends were not significant, it can be observed in Fig. 5 a slow increase by adding glycerol derivatives in diesel. The differences in torque values measured for the Diesel fuel, K1, K2, E1 and E2 blends were not significant. The engine torque is influenced by the viscosity of the fuel. When the viscosity of the fuel increases the amount of the fuel that should be filled into the oil pump decreases and the volumetric efficiency of engine remains lower, consequently resulting in the decrease of torque [15]. Also, the small viscosity increases atomization and fuel delivery rate, and reduces the droplet diameter and breakup time [16]. To note is that engine torque variation corresponds to the variation of the viscosity of the five fuels (Table 3). 3.2.2. Engine power The variation of engine power versus engine speed is presented in Fig. 6. The results show that there are no noticeable differences in the measured engine power output between the five fuels tested. It can be seen that engine power rises with the increasing of engine speed. Maximum power values were obtained at 3200 rpm. Normally, due to the lower heating value of oxygenate diesel blends engine power should
464
E.-E. Oprescu et al. / Fuel Processing Technology 126 (2014) 460–468
Fig. 3. GC-MS/MS analysis of (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl propionate.
decrease. However, as an average, the engine power increases with the addition of additive content in diesel and reaches a maximum average value for E2 blend. A slight increase in engine power by adding glycerol derivatives in diesel fuel, especially for (2-ethyl-2-methyl-1,3-dioxolan4-yl)methyl hexanoate at high engine speed can be explained by the increase in the fuel consumption (Fig. 7). Because of the greater densities of E1 and E2 blends compared with diesel and K1 and K2 blends (Table 3), for the same volume of combustion chambers a larger fuel mass flow rate was injected resulting an increase in power. At the same time, the decrease of blends viscosities means the less internal leakage in the fuel pump and results an increase in the power [17]. The presence of oxygen in the molecular structure of the additives
Table 1 Technical specification of the diesel engine. Particulars
Specifications
Model Cylinder number Cubic capacity, [cm3] Combustion system Cooling system Bore/Stroke, mm Compression ratio Power, [kW] Maximum torque, [Nm] Maximum speed, [rpm]
Renault K9K P 732 4 cylinder, inline 1461 Common rail direct injection Siemens Water cooled 76/80.5 15.3:1 78 kW at 3700 rpm 240 Nm at 2700 rpm 4000
improves combustion of diesel blends, thus compensating additive lower heating values. 3.2.3. Specific fuel consumption (sfc) Fig. 7 presents the specific fuel consumption (sfc) for the five fuels, as a function of engine speed. The highest sfc was observed for E2 blend with all speeds of the engine, while the lowest sfc's were obtained for diesel fuel. The properties of the fuel tested such as viscosity, density, and heating value influence the relationship between engine performance (the fuel injection system, mainly the spray formation) and combustion [18,19]. Therefore, the greater values of specific fuel consumption (sfc) obtained for glycerol ketal ester blends are explained by the lower heating value, higher viscosity and density (Table 3). For the same volume, due to the greater density of glycerol ketal ester blends, more fuel by mass was injected into the combustion chamber compared with the amount of diesel injected. 3.2.4. Exhaust gas temperature In analyzing of the emission characteristics of the exhaust gas temperature it is an important indicator of the heat of the fuels tested at the combustion period. The variation of exhaust gas temperature with respect to engine speed for the tested fuels is shown in Fig. 8. The exhaust gas temperature values increased with the increase of the engine speed for all five test fuels and an increase in the additive blend ratio resulted in a decrease in the exhaust temperature. The exhaust temperatures for the K1, K2, E1 and E2 blends are lower
E.-E. Oprescu et al. / Fuel Processing Technology 126 (2014) 460–468
465
Fig. 4. Schematic diagram of the experimental setup.
the injected molecules. As can be seen in Fig. 9, the glycerol ketal ester blends produced less NOx during their combustion than glycerol ketal blends, because E1 and E2 blends have a higher cetane index which leads to shorter ignition delay and decreased maximum heat release rate which results in lower cylinder temperature, and this reduces the formation of NOx. These findings are in agreement with those of Graboski et al. [26,27]. Also, in accordance with Graboski et al. [26,27], NOx emission increases for glycerol derivative blends compared with classic diesel, caused by the formation of prompt NOx due to high concentrations of oxygenated derived radicals [28].
Table 2 Technical properties of the gas analyzing device. Measured variable
Measuring range
Precision
CO CO2 HC NOx Smoke
0–10% 0–20% 0–20,000 ppm 0–5000 ppm 0–100%
0.001% 0.1% 1 ppm 1 ppm 1%
compared with Diesel fuel [20]. These results are due to the higher heating value of Diesel fuel compared to diesel blends (Table 3). 3.3. Exhaust emissions 3.3.1. Nitrogen oxide (Nox) emission The engine NOx emission for the tested fuels at different speed engines is given in Fig. 9. The NOx concentration increases with the rise of engine speed for all the fuels. The NOx emission for diesel blends with 2% additive is slightly higher than diesel blends with 1% additive. This behavior is explained by a few researchers, which reported that the high oxygen levels increase the maximum local temperature during the combustion, resulting in high NOx formation [18–20]. It is also agreed that in the production of NOx, the fuel borne oxygen is more effective than the external oxygen supplied with the air [18]. The same trend was observed by M.N. Nabi et al. [21], Bielaczyc et al. [22], Jeong et al. [23], and Schmidt et al. [24] for diesel blends with different biodiesel percents. A way to reduce NOx emission by changing the injection timing was reported by Banapurmatha et al. [25]. The increased NOx emission obtained by glycerol ketal diesel blends compared to glycerol ketal ester diesel blends may be explained by the fact that the alkyl chain strongly influenced the ignition delay periods of
3.3.2. Hydrocarbon (HC) emission Fig. 10 shows the variation of hydrocarbon (HC) emission. At a lower adding ratio, the HC emissions resulted from diesel fuel and diesel blends with additives were lower than that of diesel fuel. The reason for lower HC emissions can be the higher oxygen content in additive, which helps to complete oxidations in rich air–fuel mixture zones by increasing the oxidation reaction ratio. The decrease in HC emissions compared to diesel was about 10.42%, 6.25%, 26.04% and 20.14% for K1, K2, E1 and E2 blends, respectively. For 2% addition ratio it can be observed from Fig. 10 that the HC emission grows. An explanation could be sustained by the cetane number influence which decreases with the increasing of additive content in diesel. A lower cetane index determines the rising of the ignition delay period and increases in this way the unburned HC level from the exhaust gases [29]. The same argument may be used to understand the lower HC emissions obtained for E blends (E1—cetane index: 49.41; E2—cetane index: 48.30) compared to K blends (K1—cetane index: 46.28 and K2—cetane index: 46.07). 3.3.3. Carbon monoxide (CO) emision The characteristics of CO emission for the five fuels are presented in Fig. 11. CO is an intermediate combustion product and is formed
Table 3 Characteristics of the fuel blend components. Blends
Density at 15 °C (kg/m3)
Viscosity at 40 °C (mm2/s)
Flash point (°C)
Pour point (°C)
Cetane index
Heating value (MJ/kg)
Diesel K1 K2 K5 K7 C1 C2 C5 C7 E1 E2 E5 E7
844 843 848 853 855 845 847 851 854 848 850 853 856
2.70 2.65 2.66 2.69 2.71 2.56 2.58 2.60 2.61 2.68 2.69 2.70 2.71
61.1 54.4 56.4 61.4 63.4 55.80 57.40 62.40 67.40 64.4 67.4 67.4 70.4
–10 –13 –15 –18 –19 –13 –15 –18 –20 –16 –18 –22 –24
45.60 46.28 46.05 43.07 42.83 48.49 47.88 44,61 43.84 49.41 48.30 44.69 43.85
42.61 42.65 42.54 42.32 42.24 42.57 42.48 42.31 42.18 42.46 42.35 42.25 42.09
466
E.-E. Oprescu et al. / Fuel Processing Technology 126 (2014) 460–468
Fig. 5. Effect of (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methanol and (2-ethyl-2-methyl-1,3dioxolan-4-yl)methyl hexanoate on the engine torque with respect to the engine speed.
mainly due to incomplete combustion of fuel. If combustion is complete, CO is converted to CO2. If the combustion is incomplete due to shortage of air or due to low gas temperature, CO will be formed [17]. As shown in Fig. 11, the CO emissions generally decrease with the increase in engine speed. It is interesting to note that the engine emits lower CO using diesel blends when compared to diesel fuel. As compared to diesel the average reduction in CO emissions was about 10.19%, 7.77%, 18.93% and 13.11% for K1, K2, E1 and E2 diesel blends, respectively. For E1 and E2 diesel blends the CO emissions were lower because they have a higher cetane index compared to K1 and K2 diesel blends, which reduces the possibility of formation of rich fuel zone and thus reduces CO emissions. This explanation is supported by the studies made by Xue J. et al. and A.M. Liaquata et al. [27,30].
Fig. 7. Specific fuel consumption (sfc) for the five fuels, as a function of engine speed.
4.33% for K1, K2, E1 and E2 diesel blends, respectively. A possible explanation of the increase in the CO2 emissions when fuelling with diesel blends is attributed to the lower exhaust temperature (Fig. 8) of diesel blends compared to diesel, which indicates an earlier combustion allowing more time and crank angle for the expansion process. Therefore, there is more time for converting the formed CO to CO2 [31].
3.3.4. Carbon dioxide (CO2) emisions The characteristics of CO2 emissions are shown in Fig. 12. The CO2 emission decreases with the increase of engine speed. It can be noted that the CO2 emissions generally increase with the addition of additive because of the high oxygen level that ensures necessary oxygen to convert CO to CO2. Compared to diesel more amount of CO2 in exhaust emission was inregistrated for diesel blends. In average, the maximum increase of CO2 emissions was: 1.18%, 2.10%, 3.15% and
3.3.5. Smoke emission The smoke formation is caused by the pyrolysis of higher molecule hydrocarbon and subsequent cyclization to create an aromatic ring and to grow into a polynuclear aromatic hydrocarbon (PAH) structure. Simultaneous to this polymerisation process, the oxidative decomposition of these soot precursor molecules occurs.The variation of smoke emission with engine speed is shown in Fig. 13. Smoke emissions show decreased trends for all fuel tested with the increase in engine speed. The lowest smoke emissions have been obtained at 2700 rpm engine speed, for all test fuel. It can be observed that the production of smoke for diesel blends is lesser compared to diesel. The average smoke reduction in comparation with diesel, is about 11.01%, 13.11%, 14.88% and 19.20% for K1, K2, E1 and E2 diesel blends, respectively. The reduction of smoke emission with the increase of additive ratio can be attributed to the decrease in the aromatic
Fig. 6. Variation of engine power versus engine speed.
Fig. 8. Variation of exhaust gas temperature with respect to engine speed for the tested fuels.
E.-E. Oprescu et al. / Fuel Processing Technology 126 (2014) 460–468
467
Fig. 12. Characteristics of CO2 emissions.
Fig. 9. Engine NOx emission for the tested fuels at different speed engines.
hydrocarbon content and the increase of oxygen content, in the blended fuel [32]. 4. Conclusions
Fig. 10. Variation of hydrocarbon (HC) emission.
Fig. 11. Characteristics of CO emission for the five fuels.
In this work, the performance and exhaust emission of diesel engine fuelled with diesel, diesel–glycerol ketal blends and diesel–glycerol ketal ester blends were investigated. The first additive, glycerol ketal, was obtained by catalytic condensation of glycerol with butane-2-one over solid superacid catalyst SO24 −/TiO2 -La 2 O 3 while the second additive, glycerol ketal ester, was synthesized from the first one by transesterification with methyl hexanoate. In order to test the influence of the glycerol ketal ester chain length and concentration over diesel properties, we studied the following quality parameters of additivated diesel fuel: viscosity, pour point, flash point and cetane index. Experimental results indicated that the transesterification of glycerol ketal with methyl esters having 3 and 6 carbon atoms leads to an increase of flash point, density and cetane index, and a decrease of pour point. The performance and emission characteristics of the diesel engine powered with diesel, diesel–glycerol ketal blends and diesel–glycerol ketal ester blends at full load and variable engine speed were studied. From the experimental results, it can be summarized that compared to diesel and (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methanol diesel
Fig. 13. Variation of smoke emission with engine speed.
468
E.-E. Oprescu et al. / Fuel Processing Technology 126 (2014) 460–468
blends, (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methyl hexanoate diesel blends slightly improve engine performance but influence emission characteristic as follows: reduce HC, CO and smoke emission by 26.04%, 18.93% and 19.20%, respectively, and slightly increase NOx emission.
[15] [16]
[17]
Acknowledgement This research work was supported by the UEFISCDI, Romania, in the framework of the National Partnership Program, financing contract no. 44/2012.
[18]
[19]
[20]
Reference [1] Directive 2009/28/EC of the european parliament and of the council of 23 April 2009 on the promotion of the use of energy from renewable sources and amending and subsequently repealing Directives 2001/77/EC and 2003/30/EC, 2009. [2] E. Garcia, M. Laca, E. Perez, A. Garrido, J. Peinado, New class of acetal derived from glycerin as a biodiesel fuel component, Energy and Fuels 22 (2008) 4274–4280. [3] R. Norhasyimi, A.Z. Abdullah, A.R. Mohamed, Recent progress on innovative and potential technologies for glycerol transformation into fuel additives: a critical review, Renewable and Sustainable Energy Reviews 14 (2010) 987–1000. [4] N.M. Ribeiro, A.C. Pinto, C.M. Quintella, The role of additives for diesel and diesel blended (ethanol or biodiesel) fuels: a review, Energy and Fuels 21 (2007) 2433–2445. [5] A.A. Marchetti, M.G. Knize, M.L. Chiarappa-Zucca, R.J. Pletcher, D.W. Layton, Biodegradation of potential diesel oxygenate additives: dibutyl maleate (DBM), and tripropylene glycol methyl ether (TGME), Chemosphere 25 (2003) 861–868. [6] H.S. Kesling, L.J. Karas, F.J. Liotta, U.S. Patent 5,308,365 (1994). [7] Olah, G. A. U.S. Patent 5,520,710 (1996). [8] J. Delgado, Procedure to obtain biodiesel fuel with improved properties al low temperatures, EP Patent 1331260 (2002). [9] E.-E. Oprescu, E. Stepan, P. Rosca, R. Adrian, C.E. Enăşcuţă, Green synthesis of cyclohexanone glycerol ketal catalyzed by a solid superacid, Ovidius University Annals of Chemistry 23 (2012) 72–76. [10] E.-E. Oprescu, E. Stepan, R.-E. Dragomir, A. Radu, P. Rosca, Synthesis and testing of glycerol ketals as components for diesel fuel, Fuel Processing Technology 110 (2013) 214–217. [11] A.A. Refaat, I Correlation between the chemical structure of biodiesel and its physical properties, International Journal of Environmental Science and Technology 6 (2009) 677–694. [12] K. Gerhard, K.R. Steidley, Kinematic viscosity of biodiesel fuel components and related compounds. Influence of compound structure and comparison to petrodiesel fuel components, Fuel 84 (2005) 1059–1065. [13] J.A. Rodrigues, F.P. Cardoso, E.R. Lachter, L.R.M. Estevao, E. Lima, R.S.V. Nascimento, Correlating chemical structure and physical properties of vegetable oil esters, Journal of the American Oil Chemists' Society 83 (2006) 353–357. [14] A.M. Liaquat, H.H. Masjuki, M.A. Kalam, I.M. Rizwanul Fattah, M.A. Hazrat, M. Varman, M. Mofijur, M. Shahabuddin, Effect of coconut biodiesel blended fuels on
[21]
[22]
[23]
[24] [25] [26]
[27]
[28]
[29]
[30]
[31]
[32]
engine performance and emission characteristics, Procedia Engineering 56 (2013) 583–590. H. Aydin, H. Bayindir, Performance and emission analysis of cottonseed oil methyl ester in a diesel engine, Renewable Energy 35 (2010) 588–592. M. Shahabuddin, A.M. Liaquat, H.H. Masjuki, M.A. Kalam, M. Mofijur, Ignition delay, combustion and emission characteristics of diesel engine fueled with biodiesel, Renewable and Sustainable Energy Reviews 21 (2013) 623–632. M.W. Adaileh, K.S. AlQdah, Performance of diesel engine fuelled by a biodiesel extracted from a waste cocking oil, Energy Procedia 18 (2012) 1317–1334. C. Beatrice, C. Bertoli, J. D'Alessio, N. Del Giacomo, M. Lazzaro, P. Massoli, Experimental characterization of combustion behaviour of new diesel fuels for low emission engines, Combustion Science and Technology 120 (1996) 335–355. J. Song, K. Cheenkachorn, J. Wang, J. Perez, A.L. Boehman, P.J. Young, Effect of oxygenated fuel on combustion and emissions in a light-duty turbo diesel engine, Energy and Fuels 16 (2002) 294–301. A.B. Koc, M. Abdullah, Performance and NOx emissions of a diesel engine fueled with biodiesel–diesel–water nanoemulsions, Fuel Processing Technology 109 (2013) 70–77. A. Shirneshan, HC, CO, CO2 and NOx emission evaluation of a diesel engine fueled with waste frying oil methyl ester, Procedia - Social and Behavioral Sciences 75 (2013) 292–297. N.M. Nurun, S.M.N. Hoque, Md.S Akhter, K. Pongamia, Pinnata biodiesel production in Bangladesh, characterization of karanja biodiesel and its effect on diesel emissions, Fuel Processing Technology 90 (2009) 1080–1086. P. Bielaczyc, A. Szczotka, A study of RME-based biodiesel blend influence on performance, reliability and emissions from modern light-duty diesel engines, SAE proceedings 2008; SAE paper no. 2008-01-1938, 2008. G.T. Jeong, Y.T. Oh, D.H. Park, Emission profile of rapeseed methyl ester and its blend in a diesel engine, Applied Biochemistry and Biotechnology 129 (2006) 165–178. K. Schmidt, J.H. Van Gerpen, The effect of biodiesel fuel composition on diesel combustion and emissions, SAE proceedings 1996; SAE paper no. 961086, 1996. N.R. Banapurmatha, P.G. Tewaria, R.S. Hosmath, Experimental investigations of a four-stroke single cylinder direct injection diesel engine operated on dual fuel mode with producer gas as inducted fuel and honge oil and its methyl ester (HOME) as injected fuels, Renewable Energy 33 (2008) 2007–2018. A. Schönborn, N. Ladommatos, J. Williams, R. Allan, J. Rogerson, The influence of molecular structure of fatty acid monoalkyl esters on diesel combustion, Combustion and Flame 156 (2009) 1396–1412. C.P. Fenimore, Formation of nitric oxide in premixed hydrocarbon flames, 13th Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, PA, USA, 1971, pp. 373–379. M.S. Graboski, R.L. McCormick, T.L. Alleman, A.M. Herring, The effect of biodiesel composition on emissions from a DDC series 60 diesel engine, Report No. NREL/SR-510-31461, National Renewable Energy Laboratory, 2003. A.M. Liaquata, H.H. Masjukia, M.A. Kalama, M. Varmana, M.A. Hazrata, M. Shahabuddin, M. Mofijur, Application of blend fuels in a diesel engine, Energy Procedia 14 (2012) 1124–1133. O. Özener, L. Yüksek, A.T. Ergenç, M. Özkan, Effects of soybean biodiesel on a DI diesel engine performance, emission and combustion characteristics, Fuel 115 (2014) 875–883. A. Sarvia, C.-J. Fogelholmb, R. Zevenhovena, Emissions from large-scale mediumspeed diesel engines: influence of fuel type and operating model, Fuel Processing Technology 89 (2008) 520–527.