Fuel 84 (2005) 2380–2383 www.fuelfirst.com
Critical solubility of dimethyl ether (DME)Cdiesel fuel and dimethyl carbonate (DMC)Cdiesel fuel Xiaoming Zhao*, Meifeng Ren, Zhigang Liu State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University, Xi’an Shaanxi 710049, China Received 21 November 2003; accepted 9 May 2005 Available online 15 June 2005
Abstract An experimental apparatus was developed for measuring the critical solubility. The critical solubilities were determined for binary mixtures of DMECdiesel fuel and DMCCdiesel fuel. For DMECdiesel fuel their critical solubility temperatures ranged from 272.83 to 255.13 K while the mass fractions of DME varied from 3.44 to 95.8%; For DMCCdiesel fuel, their critical solubility temperatures were between 273.58 and 302.72 K while the mass fractions of DMC varied from 1.22 to 89.6%. q 2005 Elsevier Ltd. All rights reserved. Keywords: Critical solubility; Dimethyl ether (DME); Dimethyl carbonate (DMC); Diesel fuel
1. Introduction The exhaust of automobiles is polluting the atmosphere increasingly. The contaminations in air like NOx, CO, NMHC, etc. become an extraordinary serious problem of global environmental pollution. Furthermore, the exhaust of automobiles gradually has a tendency to cause deeper pollutions and secondly pollutions like ‘actinochemistry smog’ and ‘greenhouse effect’. So the development of automobile industry faces a great challenge. Besides, automobiles are the largest consumers of fuel resources, whereas the prospect of energy resources, especially fuel resources, is not optimistic. In view of these factors, the exploitation of alternative fuels becomes an exigent matter to be solved. Currently, various alternative fuels have been investigated for diesel engines to reduce the consumption of diesel fuel and NOx and particulate emissions. As a clean and preferred alternative to conventional diesel fuel, the dimethyl ether (DME) obtained from natural gas, coal, fossil reserves or other organic resources through syngas [1,2] is now investigated as replacement diesel fuel. A lot of researches [3–5] show that DME has excellent properties as
diesel fuel: diesel engine using DME as its fuel has higher thermal efficiency, achieving much less particulate and sulfur free emissions, and solving the energy–environment problem. But the viscosity of DME is low, which makes high-pressure-fuel pump have serious wear abrasion. Adding some diesel fuel or DMC in the DME can increase the viscosity of the fuel and improve combustion properties of fuel. Further researches [6,7] indicate that the mixed fuel of diesel fuel and DMC is also an advantaged alternative. But when the temperature, either of the engine’s working condition or of the outside environment, drops right close to the insolubility point of mixed fuel, it will become insoluble, even completely separated. As a result, the engine cannot perform well because of supplying inhomogeneous fuel and then fuel combustion in engine varies out of expectation. In this work, the critical solubility of DME and DMC in diesel fuel was measured individually, and the soluble and insoluble range was determined by drawing the ‘critical solubility temperature’ scatter figure. This may serve as an important reference for the future researches on DME or DMC mixture combustion.
2. Experimental apparatus * Corresponding author. Tel.: C86 29 82663863; fax: C86 29 82667917. E-mail address: [email protected]
0016-2361/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2005.05.014
The schematic of the experimental apparatus  used to measure the solubility of DME and DMC in diesel fuel is shown in Fig. 1. The thermostatic bath used in this work is
X. Zhao et al. / Fuel 84 (2005) 2380–2383
stainless steel tube
platinum resistor thermometer
electrical signal receiver
pressure transducer T
quartz glass tube
stirrer cooled ethanol circulation
heater Thermostatic bath insulative material
Fig. 1. Schematic of the experimental apparatus.
made of stainless steel. And its wall thickness is 110 mm and insulated with rigid polyurethane foam. The thermostatic bath has two glass windows (120 mm diameter) within inner dimension of 550!350!450 mm3. The temperature can be varied from 233 to 550 K. Ethanol, pure water, or silicon oil can be used as the bath fluids, depending on the required temperature range. The bath is filled with ethanol in this work. The temperature of ethanol in the bath is controlled with a computer through a heater and the circulation of cooled ethanol supplied by a refrigeration system. The temperature was measured with a platinum resistance device (RTD) and a thermometry bridge F18 (Automatic System Laboratories Limited). The stability and uniformity of temperature in the working area are G4 mK. The pressure of the mixture was measured with a pressure transducer (ZF3801), having an accuracy of 0.01%FS (full scale pressure is 5 MPa), connected through a thin-wall tube at the top of the sample vessel. The sample vessel device used to charge mixtures is shown in Fig. 2. The sample vessel was made of a quartz glass tube (170 mm long, 14.7 mm outer diameter, 5.2 mm in wall thickness) sandwiched between two stainless steel plates. It was pressurized by four steel bolts and one annular rubber gasket is on the upper side of the tube, another circular rubber gasket on the lower side. With this arrangement, the system was tested to be able to tolerate continuous variations in pressure (0–5 MPa) and temperature (233.15–373.15 K) without breakage of the glass tube. The sample vessel was partially charged with the diesel fuel first. Evacuating the air over diesel fuel avoids the influence of the air. And then the sample vessel was filled with DME or DMC. A balance with precision of G0.01 g was used to determinate the mass fraction of the liquid mixture. By weighing the sample vessel assembly before
Fig. 2. The device of the sample vessel.
and after each charging, the exact amounts of diesel fuel and DME or DMC were determined and the mass fraction of the DME or DMC can be obtained. The sample vessel was put into the thermostatic bath and the temperature of the thermostatic bath would be raised until the mixed fuel was completely dissolved. The temperature that the floc in mixture appears at is defined as ‘critical solubility temperature’ or ‘critical mutual solubility temperature’ at the relative mass fraction. The floc in the mixed fuel could be seen through the glass window when its temperature dropped to the critical value. The mixture is classified as ‘clear’ when it is completely transparent, ‘cloudy’ when floc in the mixture viewed through the tube appears, ‘opaque’ when nothing can be seen through it and ‘phase separated’ when two distinct phases appear. When the turbidity appears the temperature of the mixture should be raised again appreciably and kept for 20 min, then be reduced slowly again. Finally, the critical soluble point can be determined. Measuring the solubility of refrigerant/lubricant mixtures and comparing to the published data has proved the accuracy of the experimental apparatus and procedure. The deviation of the critical solubility temperature of our results and the literature  is within G0.05 K. In this work, the testing samples are DME, DMC and diesel fuel. The mass purity of DME is 99.9%, DMC 99.5%. The main compositions of diesel fuel used are alkaneC alkene (72.86 wt%) and aromatic hydrocarbon (27.14 wt%). The cetane number of the diesel fuel is 48. The density and viscosity of diesel fuel at 293.15 K are 4.27 mm2 sK1 and 832.6 kg mK3, respectively. Its freezing point is 273.15 K.
3. Results and discussions The experimental results of the critical solubility of DMECdiesel fuel are presented in Table 1. A phase curve
X. Zhao et al. / Fuel 84 (2005) 2380–2383
Table 1 Experimental results of the critical solubility temperature of DMECdiesel fuel
Table 2 Experimental results of the critical solubility temperature of DMCCdiesel fuel
x (DME mass%)
3.44 8.45 14.66 19.76 25.73 31.14 37.78 42.86 45.86 53.38 61.59 64.79 70.58 79.20 84.77 90.24 93.20 95.76
272.83 271.57 270.05 268.78 267.69 266.93 265.98 265.48 265.22 264.70 263.93 263.75 263.22 262.43 261.34 259.00 257.35 255.13
96.1 130.2 191.0 198.6 198.6 203.1 218.2 200.1 195.7 218.2 192.6 194.1 200.1 210.6 203.1 200.1 191.0 177.5
x (DMC mass%)
x (DMC mass%)
5.61 9.83 15.22 21.09 26.08 29.94 35.48 40.15 47.98 55.33 59.34 68.89 81.09 84.72 8961
273.62 273.90 275.33 278.05 283.62 287.50 291.48 293.70 296.08 298.44 300.10 302.28 301.24 299.05 293.05
105.1 109.7 109.7 111.2 112.7 114.2 115.7 118.7 120.2 121.8 121.8 120.2 117.2 118.7 111.2
1.22 2.27 24.37 39.05 43.06 47.35 49.91 57.41 64.86 72.76 81.37
273.58 273.60 281.45 293.45 295.08 296.18 296.88 299.30 301.85 302.72 301.45
103.7 103.7 112.7 118.7 118.7 120.2 121.8 120.2 118.7 118.7 118.7
Experimental data Polynomial fit of experimental data
265 Two phase region
atomizing characteristics, improving the combustion of diesel fuel burn sufficiently, and emitting much less particulate. It can be suitable for cold weather because the critical solubility temperature of the mixed fuel is higher than 268 K. When the fraction of DME is higher than about 75%, the main content of the mixed fuel is DME, the critical solubility temperature gradually decreases. On the basis of the data of critical solubility temperature, the following polynomial was fitted. T Z a 0 C a1 x C a2 x 2 C a3 x 3 C a4 x 4 C a5 x 5 a0 Z 274:30189; a1 Z K43:00784; a2 Z 125:72704; a3 Z K311:57643; a4 Z 416:38446; a5 Z K210:67492: where T is the critical solubility temperature and x the mass fraction of DME. Standard deviation of this fit is 0.1641. There are two series of data of the critical solubility temperature of DMCCdiesel fuel in Table 2. These data series 1 series 2
T ( K) critical solubility temperature
T (K ) (critical solubility temperature)
of critical solubility is shown in Fig. 3. And the results of the critical solubility of DMCCdiesel fuel are shown in Table 2. Its phase curve of critical solubility is shown in Fig. 4. The mixed fuels can be completely dissolved above the curves of critical solubility, and are insoluble or phase separated below the curves in Figs. 3 and 4. Tables 1 and 2 show that there is a difference between mixtures of DMECdiesel fuel and DMCCdiesel fuel in critical solubility temperatures. From Fig. 3, we can see that the critical solubility temperatures of DMECdiesel fuel are below 273.15 K while the mass fractions of DME vary from 0 to 100%. In Fig. 4, the critical solubility temperatures of DMCCdiesel fuel are above 273.15 K. The lower the critical solubility temperature, the higher is the possibility of putting this fuel mixture into practice. The curve in Fig. 3 also indicates that when the fraction of DME in the mixed fuel increases, the critical solubility temperature drops. The low fraction of DME, about less than 20%, is a satisfactory percentage in improving the fuel
295 two phase region 290 285 280 275 270
X % (DME mass fraction)
Fig. 3. Critical solubility temperature of DMECdiesel fuel.
40 60 x % (DMC mass fraction)
Fig. 4. Critical solubility temperature of DMCCdiesel fuel.
X. Zhao et al. / Fuel 84 (2005) 2380–2383
were plotted in Fig. 4. The tendency of the two series of data is in agreement. From Fig. 4 we realize that fuel mixture of DMCCdiesel fuel is completely not suitable for cold weather because the lowest critical solubility temperature is only 273 K. The fuel mixture of DMCCdiesel fuel with lower DMC fraction can probably be used only in warm regions, otherwise, the DMC will be separated from diesel fuel and it will be difficult to feed the fuel homogeneously. But adding a small amount of DMC into diesel fuel can improve combustion performances of diesel engine because the DMC is an oxygenous fuel.
4. Conclusion An experimental apparatus has been developed for the critical solubility measurements. The data of critical solubility temperature of DMECdiesel fuel and DMCC diesel fuel mixtures have been obtained by using the experimental apparatus. The critical solubility temperatures of DMECdiesel fuel are below 273.15 K. And the critical solubility temperature decreases gradually when the mass fraction of DME increases. The mixture fuel of DMEC diesel fuel is suitable for cold regions. The critical solubility temperatures of DMCCdiesel fuel are higher than 273.15 K for all fractions. The lower mass fraction of DMC can probably be used in warm region, or the inhomogeneous supply of fuel will occur.
Acknowledgements We acknowledge the support of the National Basic Research Priority Program of Ministry of Science and Technology of China.
References  Hansen JB, Voss B, Joensen F, Sigurdardottir ID. Large scale manufacture of dimethyl ether. A new alternative diesel fuel from natural gas. SAE Paper No. 950063; 1995.  Jiang T, Liu CJ, Rao MF, Yao CD, Fan GL. A novel synthesis of diesel fuel additives from dimethyl ether using dielectric barrier discharges. Fuel Process Technol 2001;73:143–52.  Wang HW, Chen HY, Zhou LB, Huang ZH, Jiang DM. Investigation of a direct injection diesel engine fueled with dimethyl ether. Chin Soc Intern Combust Engines 1999;17:241–6.  Fleish TH. More on diethyl ether: case is building for DME as clean diesel fuel. Diesel Prog Drives 1995;61:42–5.  Song J, Huang Z, Qiao X, Wang W. Performance of a controllable premixed combustion engine fueled with dimethyl ether. Energy Convers Manage 2004;45:2223–32.  Berioli C. Diesel combustion improvements by the use of oxygenated synthetic fuels, SAE Paper No. 972972; 1991.  Hood J. Emission from light duty vehicle operating on oxygenated fuels at low ambient temperature: a preview of published sendings, SAE Paper. No. 952403; 1995.  Wu JT, Liu ZG, Pan J, Zhao XM. Vapor pressure measurements of dimethyl ether from 233 to 399 K. J Chem Eng Data 2004;49:32–4.  Tseregounis SI, Riley MJ. Solubility of HFC-134a refrigerant in glycoltype compounds: effect of glycol structure. Environ Energy Eng 1994; 40:726–37.