An oxygenating additive for improving the performance and emission characteristics of marine diesel engines

Transcription

1 Ocean Engineering 30 (2003) An oxygenating additive for improving the performance and emission characteristics of marine diesel engines C.-Y. Lin, J.-C. Huang Department of Marine Engineering, National Taiwan Ocean University, Keelung 20224, Taiwan, ROC Received 5 June 2002; accepted 18 September 2002 Abstract Diesel engines provide the major power sources for marine transportation and contribute to the prosperity of the worldwide economy. However, the emissions from diesel engines also seriously threaten the environment and are considered one of the major sources of air pollution. The pollutants emitted from marine vessels are confirmed to cause the ecological environmental problems such as the ozone layer destruction, enhancement of the greenhouse effect, and acid rain, etc. Marine diesel engine emissions such as particulate matter and black smoke carry carcinogen components that significantly impact the health of human beings. Investigations on reducing pollutants, in particular particulate matter and nitrogen oxides are critical to human health, welfare and continued prosperity. The addition of an oxygenating agent into fuel oil is one of the possible approaches for reducing this problem because of the obvious fuel oil constituent influences on engine emission characteristics. Ethylene glycol monoacetate was found to be a promising candidate primarily due to its low poison and oxygen-rich composition properties. In this experimental study ethylene glycol monoacetate was mixed with diesel fuel in various proportions to prepare oxygenated diesel fuel. A four-cylinder diesel engine was used to test the engine performance and emission characteristics. The influences of ethylene glycol monoacetate ration to diesel oil, inlet air temperature and humidity parameters on the engine s speed and torque were considered. The experimental results show that an increase in the inlet air temperature caused an increase in brake specific fuel consumption (BSFC), carbon monoxide, carbon dioxide emission, and exhaust gas temperature, while decreasing the excess air, oxygen and nitrogen oxide emission concentrations. Increasing the inlet air humidity increased the carbon monoxide concentration while the decreased excess air, oxygen and nitrogen oxide emission concentrations. In addition, increasing ethylene glycol monoacetate ratio Corresponding author. Fax: address: lin7108@mail.ntou.edu.tw (C.-Y. Lin) /03/$ - see front matter 2003 Elsevier Science Ltd. All rights reserved. doi: /s (02)00149-x

2 1700 C.-Y. Lin, J.-C. Huang / Ocean Engineering 30 (2003) in the diesel fuel caused an increase in the BSFC while the excess air and oxygen emission concentrations decreased Elsevier Science Ltd. All rights reserved. Keywords: Marine diesel engine; Oxygenated diesel fuel; Engine performance; Emission characteristics 1. Introduction Diesel engines are a major and widely used power source for in-sea and on-land transportation vehicles due to their simple mechanism, excellent performance, easy maintenance, low fuel oil cost, low fuel consumption rate, low breakdown rate, high compression ratio, high power/weight ratio, high fuel oil density, high thermal efficiency and durability. Diesel engines are the most fuel-efficient combustion engines in human history. However, diesel engines are also considered a major source of air pollution in port and urban areas because of their black smoke, HC, NO x, particulate matter (PM), CO, CO 2,SO x emissions. The disgusting odor and noise from these engines may impair human health and the natural environment, such as ozone layer destruction, greenhouse effect enhancement and acid rain production (Lin and Pan, 2001; Lin, 2000; Linak and Wendt, 1993). While diesel engines are still the most common energy production equipment for ships, the air pollution threat caused by them cannot be neglected. The primary reason that the quantity of NO x pollutants emitted from diesel engines is greater than that from gasoline engines is the difference in the burning processes inside the cylinders. The higher compression-ignition temperature and compression ratio of diesel engines produce higher gas temperatures inside the combustion chamber and on the cylinder surface, leading to greater NO x formation based on the extended Zeldovich thermal NO mechanism (Ferguson and Kirkpatrick, 2001). The amount of particulate matter emission depends on the quality of the fuel oil and the completeness of burning in the combustion chambers. Particulate matter is generated from incomplete hydrocarbon burning when the fuel oil is injected into a cylinder and mixes with its surrounding air imperfectly. Particulate matter is generally composed of three compounds: (1) solid carbon particles produced from the burning process, particulate matter emitted from the diesel engines in the early burning stage consisting of 40 80% solid carbon particles; (2) soluble organic fractions (briefly termed as SOF), produced from the adsorption or condensation of hydrocarbons with heavy molecular weight onto the surface of the carbon particles. Most SOF come from unburned lubricant (about 40% of the total) and fuel oil (about 25% of the total); (3) sulfides, additives for fuel oil, etc. (Mayer et al., 1980). Hence, adequately controlling the burning process can effectively reduce the solid carbon particles and SOF, leading to a decrease in the exhausted particulate matter. In the case of sulfur oxides, the reaction between sulfur in the fuel oil and oxygen generates gaseous SO 2 and a few sulfide particles. Controlling the quantity of sulfur in the fuel oil is a valid approach to suppress the formation of sulfur oxides. PM 10 represents particles that have a mean diameter less than 10 µm. Small par-

3 C.-Y. Lin, J.-C. Huang / Ocean Engineering 30 (2003) ticulate like PM 10 is difficult for the respiratory organs to filter and thus becomes easily inhaled into the lungs of human beings. According to the report from the American Enviromental Protection Agency, there are about ten thousands chemical compositions adhering to the surface of PM 10, which were confirmed to cause mutation in a short-term medical test (Carel, 1998). Experiments conducted on animals showed that inhalation and deposition of particulate matter onto the lungs would lead to cancer. Particulate matter not only threatens to impair human health, but also causes destruction of the ecological enviroment. In comparison with spark-ignition engines, compression-ignition diesel engines emit more particulate matter which contains SOF ranging from 25 to 75 wt% (Jacobs and Westbrook, 1990). One of the SOF contents, polycyclic aromatic hydrocarbons (PAH) with smaller diameters derived from fuel oils and lubricants, is probably a carcinogen compound, especially PAH with two-ring and three-ring chemical structures. The use of an oxygenating agent with fuel oil to adjust the fuel constitution has been considered as one of possible approaches for improving the emission characteristics of diesel engines. After systematically evaluating some potential oxygenating agents for their physical properties, chemical characteristics, stability, availability, reliability, toxicity, cost and possibility of air-pollution improvement, ethylene glycol monoacetate, or called 1,2-ethanediol monoacetate, is considered a promising candidate. Its molecular formula is HOCH 2 CH 2 OOCCH 3,orC 4 H 8 O 3 and molecular weight is The ethylene glycol monoacetate is composed of C, H and O atoms. The specific gravity, flash point, boiling point of ethylene glycol monoacetate are 1.108, 101 and 181 C, respectively. This chemical agent may be produced either by heating ethylene glycol with acetic acid (glacial) or acetic anhydride or by passing ethylene oxide into hot acetic acid containing sodium acetate or sulfuric acid. This compound is generally used as a solvent for nitrocellulose, cellulose acetate, and camphor (Arthur and Elizabeth, 1973). The addition of ethylene glycol monoacetate into a fuel oil may enhance the fuel oxidation reaction, in particular in the high pressure reaction environment inside a diesel engine s cylinder. This occurs primarily because of the high oxygen content up to 46.1 wt%. This might result in a significant reduction in particulate matter, toxic gas and black smoke emissions. Moreover, ethylene glycol monoacetate contains a simple composition without the sulfur, sodium, and potassium metalic compounds, etc. This avoids the sulfur oxide or toxic metallic compound production that causes annoying air pollution during its combustion process. Ethylene glycol monoacetate exhibits twin emulsification polarities. The polarity property of the OH radical from C 4 H 8 O 3 makes it miscible with water and ethanol while the non-polarity of the CH 3 radical is miscible with benzene. The C 4 H 8 O 3 is a combustible, low poisonous, almost odorless liquid that could be used as an oxygenating additive for diesel oil without any modifications to the diesel engine (Arthur and Elizabeth, 1973). However, no studies have been done on the engine performance and emission characteristics using ethylene glycol monoacetate as an oxygenating fuel oil additive. Marine power plants are frequently operated under varying temperature and humidity. The temperature and humidity of the charged air could cause variations in engine emissions and performance. The International Organization of Standards

4 1702 C.-Y. Lin, J.-C. Huang / Ocean Engineering 30 (2003) (ISO) and British Standards (BS) thus proposed a modified formulae for engine brake power with inlet s air humidity and temperature (International Organization of Standards, 1987; British Standard, 1987). It is therefore of great interest to investigate the effects of using ethylene glycol monoacetate glycol as an oxygenating additive for diesel oil on the performance and emission characteristics of marine diesel engines under varying temperature and humidity of charged air in this experimental study. 2. Experimental details A four-cylinder arranged in-line, four-stroke, direct-injection, naturally air aspirated marine diesel engine (UMBDI model from the Isuzu Co. in Japan) was employed in this study. The maximum brake output, total displacement volume, compression ratio of this engine are 88 ps/2800 rpm, 3856 cc and 17, respectively. A water-cooled eddy current engine dynamometer (FE-150S model from the Borghi & Saveri Co. in Italy) was connected with the engine by a transmission shaft to vary the engine output torque and speed by adjusting the exciting current of its magnetic field. The maximum nomial horsepower of this dynamometer was 150 hp and the maximum torque measured was 28.3 kgf m. A computerized automatic testing and acquisition system was installed so that the speed, fuel oil feed throttle opening and output torque could be controlled and the burning gas temperature, pressure, rotations per minute data could be transported to this acquisition system. These data were displayed promptly on the monitor or stored by the computer. The humidity and temperature of the charged air were adjusted using an air conditioner before being admitted into the engine cylinder. A smoke meter (DSM-20A model from the Zexel Co. in Japan) was employed to measure the smoke opacity of the exhaust gas from the diesel engine based on the reflection from the light emitted from glassfiber filter. The particulate matter carried by the exhaust gas was collected using a sampling collector accompanied with a vacuum pump. The exhaust gas extracted flow rate was set at 16.7 l/min. The particulate matter with a droplet diameter less than 10 µm adhered onto the surface of a glassfiber filter used for the analyses of the particulate matter, opacity, composition, weight, etc. A gas analyzer was employed to measure the gaseous emission concentrations such as CO 2, CO, NO x,so 2 and O 2, combustion efficiency. The exhaust gas temperature was measured by a K-type thermocouple. The experimental setup is illustrated in Fig. 1. ASTM no. 2D diesel oil, a product of the Chinese Petroleum Co. in Taiwan served as the tested fuel for the diesel engine experimental study. The fuel properties analyzed using the fuel supplier are shown in Table 1. Ethylene glycol monoacetate of various proportions was mixed with ASTM no. 2D diesel oil. Good miscibility between these two compounds was observed and the ethylene glycol monoacetate mixed with ASTM no. 2D directly to prepare an oxygenating diesel fuel for this experiment. The properties of ethylene glycol monoacetate are shown in Table 2.

5 C.-Y. Lin, J.-C. Huang / Ocean Engineering 30 (2003) Fig. 1. Schematic of experimental apparatus. 3. Results and discussion This study explored the engine performance and exhaust gas characteristics of marine diesel engines using ethylene glycol monoacetate as a diesel fuel additive. The experimental results are described and discussed in the following sections Influences of ethylene glycol monoacetate/diesel oil ratios and engine speed As shown in Fig. 2, increasing the engine speed caused an increase in the brake specific fuel consumption (i.e. BSFC) because boosting the mean effective friction pressure (MEFP) at high engine speed reduced the engine mechanical efficiency. The ethylene glycol monoacetate additive is referred to EGM and the diesel oil is called D in this study. The legend D100 represents 100% diesel oil, while D95/EGM5 is 95% diesel oil mixed with 5% ethylene glycol monoacetate, and D90/EGM10 is 90% diesel oil mixed with 10% ethylene glycol monoacetate. Although the total fuel conversion efficiency increased with the increase in engine speed, the increase in MEFP played a more dominant role on the BSFC output, resulting in smoother BSFC curves. The greater the ethylene glycol monoacetate addition to the diesel fuel, the higher is the BSFC output. This result comes from the lower heating value of ethylene glycol monoacetate in comparison to diesel oil. The density of EGM at

6 1704 C.-Y. Lin, J.-C. Huang / Ocean Engineering 30 (2003) Table 1 Specifications of tested diesel oil Items ASTM no. 2D oil Units Cetane index 50.9 Kinematic viscosity at 40 C cst Density at 15 C kg/l Heating value 10,105 cal/g Carbon wt% Hydrogen wt% Sulfur 0.34 wt% Flash point 70 C Distillation temperature C (IBP) C (10 vol%) C (20 vol%) 257 C(50 vol%) C (90 vol%) C (95 vol%) C (end point) 97.9 Recovery, vol% 1.6 Residue, vol% Test report from Refining & Manufacturing Research Center, Chinese Petroleum Corporation, Taiwan, ROC, March Table 2 Properties of tested ethylene glycol monoacetate Item ASTM no. 2D oil Units Cetane index 0.1 Kinematic viscosity at 40 C 1.8 cst Density at 15 C kg/l Heating value 6188 cal/g Carbon 53.7 wt% Hydrogen 10.4 wt% Flash point 99 C Distillation temperature C (IBP) C (10 vol%) C (20 vol%) C (50 vol%) C (90 vol%) C (95 vol%) C (end point) 98.8 Recovery, vol% 0.7 Residue, vol% Test report from Refining & Manufacturing Research Center, Chinese Petroleum Corporation, Taiwan, ROC, March 2001.

7 C.-Y. Lin, J.-C. Huang / Ocean Engineering 30 (2003) Fig. 2. Effects of diesel oil/ethylene glycol monoacetate ratio and engine speed on BSFC at constant engine torque of 15 kgf m. Fig. 3. Effects of diesel oil/ethylene glycol monoacetate ratio and engine speed on excess air emission at constant engine speed of 15 kgf m.

8 1706 C.-Y. Lin, J.-C. Huang / Ocean Engineering 30 (2003) kg/l is larger than regular diesel oil s kg/l. Therefore, the greater the quantity of ethylene glycol monoacetate added into the fuel oil, the higher is the density of the fuel oil mixture, leading to an increase in the BSFC output. Fig. 3 illustrates the relationship between the engine speed and excess air concentration in the exhaust gas. When the engine speed increased from 800 to 1400 rpm, the fuel consumption rate per engine cycle remained stable, and the changes in BSFC were also small. Hence, the volumetric efficiency increased with the increase in the engine speed (Boretti et al., 1994), resulting in a rise in the quantity of excess air concentration with the engine speed. When the engine speed increased from 1400 to 2000 rpm, the quantity of excess air concentration tended to drop. This is because the increase in engine speed caused a slowdown in the changes in air flow rate and an increase of the BSFC, resulting in decreasing excess air quantity trend. Fig. 4 shows rather flat CO 2 curves primarily due to the fixed charged air per engine s cycle when the engine speed increased from 800 to 1200 rpm. While the engine speed increased from 1200 to 1400 rpm, the excess air quantity increased accordingly, as shown in Fig. 3. This diluted the exhaust gas, leading to a decreasing CO 2 concentration. When the engine speed increased from 1400 to 2000 rpm, the CO 2 concentration in the exhaust gas increased because the quantity of excess air dropped and the fuel consumption rate per engine cycle increased, as shown in the BSFC curve in Fig. 2. Fig. 5 reveals that when the engine speed increased from 800 to 1000 rpm, the NO x concentration increased, which attributed to the increase in injecting pressure Fig. 4. Effects of diesel oil/ethylene glycol monoacetate ratio and engine speed on CO 2 emission at constant engine torque of 15 kgf m.

9 C.-Y. Lin, J.-C. Huang / Ocean Engineering 30 (2003) Fig. 5. Effects of diesel oil/ethylene glycol monoacetate ratio and engine speed on NO x emission at constant engine torque of 15 kgf m. Fig. 6. Effects of diesel oil/ethylene glycol monoacetate ratio and engine speed on CO emission at constant engine torque of 15 kgf m.

10 1708 C.-Y. Lin, J.-C. Huang / Ocean Engineering 30 (2003) Fig. 7. Effects of diesel oil/ethylene glycol monoacetate ratio and engine speed on exhaust gas temperature at constant engine torque of 15 kgf m. Fig. 8. Effects of diesel oil/ethylene glycol monoacetate ratio and engine torque on BSFC at constant engine speed, inlet air temperature, and humidity at 1500 rpm, 28 C, and RH 80%, respectively.

11 C.-Y. Lin, J.-C. Huang / Ocean Engineering 30 (2003) Fig. 9. Effects of diesel oil/ethylene glycol monoacetate ratio and engine torque on excess air at constant engine speed, inlet air temperature, and humidity at 1500 rpm, 28 C, and RH 80%, respectively. Fig. 10. Effects of diesel oil/ethylene glycol monoacetate ratio and engine torque on CO emission at constant engine speed, inlet air temperature, and humidity at 1500 rpm, 28 C, and RH 80%, respectively.

12 1710 C.-Y. Lin, J.-C. Huang / Ocean Engineering 30 (2003) and lower heat loss, resulting in higher peak flame temperature during the compression stroke (Aoyagi et al., 1980). When the engine speed increased from 1000 to 2000 rpm, the burn time for the reactant mixture was shortened due to the increase in engine speed. Since the fuel oil was mixed with a larger quantity of excess air, the equivalent ratio of the fuel mixture decreased. Exhaust gas dilution by the excess air is another cause for the decrease in NO x. When the engine speed increased from 1400 to 2000 rpm, a larger ratio of ethylene glycol monoacetate mixed into the fuel oil, which produced the lower NO x emissions. This is because ethylene glycol monoacetate is an oxygen-rich fuel. When the oxygen content in the fuel oil increases, the ignition delay is shortened. The amount of premixed fuel and peak burning temperature were lowered, leading to the drop in NO x emissions. Fig. 6 displays the increasing trend for the CO concentration when the engine speed increased from 800 to 1400 rpm. The increase in engine speed shortens the oxidization time for the CO gas so that the CO 2 concentration oxidized from CO was reduced. As a result, the CO concentration increased. However, when the engine speed was increased from 1400 to 1800 rpm, probably caused by the increase in gas temperature during the late gas expansion period, the CO to CO 2 oxidation reaction accelerated which reduced the CO concentration. When the engine speed was further increased from 1800 to 2000 rpm, the shortening of oxidization time led to an acute increase in CO formation. The greater ethylene glycol monoacetate proportion in the fuel mixture caused a decrease in the CO concentration because of the low ethylene Fig. 11. Effects of diesel oil/ethylene glycol monoacetate ratio and engine torque on exhaust gas temperature at constant engine speed, inlet air temperature, and humidity at 1500 rpm, 28 C, and RH 80%, respectively.

13 C.-Y. Lin, J.-C. Huang / Ocean Engineering 30 (2003) glycol monoaetate cetane number, which extended the ignition delay period. The amount of fuel oil in the premixed burn period thus increased, leading to an increase in the burning gas temperature in the cylinders and a reduction in the equivalent ratio of the fuel oil mixture. The CO concentration was therefore decreased. Fig. 7 demonstrates that the faster the engine speed, the higher is the exhaust gas temperature. This is because the engine speed increase was accompanied with an increase in the fuel oil consumption rate. Conversely, because of the lower heating value of ethylene glycol monoacetate, the increase in the ethylene glycol monoacetate proportion in the fuel oil reduced the exhaust gas temperature Influences of the ethylene glycol monoacetate/diesel oil ratios and engine torques In this set of experiments, the inlet air temperature, humidity, and engine speed were fixed at 28 C, RH 80%, and 1500 rpm, respectively, while the engine torque and the ethylene glycol monoacetate/diesel oil (EGM/D) ratio were varied to measure and observe the engine performance and emission characteristics. As illustrated in Fig. 8, brake torque is an efficient measurement of engine performance. A larger brake torque leads to larger engine power output and lower BSFC. However, the trend toward the decrease in BSFC slowed down as the brake torque increased. This is because the increase in brake torque enhanced the net indicated horsepower and the mechanical efficiency of the engine at nearly constant horse- Fig. 12. Effects of humidity of inlet air and engine torque on excess air at constant engine speed, inlet air temperature, and diesel oil/ethylene glycol monoacetate ratio at 1500 rpm, 28 C, and 10:90, respectively.

14 1712 C.-Y. Lin, J.-C. Huang / Ocean Engineering 30 (2003) power of friction. In addition, a larger EGM/D ratio caused an increase in BSFC primarily because of the lower ethylene glycol monoacetate heating value in comparison with regular diesel oil. The larger density of EGM produced a greater density in the fuel oil mixture and thus a larger fuel mass flow rate. Larger BSFC appeared when the EGM/D ratio was increased. Fig. 9 shows that the fuel mass flow rate increased with increasing engine brake torque, leading to larger concentration of vaporized fuel oil in the combustion chamber and thus a lower air/fuel ratio. The excess air concentration in the exhaust gas was therefore decreased. Fig. 10 exhibits that the CO emission increased as the brake torques increased from 0 to 6 kgf m. This probably comes from the insufficient mixing time between the fuel oil and surrounding air, thereafter resulting in incomplete burning in this range of brake torque. When the brake torque was increased from 6 to 12 kgf m, the higher burning gas temperature expedited the CO to CO 2 oxidation rate. Lower CO emissions thus appeared. Fig. 11 shows that the exhaust gas temperature increased with the increase in brake torque. Higher burning gas temperature accelerated the CO to CO 2 oxidation rate and therefore lower CO emissions are observed in Fig Influences of inlet air temperature humidity and engine torque The brake torque and inlet air humidity were varied while the inlet air temperature, EGM/D ratio and engine speed were set at constant 28 C, 10:90 and 1500 rpm, Fig. 13. Effects of humidity of inlet air and engine torque on NO x emission at constant engine speed, inlet air temperature, and diesel oil/ethylene glycol monoacetate ratio at 1500 rpm, 28 C, and 10:90, respectively.

15 C.-Y. Lin, J.-C. Huang / Ocean Engineering 30 (2003) respectively, to observe and measure the engine performance and emission characteristics in this set of experiments. Fig. 12 illustrates that the increase in inlet air humidity caused a decrease in the excess air emissions. This is because higher inlet air humidity reduces the mass flow rate of the dry inlet air inside the gas cylinder. The excess air in the exhaust gas is thus reduced. Fig. 13 shows that the higher the relative humidity of the inlet air, the lower are the NO x emissions. This is inferred from the increase in inlet air humidity, which causes an increase in the air/fuel equivalence ratio. This condition leads to lean fuel oil combustion. Moreover, the increase in inlet air humidity causes an increase in the water vapor mass, which absorbs a greater amount of thermal energy from the burning gas in the cylinder. This action lowers the enthalpy-releasing combustion rate, resulting in a decrease in NO x emissions. Fig. 14 shows that the increase in the inlet air humidity causes a significant increase in the CO emissions. Larger CO emissions imply a less complete fuel burning, and thus formation of unburned hydrocarbons in the combustion system. Inlet air with greater humidity contains more moisture in the reactant, which absorbs a greater proportion of the reaction heat for latent water heat vaporization. The burning gas temperature was therefore reduced. It followed that the CO emissions increased with the increase in the relative humidity of the inlet air, as shown in Fig. 14. Fig. 15 shows that the increase of the brake torque caused an increase in the exhaust gas temperature. This is attributed to the Fig. 14. Effects of humidity of inlet air and engine torque on CO emission at constant engine speed, inlet air temperature, and diesel oil/ethylene glycol monoacetate ratio at 1500 rpm, 28 C, and 10:90, respectively.

16 1714 C.-Y. Lin, J.-C. Huang / Ocean Engineering 30 (2003) Fig. 15. Effects of humidity of inlet air and engine torque on exhaust gas temperature at constant engine speed, inlet air temperature, and diesel oil/ethylene glycol monoacetate ratio at 1500 rpm, 28 C, and 10:90, respectively. larger brake torque requiring a larger fuel flow rate, which therefore enhanced the exhaust gas temperature. 4. Conclusions The influences of inlet air temperature and humidity, engine speed, brake torque, and the proportion of ethylene glycol monoacetate added to fuel oil on engine performance and emission characteristics in marine diesel engines were investigated in this experimental study. The experimental results are described as follows: 1. The increase in inlet air temperature caused an increase in BSFC, CO 2, CO and exhaust gas temperature. A decrease in excess air and NO x emissions resulted from increased inlet air temperature. 2. The increase in inlet air humidity caused an increase in CO emissions, and a decrease in excess air and NO x emissions. 3. The increase in engine speed caused an increase in BSFC, with first an increase and later a decrease in excess air and CO emissions. 4. The increase in engine brake torque caused an increase in CO 2,NO x emissions, and exhaust gas temperature, with reduced BSFC and excess air emissions. 5. Ethylene glycol monoacetate addition into the diesel oil caused an increase in

17 C.-Y. Lin, J.-C. Huang / Ocean Engineering 30 (2003) BSFC, with lowered exhaust gas temperature and excess air, NO x, CO and CO 2 emissions. Acknowledgements The National Science Council, ROC under project No. NSC E provided financial support for this study. Their support is gratefully acknowledged. References Aoyagi, Y., Kamimoto, T., Matsui, Y., Matsuoka, K., A gas sampling study on the formation processes of soot and NO in a DI diesel engine. SAE paper , SAE Trans. 89. Arthur, R., Elizabeth, R., In: The Condensed Chemical Dictionary, seventh ed. Van Nostrand Reinhold Co., New York, USA, 393. Boretti, A., Borghi, M., Cantore, G., Numerical studies of volumetric efficiencies in a high speed, four valve, four cylinder spark ignition engine. SAE paper British Standard, Reciprocating internal combustion engines performance. BS 5514: part 1. Carel, R.S., Health aspects of air pollution. In: Sher, E. (Ed.), Handbook of Air Pollution from Internal Combustion Engines. Academic Press, New York, USA, pp Ferguson, C.R., Kirkpatrick, A.T., In: Internal Combustion Engines, second ed. Wiley, Singapore, pp International Organization Standards, Reciprocating Internal Combustion Engines: Performance, ISO, Jacobs, R.J., Westbrook, K., Aspects of influencing oil consumption in diesel engines for low emissions. SAE paper Lin, C.Y., Pan, J.Y., The effects of sodium sulfate on the emissions characteristics of an emulsified marine diesel oil-fired furnace. Ocean Eng. 28 (4), Lin, C.Y., Influences of vanadium compound on burning characteristics of emulsified fuel oil C. Ocean Eng. 27 (6), Linak, W.P., Wendt, J.O.L., Toxic metal emissions from incineration: mechanism and control. Prog. Energy Combust. Sci. 19, Mayer, W.J., Lechman, D.C., Hilden, D.L., The contribution of engine oil to diesel exhaust particulate emissions. SAE paper , SAE Trans. 89.