Performance and Emissions of Direct Injection Diesel Engine Fueled

504

Energy & Fuels 2006, 20, 504-511

Performance and Emissions of Direct Injection Diesel Engine Fueled with Diesel Fuel Containing Dissolved Methane Junqiang Zhang,* Deming Jiang, Zuohua Huang, Xibin Wang, and Qi Wei State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong UniVersity, Xi’an 710049, People’s Republic of China ReceiVed July 11, 2005. ReVised Manuscript ReceiVed December 7, 2005

Four blended fuels were prepared by dissolving methane into diesel fuel under different pressures to form different dissolved methane concentrations. The dissolved methane concentrations were 0, 10.1, 16.1, and 23.8 milliliters of methane per milliliter of diesel fuel (mL/mL) at standard ambient temperature of 273.16 K and pressure of 101.325 kPa, respectively. The influences of the dissolved methane in diesel fuel on engine performance and emissions were examined in a single cylinder direct injection (DI) diesel engine. The study shows that there exists both a positive and a negative influence on the brake specific fuel consumption (BSFC) and the effective thermal efficiency depending on the methane concentration in diesel fuel. The blended fuel of diesel/methane with a methane concentration of 10.1 mL/mL gives the higher BSFC and the lower effective thermal efficiency than those of pure diesel fuel, but the blended fuels with methane concentrations of 16.1 and 23.8 mL/mL show the lower BSFC and the higher effective thermal efficiency as compared with those of pure diesel fuel. The ignition delay of the diesel fuel containing dissolved methane is larger than that of pure diesel fuel, and the value increased with the increase of methane concentration. However, the maximum heat release rate decreases with the increase of methane concentration. The diesel fuels containing dissolved methane produce less NOx emissions as compared with that of pure diesel fuel, while the influences of the dissolved methane on smoke depend on the methane concentration. For the blended fuels with methane concentrations of 16.1 and 23.8 mL/mL, the smoke emission presents a decrease. At an appropriate methane concentration, both NOx and smoke emissions decrease simultaneously. The hydrocarbon emission of diesel fuel containing dissolved methane is larger than that of pure diesel fuel, and the dissolved methane has little influence on carbon monoxide emission.

Introduction Energy crisis and environmental pollution are two major global problems. Because of its high thermal efficiency, diesel engines have been widely used as power systems for various mobile or stationary equipments, such as automobiles, tractors, and generators. However, diesel engines consume a large amount of fuel and produce a great amount of various emissions, such as nitrogen oxides (NOx), carbon monoxide (CO), hydrocarbons (HC), particulate matter (PM), and other harmful compounds. With the increasing concern about environmental protection and the implementation of more stringent exhaust gas regulations as well as the further demand for energy sources, many efforts in the engine field concentrate on the improvement of thermal efficiency and the reduction of emissions. Various alternative fuels and methods have been employed to solve the problems, for example, water-emulsified fuel,1 flash boiling injection,2,3 blended fuels,4 and dual fuel engines.5 Of these methods, the flashing injection produced by dissolving gas into liquid fuel has been studied for many years; its aim is to improve * Corresponding author. Tel.: +86-2982663421; fax: +86-2982668789; e-mail: [email protected]. (1) Armasa, O.; Ballesterosa, R.; Martosb, F. J.; Agudelo, J. R. Characterization of Light Duty Diesel Engine Pollutant Emissions Using Water-Emulsified Fuel, Fuel 2005, 84, 1011-1018. (2) Oza, R. D.; Sinnamon, J. F. An Experimental and Analytical Study of Flash boiling Fuel Injection. SAE Paper, 830590, SAE Inc.: USA, 1983. (3) Park, B. S.; Lee, S. Y. An Experimental Investigation of the Flash Atomization Mechanism, Atomization Sprays 1994, 4 (2), 159-179. (4) Huang, Z. H.; Lu, H. B.; Jiang, D. M.; Zeng, K.; Liu, B.; Zhang, J. Q.; Wang, X. B. Combustion Behaviors of a Combustion-Ignition Engine Fueled with Diesel/Methanol Blends under Various Delivery Advance Angles, Bioresour. Technol. 2004, 95, 331-341.

the atomization and combustion of liquid jets and decrease emissions. Solomon et al.6 studied the effect of air dissolved in liquid fuels on the spray characteristics and the combustion flame of liquid fuels containing dissolved air under atmospheric conditions. Senda et al.,7,8 Huang et al.,9,10 Kawa et al.,11 and Shiga et al.12 investigated the phase transition of liquefied CO2 dissolved in diesel fuel to initiate flash boiling and improve (5) Papagiannakis, R.G.; Hountalas, D. T. Combustion and Exhaust Emission Characteristics of a Dual Fuel Compression Ignition Engine Operated with Pilot Diesel Fuel and Natural Gas, Energy ConVersion Management 2004, 45, 2971-2987. (6) Solomon, A. S. P.; Chen, L. D.; Faeth, G. M. InVestigation of Spray Characteristics for Flashing Injection of Fuels Containing DissolVed Air and Superheated Fuels. NASA Contractor Report, 3563; NASA: USA, 1982. (7) Senda, J.; Ikeda, M.; Yamamoto, M.; Kawaguchi, B.; Fujimoto, H. Low Emission Diesel Combustion System by Use of Reformulated Fuel with Liquefied CO2 and n-Tridecane. SAE Paper, 1999-01-1136, SAE Inc.: USA, 1999. (8) Senda, J.; Hashimoto, K.; Ifuku, Y.; Fujimoto, H. CO2 Mixed Fuel Combustion System for Reduction of NO and Soot Emission in Diesel Engine. SAE paper 970319, SAE Inc.: USA, 1997. (9) Huang, Z.; Shao, Y. M.; Shiga, S. Atomization Behavior of Fuel Containing Dissolved Gas, Atomization Sprays 1994, 4 (3), 253-262. (10) Huang, Z.; Shao, Y. M.; Shiga, S. The Orifice Flow Pattern, Pressure Characteristics, and Their Effects on the Atomization of Fuel Containing Dissolved Gas, Atomization Sprays 1994, 4 (2), 123-133. (11) Kawa, B.; Senda, J.; Fujimoto, H. Analysis of Vaporization Process in Liquefied CO2 Mixed Fuel by Use of Flash Spray Model (in Japanese). The 7th symposium (ILASS-Japan) on Atomization: Gunma, 1998; pp 337-342. (12) Shiga, S.; Kichikawa, Y.; Nakamura, H.; Ishima, T.; Obokata, T. Effect of CO2 Dissolution on the Spray Characteristics of Biomass Fuel (in Japanese). The 10th symposium (ILASS-Japan) on Atomization: Gunma, Japan 2001; pp 131-134.

10.1021/ef0502094 CCC: $33.50 © 2006 American Chemical Society Published on Web 01/19/2006

Performance and Emissions of Diesel Engine

Energy & Fuels, Vol. 20, No. 2, 2006 505

Figure 1. Schematic layout of the test setup.

atomization of diesel fuel. These studies showed that for promoting liquid atomization, the concentration of dissolved CO2 in liquid fuel should be above a certain value. Gemci et al.13 also examined the flashing atomization of a hydrocarbon solution containing n-hexadecane and n-butane. The study suggested that, under appropriate conditions, the presence of a small amount of n-butane can significantly enhance the atomization of n-hexadecane. Recently, Zhang et al.14,15 conducted research on the spray characteristics of liquid fuels containing dissolved methane, and their studies revealed that the dissolved methane can improve spray atomization under certain conditions. Most of the research mentioned previously concentrated on spray characteristics, whereas little information on combustion and emissions characteristics was presented. Senda et al.7,8 performed the experiments on the combustion and emission characteristics of diesel fuel containing CO2 in a rapid compression and expansion machine. No other reports can be found about the combustion and emission characteristics of diesel engine fueled with liquid fuel containing dissolved gas. On the basis of this consideration, an experimental study on the performance and emissions of a compression ignition engine fueled with diesel fuel containing dissolved methane was conducted. It was expected to improve the spray atomization and combustion by binary fuel, and the emissions would be reduced by methane combustion. The flashing atomization due to methane dissolution helps to form good quality mixtures of air and fuel and improve the combustion. In addition, for mixtures of diesel/methane and air in a combustion chamber, the diesel fuel burns first due to its low autoignition temperature (523 K). Its reaction products including soot will be further oxidated through late methane combustion (the autoignition temperature of methane is 923 K). As a result, the emission of soot will be reduced. In this study, the comparisons on engine combustion and emissions were performed between neat diesel fuel and diesel fuel containing dissolved methane. The results show a great influence on engine performance from the dissolved methane in diesel fuel. (13) Gemci, T.; Yakut, K.; Chigier, N.; Ho, T. C. Experimental Study of Flash Atomization of Binary Hydrocarbon Liquids, Int. J. Multiphase Flow 2004, 30, 395-417. (14) Zhang, J.; Jiang, D.; Obokata, T.; Shiga, S.; Araki, M. Experimental Study on Flashing Atomization of Methane/Liquid Fuel Binary Mixtures, Energy and Fuels 2005, 19, 2050-2055. (15) Zhang, J.; Jiang, D.; Huang, Z.; Obokata, T.; Shiga, S. An Experimental Study on Steady Spray Characteristics of Diesel Fuels Containing Dissolved CH4, Trans. CSICE 2005, 23, 10-17.

Table 1. Engine Specifications type Bore Stroke Displacement length of connecting rod shape of combustion chamber compression ratio rated power/speed diameter of nozzle holes number of nozzle holes opening pressure of nozzle diameter of pump plunger static fuel delivery advance angle inlet valve opening inlet valve closure exhaust valve opening exhaust valve closure

TY1100 100 mm 115 mm 903 cm3 190 mm ω type 18 11 kW/2300 rpm 0.3 mm 4 18.6 MPa 8.5 mm 25 CA BTDC 11 CA BTDC 49 CA ABDC 52 CA BBDC 8 CA ATDC

Experimental Setup and Test Conditions A schematic layout of the test setup is shown in Figure 1. The setup consisted of two sections. One was used to measure methane concentration and the other for the engine experiment. The engine used was a single cylinder, naturally aspirated, four stroke, watercooled DI diesel engine with a ω type combustion chamber on the top of piston. The specifications of the test engine are listed in Table 1. For the fuel injection, a high-pressure fuel pump with a plunger diameter of 8.5 mm was used. The nozzle had four orifices with diameters of 0.3 mm and an opening pressure of 18.6 MPa. Diesel fuel and methane were mixed in a high-pressure vessel, as shown in Figure 1, and this vessel also supplied fuels toward the diesel engine. Before performing the engine experiment, the concentration (C) of dissolved methane in diesel fuel was measured first and defined as C)

Vmethane (mL/mL) Vfuel

where Vmethane was the volume of dissolved methane under standard ambient conditions (273.16 K, 101.325 KPa) and Vfuel was the volume of diesel fuel in which the methane was dissolved. According to Henry’s law, the solubility of methane in diesel fuel increases with the increase of dissolving pressure, so the concentration can be controlled by the dissolving pressure. In this study, four blended fuels with methane concentrations of 0, 10.1, 16.1, and 23.8 mL/mL were designed, which had the dissolving pressures of 0.1, 2.5, 4, and 6 MPa, respectively, and for convenience, they are denoted as fuel 0, fuel 1, fuel 2, and fuel 3, respectively. Enough time was needed for achieving a uniform and saturated mixture of

506 Energy & Fuels, Vol. 20, No. 2, 2006

Zhang et al.

Table 2. Properties of Diesel Fuel and Methane properties

diesel

methane

chemical formula molecular weight (g) density (g/cm3) low heating value (MJ/kg) heat of evaporation (kJ/kg) autoignition temperature (K) cetane number stoichiometric ratio of air to fuel composition (wt %) C H O

CxHy 190-220 0.831 44 260 523 45 14.6

50 509.6 923 very low 17.27

86 14 0

75 25 0

CH4 16.04

Table 3. Properties of Diesel Fuel and Diesel/Methane Blends properties

fuel 0 fuel 1 fuel 2 fuel 3

dissolving pressure (MPa) methane concentration by volume (mL/mL) methane concentration by weight (g/g) lower heat value (MJ/kg)

0 0 0 44

2.5 4 6 10.1 16.1 23.8 0.87 1.30 2.05 44.05 44.08 44.12

diesel fuel and methane. The diesel fuel containing dissolved methane was then supplied to the diesel engine under the saturated pressure of blended fuel. The properties of diesel fuel and methane are listed in Table 2, and the properties of binary fuels are listed in Table 3. Methane concentrations in blended fuels by weight are also taken into account for the evaluation of fuel consumption. From Table 3, it can be seen that the low heat values (LHV) of blended fuels increase slightly with the increase of methane concentration due to a little methane content in diesel fuel. Thus, the influence of dissolved methane on engine performance will mainly depend on the methane properties (low cetane number, higher specific heat than air, etc.) as well as the effect of dissolved methane on fuel atomization. In this experiment, the combustion and emission characteristics were measured and analyzed for the designed fuels mentioned previously. Operating variables were the brake mean effective pressure (BMEP) and engine speed (n). The comparison of results was made for clarifying the effect of dissolved methane on engine performance. A 4/5-gas analyzer, AVL DiGas 4000, was used to measure the exhaust gas and an opacity smoke meter, AVL DiSmoke 4000, was used to measure the smoke level. Cylinder pressure (p) was recorded by a Kistler piezoelectric transducer with a resolution of 10 Pa. The crankshaft angle (φ) signal was obtained from a crank angle encoder made by Kistler mounted on the front end of the crankshaft. The top-dead-center (TDC) determination was carried out in motored engine mode by a TDC sensor based on a capacitive measurement between the piston and the sensor head. For determining the ignition delay, the needle valve lift was also measured using a needle valve lift instrument. The signal of cylinder pressure was acquired for every 0.1 CA, the acquisition duration covered 100 completed cycles, and the pressure data were used to calculate the combustion parameters. An AVL Indimeter 619 combustion analyzer was used to record the measured data.

Results and Discussions Brake Specific Fuel Consumption and Effective Thermal Efficiency. From Table 3, it can be seen that the LHV of blended fuels are a little greater than that of pure diesel fuel and that they increase with the increase of the methane concentration in diesel fuel. To evaluate the result reasonably, fuel consumption is reflected with diesel equivalent BSFC (beq), which means that the BSFC of the blended fuels measured by weight will be converted into the BSFC of pure diesel fuel according to the same LHV. The beq is calculated as follows:

beq ) be,diesel +

be,methaneHu,methane Hu,diesel

Figure 2. Variation of equivalent brake specific fuel consumption vs brake mean effective pressure: panels a and b.

where be,diesel and be,methane are the contents of diesel fuel and methane, respectively, within the blended fuel’s BSFC and Hu,diesel and Hu,methane are the LHV of diesel fuel and methane, respectively. Figure 2 shows the variation of the diesel equivalent BSFC versus brake mean effective pressure (BMEP) for the four designed fuels at engine speeds of 1800 and 2000 rpm and a fuel delivery advance angle (θfd) of 25 CA BTDC. The figures show that the diesel equivalent BSFC of fuel 1 is larger than that of fuel 0 (pure diesel fuel) over the whole range of BMEP. Two reasons are responsible for the result. One may be due to the influence of low methane concentration in diesel fuel, which leads to the suppressed atomization characteristics (including SMD and spray angle),14,15 and the other is attributed to the higher ambient pressure in the cylinder, which suppresses the separation of dissolved methane and consequently brings poor atomization. These two reasons will make a negative influence on the combustion and result in a high diesel equivalent BSFC. For fuels 2 and 3, the diesel equivalent BSFC decreases as compared with that of fuel 1 and reaches almost the same value of fuel 0 in the case of the high load (high BMEP value); at a low load (low BMEP value), the diesel equivalent BSFC gives a lower value than that of fuel 0, and it decreases with the increase of methane concentration. This may be due to the increase of methane concentration where the fuel atomization will be improved at high ambient temperature in the cylinder by overcoming the diesel fuel surface tension and



where Cp and Cv are temperature-dependent parameters, V is the cylinder volume, m is the mass of cylinder gases, T is the mean gas temperature, and R is the gas constant. dQw/dφ is the heat transfer rate, which is given by

dQw ) hcA(T - Tw) dφ

Figure 3. Variation of effective thermal efficiency vs brake mean effective pressure: panels a and b.

high ambient pressure. The results show that the dissolved methane in diesel fuel has a different influence on fuel consumption of diesel engine depending on the methane concentration. For reducing the diesel equivalent BSFC, a high concentration of dissolved methane in diesel fuel is required. The effective thermal efficiency (ηe) of blended fuels can be calculated by the following formula:

ηe )

3.6 × 106 Hu,dieselbeq

This formula indicates that the thermal efficiency is inversely proportional to the diesel equivalent BSFC. The effective thermal efficiencies for four kinds of fuels are illustrated in Figure 3 as the function of BMEP. It can be seen that fuel 1 gives the lower thermal efficiency than that of pure diesel fuel over the whole range of loads, while fuels 2 and 3 give the higher thermal efficiencies than those of pure diesel fuel. Heat Release Rate. The combustion parameters are calculated by applying the first thermodynamic law in this paper. The model neglects leakage through the piston rings, and the cylinder charge is considered to behave as an ideal gas, so the heat release rate (dQb/dφ) is expressed as follows:

Cp dV CVV dp dCV dQw dQb )p + + mT + dφ R dφ R dφ dφ dφ

where A is the wall area, Tw is the wall temperature, and hc is the heat transfer coefficient given by Woschni. The formulas of Cp, Cv, and hc are given in ref 16. Using the previous formulas and the data of cylinder pressure, some combustion related characteristics can be calculated. The heat release rates at a fuel delivery advance angle of 25 CA BTDC were calculated for four blended fuels under different experimental conditions, and the results are shown in Figure 4. As is shown in the heat release curves, the combustion starting positions of fuels containing dissolved methane are postponed as compared with that of pure diesel fuel, and the phenomena are more obvious in the case of the low load. The greater the value of the methane concentration, the later the combustion starting position. Diesel fuel containing dissolved methane has a longer ignition delay as compared with that of pure diesel fuel, and the ignition delay increases with the increase of dissolved methane concentration. Previous papers gave similar results obtained from a dual fuel engine fueled with CNG and piloted ignition by injecting diesel fuel into the cylinder.17,18 They suggested that the ignition delay of the pilot diesel fuel becomes longer due to the presence of CNG and that the concentration of CNG in the gas in the cylinder influences the ignition delay. In the present study, the dissolved methane comes out of the blended fuels and forms similar ambient conditions around the diesel fuel spray; thus, the same interpretation can be employed for the blended fuel combustion. As known, the dissociation energy of the C-H bond in CH4 is much higher than that of C-C bond in heavier hydrocarbons and also is greater than the C-H bond dissociation energy in long-chain hydrocarbons. For these reasons, it is more difficult to ignite CH4 than other hydrocarbons. The cetane number of methane is therefore lower than those of other hydrocarbons, and this will increase the ignition delay of diesel fuel containing dissolved methane. In addition, the specific heat capacity of methane is large due to its five-atom molecule. Figure 5 shows the value of constant pressure specific heat capacity (Cp) of air, carbon dioxide, and methane versus temperature. Therefore, after being injected into the cylinder along with diesel fuel, the dissolved methane absorbs more heat to raise its temperature and leads to low temperatures in the cylinder and its consequently long ignition delay. It should be noted that, as is different with the dual fuel engines, the injected dissolved methane will absorb the heat around the spray to form and grow the bubbles and lead to the decrease in ambient temperature, and consequently, there is a further increase in ignition delay. Such an influence on ignition delay is enhanced with the increase of the dissolved methane concentration. Figure 4 also shows that, for all experimental conditions, the maximum heat release rate decreases with the increase of methane concentration. This decreases the cylinder peak pressure (16) Heywood, J. B. Internal Combustion Engine Fundamentals; McGrawHill: New York, 1988. (17) Nielsen, O. B.; Qvale, B.; Sorenson, S. Ignition Delay in the Dual Fuel Engine. SAE paper, 870598, SAE Inc.: USA, 1987. (18) Liu, Z.; Kraim, G. A. The Ignition Delay Period in Duel Fuel Engines. SAE paper, 950466, SAE Inc.: USA, 1995.


Zhang et al.

Figure 4. Influence of dissolved methane on heat release rate: panels a-f.

and peak temperature and may be the main reason for low NOx emission of diesel fuel containing dissolved methane (see Figure 6). The long ignition delay indicates that more fuel exists in the premixed combustion period. The low maximum heat release rate, however, means that less combustible mixture is formed in the ignition delay period. These results reveal that a high methane concentration will produce a smaller fraction of premixed combustion mixture within the ignition delay period. Meanwhile, the presence of separated methane will suppress the premixed combustion due to the removal of air around the spray.

NOx Emission. The variation of NOx emission versus the methane concentration for four blended fuels is shown in Figure 6. It can be seen that the NOx emission decreases with the increase of the methane concentration in diesel fuel when the methane concentration is less than 16.1 mL/mL and then keeps the almost same value or increases slightly with a further increase in the methane concentration. The NOx emission gives its lowest value at certain methane concentrations. The variation is not marked for those low load conditions, and this is attributed to little total amount of the NOx emission. As was demonstrated previously, the maximum value of the heat release rate of diesel



Figure 5. Comparison of constant pressure specific heat capacity.

Figure 7. Effect of methane concentration on smoke: panels a and b.

Figure 6. Variation of NOx emission with methane concentration: panels a and b.

fuel containing dissolved methane decreases with the increase of methane concentration, and this leads to the low gas temperature in the cylinder and finally reduces the NOx emission. However, the further increase of the methane concentration makes a large spray angle and spray volume and improves spray atomization, and this decreases the fraction of the rich mixture zone and increases the fraction of the mixture near the stoichiometric equivalence ratio; thus, more fuel burns at the

equivalence ratios where NOx produces more. Therefore, we can conclude that temperature play a key role in NOx reduction at small methane concentrations, while the equivalence ratio of the mixture plays a key role in NOx reduction at large methane concentrations. Smoke Emission. In this study, smoke was measured for four blended fuels under different BMEP and two engine speeds. All measurements were conducted at a fuel delivery advance angle of 25 CA BTDC. The smoke was expressed by opacity. Figure 7 gives the variation of opacity versus the methane concentration. For same BMEP, the opacities of the fuels containing dissolved methane decrease as compared with those of pure diesel fuel except fuel 1, whose opacities were greater than those of pure diesel fuel at a few operation conditions. The decrease in smoke value may be due to the combustion of separated methane and the improvement of spray atomization. Dec19 advanced a new conceptual model of direct injection diesel combustion. He suggested that the soot formed in the early period of combustion rather than in the diffusion combustion period and first appeared just downstream of the liquidfuel region, eventually being oxidized at the diffusion flame. In the present study, the separated methane from blended fuels burns later due to its high autoignition temperature and this improves the oxidization of soot formed in the early period of (19) Dec, J. E. A Conceptual Model of DI Diesel Combustion Based on Laser-Sheet Imaging. SAE Paper, 970873, SAE Inc.: USA, 1997.


Figure 8. Hydrocarbon emission vs BMEP and methane concentration: panels a and b.

combustion, finally leading to the low soot emission. In addition, with the increase of methane concentration, the spray angle and spray volume increase, and this decreases the fraction of the rich mixture zone. As smoke is strongly related to the rich mixture in spray, the improvement of spray atomization in the presence of dissolved methane makes the combustion at a relative lean mixture environment and produces less smoke. For fuel 1, the suppressed atomization due to low methane concentration14,15 and a little separated methane is responsible for the increase in opacity at a few experimental conditions. HC and CO Emissions. The variation of hydrocarbon emissions versus BMEP for different blended fuels is shown in Figure 8 at two engine speeds and fuel delivery advance angle of 25 CA BTDC. It can be seen that all fuels containing dissolved methane produce high values of hydrocarbon emissions as compared with those of pure diesel fuel. This is due to the unburned methane separated from the blended fuels. In addition, a large spray volume will also increase the fraction of the over-lean mixture as compared with the small spray volume, which produces more unburned hydrocarbons. All these make the increase of hydrocarbon emissions for diesel fuel containing dissolved methane. Figure 9 shows the effect of dissolved methane on carbon monoxide. No remarkable variation among different fuels is observed. It means that the dissolved methane has little influence on carbon monoxide emission.

Zhang et al.

Figure 9. Carbon monoxide emission vs BMEP and methane concentration: panels a and b.

Conclusions On the basis of the analysis of the experimental results in diesel engine fueled with diesel/methane blended fuels, the following conclusions can be drawn: (1) The influence of dissolved methane in diesel fuel on the brake specific fuel consumption and the effective thermal efficiency relates to the methane concentration in diesel fuel. In the experimental conditions, the saturated blend with methane concentration of 10.1 mL/mL gives a higher BSFC and lower effective thermal efficiency as compared with those of pure diesel fuel. The blended fuels with methane concentrations of 16.1 and 23.8 mL/mL, however, give a lower BSFC and a higher effective thermal efficiency than those of pure diesel fuel due to the improvement of fuel atomization by high methane concentration. (2) Diesel fuel containing dissolved methane has a longer ignition delay than that of pure diesel fuel, and the value increases with the increase of methane concentration. The maximum heat release rate decreases with the increase of methane concentration. (3) Diesel fuel containing dissolved methane produces less NOx emissions as compared with that of pure diesel fuel in this experiment. The decrease in cylinder gas temperature is be responsible for this. (4) The influence of dissolved methane on smoke depends on the methane concentration. For the fuel with low methane concentrations, its smoke is greater than that of pure diesel fuel


under certain operating conditions. For the fuel with high methane concentrations, its smoke is always less than that of pure diesel fuel. (5) At an appropriate methane concentration, the NOx and smoke emission may be decreased simultaneously as compared with those of pure diesel fuel. (6) Diesel fuel with dissolved methane produces higher hydrocarbon emissions than that of pure diesel fuel, while it has little influence on carbon monoxide emission.

Energy & Fuels, Vol. 20, No. 2, 2006 511 Acknowledgment. This work was supported by the State Key Project of Fundamental Research Plan under Grant 2001CB209208, the National Natural Science Foundation of China through Grant 50136040, the Research Fund of the Doctoral Program of Higher Education of China through Grant 20020698044, and the State Key Laboratory Awarding Fund through Grant 50323001. EF0502094

Performance and Emissions of Direct Injection Diesel Engine Fueled

Recommend Documents