Effect of Injection Timing and Mixing Rate of Water in Jatropha Emulsion on Combustion and Performance of DI Diesel Engine Nguyen Kim Bao1 Vietnam Maritime University; E-mail: nguyenkimbao@vimaru.edu.vn Address: 484 Lach tray street, Hai phong City, Vietnam Abstract The current paper studies the effect of the injection timing and Jatropha water emulsion (JWE) with different mixing ratios on the combustion and performance characteristics of a direct injection diesel engine The experimental study was carried out using a four-stroke, high speed, small capacity, direct-injection diesel engine The engine ran on the Light oil (LO) and neat Jatropha oil (JO) for baseline data In this study, Jatropha emulsion was made by mixing mass ratios of 10% and 20% of water so called JWE10%, and JWE20%, respectively While changing fuels from LO to JO, JWE10%, and JWE20%, we tested the engine with various injection timings of 17, 20, and 23 degree crank angle before top dead center (o BTDC) The acquired data was analyzed for various combustion parameters such as in-cylinder pressure, heat release rate (HRR), ignition delay (ID); for performance parameters such as exhaust gas temperature and brake thermal efficiency (BTE) At the original injection timing, the peak of in-cylinder pressure, and the HRR reduced, and they marginally increased when advancing the injection timing in comparison with those of the Jatropha oil at original injection timing Ignition delay increased with an increase of the injection timing for both emulsion fuels When advancing the injection timing to 23o BTDC, the emulsion fuels reduced exhaust gas temperature BTE increased when using emulsion fuels, particularly the JWE10% Overall, the optimum water mixing rate was 10%, while the optimum injection timing was 20o BTDC Keywords: Jatropha water emulsion, mixing rate, injection timing, combustion, performance Introduction Diesel engines have been faced with problems like the fossil fuel crisis, and the more stringent criteria regulated by governments the world over attempting to protect the air quality The main harmful pollutants, namely NOx and particulates, which are trade-offs in using diesel engines, have been closely watched Additionally, the production of global warming gas (CO2) is unavoidable whatever the fuel when using diesel engines To allay these concerns, vegetable oils have recently gained attention as a promising alternative fuel for a greener future Short-term tests have revealed that most vegetable oils are capable of being used directly in existing diesel engines with little or no modification However, long-term test has reported some operational problem such as piston ring sticking, injector and engine deposits, gum formation and oil thickening [1] Physical properties of the vegetable oils such as high viscosity, poor volatility, and bulky molecules result in an increase in CO, HC and PM, but lower NOx emissions compared to those of diesel oil alone [2-4] Among vegetable oils, Jatropha has been of interest because it is not a food source [3] Jatropha oil was identified as a leading candidate for an alternative fuel among various non-edible vegetable oils [5] since the plant does not suffer excessively from droughts, or need concentrated irrigation Higher smoke, HC, CO have been observed [3, 7, 8], while NOx emissions have also been reported lower when engines run on Jatropha oil [3, 8] In the performance aspect, the brake thermal efficiencies of engines fueled with Jatropha have been generally lower in comparison with those using diesel oil [3, 6-9] This is attributed to the physical-chemicalproperties of Jatropha oil such as high viscosity, poor volatility, bulky molecular structure, and low cetane number The drawbacks of Jatropha oil may be overcome by preheating [7, 8], and/or blending with diesel [10, 11] The usage of water emulsion fuel is a well-known way to significantly reduce NOx emissions due to the cooling effect of the vaporization of water in the emulsion fuel [12-16]; while the reduction of soot 214 is seen as a consequence of the micro-explosion [13, 15], or the presence of OH radicals releasing during the combustion process [13, 15], or more air entrainment [16] From this one might surmise that a combination of a change in injection timing with Jatropha water emulsion may reduce both NOx emissions and soot in diesel engine Moreover, it may improve performance of the engine as a result the effect of micro-explosion However, as yet this combination has not been tried to the best of our knowledge Our current experimental research was conducted to remedy this situation We investigated the effect of injection timing and Jatropha water emulsion on the combustion, performance, and emissions characteristics of a diesel engine During the experiments, the engine were varied with different injection timings of 17o (default value), 20o, and 23o BTDC, while we changed the test fuel from LO and JO to the JWE with water mass mixing ratios of 10% and 20% Experimental setup and procedures Figure Diagram of experimental setup Table Specifications of test engine Model Engine type Combustion type Bore × Stroke Displacement Compression ratio Rated output Injection nozzle Nozzle opening pressure YANMAR NFD 13-ME Horizontal, 1-cylinder, 4-stroke Direct injection 92 × 96 mm 0.638 liter 17.7 8.1 kW @ 2400 rpm 4-hole nozzle 19MPa Experiments were conducted on a single cylinder, four-stroke, high speed, direct injection diesel engine (Yanmar Co., Ltd., Japan) The scheme of experimental setup is shown in Fig and the main specifications of the test engine are given in Table The fuel injection system of the engine was modified to a common rail injection system Main components of the common rail system include a motor-driven-pump (radial piston pump), a common rail (high pressure tube), an electronic injector, and an electronic control unit (ECU) The ECU was connected to a computer via a combustion analyzer (Yokogawa) to record the data The in-cylinder pressures were measured using a piezoelectric pressure transducer (Kistler) fitted into the cylinder of the engine and connected to a charge amplifier Load of the engine was set through an electrical-dynamometer (Toyo Electric Co., Ltd.) coupled to the shaft of the engine A set of gas analyzers VIA-510, CLA-510SS (Horiba) was used to measure the emissions of CO2, NOx, respectively, and along with MEXA-324J (Horiba) for measurement of CO, HC Dust matters were trapped on the ADVANTEC PG-60 paper filters (glass fiber Fluorine coated filter, Toyo 215 Roshi Kaisha, Ltd.) in 10 liters of exhaust gas at each step of the experiments with the help of a D-25UP gas sampler (OCT science, Ltd.) In each experiment step, we collected the dust on paper filter sheets Afterward, soluble organic fraction in the dust trapped filters was dissolved by dichloromethane and was calculated by balancing the mass of the filters before and after extraction (average value) In-soluble organic fraction was calculated by subtraction of the paper filter mass after SOF dissolving and the original filter Measurements were carried out using LO, JO, JWE10%, and JWE 20% To make the emulsion fuel, a mixing system with a tank for JO; a tank for water; a circulating pump; and a static mixer was used The engine was fed with LO, and JO at the injection timings of 17, 20, and 23o BTDC for baseline data These timings were also set to investigate the effect of the Jatropha emulsion with different water mass mixing rates Water with 10% and 20% in mass was added to the Jatropha creating emulsion fuels prior to the experiments The experimental conditions (injection timing and test fuels) of the experiments are provided in Table All experimental steps were conducted at room temperature and the results were recorded at steady operational conditions of the engine During the experiments, the engine load was set at different values of 3.0 kW, 4.5 kW, and 6.0 kW with a speed of 2000 rpm, while the rail pressure was kept at 100 MPa The gas emissions including CO, CO2, HC, smoke, and NOx were read during each step of the experiments While, the concentration of dust, in-soluble organic fraction (ISF), and SOF were determined in experiments, as well Table Experimental conditions Engine Speed [rpm] Injection timing Light Jatroha [o BTDC] oil oil 2000 2000 2000 17 20 23 Test fuels Jatropha emulsion 10% 20% LO-17 JO-17 JWE10%-17 JWE20%-17 JWE10%-20 JWE20%-20 JWE10%-23 JWE20%-23 Results and discussions 3.1 Combustion characteristics In this section, the combustion characteristics are demonstrated by a number of factors, namely combustion pressure, heat release rate, and ignition delay In-cylinder pressure of the engine is indicated in Fig It is clear that the peak pressures of the engine depend on the injection pattern as well as the fuel Perhaps, for emulsion fuels, the development of the pressure in the cylinder depends on some factor, such as the cooling effect; the combustion of cumulated fuel; and the help of second-atomization When compared with JO-17, the JWE10% reduced the peak pressures of 5%, 5.8%, and 4.5%, while the JWE20% had a minor reduction of 0.1%, 0.9% and 0.2% at 3.0, 4.5 and 6.0 kW, respectively At this timing, it can be seen that for the emulsion fuels the developments of pressure were retarded when compared with JO or LO The reduction and retardation of peak pressures can be resulted from the cooling effect and higher viscosity of the emulsion fuels When advancing injection timing, most emulsion fuel increased peak pressures in the cylinder, particularly for the 23o BTDC At lower powers, the JWE10% had a relative increment of peak pressure of 7.0% and 8.8%, while the JWE20% had peak pressure of 7.0% and 5.5% higher in comparison with those of the JO-17 At 6.0 kW, the JWE20% had an increment of 5.9%, while the JWE10% had 7.1% higher in comparison with peak pressure of the JO17 The increment of the peak pressure may result from either the combustion of the fuel cumulated in the combustion chamber or the help of micro-explosion contributing to the better mixing of fuel and air in the combustion chamber At the 20o BTDC, for the JWE10%, the minor reductions are seen at lower powers, while it had a marginal increase of 6.2% when compared with JO-17 These may result from the cooling effect could over the other factors at lower loads, while at higher power the cumulated fuel and second-atomization could enhanced the development of the in-cylinder pressure At this timing, and at lower power, the JWE20% had slight increment of 4.3% and 5.8%, while the pressure was comparable with those of the JO-17 at 6.0 kW This can be explained as the high enough water content 216 in the JWE20% resulting in the dominant second- atomization at lower powers, and it would be enough for cooling effect at high load, respectively In-cylinder pressure [MPa] Heat release rate (HRR) in the cylinder of the engine is presented in Fig The peak of HRR reduced from 65.9, 66.2, and 64 J/deg of the LO-17 to 62.5, 59, and 57 J/deg of the JO-17 at 3.0, 4.5, and 6.0 kW, respectively This is resulted from properties of the JO such as higher viscosity, lower volatility, and lower cetane number At the 17o BTDC, the HRR of the emulsion fuels had a relative reduction of 13.1%, 12.9%, and 11% for the JWE10%, and 3.1%, 8.1%, and -1.5% for the JWE20% in comparison with those of the JO-17 at 3.0, 4.5, and 6.0 kW, respectively The reduction of the HRR may attribute to the cooling effect of the water in the emulsion fuels However, less reduction of the HRR for the JWE20% may result from the aid of dominant micro-explosion over the cooling effect When advancing the injection of the emulsion fuels the HRR start increasing in comparison with those of the JO-17, particularly for the injection timing of 23o BTDC At the 20o BTDC, the JWE10% reduced the HRR 6% at 3.0 kW, while it increased the HRR 10.6% and 19.7% at 4.5 and 6.0 kW At this timing, the JWE20% increased HRR 12.1% and 16.5% at 3.0 and 4.5 kW, and it had a reduction of 6.5% at 6.0 kW At the 23o BTDC, for the JWE10%, the HRR of had an increment of 9.6%, 33.2% and 31.4%, while for the JWE20%, the reduction was 14%, 13.6%, and 9.7% in comparison with those of the JO17 at 3.0, 4.5, and 6.0 kW This may result from the dominant cooling effect of the JWE20% over the JWE10%, especially for higher engine powers (a) LO-17 JO-17 JWE10%-17 JWE10%-20 JWE10%-23 JWE20%-17 JWE20%-20 JWE20%-23 320 In-cylinder pressure [MPa] 340 360 380 Crank angle [deg.] 400 420 (b) LO-17 JO-17 JWE10%-17 JWE10%-20 JWE10%-23 JWE20%-17 JWE20%-20 JWE20%-23 320 In-cylinder pressure [MPa] 340 360 380 Crank angle [deg.] 400 420 (c) LO-17 JO-17 JWE10%-17 JWE10%-20 JWE10%-23 JWE20%-17 JWE20%-20 JWE20%-23 320 340 360 380 Crank angle [deg.] 400 420 Figure In-cylinder pressures at (a) 3.0 kW, (b) 4.5 kW, and (c) 6.0 kW at a speed of 2000 rpm 217 Ignition delay is shown in Fig The ignition delay is the duration from the start of injection to the start of combustion The start of combustion is determined by the timing at which the HRR changes from a negative to a positive value The ignition delay was shorter for LO and JO, while the emulsion fuel increased the ID and also increased with an increase of injection timing At default timing, the JWE10% increased the ID from 6.4% to 8.3%, while at the 23o BTDC the ID had an increment of 22.9% to 29.9% when compared with those of the JO-17 For the JWE20%, at the 17o BTDC, the ID increased 4.0% to 6.4%, and it increased up to around 30% when timing advanced to the 23o BTDC in comparison to those of the JO-17 The increment of the ID for the emulsion fuels and when advancing the injection timing can be attributed to the cooling effect of water in the emulsion fuels and the worse combustion conditions at advanced injection timing, respectively Heat release rate [J/deg.] 120 LO-17 JO-17 JWE10%-17 JWE10%-20 JWE10%-23 JWE20%-17 JWE20%-20 JWE20%-23 (a) 100 80 60 40 20 -15 15 30 45 -20 Crank angle [deg.] Heat release rate [J/deg.] 120 LO-17 JO-17 JWE10%-17 JWE10%-20 JWE10%-23 JWE20%-17 JWE20%-20 JWE20%-23 (b) 100 80 60 40 20 -15 15 30 45 -20 Crank angle [deg.] Heat release rate [J/deg.] 120 LO-17 JO-17 JWE10%-17 JWE10%-20 JWE10%-23 JWE20%-17 JWE20%-20 JWE20%-23 (c) 100 80 60 40 20 -15 15 30 45 -20 Crank angle [deg.] Figure Heat r elease rates at (a) 3.0 kW, (b) 4.5 kW, and (c) 6.0 kW at a speed of 2000 rpm 218 3.0 Ignition delay [ms] 2.5 2.0 LO-17 JO-17 JWE10%-17 JWE10%-20 JWE10%-23 JWE20%-17 JWE20%-20 JWE20%-23 1.5 1.0 0.5 0.0 3.0 4.5 Engine power [kW] 6.0 Figure Ignition delay at different powers and at a speed of 2000 rpm 3.2 Performance characteristics The performance parameters of the engine, such as in-cylinder and exhaust gas temperatures, and brake thermal efficiency will be introduced in this section Exhaust gas temperature is shown in Fig Exhaust gas temperatures increased with an increase in the engine power This is due to more fuel injected and combustion which generates more engine power At most injection timing, for JWE10%, the exhaust gas temperature reduced when compared with those of the JO-17 At the 17o and 20o BTDC, the exhaust gas temperatures reduced from 2.1% to 3.1% when compared with those of the JO-17 At the 23o BTDC, they had more relative reduction of 5.2%, 5.9%, and 2.0% at 3.0, 4.5, and 6.0 kW, respectively in comparison with those of the JO-17 This may result from the cooling effect of the water in the emulsion fuel, also when advancing the injection timing, the heat released more early resulting in early combustion in the combustion chamber For the JWE20%, at the original timing, the exhaust gas temperature had a relative reduction of 2.6% to 3.4%, while at the 23o BTDC the reduction was 3.9%, 2.8%, and 0.6% at 3.0, 4.5, and 6.0 kW, respectively At the 20o BTDC, the exhaust gas temperature was comparable with those of the JO-17 Exhaust gas temperature [oC] 800 600 LO-17 JWE10%-17 JWE10%-23 JWE20%-20 JO-17 JWE10%-20 JWE20%-17 JWE20%-23 400 200 3.0 4.5 Engine power [kW] 6.0 Figure Exhaust gas temperatures at different powers and at a speed of 2000 rpm Brake thermal efficiency of the engine is indicated in Fig The emulsion fuel significantly increased the BTE, especially for the advancing timing, when compared with those of the neat Jatropha oil at the original timing At the default timing, at higher engine powers, the JWE10% had a relative increment 219 of 3% to 6%, while the JWE20% had a relative increment of 8% to 10.7% in comparison with those of the JO-17 50 LO-17 JWE10%-17 JWE10%-23 JWE20%-20 Brake thermal efficiency [%] 45 40 35 JO-17 JWE10%-20 JWE20%-17 JWE20%-23 30 25 20 15 10 3.0 4.5 Engine power [kW] 6.0 Figure Brake thermal efficiencies at different powers and at a speed of 2000 rpm At 20o BTDC, the JWE10% increased from 13.6% to 21%, while the JWE20% increased around 12.5% when compared with those of the JO-17 The relative increment was 17% to 23.5% of the JWE10% and 10.9% to 14.9% of the JWE20% at 23o BTDC At medium power, and at the 23o BTDC, the JWE10% had optimum BTE up to 31.8% that overs the BTE of the LO-17 of 30.7% The increment of the BTE of the emulsion fuels may attribute to the effect of micro-explosion resulting to the better mixing of fuel and air in the combustion chamber 3.3 Emissions characteristics CO2 emissions [g/kWh] 900 800 (a ) 700 LO-17 JWE10%-17 JWE10%-23 JWE20%-20 JO-17 JWE10%-20 JWE20%-17 JWE20%-23 600 500 0.3 LO-17 JO-17 JWE10%-17 JWE10%-20 JWE10%-23 (c) 0.25 HC emissions [g/kWh] 1000 0.2 0.15 400 300 200 0.1 0.05 100 0 3.0 14 6.0 14 LO-17 JO-17 JWE10%-17 JWE10%-20 JWE10%-23 (b ) 10 3.0 NOx emissions [g/kWh] CO emissions [g/kWh] 12 4.5 Engine power [kW] 12 4.5 Engine power [kW] 6.0 LO-17 JO-17 JWE10%-17 JWE10%-20 JWE10%-23 (d ) 10 3.0 4.5 Engine power [kW] 6.0 3.0 4.5 Engine power [kW] 6.0 Figure Exhaust gas emissions at different powers and at a speed of 2000 rpm 220 ... the effect of injection timing and Jatropha water emulsion on the combustion, performance, and emissions characteristics of a diesel engine During the experiments, the engine were varied with different... that a combination of a change in injection timing with Jatropha water emulsion may reduce both NOx emissions and soot in diesel engine Moreover, it may improve performance of the engine as a result... increment of the ID for the emulsion fuels and when advancing the injection timing can be attributed to the cooling effect of water in the emulsion fuels and the worse combustion conditions at advanced