2 Journal of Scientific & Industrial Research J SCI IND RES VOL 7 MARCH 11 Vol. 7, March 11, pp. 2-224 Effects of advanced injection timing on performance and emission of a supercharged dual-fuel diesel engine fueled by producer gas from downdraft gasifier S Hassan 1*, Z A Zainal 1 and M A Miskam 2 1 School of Mechanical Engineering, Engineering Campus, Universiti Sains Malaysia, Seri Ampangan, 14 Nibong Tebal, Pulau Pinang, Malaysia 2 Collaborative Microelectronic Design Excellence Centre, Engineering Campus, Universiti Sains Malaysia, Seri Ampangan, 14 Nibong Tebal, Pulau Pinang, Malaysia Received 13 October 1; revised 23 January 11; accepted 28 January 11 This study presents effects of advanced injection timing on engine performance and emission characteristics of a supercharged producer gas-diesel dual fuel diesel engine fueled by producer gas from a downdraft gasifier. Original injection timing of engine was 14 before top dead center (BTDC), and tests were conducted at advanced three different injection timings (17,, and 23 ) by changing thickness of copper shim. Experiments were carried out at a constant injection pressure (2 bar) with varying injection flow rates of both producer gas and air at different engine speeds and loads. Advancing injection timing in a supercharged engine showed that diesel fuel displacement and brake thermal efficiency increased, with a significant reduction in carbon monoxide emission and specific energy consumption compared with original injection timing of premixed producer gasdiesel dual fuel. Keywords: Dual fuel engine, Gasification, Injection timing, Producer gas, Supercharging Introduction Producer gas, generated from biomass gasification process, is one of the alternative fuels capable of displacing diesel fuel partially in dual fuel mode of a diesel engine. Only problem with producer gas is its lower heating value; thus, engines lose their power or power de-rating. Supercharging of intake air 1,2 and advancing fuel injection timing 3-7 is a way of improving engine power and combustion characteristics of dual-fuel engines. This technique shows similar trends to those in using producer gas in dual-fuel diesel engines 8. This study presents effects of advanced injection timing on performance and exhaust gas emissions of a supercharged dual-fuel diesel engine fuelled by producer gases produced from a downdraft biomass gasifier. Experimental Section Downdraft Gasification System In gasifier system [biomass fuel, off-cut furniture wood; particle size, -1 mm; rated biomass *Author for correspondence Tel: +64-59996358; Fax: +64-594125 E-mail: suhas99@yahoo.com consumption, 1 kg/h; hopper capacity (max.), 1 kg; conversion efficiency, 7-75% ; gas composition (CO, ±4%; H 2, 14±2%; CO 2, 12±3%; N 2, 45%; CH 4, 2.5%); and average gas calorific value, 4.2-4.5MJ/m 3 (values are comparable with reported studies 8,9 )], biomass fuel is fed through top opening, and air is supplied to gasifier using a rotary blower, in which capacity is higher than required airflow rate. Air enters combustion zone, and producer gas generated exits near the bottom of gasifier. Once steady operation of gasifier is achieved, hot producer gas is then allowed to pass through cyclone separator, heat exchanger, and gas filter for cleaning and cooling processes (Fig. 1). Engine Test System Experiments were carried out on a four-stroke single cylinder direct injection diesel engine [model, Yanmar L7AE-DTM; capacity, 296 cc; power (max.), 4.9kW @ 36 rpm; compression ratio, 19.1; and injection timing, 14 ± 1 BTDC]. An electrical eddy current dynamometer is directly coupled to the engine, and engine load applied is measured from an engine controller. A glass burette ( ml) and a stopwatch are
HASSAN et al : PERFORMANCE OF A GASIFIER FUELLED DIESEL ENGINE 221 Brake thermal efficiency, % 25 15 1 5 Fig. 1 Schematic diagram of gasifier system used to determine fuel consumption. Exhaust emissions and exhaust gas temperature are measured and determined using a Kane Automotive Gas Analyzer and K-type thermocouple, respectively. Test Procedure At standard fuel injection timing of 14 BTDC, experiments were conducted using diesel fuel only, premixed dual fuel producer gas-diesel (PDF), and supercharged dual fuel producer gas-diesel (SC). Fuel injection timings were also advanced to three injection timings (17,, and 23 BTDC) of both PDF and SC. All tests were conducted at start up with diesel fuel only. In experiments for PDF and SC conditions, operation began min after gasifier was initiated. Engine was initially run at full load using diesel fuel to measure maximum brake power and fuel consumption. Engine torques of 3, 5, 7, and 9 Nm were selected, and each load was applied at a three engine speeds (16,, and rpm). In SC condition, producer gas from gasifier was compressed before the gas was injected and mixed with compressed air at intake port of engine s cylinder. Supercharged producer gas and air were kept constant at kpa throughout the experiment. In both PDF and SC operations, supply of producer gas was adjusted manually to obtain maximum (%) diesel displacement. For all cases, engine was operated at a standard fuel injection pressure of 196 bar, and experiment for each test was replicated three times (total percentage uncertainty for the whole experiment is obtained to be ± 3.1%). Engine and exhaust emission parameters were measured in each experiment. Results and Discussion Brake Thermal Efficiency (BTE) BTE of a dual-fueled engine with respect to brake mean effective pressures (BMEP) was always lower Specific energy consumption, MJ/kWh 4 1 Fig. 2 Effect of BMEP on: BTE; and SEC [+ - Diesel 14 BTDC; - PDF 23 BTDC; - SC 14 BTDC; - SC 17 BTDC; ο - SC BTDC; - SC 23 BTDC] (Fig. 2 than that of diesel fuel; maximum efficiency achieved was by diesel fuel (26.27%) compared with premixed dual fuel (18.86%). In supercharged dual fuel operation, BTE at injection timings of 14, 17,, and 23 BTDC were calculated as 19.18%, 19.87%,.7%, and 22.15%, respectively. Further increase in engine load results in decrease in BTE efficiency due to low calorific value of producer gas mixture. Improvement in BTE by advancing injection timing in supercharged engine was due to higher combustion temperature that led to a better combustion rate. Specific Energy Consumption (SEC) In dual fuel mode, SEC was selected to compare performance of two types of fuels with different calorific values and densities. SEC is calculated based on fuel consumption and calorific value of brake power of engine. SEC in dual fuel mode was higher than that of diesel mode in all operating conditions (Fig. 2. Increase in SEC indicates reduction in efficiency of dual fuel mode, could be due to reduction in air flow that leads to incomplete combustion, similar to premixed dual fuel operation. However, SEC of supercharged dual fuel was reduced moderately by advancing injection timing, due to increased charge density of air and sufficient mixing of
222 J SCI IND RES VOL 7 MARCH 11 Diesel displacement, % Diesel displacement, % 6 55 45 4 35 25 8 75 7 65 6 55 45 4 35 Fig. 3 Diesel displacement at: rpm; and 16 rpm [ - PDF 23 BTDC; - SC 14 BTDC; - SC 17 BTDC; ο - SC BTDC; - SC 23 BTDC] producer gas-air that resulted in complete combustion of fuel mixture. Values of SEC at 8% load were: diesel fuel, 14.12 MJ/kWH; and premixed dual fuel,.6 MJ/ kwh. In supercharged operation, SEC at injection timings of 14, 17,, and 23 BTDC were calculated as 18.86, 18.12, 17.39, and 16.25 MJ/kWh, respectively. Diesel Displacement Use of producer gas in dual fuel mode operation reduced consumption of diesel fuel at all engine loads for engine speeds of (Fig. 3 and 16 rpm (Fig. 3. At rpm, maximum diesel displacement was recorded at 47.1% and 48.7% at a standard injection timing of 14 BTDC in premixed and supercharged dual fuels, respectively. Advancing injection timing in supercharged dual fuel increased diesel displacement; this trend was similar in all injection timings. Maximum diesel displacement obtained at (.1%) and 16 rpm (7.4%) was at an injection timing of 23 BTDC. Continuous injection of producer gas and air increased their density, and advancing injection timing in low speed engine allowed more time for sufficient mixing of producer gas-air in supercharged dual fuel. Therefore, maximum diesel displacement was achieved at a lower engine speed and at advanced injection timing. At both engine speeds, diesel displacement was observed to decrease at low and high load conditions, and displaced maximum diesel fuel decreased at mid load condition, due to insufficient oxygen to complete combustion at a low load; at high load operation, insufficient producer gas flow decreased diesel displacement. Carbon Monoxide (CO) CO emission in a producer gas-diesel dual fuel mode is always higher than that in diesel mode alone in all operating conditions (Fig. 4. Higher concentration of CO emission in dual fuel is a result of incomplete combustion due to insufficient air required for complete combustion. However, supercharged duel fuel and advanced injection timing exhibits better performance than conventional premixed dual fuel. Continuous injection of air increases its density and improves fuel combustion efficiency. Moreover, better fuel combustion usually results in lower CO emission. However, advancing injection timing causes early start of combustion that result in a relatively higher temperature in combustion chamber, thus lowering CO emission. Nitrogen Oxides (NOx) Formation of NOx in engine depends on maximum temperature in the cycle; equivalence ratio, percentage of load applied, and amount of oxygen concentration in cylinder. NOx increases with increase in load for diesel alone and dual fuel modes (Fig. 4. Supercharging air into engine cylinder provides more air and causes higher combustion temperature; main reason for higher NOx emissions in supercharged dual fuel mode. Advancing injection timing causes most of the fuel mixture to be burnt during compression stroke BTDC, resulting in a high peak temperature and hence in higher NOx emissions. In diesel mode alone, organic nitrogen in air is main cause of NOx formation. Producer gas does not have organic nitrogen but only atmospheric inorganic nitrogen 9. Exhaust Gas Temperature (EGT) Variation of EGT of dual fuel mode is always higher than that of diesel mode alone due to excess energy supplied to engine (Fig. 4c). EGT of supercharged dual
2 HASSAN et al : PERFORMANCE OF A GASIFIER FUELLED DIESEL ENGINE 223 CO emission, % 2. 1.8 1.6 1.4 1.2 1..8.6.4.2. Exhaust gas temperature, C 4 3 2 c) 1 1 1 2 3 4 4 BME, kpa NOx emission, ppm 4 1 CO2 emission, % 12. 11. 1. 9. 8. 7. 6. 5. 4. d) 3. 2. 1.. 1 1 2 3 4 4 Fig. 4 Effect of BMEP on: CO; NOx; c) EGT; and d) CO 2 [+ - Diesel 14 BTDC; - PDF 23 BTDC; - SC 14 BTDC; - SC 17 BTDC; ο - SC BTDC; - SC 23 BTDC] fuel mode was found to be higher than that of premixed dual fuel because of increase in density of fuel mixture entering engine. In dual fuel engine, higher EGT in combustion chamber is an indication of high NOx emissions. However, advancing injection timing results in a lower EGT, where most of the fuel mixture is burnt, and peak combustion temperature is achieved BTDC. Carbon Dioxide (CO 2 ) There is an increase in CO 2 emission with increase in engine load, and trend is similar in both diesel fuel and dual fuel modes (Fig 4d). As producer gas is a mixture of CO, CH 4, and CO 2, combustion of producer gas increases CO 2 emission. However, by supercharging and advancing injection timing, a significant reduction in CO 2 emission was observed at all engine loads. This could be due to increase in oxygen content in air charge by continuous port injection that leads to better fuel combustion in combustion chamber, as a results reduced CO 2 emission, moderately. Conclusions Application of a supercharger provides increased oxygen content to engine and enables sufficient mixing of fuel-air in combustion chamber. Combination of supercharging producer gas-air and advancing injection timing has improved moderately BTE of engine, due to corresponding increase in air density and sufficient producer gas-air fuel mixture that leads a faster combustion rate in engine. Maximum diesel displacement is achieved at a lower engine speed with advanced injection timing under a supercharged condition. Reduction in specific energy consumption in supercharged
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