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EXPERIMENTAL VALIDATION AND COMBUSTION CHAMBER GEOMETRY OPTIMIZATION OF DIESEL
ENGINE BY USING DIESEL –RK
SK. Abdul Siddique1, K. Vijaya Kumar Reddy2
1Research Scholar, Jawaharlal Nehru Technological University Hyderabad
2Professor, Jawaharlal Nehru Technological University Hyderabad
ABSTRACT
Compression ignition diesel engines are very popular both in stationary and mobile applications. These engines find large applications because of their higher compression ratios, robustness in design and higher thermal efficiencies. Air is sucked in to the chamber when the piston moves from TDC to BDC through the intake manifold during suction stroke. The fuel in atomized form is sprayed onto the compressed air in the chamber. The proper mixing of air and fuel in shorter time is essential to lessen the ignition lag phase. In order to get proper air fuel mixing, a systematic air movement also called swirl is essential, which produce higher relative velocity between fuel droplets and air. The spray cone of the injected liquid fuel gets disturbed because of air movement and turbulence inside the chamber. Since, the turbulence is mandatory for proper mixing and the fact that this could be achieved by the shape of the combustion chamber geometry, makes this research work is necessary. The present research work concentrates on combustion chamber geometry of single cylinder four stroke DI diesel engine with specification of 5.2kw, 1500rpm.
Key Words: Diesel Engine, Simulation, Air-Fuel Ratio, Turbulence.
INTRODUCTION
Internal combustion engine is a reliable power source in the transportation, industrial and agriculture fields. From the literature, it is noted that several research studies are conducted to increase the performance of the diesel engine by modifying injection pressure, injection timing, exhaust gas recirculation etc,. The proper mixing of air and fuel in shorter time is essential to lessen ISSN 0976 – 6340 (Print)
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the ignition lag phase. In order to get proper air fuel mixing, a systematic air movement also called swirl is essential, which produce higher relative velocity between fuel droplets and air. The spray cone of the injected liquid fuel gets disturbed because of air movement and turbulence inside the chamber. The present research work concentrates on combustion chamber geometry of single cylinder four stroke DI diesel engine with specification of 5.2kw, 1500rpm. This system is having a hemi spherical shaped combustion chamber with single injector having three 0.3mm nozzles. In this research paper, four combustion chamber geometries (1) Toroidal, (2) Shallow Depth, (3) Re-entrant and (4) Double wedge shallow are considered for optimisation. Computational Fluid Dynamics software Diesel-RK is used to model the combustion phenomenon in compression ignition diesel engine. Hemispherical combustion chamber is the baseline geometry considered for validation of CFD tool Diesel-RK.
MODELLING AND SIMULATION
Diesel-RK is a modeling and simulation software specifically developed for thermodynamic engine simulation. DIESEL-RK software is developed in 1981-82 in the department of Internal Combustion Engines (Piston Engines), Bauman Moscow State Technical University. It is mainly designed for simulating and optimizing the working processes of internal combustion engines with all types of boosting. This software is used for torque curves, engine performance predictions, fuel consumption predictions, emission analysis and optimization of fuel injection profile including multiple injection, sprayer design and location as well as piston bowl shape optimization in models of DI Diesel engines. In the present simulation study, Diesel-RK software is used for calculation of performance and emission values for hemispherical piston bowl in which Diesel is used as fuel. In figure 1 shows hemispherical piston bowl modelled with Diesel- RK.
Fig. (1): Modeling of hemispherical combustion chamber
EXPERIMENTATIONS
Experimentation is done on a single cylinder, four stroke, vertical, water cooled, direct injection computerized Kirloskar make CI Engine. The specifications of the engine are mentioned in the table 1. Fig 2 shows the experimental setup of the engine. The engine is attached with a DC electrical dynamometer to measure its output. Smoke measurement is done by using photo electronic smoke detection. Other emissions like Carbon dioxide, Nitrogen oxide and unused oxygen are found in 5 gas emission analyser. The experiments are conducted at different loads at constant rated speed of 1500rpm.
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Fig (2): Experimental setup
Table 1. Engine specifications
No. of cylinders 01
No. of Strokes 04
Fuel Diesel
Power rating 5.2 KW/7 hp @ 1500 RPM
Bore & Stroke 87.5 & 110 mm
C R 17.5:1
Dynamometer arm length 185 mm
Validation of CFD tool Diesel – RK
The comparison of the results obtained from the experimental investigations and from simulations by DIESEL-RK software are presented in figure (3). All the results are analysed by varying the load at rated constant speed of 1500rpm. The simulations are carried out on hemispherical combustion chamber geometry. The simulation results such as specific fuel consumption, mechanical efficiency, and exhaust emission CO2, NOx are showed good agreement with experimental results.
Variation of SFC w.r.t BP Variation of Mech. Efficiency w.r.t BP
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Variation of CO2 w.r.t BP Variation of NOx w.r.t BP Fig. (3) Hemispherical chamber simulation results
Optimization study of combustion chamber geometry
Fig. (4) Modeling of combustion chamber geometries
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Table (1): Input Parameters considered for simulation
In diesel engines, fuel is injected into the combustion chamber and mixed with the compressed air. Proper mixing of fuel and air is important to produce controlled burn rate.
Combustion chamber geometry is the key element in air fuel mixing process. In the present research paper, an attempt is made to simulate the critical combustion and put efforts to optimize the combustion chamber geometry. In this research paper, four combustion chamber geometries (1) Toroidal, (2) Shallow Depth, (3) Re-entrant and (4) Double wedge shallow are considered for investigation. Fig (4) shows the four combustion chamber models developed in Diesel –RK for simulation. The input parameters considered for simulation are mentioned in table (1).
RESULTS
In this investigation, four pistons of different configurations suitable to 5.2kw single cylinder four stroke DI diesel engine are considered. The hemispherical shaped geometry is taken as a base engine combustion chamber geometry. In the present work, simulations are conducted to investigate the performance, emission and combustion characteristics using diesel fuel alone at different loads by using DIESEL -RK. The following graphs shows the results of different efficiencies, exhaust emissions, specific fuel consumptions and cylinder pressures for all combustion chamber geometries.
Engine Specifications Single cylinder, 4 stroke Diesel, water cooled, power 5.2 kW at 1500 rpm, stroke 110 mm, bore 87.5 mm. 661 cc, CR 17.5 Connecting rod length 234mm
No. of fuel injectors 01 No. of nozzles 03 Injector nozzle bore 0.3 mm
Inlet valves opening 4.50 before TDC Inlet valve closing 35.50 after BDC Start of fuel injection 230 before TDC Exhaust valve
opening
35.50 before BDC Exhaust valve closing 4.50 after TDC
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Fig (3) Simulation results
CONCLUSION
The 5.2kW, Kirlosker make single cylinder, four stroke engine is selected for investigation because it can withstand higher pressures and also is used extensively in agriculture and industrial sectors. The DIESEL-RK is used to simulate the combustion characteristics of direct injection diesel engine. The CFD tool is validated with experimental results. A good agreement between the modelling and experimental data ensures the accuracy of the numerical predictions. Four combustion chamber geometries, toroidal, shallow depth, re-entrant and double wedge shallow shapes are selected for simulation. Simulated results including specific fuel consumption, rate of pressure rise, heat release rate, mechanical efficiency, volumetric efficiency and exhaust emission have been analysed. The comparison revels that re-entrant combustion chamber geometry is the best among the selected geometry configurations. It exhibits lower emissions, lower specific fuel consumption rate, improved performance compared to other shapes. From the results, it is concluded that the numerical simulation is one of the powerful tool for optimisation and to improve performance of internal combustion engine instead of developing a new proto type systems and test and evaluate every time.
98 REFERENCES
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