International Journal of Mechanical Engineering and Technology (IJMET) Volume 8, Issue 6, June 2017, pp. 393 402, Article ID: IJMET_08_06_041 Available online at http://www.iaeme.com/ijmet/issues.asp?jtype=ijmet&vtype=8&itype=6 ISSN Print: 0976-6340 and ISSN Online: 0976-6359 IAEME Publication Scopus Indexed EXPERIMENTAL AND COMPUTATIONAL EVALUATION OF EMISSIONS OF AN ENGINE WITH A RE-ENTRANT PISTON BOWL - A VALIDATION M. Thamarai Kannan, Rupesh P L, Raja K and M.P. Siva Assistant Professor, Department of Mechanical Engineering, Veltech Dr. RR & Dr.SR University, Avadi, Chennai, Tamilnadu, India ABSTRACT Reductions in fuel consumption and pollutant emissions from direct injection diesel engines are important issues in engine research. To achieve these reductions, rapid and better fuel air mixing is the most important requirement, the design of the piston bowl and the nozzle configuration perform a defining role. The shape of the combustion chamber can also help to form better mixtures. The change in shape of the combustion chamber leads to different changes in measurements of pip region, bowl lip area, and toroidal radius etc. and this makes high cost for manufacturing. The selection of an optimised shape of combustion chamber from the manufacturing of different shapes and experimental observation of those shapes may lead to high cost. The aim of this study focuses on the validation of the experimental results with that of the computational using an engine with re-entrant piston bowl. The computational results hold in agreement with experimental results which leads to the future scope of simulation of different piston bowl configurations using the computational model in order to choose an optimised combustion chamber of an existing diesel engine in order to meet CPCB-II emission Norms. Key words: Direct Injection Diesel Engine, Piston bowl, Re-entrant type, Bowl radius, Emissions. Cite this Article: M. Thamarai Kannan, Rupesh P L, Raja K and M.P. Siva. Experimental and Computational Evaluation of Emissions of an Engine with a Re- Entrant Piston Bowl - A Validation. International Journal of Mechanical Engineering and Technology, 8(6), 2017, pp. 393 402. http://www.iaeme.com/ijmet/issues.asp?jtype=ijmet&vtype=8&itype=6 1. INTRODUCTION Environmental concerns have led to progressively more stringent emission regulations for diesel engines, and much research has addressed this issue. Incomplete combustion of the fuel is mainly responsible for the HC and PM emissions and better mixture formation would be the best way to improve the combustion and emission quality. Especially in small DI diesel engines a major part of the injected fuel impinges on the cavity (combustion chamber) walls. http://www.iaeme.com/ijmet/index.asp 393 editor@iaeme.com
Experimental and Computational Evaluation of Emissions of an Engine with a Re-Entrant Piston Bowl - A Validation This causes the formation of a fuel film on the cavity wall when the wall temperature is low and forms rich mixtures near the cavity wall when operating loads are high, giving a significant effect on unburnt HC and soot emissions. Compact high speed DI diesel engines are attractive power sources for modern passenger cars due to their low carbon dioxide emissions. However, these engines still emit objectionable PM and NOx at a time when emission regulations are becoming more stringent. Much research has attempted to reduce the PM emissions by injecting fuels at high pressure without increasing NOx emissions. In small DI diesel engines much of the spray reaches the cavity wall even when injected at high pressures. At low temperatures and at light loads a film of impinged fuel forms on the cavity wall. The fuel adhering to the wall is thought to be the major source of unburnt HC emissions. Pilot injection and retarded timings have been used to reduce NOx emissions and engine noise. Direct-injection (DI) diesel engines have served in both light-duty and heavy-duty vehicles because of the evident benefit of higher thermal efficiency than all other engines. However, due to the short period of fuel air mixing time, it is unfavorable to the combustion process. As the results, DI diesel engine emits more particulates and nitrogen oxides (NOx) than its counterparts. The methods of emission reduction from an engine include In-cylinder emission reduction techniques and after treatment techniques which is shown in Fig.1. Emission reduction techniques In-cylinder techniques After treatment devices 1.Combustion bowl shape optimization 2.Exhaust Gas Regeneration 3.Rate and timing of fuel injection 4.Compression ratio 1.Catalytic Converter 2.Diesel Particulate filter 3.Diesel oxidation catalyst 4.Selective catalytic reduction Figure 1 Emission reduction techniques To achieve a better combustion with less pollutant emissions in DI diesel engines, the method, which is widely used and proved effective, is accelerating the fuel air mixing to improve the combustion in cylinder and reduce the combustion period. The basic nomenclature of combustion bowl is as shown in the fig.2. http://www.iaeme.com/ijmet/index.asp 394 editor@iaeme.com
M. Thamarai Kannan, Rupesh P L, Raja K and M.P. Siva Figure 2 Basic nomenclature of a combustion bowl Katsuhiko Miyamoto et al [1] investigated the effects of tumble & squish in the context of in-cylinder flows on partial load fuel consumption for gasoline engines and also compared three piston cavities for heat release rate & incoming air flow along with the study on effects of variation of ignition timing & torque. Caroline L. Genzale et al studied the effects of variation of piston bowl geometry parameters for soot & NOx emission using computational investigation into the effects of spray targeting, bowl geometry and swirl ratio for low temperature combustion in a heavy duty diesel engine [2]. Ramchandra Divakar & Satbir singh prepared a simulation model for a DI diesel engine operating under Premixed charge Compression Ignition (PCCI) combustion model [3] in order to find out the importance of spray-bowl interaction in the engine and validated for experimental results. Effects of start of injection (SOI) and spray cone angle are studied on combustion & emission. Lu Lin et al [4] investigated the combustion shape effects on in cylinder air motion and performance of a DI diesel engine. The results show that, by optimizing the combustion chamber shape, the duration of high turbulence in cylinder is prolonged, and the diffuse combustion during the later period of combustion process is enhanced. Rahman M et al [5] found that a re-entrant type combustion chamber with round lip and round bottom corners provides better air and fuel distribution than a simple cylindrical combustion chamber. The results shows that the re-entrant cavity with round lip produces larger spray volumes, wider spray spreading, and better balance of fuel inside and outside the cavity than the simple cylindrical cavity. Rahman Md. et al [6] designed a new combustion chamber concept for small DI diesel engines. The spray formation and its distribution inside and outside the combustion chamber was investigated photographically in a small DI diesel engine with transparent cylinder and piston. The inferences drawn from the above literature survey shows that individual research has been carried out for experimental and computational tests. This shows that a validation of experimental results with that of computational is required. This provided the objective for the current work. After validation if the experimental results hold in good agreement with that of computational, we can able to optimize the piston bowl of an existing diesel engine using the current simulation model in order to meet CPCB-II emission Norms. The methodology of the research work has been categorized in 5 steps which is shown in a flow diagram depicted in Fig. 4. http://www.iaeme.com/ijmet/index.asp 395 editor@iaeme.com
Experimental and Computational Evaluation of Emissions of an Engine with a Re-Entrant Piston Bowl - A Validation 1 2 3 4 5 Detailed study of existing piston bowl. Experimental observation of emissions using test rig of a directinjection diesel engine with a re-entrant type piston bowl Modeling of piston bowl as per specifications of the experimental test rig Simulation of piston bowl geometry for emission behavior Validation of experimentaal results with computational Figure 4 Methodology of the research 2. EXPERIMENTAL SETUP Fig.5. (a) shows a CAD model of the engine designed in Pro-E used for simulation purpose. The engine used for experimental purpose is also shown in Fig.5. (b) (a) (b) Figure 5 (a) Engine- CAD Model; (b) Experimental Test rig- DI Engine The engine with the specifications shown in Table 1 is used for experimental test with the operating conditions shown in Table 2. Table 1 Engine Specifications Engine Parameters Specifications Displacement (cm 3 ) 1997 Number of cylinders 4 Number of valves 16 Engine breathing Turbo Bore x Stroke 85 x 88 mm Compression ratio 18:1 Max power @ 4000rpm 66kW http://www.iaeme.com/ijmet/index.asp 396 editor@iaeme.com
M. Thamarai Kannan, Rupesh P L, Raja K and M.P. Siva Parameters Table 2 Operating Conditions Desired Values Engine water circuit pressure 1.4 bar Engine speed 4000 rpm Water temperature control lower threshold 80 C Water temperature control higher threshold 85 C Water temperature alert threshold 95 C Water temperature alarm threshold 98 C Oil temperature alert threshold 85 C Oil temperature alarm threshold 98 C Oil pressure alert threshold 1 bar Oil pressure alarm threshold 0.8 bar 2.1. Emission Test and Measurements Emission test on constant speed diesel engine has been carried out at five different load conditions 10%, 25%, 50%, 75%, 100% respectively using transient dynamometer. Table 3 shows the performance measurement of the experimental test rig and the observed emission measurements is shown in Table 4. Table 3 Test Readings I Sl.No. Load (%) Torque (Nm) Power (kw) BMEP (bar) BSFC (g/kwh) 1 10 18.56 2.92 1.17 416.0 2 25 46.36 7.29 2.92 275.2 3 50 91.49 14.39 5.76 236.8 4 75 136.14 21.41 8.57 223.8 5 100 180.58 28.40 11.36 229.1 Sl.No. Load (%) Weight factor Engine Speed (rpm) Table 4 Test Readings II CO emissions (g/hr) HC emissions (g/hr) NoX emissions (g/hr) PM (g/hr) 1 10 0.1 1502 31.2 7.8 18.3 0.9 2 25 0.3 1501 22.0 4.6 37.5 0.8 3 50 0.3 1502 15.2 3.0 76.4 1.0 4 75 0.25 1502 13.4 2.7 175.3 1.7 5 100 0.05 1502 14..5 3.2 230.1 5.0 Fig. 6 (a) & (b) shows the variation of CO and HC emissions along with change in load respectively in the form of plot. It has been observed that CO & HC emissions decrease with increase in load. http://www.iaeme.com/ijmet/index.asp 397 editor@iaeme.com
Experimental and Computational Evaluation of Emissions of an Engine with a Re-Entrant Piston Bowl - A Validation (a) (b) Figure 6 (a) Load (%) Vs CO emissions (g/hr); (b) Load (%) Vs HC emissions (g/hr) The variation of Particulate and NOx emissions along with load has been depicted in the form of graph which is shown in Fig. 7 (a) & (b) respectively. As the load increases, particulate and NOx emissions increases simultaneously which is observed in the graph. (a) (b) Figure 7 (a) Load (%) Vs NoX emissions (g/hr); (b) Load (%) Vs PM emissions (g/hr) Table 5 shows the results of emission test which indicated the rate of emission of No x, Co, HC & PM in g/kwhr. Emission Table 5 Emission results g/kwhr No x 6.223 Co 2.472 HC 0.555 PM 0.114 http://www.iaeme.com/ijmet/index.asp 398 editor@iaeme.com
3. COMPUTATIONAL MODEL M. Thamarai Kannan, Rupesh P L, Raja K and M.P. Siva 3.1. Design of Piston Bowl The Fig 8 (a) & (b) shows the piston bowl in 2D and 3D model selected for the current work. The bowl specifications were shown in Table 6. Table 6 Bowl Specifications Bowl Throat Dia (mm) Bowl Radius (mm) Lip Radius (mm) Compression Ratio Base Bowl 38 6.5 1 18 An engine model of closed surface geometry is created which is shown in below fig 9 for the CFD simulation work. This closed surface geometry is converted into STL file and then it is imported in the CFD software. While importing this surface geometry file into CFD software there may be loss of surface occur. Those surfaces can be repaired or reproduced in the CFD software (a) (b) Figure 8 Piston Bowl (a) 2D Model (b) 3D Model (a) (b) Figure 9 (a) Engine model for simulation; (b) Imported Engine model for simulation Model is prepared to simulate actual operating conditions of engine. Validation of model is done by comparing available engine measurements. The engine under simulation is used for power generation application. The engine runs at constant speed of 1500 rpm and hence the same is considered during simulation. Other important parameters to be used are swirl no. at inlet valve closure, injection duration, spray cone angle, EGR rate. Engine and spray data used for the simulation of computational model is shown in Table 7 (a) and (b). http://www.iaeme.com/ijmet/index.asp 399 editor@iaeme.com
Experimental and Computational Evaluation of Emissions of an Engine with a Re-Entrant Piston Bowl - A Validation Table 7 (a) Engine Data Bore (mm) 85 Stroke (mm) 88 Compression Ratio Base Engine18 Connecting Rod Length 145 Engine Speed (rpm) 1500 EGR % 20 IVC and EVO crank angles 234 &478 Table 7 (b) Spray Data Fuel Type Diesel Start of Injection 10 deg BTDC Injection Duration 17 deg No of holes 5 Nozzle hole size (mm) 0.129mm Table 8 shows the comparison of engine test result with simulated result. Simulated results are within ± 5% except CO emissions. Table 8 Simulation readings Parameter Experimental Reading Predicted CPCB-I limits CO emissions(g/kwh) 2.472 2.902 3.5 HC emissions(g/kwh) 0.555 0.567 1.3 NoX emissions(g/kwh) 6.223 6.287 9.2 4. VALIDATION OF COMPUTATIONAL RESULTS WITH EXPERIMENTAL http://www.iaeme.com/ijmet/index.asp 400 editor@iaeme.com
M. Thamarai Kannan, Rupesh P L, Raja K and M.P. Siva Figure 10 (a) Load (%) Vs CO emissions (g/hr); (b) Load (%) Vs HC emissions (g/hr); (c) Load (%) Vs NoX emissions (g/hr) The results of simulation of the computational model are compared with those of experimental which are depicted as graphs indicating the load variation with CO, HC and No x emissions. Fig. 10 (a), (b) & (c) shows the variation of both experimental and simulation and it indicates that both hold in good agreement with each other. 5. CONCLUSIONS In this work CONVERGE CFD software is used to optimize the piston bowl for constant speed power generation direct injection diesel engine. The model was first validated with available engine measurements and used to predict emissions. It has been concluded after validation that the experimental results hold in good agreement with that of computational and we can able to optimize the piston bowl of an existing diesel engine using the current simulation model in order to meet CPCB-II emission Norms. The present study also reveals the role of combustion bowl shape and nozzle geometry on emissions of a DI Diesel Engine. REFERENCES [1] Katsuhiko, Miyamoto et al Enhancement of Combustion by Means of Squish piston, Technical Series 2006 No. 18. [2] Genzale, C., Reitz, R., and Wickman, D., A Computational Investigation into the Effects of Spray Targeting, Bowl Geometry and Swirl Ratio for Low- Temperature Combustion in a Heavy-Duty Diesel Engine, SAE Technical Paper 2007-01-0119, 2007, doi: 10.4271/2007-01-0119. [3] Diwakar, R. and Singh, S., Importance of Spray-Bowl Interaction in a DI Diesel Engine Operating under PCCI Combustion Mode, SAE Technical Paper 2009-01-0711, 2009, doi:10.4271/2009-01-0711. [4] Lu Lin, Duan Shulin, Xiao Jin, Wu Jinxiang and Gao Xiaohong, Effects of Combustion Chamber Geometry on In-Cylinder Air Motion and Performance in DI Diesel Engine, SAE Technical Paper Series 2000-01-0510 [5] Rahman M. Montajir, H. Tsunemoto H. Ishitani and T. Minami, Fuel Spray Behavior in a Small DI Diesel Engine: Effect of Combustion Chamber Geometry, SAE Technical Paper Series 2000-01-0946 http://www.iaeme.com/ijmet/index.asp 401 editor@iaeme.com
Experimental and Computational Evaluation of Emissions of an Engine with a Re-Entrant Piston Bowl - A Validation [6] Rahman Md. Montajir, Hideyuki Tsunemoto, Hiromi Ishitani, Tsukamoto Koji and Kubo Kenichi, A New Combustion Chamber Concept for Low Emissions in Small DI Diesel Engines SAE Technical Paper Series 2001-01-326 [7] Shubham Sawant and Deep Prajapati. A Review on Zero Emissions Vehicles. International Journal of Mechanical Engineering and Technology, 8(2), 2017, pp. 198 202. [8] Min-Seok Oh and Seunguk Na. Building Information Modelling (BIM) Based Co2 Emissions Assessment in the Early Design Stage. International Journal of Civil Engineering and Technology, 8(5), 2017, pp. 1411 1425. [9] C. Ajay Sekar, Combustion Study and Emission Characteristics of Blends of Diesel and Hythane for Gas Turbine Engines. International Journal of Mechanical Engineering and Technology, 7(6), 2016, pp. 105 113. http://www.iaeme.com/ijmet/index.asp 402 editor@iaeme.com