Computational Investigation of Performance and Emission Characteristics of Diesel Engine Running on Soybean Biodiesel with Varying Injection Timing

Computational Investigation of Performance and Emission Characteristics of Diesel Engine Running on Soybean Biodiesel with Varying Injection Timing

Shubham Mehta

PG Scholar

Department of Mechanical Engineering Rajiv Gandhi Proudyogiki Vishwavidyalaya Bhopal, India

Dr. Nitin Shrivastava

Asst. Professor Department of Mechanical Engineering

Rajiv Gandhi Proudyogiki Vishwavidyalaya Bhopal, India

Abstract On account of the energy crisis and search for possible next generation alternative fuel, biodiesels have emerged as a popular choice for research in case of diesel engines. The characteristics of biodiesel are similar to diesel and thus they have been the subject of research for many years. Efforts are being made to increase the Brake Thermal efficiency and decrease the NOx emissions from diesel engines when running on biodiesels. For this, extensive experimentation is required which is cost ineffective and exhaustive. This work investigates the performance and emissions of a single cylinder diesel engine running on Soybean Biodiesel by varying the Injection Timing via the numerical approach using Diesel-RK software. Simulations were carried out for three different injection timings of 23°, 26°, and 29° bTDC for Soybean Methyl Ester (SME), at different load conditions in terms of brake power and constant speed of 1500 rpm and the results have been compared with those of baseline diesel fuel. The predicted results show better engine emission characteristics for the advancement of injection timing except NOx emissions while engine performance is better for retardation of timing except PM and Smoke emissions. The performance of diesel fuel is better than Soybean biodiesel, while SME exhibits low Smoke and PM emissions.

Keywords Biodiesel, SME, Injection Timing, Simulation, Diesel-RK software.

1. INTRODUCTION

   The transportation sector is an important unit which affects the economy of a nation. Most of the vehicles used today, be it commercial passenger cars, buses, motorcycles, or heavy-duty vehicles such as trucks and locomotives are reliant on fossil fuels such as Petrol and Diesel as an energy source. However, these fuels being a product of petroleum are non-renewable and will become scarce in the near future. Further, the emissions from engines using these fuels cause serious environmental problems of air pollution. Thus, extensive research has been going on in the field of alternative fuels. In the case of compression ignition engines, such as those running with diesel fuel, biodiesel has emerged as an important alternative [1].

   Biodiesel has emerged as a promising alternative due to its favorable properties which are quite close to that of diesel fuel. Further, diesel engines can be run while fuelled with biodiesel with little or no modification. Biodiesels contain

   oxygen in their chemical structure, which enhances the combustion characteristics. However, reports indicated that usage of biodiesels results in high NOx emissions [2]. Also, under similar operating conditions, BSFC is more in the case of biodiesels. Thus, research is going on for establishing the compatibility of biodiesel for present diesel engines.

   In diesel engines, the fuel is injected some moments before the piston reaches top dead centre (TDC) position. The timing of injection is reported in terms of crank angle and is known as Injection Timing. This has a significant effect on the combustion, performance, and emissions, and one of them is NOx, where retardation of injection timing has resulted in the decrease of NOx emissions [3].

   Experimental studies have reported significant results about the effect of injection timing, where the advancement has led to improvement in engine performance except NOx emissions [4]. In another study, injection timing advance led to a considerable decrease in CO, HC, and smoke emissions [5]. Also, a study with waste plastic oil reported increase in BTE with retardation of injection timing [3], and a similar trend was observed for the study with Mahua oil methyl ester [6].

   Thus, many experimental studies have been done on biodiesel as an alternative fuel, but the case of injection timing has not been addressed much. Furthermore, the reported studies are largely experimental in nature, which takes time and is expensive. Therefore, in this work, a commercially available engine simulation software Diesel-RK has been used to simulate the performance and emission characteristics of the engine with varying injection timings of 23°, 26°, and 29° bTDC for Diesel No. 2 (B0) and Soybean Methyl Ester (SME) (B100) fuels.

2. DIESEL-RK SIMULATION MODEL

   Diesel-RK is intended for full-cycle thermodynamic simulation of IC Engines and is used for combustion, performance, and emission analysis. It has advanced RK model which can be used to predict the performance and emissions over the whole operating range [7] and also provides simulation capability for biofuels and their blends with diesel [8]. In this work Diesel-RK has been used since its agreement with actual experimental data is reported to be very

   good [7], and recalibration of the model is not necessary for different operating modes of the engine [9]. Also, several studies have reported the validity of the model to be used for IC Engine simulation [10], [11]. Diesel-RK is intended for full-cycle thermodynamic simulation of IC Engines and is used for combustion, performance, and emission analysis. It has advanced RK model which can be used to predict the performance and emissions over the whole operating range [7] and also provides simulation capability for biofuels and their blends with diesel [8]. In this work Diesel-RK has been used since its agreement with actual experimental data is reported to be very good [7], and recalibration of the model is not necessary for different operating modes of the engine [9]. Also, several studies have reported the validity of the model to be used for IC Engine simulation [10], [11].

3. PROPERTIES OF FUEL AND METHODOLOGY Soybean Methyl Esters (SME) or Soybean biodiesel can

   be produced via transesterification process of soybean vegetable oil using a catalyst. This transforms the large branched molecular structure of oil to smaller straight-chained hydrocarbon structure for combustion in regular diesel engines and also reduces the viscosity of the oil. Further, soybean biodiesel has excellent lubricity and contains very small quantities of phosphorous and sulphur. Thus, SO2 emissions are almost negligible. Important properties of Soybean biodiesel are given in Table 1 with those of diesel for comparison.

   The simulation is based on a single cylinder engine whose specifications are taken from [12] and are mentioned in Table

   2. Performance parameters such as BSFC, BTE, and emission parameters such as EGT, NOx, CO2, PM, and Smoke emissions have been calculated for three different injection timings at variable loads in terms of brake power at a constant speed of 1500 rpm for both the fuels. The results are discussed in sections that follow.

   TABLE I. PROPERTIES OF FUEL

   Property	SME (B100)	Diesel No. 2
   Cetane Number	51.3	48
   Calorific Value (MJ/kg)	36.22	42.5
   Molecular mass	292.2	190
   C	0.7731	0.87
   H	0.1188	0.126
   O	0.1081 /td>	0.004
   Sulphur Fraction	0.005	0
   Flash Point (°C)	168	63

   TABLE II. ENGINE SPECIFICATIONS

   Manufacturer	Kirloskar
   Model	DAF-8
   Type	4 Stroke
   Rated Brake Power (bhp/kW)	8/5.9
   No. of cylinder	One
   Bore x Stroke (mm)	95 x 110
   Compression Ratio	17.5
   Cooling System	Air-cooled
   Cubic capacity	0.78 Litres
   Inlet Valve Open	4.5° bTDC
   Inlet Valve Closed	35.5° aBDC
   Exhaust Valve Open	35.5° bBDC
   Exhaust Valve Closed	4.5° aTDC
   Fuel Injection Timing	26° bTDC

4. RESULTS AND DISCUSSION

   The results of simulation for Diesel (B0) and SME (B100) are reported and discussed in this section. Among performance parameters, the variations of BSFC and BTE are plotted with Brake Power (% of Rated Power) with different injection timings. Among emission parameters, the variations of EGT, NOx, CO2, Smoke and PM emissions have been presented in similar fashion.

   1. Variation of Brake Specific Fuel Consumption

      The variations of BSFC with Brake Power (% of Rated Power) for injection timings of 23°, 26°, and 29° bTDC are shown in Figure 1. It is seen that BSFC increases with advancement and decreases with retardation of injection timing for both the fuels. In the case of full load (rated power), the BSFC increased by 1.71% for diesel and 4.93% for SME by the advancement of injection timing by 3° CA from the standard setup of 26° bTDC. Also, the BSFC decreased by 3.74% for SME by retardation of timing by 3° CA. Retarding the injection timing decreases the ignition delay period, thus leading to less accumulation of fuel and decreasing overall fuel consumption. On the comparison between the two fuels, it is seen that BSFC for diesel is always lower than that of SME for all loads and injection timings. This is due to the lower calorific value of SME and thus more fuel is needed to produce the same power. Therefore, the variation shows lowest BSFC for retarded timing (23° bTDC) and highest BSFC for advanced timing (29° bTDC) for diesel as well as for SME. Similar trends were reported in an experimental study [13].

      Fig. 1 Variation of Brake Specific Fuel Consumption

   2. Variation of Brake Thermal Efficiency

      The variations of BTE with Brake Power (% of Rated Power) for injection timings of 23°, 26°, and 29° bTDC are shown in Figure 2. It shows that thermal efficiency decreases with advanced injection timing and increases with retarded timing for both the fuels. For full load condition, BTE increased to 32.57% from 31.84% for Diesel while it increased to 31.27% from 30.1 % for SME for retarded injection timing from 26° bTDC to 23° bTDC. Also, it decreased from 31.84% to 31.31% for Diesel while it decreased from 30.1% to 28.69% for SME for advanced injection timing from 26° bTDC to 29° bTDC. Retarding the injection timing decreases the ignition delay period which results in combustion continuing up to the power stroke leading to better thermal efficiency [14]. It can be observed that Diesel exhibits better BTE than SME for all injection timings. This is due to lower calorific value and higher density of SME than diesel which results in lower thermal efficiency. Thus, BTE is highest for retarded injection timing of 23° bTDC and lowest for advanced injection timing of 29° bTDC for both the fuels.

      Fig. 2 Variation of Brake Thermal Efficiency

      Fig. 3 Variation of Exhaust Gas Temperature

   3. Variation of Exhaust Gas Temperature

      The variations of Exhaust Gas Temperatures for the respective cases are shown in Figure 3. A similar trend is seen for both the fuels where exhaust gas temperature slightly increases with advanced injection timing. As stated earlier, advanced injection timing increases the ignition delay, leading to higher fuel consumption and consequently higher cylinder temperatures. However, the increase in EGT is much more in the case of SME than Diesel. This is primarily due to the presence of oxygen in the chemical composition of SME biodiesel which leads to better combustion process. Thus, maximum EGT is observed for SME for 29° bTDC injection timing.

   4. Variation of NOx Emissions:

      The variations of NOx emissions for the three injection timings are shown in Figure 4. It is seen that NOx emissions increase with advanced injection timing and decrease with retarded injection timing for both diesel and SME. As stated earlier, the increase in ignition delay due to timing advancement increases the cylinder temperatures and provides favourable conditions for NOx formation. For the advance of 3° CA in injection timing, NOx emissions increased by 7.65% and 15.03% for diesel and SME respectively for full load condition. On the other hand, NOx emissions decreased by 11.63% and 15.82% for diesel and SME respectively by retarding injection timing by 3° CA. If both fuels are compared for same injection timing at the same load, it is clear that NOx emissions are predominantly higher for SME than those of diesel. This is due to oxygen-rich chemical composition of SME biodiesel. Further, all biodiesels emit higher NOx emissions than diesel due to the presence of oxygen in their molecules. The predicted trends match qualitatively with experimental results reported in the literature [3], [15].

      Fig. 4 Variation of NOx Emissions

   5. Variation of CO2 Emissions

      The variations of CO2 emissions under varying injection timing are shown in Figure 5. CO2 emissions follow increasing trend with advancement and decreasing trend with retardation of injection timing for both diesel and SME. Clearly, injection timing advance increases the delay period which provides longer time for combustion, hence efficient combustion occurs which increases CO2 emissions while decreasing CO emission. Advance in injection timing decreases the thermal energy lost due to incomplete combustion products since CO emissions are reported to be decreased [16]. It is to be noted that CO2 emissions are more for SME than diesel with highest emissions occurring for SME at 29° bTDC injection timing. This is again due to oxygen rich composition of biodiesels leading to better combustion.

      Fig. 5 Variation of CO2 Emissions

   6. Variation of Specific PM and Smoke Emissions

   The variations of Specific Particulate Matter (SPM) and Smoke (in terms of Bosch Smoke Number) emissions are shown in Figures 6 and 7 respectively. The trend shows that there is a decline in both SPM and Smoke emissions with the advancement of injection timing for either diesel or SME. The primary reason is the increase in ignition delay as a result of timing advance which provides more time for combustion,

   hence enhancing combustion efficiency and reducing incomplete products in the exhaust. Also, these emissions are much lesser for SME than diesel for same operating conditions. Thus, SME burns more cleanly than diesel due to its inherent oxygen content leading to efficient combustion. Lowest Smoke and PM emissions are for 29° bTDC injection timing for both diesel and SME, the lowest being for soybean biodiesel. Similar observations were reported in other experimental studies [15].

   Fig. 6 Variation of Specific PM Emissions

   Fig. 7 Variation of Smoke Emissions

5. SUMMARY & CONCLUSION

The numerical investigation was conducted for a single cylinder four stroke diesel engine to study the effect of injection timing on performance and emission characteristics when the engine was run with diesel and Soybean biodiesel. Simulation method was chosen as it reduces manpower, exhaustive experimentation, and time for a research study. A commercially available software Diesel-RK based on multi- zone fuel spray combustion model was chosen for this approach since it is user-friendly, freely available, and experimental studies have validated its use for ICE simulation. Following conclusions were drawn from this study:

• Injection timing influences engine performance and emission characteristics since it affects the ignition delay period.

• Retarding the injection timing has improved performance characteristics of the engine such as BTE and BSFC for both diesel and soybean biodiesel. Further, significant reductions in NOx emissions are seen for both fuels. However, it has resulted in an increase of SPM and Smoke emissions due to less time available for combustion resulting in incomplete products in exhaust.

• On the other hand, advanced injection timing has resulted in improved emission characteristics of the engine such as low PM, and Smoke emissions while decreasing the engine performance slightly.

• Comparing the two fuels, diesel gives better performance than soybean biodiesel and emissions of CO2 and NOx are lower, while the usage of Soybean biodiesel results in lower Smoke and PM emissions.

• Soybean biodiesel can be used with advanced injection timing to reduce smoke and PM emissions with slight decrease in performance, while NOx emissions are taken care of by Exhaust Gas Recirculation technique or with retarded injection timing to reduce NOx emissions, while PM and Smoke are taken care of by exhaust after- treatment system, thus providing a two-fold strategy for trade-off between performance and sustainability to the end user.

REFERENCES

1. V. W. Khond and V. M. Kriplani, Effect of nanofluid additives on performances and emissions of emulsified diesel and biodiesel fueled stationary CI engine: A comprehensive review, Renewable and Sustainable Energy Reviews, vol. 59. pp. 13381348, 2016.

2. A. N. Ozsezen and M. Canakci, Determination of performance and combustion characteristics of a diesel engine fueled with canola and waste palm oil methyl esters, in Energy Conversion and Management, 2011, vol. 52, no. 1, pp. 108116.

3. M. Mani and G. Nagarajan, Influence of injection timing on performance, emission and combustion characteristics of a DI diesel engine running on waste plastic oil, Energy, vol. 34, no. 10, pp. 1617 1623, 2009.

4. J. Narayana Reddy and A. Ramesh, Parametric studies for improving the performance of a Jatropha oil-fuelled compression ignition engine, Renew. Energy, vol. 31, no. 12, pp. 19942016, 2006.

5. C. Sayin and M. Gumus, Impact of compression ratio and injection parameters on the performance and emissions of a di diesel engine fueled with biodiesel-blended diesel fuel, Appl. Therm. Eng., vol. 31, no. 16, pp. 31823188, 2011.

6. C. Solaimuthu and P. Govindarajan, Effect of injection timing on performance , combustion and emission characteristics of diesel engine using mahua oil methyl ester as fuel, J. Sci. Ind. Res., vol. 71, pp. 69 74, 2012.

7. A. S. Kuleshov, Model for predicting air-fuel mixing, combustion and emissions in DI diesel engines over whole operating range, SAE Pap., no. 200501, p. 2119, 2005.

8. A. Kuleshov and K. Mahkamov, Multi-zone diesel fuel spray combustion model for the simulation of a diesel engine running on biofuel, Proc. Inst. Mech. Eng. Part A J. Power Energy, vol. 222, no. 3, pp. 309321, 2008.

9. M. A. Hamdan and R. H. Khalil, Simulation of compression engine powered by Biofuels, Energy Convers. Manag., vol. 51, no. 8, pp. 17141718, 2010.

10. A. Alahmer, J. Yamin, A. Sakhrieh, and M. A. Hamdan, Engine performance using emulsified diesel fuel, Energy Convers. Manag., vol. 51, no. 8, pp. 17081713, 2010.

11. M. F. Al-Dawody and S. K. Bhatti, Optimization strategies to reduce the biodiesel NOx effect in diesel engine with experimental verification, Energy Convers. Manag., vol. 68, pp. 96104, 2013.

12. P. K. Sahoo and L. M. Das, Combustion analysis of Jatropha, Karanja and Polanga based biodiesel as fuel in a diesel engine, Fuel, vol. 88, no. 6, pp. 994999, 2009.

13. S. Jindal, Combustion, performance and emissions of a DI-CI engine running on Karanj methyl ester: influence of injection timing, Int. J. Sustain. Eng., vol. 4, no. 2, pp. 136144, Jun. 2011.

14. C. Sayin, M. Ilhan, M. Canakci, and M. Gumus, Effect of injection timing on the exhaust emissions of a diesel engine using diesel methanol blends, Renew. Energy, vol. 34, no. 5, pp. 12611269, 2009.

15. G. R. Kannan and R. Anand, Effect of injection pressure and injection timing on DI diesel engine fuelled with biodiesel from waste cooking oil, Biomass and Bioenergy, vol. 46, pp. 343352, 2012.

16. R. Senthil, R. Silambarasan, and N. Ravichandiran, Influence of injection timing and compression ratio on performance, emission and combustion characteristics of Annona methyl ester operated diesel engine, Alexandria Eng. J., vol. 54, no. 3, pp. 295302, 2015.