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Numerical investigation of two-stroke marine diesel engine emissions using exhaust gas recirculation at different injection time
Ocean Engineering 144 (2017) 90–97
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Ocean Engineering journal homepage: www.elsevier.com/locate/oceaneng
Numerical investigation of two-stroke marine diesel engine emissions using exhaust gas recirculation at different injection time Xiuxiu Sun, Xingyu Liang *, Gequn Shu, Jiansheng Lin, Yuesen Wang, Yajun Wang State Key Laboratory of Engines, Tianjin University, Tianjin 30002, China
A R T I C L E I N F O
A B S T R A C T
Keywords: Marine diesel engine Emission Inlet pressure EGR Injection time
The computational fluid dynamic (CFD) model was established for a two-stroke marine diesel engine. The detailed chemical solver was adopted as combustion model. n-tetradecane was used as an alternative fuel. The simulation model was validated using experimental data. The effects of inlet pressure, exhaust gas recirculation (EGR) and start of injection (SOI) time were investigated on the emission of marine diesel engine. The base parameters were compared, including mean in-cylinder pressure, indicated power and indicated specific fuel consumption (ISFC). The trade-off between NOx and ISFC was also researched. Results show that NOx emissions become less and less when the inlet pressure exceeds 0.369 MPa. NOx emissions reduce strongly when the EGR is used. The quantity of NOx emissions meets the requirement of Tier III when the EGR rate reaches 20%. Analysis results reveal that the quantity of NOx emissions declined with retarded SOI; however, ISFC increases. The decrement in NOx emissions is quite small under high EGR rate; however, the associated increase in ISFC is large. Coupling EGR with SOI not only decreases NOx, emissions but also lowers ISFC. This paper provides a workable technological method to optimize marine diesel engine emissions.
1. Introduction
temperature also effects the performance and emissions of heavy duty direct injection diesel engines (Hountalas et al., 2008). The low temperature EGR improves brake specific fuel consumption (BSFC) and lowers soot, but has only a small positive effect on NOx emissions. Low EGR temperature has a stronger effect at higher EGR rates. Yu et al. (2014) showed that with increasing EGR rate, the cylinder pressure and combustion temperature reduces and the peak of soot also shows a downward but more gentle trend, under the same load conditions. Although EGR is a useful technology for diminishing NOx emissions, it is necessary to use other methods to limit the associated reduce in BSFC. Wagner et al. (2003) described the simultaneous decreases of NOx and PM emissions in a modern light-duty diesel engine under high EGR levels. They used a combination of EGR and manipulation of injection parameters. Their results showed that improved understanding of this combustion regime will lead to wider EGR utilization to meet the lower performance requirements of post-combustion emissions controls. Verschaeren et al. (2014) investigated NOx emissions in a medium-speed heavy-duty diesel engine using EGR and Miller timing. An injection advance during low-load operation raised combustion pressures and shortened combustion duration. Chen et al. (2014) studied pilot injection for improvement of combustion characteristics in a heavy-duty diesel engine. Their results demonstrated that with the advance of pilot
Environmental pollution is of global concern. Marine diesel engines produce more emissions than do vehicle engines. Emission regulations have recently become more stringent for marine engines. The International Maritime Organization Tier III requires NOx emissions not exceed 3.4 g/kWh, when operating inside an emission control area (Emission Standards, 2016). Many technologies have been proposed to make marine engines meet these requirements, such as alternative fuels, internal engine modifications, humid air motors, exhaust gas recirculation (EGR), and selective catalytic reduction (Yang et al., 2012; Roskilly et al., 2015; Zhou et al., 2013). Diesel engines commonly employ EGR to lower NOx emissions. Raptotasios et al. (2015a) showed that NOx emissions meet the Tier III requirement when the EGR rate exceeds 35% for the two-stroke 4T50ME-X test marine diesel engine. Deepak et al. (Agarwal et al., 2011) studied the effect of EGR on the performance, emission, deposits and durability for a constant speed compression ignition engine. Decreases in NOx and exhaust gas temperature were observed but emissions of particulate matter (PM), HC, and CO were found to increase with EGR use. At the same time, higher carbon deposits and higher wear of piston rings were observed on the engine parts operating with EGR. The EGR * Corresponding author. E-mail address: [email protected] (X. Liang).
http://dx.doi.org/10.1016/j.oceaneng.2017.08.044 Received 13 March 2017; Received in revised form 27 August 2017; Accepted 28 August 2017 0029-8018/© 2017 Published by Elsevier Ltd.
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injection timing, the peak in-cylinder pressure dropped down, the ignition delay of the main combustion is shortened, and the NOx and soot emissions are reduced, whereas the HC and CO emissions are increased. Tadros et al. (2016) studied the effect of different start angles of combustion on performance and the exhaust emissions of a marine diesel engine. The start angles of combustion at the lowest speed of the engine are retarded top dead center, which reduces the exhaust emissions and decreases the brake power a little bit. Saravanan (2015) studied the effect of EGR and advanced injection timing on the combustion characteristics of a diesel engine. From their experimental results it can be concluded that NOx and smoke emissions can be controlled simultaneously with less variation in the combustion characteristics of the engine. The trade-off relationship between BSFC and NOx can be improved by applying EGR and adjusting the injection timing (Verschaeren et al., 2014; Aldajah et al., 2007; Thangaraja and Kannan, 2016; Li et al., 2014). Computer simulations have increased in potential applications with the development of computers. It is now practical to use computer simulations to model marine diesel engines. Owing to the large volume of a marine engine, experimental research is difficult and expensive. Pang et al. (2016) investigated soot formation and oxidation processes in a large two-stroke marine diesel engine using integrated computational fluid dynamic (CFD)-chemical kinetics. They developed a new n-heptane skeletal diesel surrogate model for analyzing combustion and soot. Panagiotis et al. (Kontoulis et al., 2008) used the KIVA-3 code as the modeling platform to study the effects of advanced injection strategies. They demonstrated that by adding an appropriately timed pilot injection, fuel savings of the order of 1.7% can be achieved, without increasing NOx emissions. They used n-tetradecane as an alternative fuel. Sun et al. (2017a) compared the performance of n-heptane and n-tetradecane as alternative fuels in a marine diesel engine. The quantity of emissions is related to the combustion models and alternative fuels. It is important to choose an appropriate combustion model and alternative fuel for the simulation of a marine diesel engine. In this paper, a CFD model of a two-stroke marine diesel engine is established and validated using experimental data. The effects of inlet pressure, EGR rate and injection time on the performance of marine diesel engines are studied. The optimal method is proposed to lower NOx emissions while minimizing the increase in indicated specific fuel consumption. This paper provides a solution to make a two-stroke marine diesel engine meet the requirement of Tier III.
Fig. 1. The three-dimensional geometric structure.
emissions generate models, the Extended Zeldovich NOx mechanism is applied to simulate the production of NOx. Hiroyasu-NSC Model is used to simulate soot production respectively. The injected liquid temperature is set to 345 K. The injection duration is 15.36 C A and the total injection mass is 0.0126 kg, which was obtained from experimental data. These models participate in calculated process of CFD model. In addition to these, the marine engine numerical simulation also is based upon continuity, momentum and energy conservation laws (Amsden et al., 1989). The continuity equation of flow field is:
∂ρ ⇀ þ ∇⋅ ρu ¼ ρ_ s ∂t ⇀
u is the velocity vector, ρ is the fluid density. ρ_ s is the source item. The equations of momentum conservation law on the x, y, and z directions as follows:
2. Brief description of the model
⇀ ∂ ρu
The CFD model is based on a marine diesel engine (6S35ME-B9). The main particulars are listed in Table 1. The engine speed is 142 r/min when operated at 100% load. The in-cylinder pressure and emission products were tested and used to validate the accuracy of the model. The engine simulation is performed using the commercial CFD software package CONVERGE 2.3. Fig. 1 shows the three-dimensional structure of model. This model includes a scavenge box, cylinder and exhaust port. The k-ε two-equation mode is used as turbulence model. Kelvin Helmholtz-Rayleigh Taylor model is applied to the simulation of spray breakup. The NTC collision model is implemented to simulate the fuel collision. The wall splash model is used in the O'Rourke model based on Weber number, film thickness and viscosity. The detailed chemical solver combustion model is used to simulate the fuel ignition. For the
∂t
⇀s 1 2 ⇀⇀ þ ∇⋅ ρu u ¼ 2 ∇P А0 ∇ ρk þ ∇⋅σ þ F þ Pg a 3
(2)
a is the dimensionless quantity of different fluid properties. P is the pressure; g represents the gravity; k is the turbulence energy; A0 has relationship with turbulence model (laminar flow A0 ¼ 0, turbulent flow A0 ¼ 1); σ is the viscous stress. The equation of energy conservation law as follow:
⇀ ∂ðρIÞ C S ⇀ ⇀ þ ∇⋅ ρuI ¼ P∇⋅u þ ð1 А0 Þσ⋅∇⋅J þ А0 ρε þ Q_ þ Q_ ∂t
(3)
⇀
I is the specific heat energy including chemical energy; J is the heat equator flux vector.
Table 1 6S35ME-B9 test engine specifications. cylinder number Bore (mm) Stroke (mm) Displacement (L) Connecting rod length (mm) Speed (r/min) Power (kW)
(1)
3. Model validation 6 350 1550 149 1550 142 3575
n-tetradecane is often used as an alternative fuel for the simulation of marine diesel engines Struckmeier et al. (2009) research the multi-component modeling of evaporation, ignition and combustion processes. The effects of fuel component properties on the ignition and combustion properties of the fuel blend have been investigated. The
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compress pressure and combustion are 0.8% and 1.5%, respectively. The time of change pressure delay is 0.846 C A for the model. The in-cylinder pressure is in good agreement with the experimental data. The model can accurately predict the pressure of marine diesel engine. The NOx and CO2 emissions are also compared to validate the accuracy of model, which are shown in Fig. 5. For NOx, the error is 2.8% for the simulation and for the experiment, which is acceptable for predicting the quantity of NOx. The error for CO2 is larger than that for NOx, owing to the combustion. The single component n-tetradecane is used as alternative fuel to simulate the combustion process. And, the new n-tetradecane mechanism is reduced for decreasing the calculated time. Some reactions are disappeared for CO2 produce mechanism. The quantity of NOx is close to the experimental data, that is to say: the CFD model can accurately predict the quantity of NOx using n-tetradecane as alternative fuel. The CFD model prediction of marine diesel engine performance is validated by simulation and experiment. This CFD model is used to study the effect of inlet pressure, EGR and start of injection time in this paper. The trade-off between ISFC and emissions is also investigated.
chemical reaction equations are solved assuming tetradecane. Panagiotis et al. (Raptotasios et al., 2015b) study the effects of advanced injection strategies on the performance marine diesel engine using Computational Fluid Dynamics (CFD) and T-φ Mapping. The tetradecane has been used as surrogate fuel. The new n-tetradecane mechanism was established in a previous study (Sun et al., 2017b). The n-tetradecane chemical property is more close to the real combustion for the marine diesel engine (Sun et al., 2017a). Fig. 2 shows the comparison of ignition delay times for the 62-species mechanism, the experiment (Shen et al., 2009), the detailed mechanism (Westbrook et al., 2009) and the simplified mechanism (Chang et al., 2013) under different pressure and equivalence ratio conditions. The ignition delay times of the 62-species mechanism are in good agreement with the experimental data for different conditions. The values of the new mechanism are closer to the experimental data than those of the detailed mechanism. So, the 62-species n-tetradecane mechanism is used in the CFD model to predict the performance of the marine diesel engine. The n-tetradecane used as an alternative fuel in the marine diesel engine is also used in the CFD model. Mesh grid size is decided based on the desired calculation time and calculation accuracy. Grid control includes a base grid, adaptive mesh refinement and fixed embedding. The effect of the base grid and the adaptive mesh refinement are shown in Fig. 3. As seen in Fig. 3 (a), the compression pressure of base grid 0.04 m is in agreement with that of base grid 0.03 m. The calculation accuracy increases gradually with decreasing base grid size. If the adaptive mesh refinement is set to 4, the calculated pressure is in good agreement with the experiment data, as shown in Fig. 3 (b). However, the calculation time also increases. Setting the base grid to 0.04 m and the adaptive mesh refinement to 4 can ensure the accuracy of the simulation. Fig. 4 shows the in-cylinder pressure comparison between the calculated value and experimental data. The errors of maximum
4. Results and discussion 4.1. Effect of inlet pressure Inlet pressure changes with the varying of EGR rate. The inlet pressure affects gas mass, which causes the variation of equivalence ratio. Thus, inlet pressure has an effect on the quantity of NOx. Fig. 6 shows the variation of in-cylinder pressure under different inlet pressure. The incylinder pressure cut down with decreasing inlet pressure. The main reason is that the gas mass is reduced, as shown in Fig. 7. The less gas mass, the lower the in-cylinder pressure, for the same geometry
Fig. 2. Comparison of ignition delay time for the new n-tetradecane mechanism. 92
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Fig. 3. The effect of grid on the pressure: (a) base grid (b) adaptive mesh refinement.
Fig. 6. The comparison of in-cylinder pressure under different inlet pressure conditions.
Fig. 4. Comparison of in-cylinder pressure for the simulation and experiment.
inlet pressure is similar to the outlet pressure, which is 0.339 MPa. The more residual exhaust gas, the higher the in-cylinder temperature is. Thus, the inlet gas mass reduces as the inlet pressure drops. Fig. 8 shows the comparison of NOx emissions under different inlet pressure. The quantity of NOx drops with increasing inlet pressure. The NOx emissions are lower when the inlet pressure exceeds 0.369 MPa. The oxygen concentrations remain almost the same when the inlet pressure exceeds 0.369 MPa, which was obtained from Fig. 7. The more exhaust gas remaining in the cylinder, the higher the temperature is. This higher temperature produces more NOx. The in-cylinder pressure and emission vary slightly when the inlet pressure exceeds 0.369 MPa. The main reason is that sufficient oxygen exists in cylinder, owing to the two-stroke scavenging method. It is necessary that the turbocharger keeps the inlet pressure at least 0.03 MPa higher than the outlet pressure. 4.2. Effect of EGR EGR is the standard method for controlling NOx emissions (Hountalas et al., 2008; Verschaeren et al., 2014; Zamboni and Capobianco, 2012). The decreased oxygen concentration, increased charge mixture specific heat capacity, and recirculated water vapor and CO2 affect the formation of NOx (Raptotasios et al., 2015a). The inlet pressure is kept at 0.369 MPa. The CFD model was used to evaluate the potential of EGR to lower the NOx emissions in a marine diesel engine. Fig. 9 shows the
Fig. 5. Comparison of NOx and CO2 for the simulation and experiment.
compression ratio. The in-cylinder pressure has maximum decrement when the inlet pressure is 0.349 MPa. For scavenging in a two-stroke cycle, the inflow gas actuates the emission products access to the exhaust pipe. More emission products remain in the cylinder when the
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Fig. 7. The comparison of gas mass under different inlet pressure conditions. Fig. 9. The comparison of in-cylinder pressure under different EGR rates: the case “NO” represents the EGR rate 0%.
Fig. 8. The comparison of NOx under different inlet pressure conditions. Fig. 10. The comparison of C14H30 mass under different EGR rates.
variation of in-cylinder pressure at different EGR rates. The maximum compress pressures are almost same for different EGR rates, because the inlet gas mass remains almost the same. However, the maximum combustion pressure drops with increasing EGR rate, primarily reason is that the quantity of unburned fuel increases. The oxygen concentration decreases, so more fuel will be unburned with increasing EGR rate, as shown in Fig. 10. Fig. 10 also shows the variation of fuel mass (C14H30) in cylinder. The higher EGR rate slows the combustion rate, and resulting in low in-cylinder temperature. Fig. 11 clearly shows that the maximum in-cylinder temperature reduced with increasing EGR rate. The main aim of the present study is to decline NOx emissions using EGR. Fig. 12 shows the variations of NOx and soot with increasing EGR rates. The quantity of NOx emissions falls with increasing EGR rate; however, soot has the opposite trend. The quantity of NOx emissions reduces to 2.96 g/kWh when the EGR rate is 20%. The quantity of NOx emissions is below 3.4 g/kWh, which is the limit value of NOx for Tier III. However, the quantity of soot increases to three times than that of the soot value when using 0% EGR. Higher EGR rate means lower oxygen concentrations and temperature. However, the NOx is produced in high temperature and rich oxygen. The formation of soot is related to fuel combustion. The increasing EGR rate slows the combustion rate, increasing the mass of unburned fuel, accelerating the formation rate of soot. Fig. 13 shows the variations of indicated power and indicated specific
Fig. 11. The comparison of in-cylinder mean temperature under different EGR rates. 94
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Fig. 12. The comparison of soot and NOx under different EGR rates.
fuel consumption (ISFC) at different EGR rates. The increasing EGR rate decreases indicated power and increases ISFC. Indicated power decreased by 4.7% compared with no EGR, whereas ISFC increases by 5.1%. The augment EGR rate causes combustion pressure droop (Fig. 9); indicated power is directly proportional to in-cylinder pressure. The injection mass is constant, so ISFC is inversely proportional to incylinder pressure. The trade-off between NOx emissions and ISFC cannot be ignored when EGR is used in marine diesel engines. It is necessary to take measures to control fuel consumption.
Fig. 14. Effect of SOI on the in-cylinder pressure.
4.3. Effect of start of injection time The start of injection (SOI) decides the initial time of combustion. Marine diesel engine performance is influenced by SOI. Fig. 14 shows the effect of SOI on in-cylinder pressure. The maximum combustion pressure increases with advanced SOI. The in-cylinder pressure and temperature are higher with advanced SOI, which occurs after top dead center. Incylinder pressure increases continuously with fuel injection. Higher pressures and temperatures shorten fuel atomization time. The combustion rate increases, causing the pressure to increase. Indicated power and ISFC are influenced by SOI, as shown in Fig. 15. Indicated power decreases and ISFC increases with retarded SOI. Retarded SOI delays the combustion process and shortens ignition time. Thus, the combustion is incomplete and the ISFC increases by about 1.5% when the SOI is delayed by 1 C A. The resulting indicated power falls by about 50 kW.
Fig. 15. Effect of SOI on the indicated power and ISFC.
Fig. 16 shows the variation of quantity of NOx with retarded SOI. The quantity of NOx reduces by about 3.7% when SOI is delayed by 1 C A. The quantity of NOx is almost the same when the injection time is 361.6 C A. Retarded SOI lowers the in-cylinder pressure and temperature. The temperature lowers the quantity of NOx for a given inlet oxygen concentration.
Fig. 13. The comparison of indicated power and ISFC under different EGR rates.
Fig. 16. Effect of SOI on the NOx. 95
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3. The quantity of NOx emissions falls with retarded SOI; however, the ISFC rises. The decrease in NOx emissions is quite small under high EGR rate but the increase in ISFC is large. 4. The increase in ISFC is improved by using advanced SOI under high EGR rate. This is a useful method for improving the performance of marine diesel engines.
4.4. Effect of EGR coupling with SOI The trade-off between ISFC and NOx is found for a marine diesel engine. The quantity of NOx emissions meets the limited value of Tier III when the EGR rate is reduced to 20%. However, ISFC increases by 8 g/ kWh. The quantity of NOx drops to 2 g/kWh and ISFC increases to 10 g/ kWh when the injection time changes from 360.6 C AA to 364.6 C AA. The EGR method is able to reduce the NOx emissions extensively, but the corresponding ISFC increases. Advancing SOI droops ISFC; however, this limits the decrease in NOx emissions. The trade-off between NOx emissions and ISFC can be solved by using EGR coupling with SOI. Fig. 17 shows the trade-off between ISFC and NOx under different EGR rates and SOI times. The quantity of NOx emissions increases by 7.5% and ISFC diminishes by 1.2% when SOI is delayed from 362.6 C A to 363.6 C A without EGR. The quantity of NOx emissions increases by 1.9% and ISFC falls by 1% when the EGR rate is 15%. The increment of NOx emissions is quite small under the high EGR rate; However, there is a marked decrease in ISFC. That is, ISFC is improved by advancing SOI under high EGR rate. Fig. 17 shows that the quantity of NOx emissions meets the requirement of Tier III when the EGR rate is 20%. However, ISFC increases to 8 g/kWh. ISFC is reduced by 1.44% when the SOI is advanced from 362.6 C AA to 361.6 C AA. Adjusting SOI is an effective method to decrease ISFC under high EGR rate.
Acknowledgements This work was supported by National Natural Science Foundation of China (No. 51376136 and No. 91641111), National Sci-Tech Support of China (2015BAG16B01) and the author also wants to appreciate the support of high-tech Ship Research Program of MIIT. References Agarwal, D., Singh, S.K., Agarwal, A.K., 2011. Effect of Exhaust Gas Recirculation (EGR) on performance, emissions, deposits and durability of a constant speed compression ignition engine. Appl. Energy 88 (2011), 2900–2907. Aldajah, S., Ajayi, O.O., Fenske, G.R., Goldblatt, I.L., 2007. Effect of exhaust gas recirculation (EGR) contamination of diesel engine oil on wear. Wear 263 (2007), 93–98. Amsden, A.A., Orourke, P.J., Butler, T.D., 1989. KIVA-2: a computer program for chemically reactive flows with sprays. Nasa Sti/recon Tech. Rep. N 89 (1989). Chang, Y., Jia, M., Liu, Y., Li, Y., Xie, M., Yin, H., 2013. Application of a decoupling methodology for development of skeletal oxidation mechanisms for heavy n -alkanes from n-octane to n-hexadecane. Energy & Fuels 27 (2013), 3467–3479. Chen, L., Zeng, H., Cheng, X.B., 2014. Study of pilot injection for the improvement of combustion and emissions characteristics in a heavy-duty diesel engine. Appl. Mech. Mater. 651–653 (2014), 866–874. Emission Standards, 2016. IMO Marine Engine. http://www.DieselNet.com/standards (Accessed July 12 2008). Hountalas, D.T., Mavropoulos, G.C., Binder, K.B., 2008. Effect of exhaust gas recirculation (EGR) temperature for various EGR rates on heavy duty DI diesel engine performance and emissions. Energy 33 (2008), 272–283. Kontoulis, P., Chryssakis, C., Kaiktsis, L., 2008. DE3-1: evaluation of pilot injections in a large two-stroke marine diesel engine, using CFD and t-φ mapping (DE: diesel engine Combustion,General session papers). In: The International Symposium on Diagnostics and Modeling of Combustion in Internal Combustion Engines, 2008, pp. 181–188. Li, X., Xu, Z., Guan, C., Huang, Z., 2014. Impact of exhaust gas recirculation (EGR) on soot reactivity from a diesel engine operating at high load. Appl. Therm. Eng. 68 (2014), 100–106. Pang, K.M., Karvounis, N., Walther, J.H., Schramm, J., 2016. Numerical investigation of soot formation and oxidation processes under large two-stroke marine diesel enginelike conditions using integrated CFD-chemical kinetics. Appl. Energy 169 (2016), 874–887. Raptotasios, S.I., Sakellaridis, N.F., Papagiannakis, R.G., Hountalas, D.T., 2015. Application of a multi-zone combustion model to investigate the NOx reduction potential of two-stroke marine diesel engines using EGR. Appl. Energy 157 (2015), 814–823. Raptotasios, S.I., Sakellaridis, N.F., Papagiannakis, R.G., Hountalas, D.T., 2015. Application of a multi-zone combustion model to investigate the NOx reduction potential of two-stroke marine diesel engines using EGR. Appl. Energy 157 (2015), pp.814–823. Roskilly, A.P., Palacin, R., Yan, J., 2015. Novel technologies and strategies for clean transport systems. Appl. Energy 157 (2015), 563–566. Saravanan, S., 2015. Effect of EGR at advanced injection timing on combustion characteristics of diesel engine. Alexandria Eng. J. 54 (2015), 339–342. Shen, H.S., Steinberg, J., Vanderover, J., Oehlschlaeger, M.A., 2009. A shock tube study of the ignition of n-heptane, n-decane, n-dodecane, and n-tetradecane at elevated pressures. Energy & Fuels 23 (2009), 2482–2489. Struckmeier, D., Tsuru, D., Kawauchi, S., Tajima, H., 2009. Multi-component Modeling of Evaporation, Ignition and Combustion Processes of Heavy Residual Fuel Oil. SAE Technical Papers, (2009). Sun, X., Liang, X., Shu, G., Wang, Y., Wang, Y., Yu, H., 2017. Effect of different combustion models and alternative fuels on two-stroke marine diesel engine performance. Appl. Therm. Eng. 115 (2017), 597–606. Sun, X., Liang, X., Shu, G., Wang, Y., Wang, Y., Yu, H., 2017. Development of a reduced ntetradecane-PAH mechanism for application on two-stroke marine diesel engine. Energy & Fuels 31 (2017), 941–952. Tadros, M., Ventura, M., Soares, C.G., 2016. Assessment of the performance and the exhaust emissions of a marine diesel engine for different start angles of combustion. Marit. Technol. Eng. 3 (2016). Thangaraja, J., Kannan, C., 2016. Effect of exhaust gas recirculation on advanced diesel combustion and alternate fuels - a review. Appl. Energy 180 (2016), 169–184. Verschaeren, R., Schaepdryver, W., Serruys, T., Bastiaen, M., Vervaeke, L., Verhelst, S., 2014. Experimental study of NOx reduction on a medium speed heavy duty diesel engine by the application of EGR (exhaust gas recirculation) and Miller timing. Energy 76 (2014), 614–621.
5. Conclusions A CFD model of a two-stroke marine diesel engine was established, and n-tetradecane was used as an alternative fuel. The simulation model was validated using experimental data. The model was used to assess the potential of EGR and SOI for reducing NOx emissions. The in-cylinder pressure, indicated power and ISFC were compared. The main results are as follows: 1. The quantity of NOx emissions increases by a large margin when the inlet pressure is close to the outlet pressure. At the same time, incylinder pressure decreases. However, the decrement of NOx emissions is small when the inlet pressure exceeds 0.369 MPa. The inlet pressure needs to remain 0.03 MPa higher than the outlet pressure. Otherwise, the performance of marine diesel engines is strongly impaired. 2. The quantity of NOx emissions strongly reduces when EGR is used in marine diesel engines. The value of NOx emissions meets the requirement of Tier III when the EGR rate is 20%. However, the indicated power declines and ISFC rise with increasing EGR rate.
Fig. 17. The relationship with ISFC and NOx. 96
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Ocean Engineering 144 (2017) 90–97 Yu, H.L., Yu, G.Z., Duan, S.L., 2014. Effects of exhaust gas recirculation on combustion and emission of a marine diesel engine. Adv. Mater. Res. 926–930 (2014), 905–908. Zamboni, G., Capobianco, M., 2012. Experimental study on the effects of HP and LP EGR in an automotive turbocharged diesel engine. Appl. Energy 94 (2012), 117–128. Zhou, S., Liu, Y., Zhou, J.X., 2013. A study on exhaust gas emission control technology of marine diesel engine. Adv. Mater. Res. 864–867 (2013), 1804–1809.
Wagner, R.M., Green, J.B., Dam, T.Q., Edwards, K.D., Storey, J.M., 2003. Simultaneous low engine-out NOx and particulate matter with highly diluted diesel combustion. Sae Trans. (2003) Westbrook, C.K., Pitz, W.J., Herbinet, O., Curran, H.J., Silke, E.J., 2009. A comprehensive detailed chemical kinetic reaction mechanism for combustion of n-alkane hydrocarbons from n-octane to n-hexadecane. Combust. Flame 156 (2009), 181–199. Yang, Z.L., Zhang, D., Caglayan, O., Jenkinson, I.D., Bonsall, S., Wang, J., Huang, M., Yan, X.P., 2012. Selection of techniques for reducing shipping NOx and SOx emissions. Transp. Res. Part D Transp. Environ. 17 (2012), 478–486.
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Contents lists available at ScienceDirect
Ocean Engineering journal homepage: www.elsevier.com/locate/oceaneng
Numerical investigation of two-stroke marine diesel engine emissions using exhaust gas recirculation at different injection time Xiuxiu Sun, Xingyu Liang *, Gequn Shu, Jiansheng Lin, Yuesen Wang, Yajun Wang State Key Laboratory of Engines, Tianjin University, Tianjin 30002, China
A R T I C L E I N F O
A B S T R A C T
Keywords: Marine diesel engine Emission Inlet pressure EGR Injection time
The computational fluid dynamic (CFD) model was established for a two-stroke marine diesel engine. The detailed chemical solver was adopted as combustion model. n-tetradecane was used as an alternative fuel. The simulation model was validated using experimental data. The effects of inlet pressure, exhaust gas recirculation (EGR) and start of injection (SOI) time were investigated on the emission of marine diesel engine. The base parameters were compared, including mean in-cylinder pressure, indicated power and indicated specific fuel consumption (ISFC). The trade-off between NOx and ISFC was also researched. Results show that NOx emissions become less and less when the inlet pressure exceeds 0.369 MPa. NOx emissions reduce strongly when the EGR is used. The quantity of NOx emissions meets the requirement of Tier III when the EGR rate reaches 20%. Analysis results reveal that the quantity of NOx emissions declined with retarded SOI; however, ISFC increases. The decrement in NOx emissions is quite small under high EGR rate; however, the associated increase in ISFC is large. Coupling EGR with SOI not only decreases NOx, emissions but also lowers ISFC. This paper provides a workable technological method to optimize marine diesel engine emissions.
1. Introduction
temperature also effects the performance and emissions of heavy duty direct injection diesel engines (Hountalas et al., 2008). The low temperature EGR improves brake specific fuel consumption (BSFC) and lowers soot, but has only a small positive effect on NOx emissions. Low EGR temperature has a stronger effect at higher EGR rates. Yu et al. (2014) showed that with increasing EGR rate, the cylinder pressure and combustion temperature reduces and the peak of soot also shows a downward but more gentle trend, under the same load conditions. Although EGR is a useful technology for diminishing NOx emissions, it is necessary to use other methods to limit the associated reduce in BSFC. Wagner et al. (2003) described the simultaneous decreases of NOx and PM emissions in a modern light-duty diesel engine under high EGR levels. They used a combination of EGR and manipulation of injection parameters. Their results showed that improved understanding of this combustion regime will lead to wider EGR utilization to meet the lower performance requirements of post-combustion emissions controls. Verschaeren et al. (2014) investigated NOx emissions in a medium-speed heavy-duty diesel engine using EGR and Miller timing. An injection advance during low-load operation raised combustion pressures and shortened combustion duration. Chen et al. (2014) studied pilot injection for improvement of combustion characteristics in a heavy-duty diesel engine. Their results demonstrated that with the advance of pilot
Environmental pollution is of global concern. Marine diesel engines produce more emissions than do vehicle engines. Emission regulations have recently become more stringent for marine engines. The International Maritime Organization Tier III requires NOx emissions not exceed 3.4 g/kWh, when operating inside an emission control area (Emission Standards, 2016). Many technologies have been proposed to make marine engines meet these requirements, such as alternative fuels, internal engine modifications, humid air motors, exhaust gas recirculation (EGR), and selective catalytic reduction (Yang et al., 2012; Roskilly et al., 2015; Zhou et al., 2013). Diesel engines commonly employ EGR to lower NOx emissions. Raptotasios et al. (2015a) showed that NOx emissions meet the Tier III requirement when the EGR rate exceeds 35% for the two-stroke 4T50ME-X test marine diesel engine. Deepak et al. (Agarwal et al., 2011) studied the effect of EGR on the performance, emission, deposits and durability for a constant speed compression ignition engine. Decreases in NOx and exhaust gas temperature were observed but emissions of particulate matter (PM), HC, and CO were found to increase with EGR use. At the same time, higher carbon deposits and higher wear of piston rings were observed on the engine parts operating with EGR. The EGR * Corresponding author. E-mail address: [email protected] (X. Liang).
http://dx.doi.org/10.1016/j.oceaneng.2017.08.044 Received 13 March 2017; Received in revised form 27 August 2017; Accepted 28 August 2017 0029-8018/© 2017 Published by Elsevier Ltd.
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injection timing, the peak in-cylinder pressure dropped down, the ignition delay of the main combustion is shortened, and the NOx and soot emissions are reduced, whereas the HC and CO emissions are increased. Tadros et al. (2016) studied the effect of different start angles of combustion on performance and the exhaust emissions of a marine diesel engine. The start angles of combustion at the lowest speed of the engine are retarded top dead center, which reduces the exhaust emissions and decreases the brake power a little bit. Saravanan (2015) studied the effect of EGR and advanced injection timing on the combustion characteristics of a diesel engine. From their experimental results it can be concluded that NOx and smoke emissions can be controlled simultaneously with less variation in the combustion characteristics of the engine. The trade-off relationship between BSFC and NOx can be improved by applying EGR and adjusting the injection timing (Verschaeren et al., 2014; Aldajah et al., 2007; Thangaraja and Kannan, 2016; Li et al., 2014). Computer simulations have increased in potential applications with the development of computers. It is now practical to use computer simulations to model marine diesel engines. Owing to the large volume of a marine engine, experimental research is difficult and expensive. Pang et al. (2016) investigated soot formation and oxidation processes in a large two-stroke marine diesel engine using integrated computational fluid dynamic (CFD)-chemical kinetics. They developed a new n-heptane skeletal diesel surrogate model for analyzing combustion and soot. Panagiotis et al. (Kontoulis et al., 2008) used the KIVA-3 code as the modeling platform to study the effects of advanced injection strategies. They demonstrated that by adding an appropriately timed pilot injection, fuel savings of the order of 1.7% can be achieved, without increasing NOx emissions. They used n-tetradecane as an alternative fuel. Sun et al. (2017a) compared the performance of n-heptane and n-tetradecane as alternative fuels in a marine diesel engine. The quantity of emissions is related to the combustion models and alternative fuels. It is important to choose an appropriate combustion model and alternative fuel for the simulation of a marine diesel engine. In this paper, a CFD model of a two-stroke marine diesel engine is established and validated using experimental data. The effects of inlet pressure, EGR rate and injection time on the performance of marine diesel engines are studied. The optimal method is proposed to lower NOx emissions while minimizing the increase in indicated specific fuel consumption. This paper provides a solution to make a two-stroke marine diesel engine meet the requirement of Tier III.
Fig. 1. The three-dimensional geometric structure.
emissions generate models, the Extended Zeldovich NOx mechanism is applied to simulate the production of NOx. Hiroyasu-NSC Model is used to simulate soot production respectively. The injected liquid temperature is set to 345 K. The injection duration is 15.36 C A and the total injection mass is 0.0126 kg, which was obtained from experimental data. These models participate in calculated process of CFD model. In addition to these, the marine engine numerical simulation also is based upon continuity, momentum and energy conservation laws (Amsden et al., 1989). The continuity equation of flow field is:
∂ρ ⇀ þ ∇⋅ ρu ¼ ρ_ s ∂t ⇀
u is the velocity vector, ρ is the fluid density. ρ_ s is the source item. The equations of momentum conservation law on the x, y, and z directions as follows:
2. Brief description of the model
⇀ ∂ ρu
The CFD model is based on a marine diesel engine (6S35ME-B9). The main particulars are listed in Table 1. The engine speed is 142 r/min when operated at 100% load. The in-cylinder pressure and emission products were tested and used to validate the accuracy of the model. The engine simulation is performed using the commercial CFD software package CONVERGE 2.3. Fig. 1 shows the three-dimensional structure of model. This model includes a scavenge box, cylinder and exhaust port. The k-ε two-equation mode is used as turbulence model. Kelvin Helmholtz-Rayleigh Taylor model is applied to the simulation of spray breakup. The NTC collision model is implemented to simulate the fuel collision. The wall splash model is used in the O'Rourke model based on Weber number, film thickness and viscosity. The detailed chemical solver combustion model is used to simulate the fuel ignition. For the
∂t
⇀s 1 2 ⇀⇀ þ ∇⋅ ρu u ¼ 2 ∇P А0 ∇ ρk þ ∇⋅σ þ F þ Pg a 3
(2)
a is the dimensionless quantity of different fluid properties. P is the pressure; g represents the gravity; k is the turbulence energy; A0 has relationship with turbulence model (laminar flow A0 ¼ 0, turbulent flow A0 ¼ 1); σ is the viscous stress. The equation of energy conservation law as follow:
⇀ ∂ðρIÞ C S ⇀ ⇀ þ ∇⋅ ρuI ¼ P∇⋅u þ ð1 А0 Þσ⋅∇⋅J þ А0 ρε þ Q_ þ Q_ ∂t
(3)
⇀
I is the specific heat energy including chemical energy; J is the heat equator flux vector.
Table 1 6S35ME-B9 test engine specifications. cylinder number Bore (mm) Stroke (mm) Displacement (L) Connecting rod length (mm) Speed (r/min) Power (kW)
(1)
3. Model validation 6 350 1550 149 1550 142 3575
n-tetradecane is often used as an alternative fuel for the simulation of marine diesel engines Struckmeier et al. (2009) research the multi-component modeling of evaporation, ignition and combustion processes. The effects of fuel component properties on the ignition and combustion properties of the fuel blend have been investigated. The
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compress pressure and combustion are 0.8% and 1.5%, respectively. The time of change pressure delay is 0.846 C A for the model. The in-cylinder pressure is in good agreement with the experimental data. The model can accurately predict the pressure of marine diesel engine. The NOx and CO2 emissions are also compared to validate the accuracy of model, which are shown in Fig. 5. For NOx, the error is 2.8% for the simulation and for the experiment, which is acceptable for predicting the quantity of NOx. The error for CO2 is larger than that for NOx, owing to the combustion. The single component n-tetradecane is used as alternative fuel to simulate the combustion process. And, the new n-tetradecane mechanism is reduced for decreasing the calculated time. Some reactions are disappeared for CO2 produce mechanism. The quantity of NOx is close to the experimental data, that is to say: the CFD model can accurately predict the quantity of NOx using n-tetradecane as alternative fuel. The CFD model prediction of marine diesel engine performance is validated by simulation and experiment. This CFD model is used to study the effect of inlet pressure, EGR and start of injection time in this paper. The trade-off between ISFC and emissions is also investigated.
chemical reaction equations are solved assuming tetradecane. Panagiotis et al. (Raptotasios et al., 2015b) study the effects of advanced injection strategies on the performance marine diesel engine using Computational Fluid Dynamics (CFD) and T-φ Mapping. The tetradecane has been used as surrogate fuel. The new n-tetradecane mechanism was established in a previous study (Sun et al., 2017b). The n-tetradecane chemical property is more close to the real combustion for the marine diesel engine (Sun et al., 2017a). Fig. 2 shows the comparison of ignition delay times for the 62-species mechanism, the experiment (Shen et al., 2009), the detailed mechanism (Westbrook et al., 2009) and the simplified mechanism (Chang et al., 2013) under different pressure and equivalence ratio conditions. The ignition delay times of the 62-species mechanism are in good agreement with the experimental data for different conditions. The values of the new mechanism are closer to the experimental data than those of the detailed mechanism. So, the 62-species n-tetradecane mechanism is used in the CFD model to predict the performance of the marine diesel engine. The n-tetradecane used as an alternative fuel in the marine diesel engine is also used in the CFD model. Mesh grid size is decided based on the desired calculation time and calculation accuracy. Grid control includes a base grid, adaptive mesh refinement and fixed embedding. The effect of the base grid and the adaptive mesh refinement are shown in Fig. 3. As seen in Fig. 3 (a), the compression pressure of base grid 0.04 m is in agreement with that of base grid 0.03 m. The calculation accuracy increases gradually with decreasing base grid size. If the adaptive mesh refinement is set to 4, the calculated pressure is in good agreement with the experiment data, as shown in Fig. 3 (b). However, the calculation time also increases. Setting the base grid to 0.04 m and the adaptive mesh refinement to 4 can ensure the accuracy of the simulation. Fig. 4 shows the in-cylinder pressure comparison between the calculated value and experimental data. The errors of maximum
4. Results and discussion 4.1. Effect of inlet pressure Inlet pressure changes with the varying of EGR rate. The inlet pressure affects gas mass, which causes the variation of equivalence ratio. Thus, inlet pressure has an effect on the quantity of NOx. Fig. 6 shows the variation of in-cylinder pressure under different inlet pressure. The incylinder pressure cut down with decreasing inlet pressure. The main reason is that the gas mass is reduced, as shown in Fig. 7. The less gas mass, the lower the in-cylinder pressure, for the same geometry
Fig. 2. Comparison of ignition delay time for the new n-tetradecane mechanism. 92
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Fig. 3. The effect of grid on the pressure: (a) base grid (b) adaptive mesh refinement.
Fig. 6. The comparison of in-cylinder pressure under different inlet pressure conditions.
Fig. 4. Comparison of in-cylinder pressure for the simulation and experiment.
inlet pressure is similar to the outlet pressure, which is 0.339 MPa. The more residual exhaust gas, the higher the in-cylinder temperature is. Thus, the inlet gas mass reduces as the inlet pressure drops. Fig. 8 shows the comparison of NOx emissions under different inlet pressure. The quantity of NOx drops with increasing inlet pressure. The NOx emissions are lower when the inlet pressure exceeds 0.369 MPa. The oxygen concentrations remain almost the same when the inlet pressure exceeds 0.369 MPa, which was obtained from Fig. 7. The more exhaust gas remaining in the cylinder, the higher the temperature is. This higher temperature produces more NOx. The in-cylinder pressure and emission vary slightly when the inlet pressure exceeds 0.369 MPa. The main reason is that sufficient oxygen exists in cylinder, owing to the two-stroke scavenging method. It is necessary that the turbocharger keeps the inlet pressure at least 0.03 MPa higher than the outlet pressure. 4.2. Effect of EGR EGR is the standard method for controlling NOx emissions (Hountalas et al., 2008; Verschaeren et al., 2014; Zamboni and Capobianco, 2012). The decreased oxygen concentration, increased charge mixture specific heat capacity, and recirculated water vapor and CO2 affect the formation of NOx (Raptotasios et al., 2015a). The inlet pressure is kept at 0.369 MPa. The CFD model was used to evaluate the potential of EGR to lower the NOx emissions in a marine diesel engine. Fig. 9 shows the
Fig. 5. Comparison of NOx and CO2 for the simulation and experiment.
compression ratio. The in-cylinder pressure has maximum decrement when the inlet pressure is 0.349 MPa. For scavenging in a two-stroke cycle, the inflow gas actuates the emission products access to the exhaust pipe. More emission products remain in the cylinder when the
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Fig. 7. The comparison of gas mass under different inlet pressure conditions. Fig. 9. The comparison of in-cylinder pressure under different EGR rates: the case “NO” represents the EGR rate 0%.
Fig. 8. The comparison of NOx under different inlet pressure conditions. Fig. 10. The comparison of C14H30 mass under different EGR rates.
variation of in-cylinder pressure at different EGR rates. The maximum compress pressures are almost same for different EGR rates, because the inlet gas mass remains almost the same. However, the maximum combustion pressure drops with increasing EGR rate, primarily reason is that the quantity of unburned fuel increases. The oxygen concentration decreases, so more fuel will be unburned with increasing EGR rate, as shown in Fig. 10. Fig. 10 also shows the variation of fuel mass (C14H30) in cylinder. The higher EGR rate slows the combustion rate, and resulting in low in-cylinder temperature. Fig. 11 clearly shows that the maximum in-cylinder temperature reduced with increasing EGR rate. The main aim of the present study is to decline NOx emissions using EGR. Fig. 12 shows the variations of NOx and soot with increasing EGR rates. The quantity of NOx emissions falls with increasing EGR rate; however, soot has the opposite trend. The quantity of NOx emissions reduces to 2.96 g/kWh when the EGR rate is 20%. The quantity of NOx emissions is below 3.4 g/kWh, which is the limit value of NOx for Tier III. However, the quantity of soot increases to three times than that of the soot value when using 0% EGR. Higher EGR rate means lower oxygen concentrations and temperature. However, the NOx is produced in high temperature and rich oxygen. The formation of soot is related to fuel combustion. The increasing EGR rate slows the combustion rate, increasing the mass of unburned fuel, accelerating the formation rate of soot. Fig. 13 shows the variations of indicated power and indicated specific
Fig. 11. The comparison of in-cylinder mean temperature under different EGR rates. 94
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Fig. 12. The comparison of soot and NOx under different EGR rates.
fuel consumption (ISFC) at different EGR rates. The increasing EGR rate decreases indicated power and increases ISFC. Indicated power decreased by 4.7% compared with no EGR, whereas ISFC increases by 5.1%. The augment EGR rate causes combustion pressure droop (Fig. 9); indicated power is directly proportional to in-cylinder pressure. The injection mass is constant, so ISFC is inversely proportional to incylinder pressure. The trade-off between NOx emissions and ISFC cannot be ignored when EGR is used in marine diesel engines. It is necessary to take measures to control fuel consumption.
Fig. 14. Effect of SOI on the in-cylinder pressure.
4.3. Effect of start of injection time The start of injection (SOI) decides the initial time of combustion. Marine diesel engine performance is influenced by SOI. Fig. 14 shows the effect of SOI on in-cylinder pressure. The maximum combustion pressure increases with advanced SOI. The in-cylinder pressure and temperature are higher with advanced SOI, which occurs after top dead center. Incylinder pressure increases continuously with fuel injection. Higher pressures and temperatures shorten fuel atomization time. The combustion rate increases, causing the pressure to increase. Indicated power and ISFC are influenced by SOI, as shown in Fig. 15. Indicated power decreases and ISFC increases with retarded SOI. Retarded SOI delays the combustion process and shortens ignition time. Thus, the combustion is incomplete and the ISFC increases by about 1.5% when the SOI is delayed by 1 C A. The resulting indicated power falls by about 50 kW.
Fig. 15. Effect of SOI on the indicated power and ISFC.
Fig. 16 shows the variation of quantity of NOx with retarded SOI. The quantity of NOx reduces by about 3.7% when SOI is delayed by 1 C A. The quantity of NOx is almost the same when the injection time is 361.6 C A. Retarded SOI lowers the in-cylinder pressure and temperature. The temperature lowers the quantity of NOx for a given inlet oxygen concentration.
Fig. 13. The comparison of indicated power and ISFC under different EGR rates.
Fig. 16. Effect of SOI on the NOx. 95
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3. The quantity of NOx emissions falls with retarded SOI; however, the ISFC rises. The decrease in NOx emissions is quite small under high EGR rate but the increase in ISFC is large. 4. The increase in ISFC is improved by using advanced SOI under high EGR rate. This is a useful method for improving the performance of marine diesel engines.
4.4. Effect of EGR coupling with SOI The trade-off between ISFC and NOx is found for a marine diesel engine. The quantity of NOx emissions meets the limited value of Tier III when the EGR rate is reduced to 20%. However, ISFC increases by 8 g/ kWh. The quantity of NOx drops to 2 g/kWh and ISFC increases to 10 g/ kWh when the injection time changes from 360.6 C AA to 364.6 C AA. The EGR method is able to reduce the NOx emissions extensively, but the corresponding ISFC increases. Advancing SOI droops ISFC; however, this limits the decrease in NOx emissions. The trade-off between NOx emissions and ISFC can be solved by using EGR coupling with SOI. Fig. 17 shows the trade-off between ISFC and NOx under different EGR rates and SOI times. The quantity of NOx emissions increases by 7.5% and ISFC diminishes by 1.2% when SOI is delayed from 362.6 C A to 363.6 C A without EGR. The quantity of NOx emissions increases by 1.9% and ISFC falls by 1% when the EGR rate is 15%. The increment of NOx emissions is quite small under the high EGR rate; However, there is a marked decrease in ISFC. That is, ISFC is improved by advancing SOI under high EGR rate. Fig. 17 shows that the quantity of NOx emissions meets the requirement of Tier III when the EGR rate is 20%. However, ISFC increases to 8 g/kWh. ISFC is reduced by 1.44% when the SOI is advanced from 362.6 C AA to 361.6 C AA. Adjusting SOI is an effective method to decrease ISFC under high EGR rate.
Acknowledgements This work was supported by National Natural Science Foundation of China (No. 51376136 and No. 91641111), National Sci-Tech Support of China (2015BAG16B01) and the author also wants to appreciate the support of high-tech Ship Research Program of MIIT. References Agarwal, D., Singh, S.K., Agarwal, A.K., 2011. Effect of Exhaust Gas Recirculation (EGR) on performance, emissions, deposits and durability of a constant speed compression ignition engine. Appl. Energy 88 (2011), 2900–2907. Aldajah, S., Ajayi, O.O., Fenske, G.R., Goldblatt, I.L., 2007. Effect of exhaust gas recirculation (EGR) contamination of diesel engine oil on wear. Wear 263 (2007), 93–98. Amsden, A.A., Orourke, P.J., Butler, T.D., 1989. KIVA-2: a computer program for chemically reactive flows with sprays. Nasa Sti/recon Tech. Rep. N 89 (1989). Chang, Y., Jia, M., Liu, Y., Li, Y., Xie, M., Yin, H., 2013. Application of a decoupling methodology for development of skeletal oxidation mechanisms for heavy n -alkanes from n-octane to n-hexadecane. Energy & Fuels 27 (2013), 3467–3479. Chen, L., Zeng, H., Cheng, X.B., 2014. Study of pilot injection for the improvement of combustion and emissions characteristics in a heavy-duty diesel engine. Appl. Mech. Mater. 651–653 (2014), 866–874. Emission Standards, 2016. IMO Marine Engine. http://www.DieselNet.com/standards (Accessed July 12 2008). Hountalas, D.T., Mavropoulos, G.C., Binder, K.B., 2008. Effect of exhaust gas recirculation (EGR) temperature for various EGR rates on heavy duty DI diesel engine performance and emissions. Energy 33 (2008), 272–283. Kontoulis, P., Chryssakis, C., Kaiktsis, L., 2008. DE3-1: evaluation of pilot injections in a large two-stroke marine diesel engine, using CFD and t-φ mapping (DE: diesel engine Combustion,General session papers). In: The International Symposium on Diagnostics and Modeling of Combustion in Internal Combustion Engines, 2008, pp. 181–188. Li, X., Xu, Z., Guan, C., Huang, Z., 2014. Impact of exhaust gas recirculation (EGR) on soot reactivity from a diesel engine operating at high load. Appl. Therm. Eng. 68 (2014), 100–106. Pang, K.M., Karvounis, N., Walther, J.H., Schramm, J., 2016. Numerical investigation of soot formation and oxidation processes under large two-stroke marine diesel enginelike conditions using integrated CFD-chemical kinetics. Appl. Energy 169 (2016), 874–887. Raptotasios, S.I., Sakellaridis, N.F., Papagiannakis, R.G., Hountalas, D.T., 2015. Application of a multi-zone combustion model to investigate the NOx reduction potential of two-stroke marine diesel engines using EGR. Appl. Energy 157 (2015), 814–823. Raptotasios, S.I., Sakellaridis, N.F., Papagiannakis, R.G., Hountalas, D.T., 2015. Application of a multi-zone combustion model to investigate the NOx reduction potential of two-stroke marine diesel engines using EGR. Appl. Energy 157 (2015), pp.814–823. Roskilly, A.P., Palacin, R., Yan, J., 2015. Novel technologies and strategies for clean transport systems. Appl. Energy 157 (2015), 563–566. Saravanan, S., 2015. Effect of EGR at advanced injection timing on combustion characteristics of diesel engine. Alexandria Eng. J. 54 (2015), 339–342. Shen, H.S., Steinberg, J., Vanderover, J., Oehlschlaeger, M.A., 2009. A shock tube study of the ignition of n-heptane, n-decane, n-dodecane, and n-tetradecane at elevated pressures. Energy & Fuels 23 (2009), 2482–2489. Struckmeier, D., Tsuru, D., Kawauchi, S., Tajima, H., 2009. Multi-component Modeling of Evaporation, Ignition and Combustion Processes of Heavy Residual Fuel Oil. SAE Technical Papers, (2009). Sun, X., Liang, X., Shu, G., Wang, Y., Wang, Y., Yu, H., 2017. Effect of different combustion models and alternative fuels on two-stroke marine diesel engine performance. Appl. Therm. Eng. 115 (2017), 597–606. Sun, X., Liang, X., Shu, G., Wang, Y., Wang, Y., Yu, H., 2017. Development of a reduced ntetradecane-PAH mechanism for application on two-stroke marine diesel engine. Energy & Fuels 31 (2017), 941–952. Tadros, M., Ventura, M., Soares, C.G., 2016. Assessment of the performance and the exhaust emissions of a marine diesel engine for different start angles of combustion. Marit. Technol. Eng. 3 (2016). Thangaraja, J., Kannan, C., 2016. Effect of exhaust gas recirculation on advanced diesel combustion and alternate fuels - a review. Appl. Energy 180 (2016), 169–184. Verschaeren, R., Schaepdryver, W., Serruys, T., Bastiaen, M., Vervaeke, L., Verhelst, S., 2014. Experimental study of NOx reduction on a medium speed heavy duty diesel engine by the application of EGR (exhaust gas recirculation) and Miller timing. Energy 76 (2014), 614–621.
5. Conclusions A CFD model of a two-stroke marine diesel engine was established, and n-tetradecane was used as an alternative fuel. The simulation model was validated using experimental data. The model was used to assess the potential of EGR and SOI for reducing NOx emissions. The in-cylinder pressure, indicated power and ISFC were compared. The main results are as follows: 1. The quantity of NOx emissions increases by a large margin when the inlet pressure is close to the outlet pressure. At the same time, incylinder pressure decreases. However, the decrement of NOx emissions is small when the inlet pressure exceeds 0.369 MPa. The inlet pressure needs to remain 0.03 MPa higher than the outlet pressure. Otherwise, the performance of marine diesel engines is strongly impaired. 2. The quantity of NOx emissions strongly reduces when EGR is used in marine diesel engines. The value of NOx emissions meets the requirement of Tier III when the EGR rate is 20%. However, the indicated power declines and ISFC rise with increasing EGR rate.
Fig. 17. The relationship with ISFC and NOx. 96
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Ocean Engineering 144 (2017) 90–97 Yu, H.L., Yu, G.Z., Duan, S.L., 2014. Effects of exhaust gas recirculation on combustion and emission of a marine diesel engine. Adv. Mater. Res. 926–930 (2014), 905–908. Zamboni, G., Capobianco, M., 2012. Experimental study on the effects of HP and LP EGR in an automotive turbocharged diesel engine. Appl. Energy 94 (2012), 117–128. Zhou, S., Liu, Y., Zhou, J.X., 2013. A study on exhaust gas emission control technology of marine diesel engine. Adv. Mater. Res. 864–867 (2013), 1804–1809.
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