Benefits of E85 versus gasoline as low reactivity fuel for an automotive diesel engine operating in reactivity controlled compression ignition combustion mode

[EN] This work shows the capabilities of E85 fuel to be used as low reactivity fuel in a high compression ratio light-duty diesel engine (17.1:1) running under reactivity controlled compression ignition concept. To do this, experimental steady-state engine maps are obtained in a single-cylinder engine with diesel-E85 fuel combination. The engine mapping was performed following the same procedure used in previous works with other fuel combinations to allow the results comparison. Considering the mechanical and emissions limits imposed during the engine mapping, it was found that with diesel-E85 the combustion concept is limited to the region defined from 2 to 7 bar at 1000 rpm, and from 1.5 to 9 bar indicated mean effective pressure at 3000 rpm. This operating region was satisfied with nitrogen oxides, soot and pressure rise rate levels below 0.4 g/kWh, 0.01 g/kWh and 10 bar/CAD, respectively. The reactivity controlled compression ignition maps with diesel-E85 were obtained taking as reference the total fuel energy used in a previous work to map the engine with diesel-gasoline. The direct comparison of both combustion concepts (diesel-E85 and diesel-gasoline) revealed that E85 allows to extend the engine map around 2 bar indicated mean effective pressure towards the high load region. Moreover, the minimum load achieved at high engine speeds was decreased down to 1.5 indicated mean effective pressure. Finally, the differences in terms of emissions and performance between both reactivity controlled compression ignition concepts are highlighted by doing the difference between the maps of several variables.The authors gratefully acknowledge General Motors Global Research & Development for providing the engine used in this investigation. The authors also acknowledge FEDER and Spanish Ministerio de Economia y Competitividad for partially supporting this research through HiReCo project (TRA2014-58870-R).Benajes, J.; García Martínez, A.; Monsalve-Serrano, J.; Villalta-Lara, D. (2018). Benefits of E85 versus gasoline as low reactivity fuel for an automotive diesel engine operating in reactivity controlled compression ignition combustion mode. Energy Conversion and Management. 159:85-95. https://doi.org/10.1016/j.enconman.2018.01.015S859515

Experimental investigation on the efficiency of a diesel oxidation catalyst in a medium-duty multi-cylinder RCCI engine

[EN] Reactivity controlled compression ignition (RCCI) combustion is one of the most promising low temperature combustion (LTC) techniques, as it is able to provide ultra-low NOx and soot emissions together with higher thermal efficiency than conventional diesel combustion (CDC) in a wide range of operating conditions. However, the unburned hydrocarbon (UHC) and carbon monoxide (CO) emission levels are orders of magnitude higher than CDC, which can result in a major problem for implementing the RCCI concept in real engines. In this sense, the high levels of UHC and CO emissions together with the low exhaust temperatures during RCCI operation could compromise the diesel oxidation catalyst (DOC) conversion efficiency. The objective of this work is to evaluate the efficiency of a conventional DOC in oxidizing the UHC and CO emissions from RCCI combustion. To do this, a medium-duty multi-cylinder diesel engine equipped with its original after treatment system has been used. First, the DOC conversion efficiency is evaluated under some steady-state conditions. Later, the influence of the thermal inertia on the DOC response has been evaluated by means of transient tests. In this sense, different engine load-speed steps as well some simplified conditions from the worldwide harmonized vehicle cycle (WHVC) and the supplemental engine transient cycle (SET) are evaluated. In steady-state conditions, with DOC-inlet temperatures of 200-300 degrees C, the results show conversion efficiencies of 100% for CO and 85-95% for HC. At 10% and 25% load, the DOC-outlet UHC levels are unacceptable considering the EURO VI regulation, while at 50% load the tailpipe emissions fulfill the emissions standard. The results in transient conditions are more promising thanks to effect of the thermal inertia, showing 100% conversion efficiency for CO and greater than 90% for UHC during large periods of engine operation.The authors thanks VOLVO Group Trucks Technology and ARAMCO Overseas Company for supporting this research. The authors also acknowledge FEDER and Spanish Ministerio de Economia y Competitividad for partially supporting this research through TRANCO project (TRA2017-87694-R).Benajes, J.; García Martínez, A.; Monsalve-Serrano, J.; Lago-Sari, R. (2018). Experimental investigation on the efficiency of a diesel oxidation catalyst in a medium-duty multi-cylinder RCCI engine. Energy Conversion and Management. 176:1-10. https://doi.org/10.1016/j.enconman.2018.09.016S11017

Evaluation of massive exhaust gas recirculation and Miller cycle strategies for mixing-controlled low temperature combustion in a heavy duty diesel engine

The future of compression ignition engines depends on their ability for keeping their competitiveness in terms of fuel consumption compared to spark-ignition engines. In this competitive framework, the Low Temperature Combustion (LTC) concept is a promising alternative to decrease NOx and soot emissions. Thus, this research focuses on implementing the LTC concept, but keeping the conventional mixing-controlled combustion process to overcome the well-known drawbacks of the highly-premixed combustion concepts, including load limitations and lack of combustion control. Two strategies for implementing the mixing-controlled LTC concept were evaluated. The first strategy relies on decreasing the intake oxygen concentration introducing high rates of cooled EGR. The second strategy consists of decreasing the compression temperature by advancing the intake valves closing angle to reduce the effective compression ratio, compensating the air mass losses by increasing boost pressure (Miller cycle). These strategies were tested in a single-cylinder heavy-duty research engine. Additionally, 3D-CFD modeling was used to give insight into local in-cylinder conditions during the injection-combustion process. Results confirm the suitability of both strategies for reducing NOx and soot emissions, while their main drawback is the increment in fuel consumption. However, they present intrinsic differences in terms of local equivalence ratios and temperatures along combustion.The authors of this paper thank the Spanish Ministry of Economic and Competitively for the financial support of this research through the project TRA2010-20271 (LOWTECOM).Benajes Calvo, JV.; Molina Alcaide, SA.; Novella Rosa, R.; Belarte Mañes, E. (2014). Evaluation of massive exhaust gas recirculation and Miller cycle strategies for mixing-controlled low temperature combustion in a heavy duty diesel engine. Energy. (71):355-366. https://doi.org/10.1016/j.energy.2014.04.083S3553667

The potential of RCCI concept to meet EURO VI NOx limitation and ultra-low soot emissions in a heavy-duty engine over the whole engine map

This work investigates the potential of RCCI concept to achieve ultra-low NOx and soot emissions over a wide range of engine speed and loads. For this purpose, a detailed experimental methodology has been defined and applied in a heavy-duty single-cylinder engine fueled with diesel and gasoline. In addition, to assess the influence of the engine compression ratio on RCCI capabilities two different compression ratios, 14.4:1 and 11:1, have been tested. Results suggest that a low compression ratio allows to fulfill all the self-imposed constraints (maximum cylinder pressure rise rate of 25 bar/CAD, NOx < 0.4 g/kW h and soot* < 0.01 g/kW h) from idle to full load and engine speeds from 900 to 1800 rpm. However, the use of higher compression ratio requires a delayed injection strategy to avoid excessive knocking levels, which results in unacceptable soot emissions at loads higher than 50%, even when gasoline fractions around 90% are used.The authors would like to acknowledge VOLVO Group Trucks Technology for supporting this research and to express their gratitude to Spanish economy and competitiveness ministry for partially funding this research under the project HiReCo TRA2014-58870-R.Benajes Calvo, JV.; Pastor Soriano, JV.; García Martínez, A.; Monsalve Serrano, J. (2015). The potential of RCCI concept to meet EURO VI NOx limitation and ultra-low soot emissions in a heavy-duty engine over the whole engine map. Fuel. 159:952-961. https://doi.org/10.1016/j.fuel.2015.07.064S95296115

In-cylinder soot radiation heat transfer in direct-injection diesel engines

The efficiency and CO2 are one of the main concerns of automotive manufacturers. There are several strategies under investigation to solve this problem. In the present work, the research effort has been focused on improving knowledge of in-cylinder heat transfer and its impact on engine efficiency. In particular, soot radiation was studied since it can be considered a significant source of the efficiency losses in modern diesel engines. Considering previous studies, the portion of total chemical energy released during combustion lost due to radiation heat transfer varies widely from 0.5% up to 10%, depending on engine parameters and combustion process. Thus, the main objective of this work was to evaluate the amount of energy lost to soot radiation relative to the input fuel chemical energy during the combustion event under different operating conditions in a completely controlled environment provided by an optical engine. Under these simplified conditions, two-color method was applied by using high speed imaging pyrometer with cameras (two dimensional results) and optoelectronic pyrometer (zero dimensional results). Once a detailed comparison between both diagnostics was performed, optoelectronic pyrometer was used to characterize radiant energy losses in a fully instrumented 4-cylinder direct-injection lightduty diesel engine. In particular swirl ratio, 'EGR and combustion phasing effects on radiation heat transfer were evaluated.The authors acknowledge General Motors Global R&D for supporting this research and to express their gratitude to Spanish economy and competitiveness ministry for partially funding this research under the project HiReCo TRA2014-58870-R.Benajes Calvo, JV.; Martín Díaz, J.; García Martínez, A.; Villalta Lara, D.; Warey, A. (2015). In-cylinder soot radiation heat transfer in direct-injection diesel engines. Energy Conversion and Management. 106:414-427. https://doi.org/10.1016/j.enconman.2015.09.059S41442710

Effects of direct injection timing and blending ratio on RCCI combustion with different low reactivity fuels

This work investigates the effects of the direct injection timing and blending ratio on RCCI performance and engine-out emissions at different engine loads using four low reactivity fuels: E10-95, E10-98, E20-95 and E85 (port fuel injected) and keeping constant the same high reactivity fuel: diesel B7, (direct injected). The experiments were conducted using a heavy-duty single-cylinder research diesel engine adapted for dual-fuel operation. All the tests were carried out at 1200 rpm. To assess the blending ratio effect, the total energy delivered to the cylinder coming from the low reactivity fuel was kept constant for the different fuel blends investigated by adjusting the low reactivity fuel mass as required in each case. In addition, a detailed analysis of the air/fuel mixing process has been developed by means of a 1-D in-house developed spray model. Results suggest that notable higher diesel amount is required to achieve a stable combustion using E85. This fact leads to higher NOx levels and unacceptable ringing intensity. By contrast, EURO VI NOx and soot levels are fulfilled with E20-95, E10-98 and E10-95. Finally, the higher reactivity of E10-95 results in a significant reduction in CO and HC emissions, mainly at low load.The authors acknowledge VOLVO Group Trucks Technology and TOTAL for supporting this research.Benajes Calvo, JV.; Molina, S.; García Martínez, A.; Monsalve Serrano, J. (2015). Effects of direct injection timing and blending ratio on RCCI combustion with different low reactivity fuels. Energy Conversion and Management. 99:193-209. doi:10.1016/j.enconman.2015.04.046S1932099

An experimental investigation on the influence of piston bowl geometry on RCCI performance and emissions in a heavy-duty engine

This experimental work investigates the effects of piston bowl geometry on RCCI performance and emissions at low, medium and high engine loads. For this purpose three different piston bowl geometries with compression ratio 14.4:1 have been evaluated using single and double injection strategies. The experiments were conducted in a heavy-duty single-cylinder engine adapted for dual fuel operation. All the tests were carried out at 1200 rev/min. Results suggest that piston geometry has great impact on combustion development at low load conditions, more so when single injection strategies are used. It terms of emissions, it was proved that the three geometries enables ultra-low NOx and soot emissions at low and medium load when using double injection strategies. By contrast, unacceptable emissions were measured at high load taking into account EURO VI limitations. Finally, the application of a mathematical function considering certain self-imposed constraints suggested that the more suitable piston geometry for RCCI operation is the stepped one, which has a modified transition from the center to the squish region and reduced piston surface area than the stock geometry.The authors acknowledge VOLVO Group Trucks Technology for supporting this research.Benajes Calvo, JV.; Pastor Soriano, JV.; García Martínez, A.; Monsalve Serrano, J. (2015). An experimental investigation on the influence of piston bowl geometry on RCCI performance and emissions in a heavy-duty engine. Energy Conversion and Management. 103:1019-1030. doi:10.1016/j.enconman.2015.07.047S1019103010

On the relation between the external structure and the internal characteristics in the near-nozzle field of diesel sprays

[EN] In this paper, a high-resolution visualization technique has been used in combination with an extensively validated 0D model in order to relate the external structure of a diesel spray to the internal properties in the vicinity of the nozzle. For this purpose, three single-hole convergent nozzles with different diameters have been tested for several pressure conditions. The analysis of the obtained images shows that the spray width significantly changes along the very first millimeters of the spray. From the high resolution images captured, two parameters have been evaluated. The first one is the external non-perturbed length, where droplet detachment has not been observed. The second one is a transitional length, defined as the axial position where the spray width increases linearly after a transient behavior, making it possible to establish a spray cone angle definition. Furthermore, the internal liquid core length has been estimated for these nozzles using an extensively validated zero-dimensional model. The intact liquid core length has proved to be correlated with both the transitional length and the non-perturbed length with a very high degree of reliability. In the case of the transitional length, a quadratic correlation has been observed, whereas a linear relationship has been confirmed between the intact core length and the non-perturbed length. The results presented here may help to shed light on better understanding of such a complex process as atomization.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the Ministerio de Economia y Competitividad, Spanish Government, under the project 'Comprension de la influencia de combustibles no convencionales en el proceso de injeccion y combustion tipo diesel' (project number TRA2012-36932) The PhD studies of D. Jaramillo have been funded by "Conselleria d'Educacio'Cultura i Esports'' of "Generalitat Valenciana'', Spain, by means of ''Programa Vali+ d per a personal investigador en formacio''. Reference ACIF/2015/040.Benajes, J.; Salvador, FJ.; Carreres, M.; Jaramillo-Císcar, D. (2017). On the relation between the external structure and the internal characteristics in the near-nozzle field of diesel sprays. Proceedings of the Institution of Mechanical Engineers Part D Journal of Automobile Engineering. 231(3):360-371. https://doi.org/10.1177/0954407016639464S3603712313Desantes, J. M., Payri, R., Salvador, F. J., & Gil, A. (2006). Development and validation of a theoretical model for diesel spray penetration. Fuel, 85(7-8), 910-917. doi:10.1016/j.fuel.2005.10.023Kim, H. J., Park, S. H., & Lee, C. S. (2010). A study on the macroscopic spray behavior and atomization characteristics of biodiesel and dimethyl ether sprays under increased ambient pressure. Fuel Processing Technology, 91(3), 354-363. doi:10.1016/j.fuproc.2009.11.007Klein-Douwel, R. J. H., Frijters, P. J. M., Seykens, X. L. J., Somers, L. M. T., & Baert, R. S. G. (2009). Gas Density and Rail Pressure Effects on Diesel Spray Growth from a Heavy-Duty Common Rail Injector†. Energy & Fuels, 23(4), 1832-1842. doi:10.1021/ef8003569Lee, C. S., Lee, K. H., Reitz, R. D., & Park, S. W. (2006). EFFECT OF SPLIT INJECTION ON THE MACROSCOPIC DEVELOPMENT AND ATOMIZATION CHARACTERISTICS OF A DIESEL SPRAY INJECTED THROUGH A COMMON-RAIL SYSTEM. Atomization and Sprays, 16(5), 543-562. doi:10.1615/atomizspr.v16.i5.50Desantes, J. M., Payri, R., Salvador, F. J., & De la Morena, J. (2010). Influence of cavitation phenomenon on primary break-up and spray behavior at stationary conditions. Fuel, 89(10), 3033-3041. doi:10.1016/j.fuel.2010.06.004Payri, R., Salvador, F. J., Gimeno, J., & Soare, V. (2005). Determination of diesel sprays characteristics in real engine in-cylinder air density and pressure conditions. Journal of Mechanical Science and Technology, 19(11), 2040-2052. doi:10.1007/bf02916497Desantes, J. M., Salvador, F. J., López, J. J., & De la Morena, J. (2010). Study of mass and momentum transfer in diesel sprays based on X-ray mass distribution measurements and on a theoretical derivation. Experiments in Fluids, 50(2), 233-246. doi:10.1007/s00348-010-0919-8Salvador, F. J., Ruiz, S., Gimeno, J., & De la Morena, J. (2011). Estimation of a suitable Schmidt number range in diesel sprays at high injection pressure. International Journal of Thermal Sciences, 50(9), 1790-1798. doi:10.1016/j.ijthermalsci.2011.03.030Linne, M. A., Paciaroni, M., Berrocal, E., & Sedarsky, D. (2009). Ballistic imaging of liquid breakup processes in dense sprays. Proceedings of the Combustion Institute, 32(2), 2147-2161. doi:10.1016/j.proci.2008.07.040Kastengren, A. L., Tilocco, F. Z., Duke, D. J., Powell, C. F., Zhang, X., & Moon, S. (2014). TIME-RESOLVED X-RAY RADIOGRAPHY OF SPRAYS FROM ENGINE COMBUSTION NETWORK SPRAY A DIESEL INJECTORS. Atomization and Sprays, 24(3), 251-272. doi:10.1615/atomizspr.2013008642Kastengren, A., & Powell, C. F. (2014). Synchrotron X-ray techniques for fluid dynamics. Experiments in Fluids, 55(3). doi:10.1007/s00348-014-1686-8Som, S., & Aggarwal, S. K. (2010). Effects of primary breakup modeling on spray and combustion characteristics of compression ignition engines. Combustion and Flame, 157(6), 1179-1193. doi:10.1016/j.combustflame.2010.02.018Lebas, R., Menard, T., Beau, P. A., Berlemont, A., & Demoulin, F. X. (2009). Numerical simulation of primary break-up and atomization: DNS and modelling study. International Journal of Multiphase Flow, 35(3), 247-260. doi:10.1016/j.ijmultiphaseflow.2008.11.005Shinjo, J., & Umemura, A. (2010). Simulation of liquid jet primary breakup: Dynamics of ligament and droplet formation. International Journal of Multiphase Flow, 36(7), 513-532. doi:10.1016/j.ijmultiphaseflow.2010.03.008Shinjo, J., & Umemura, A. (2011). Detailed simulation of primary atomization mechanisms in Diesel jet sprays (isolated identification of liquid jet tip effects). Proceedings of the Combustion Institute, 33(2), 2089-2097. doi:10.1016/j.proci.2010.07.006Ménard, T., Tanguy, S., & Berlemont, A. (2007). Coupling level set/VOF/ghost fluid methods: Validation and application to 3D simulation of the primary break-up of a liquid jet. International Journal of Multiphase Flow, 33(5), 510-524. doi:10.1016/j.ijmultiphaseflow.2006.11.001Bermúdez, V., Payri, R., Salvador, F. J., & Plazas, A. H. (2005). Study of the influence of nozzle seat type on injection rate and spray behaviour. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 219(5), 677-689. doi:10.1243/095440705x28303Payri, F., Bermúdez, V., Payri, R., & Salvador, F. J. (2004). The influence of cavitation on the internal flow and the spray characteristics in diesel injection nozzles. Fuel, 83(4-5), 419-431. doi:10.1016/j.fuel.2003.09.010Payri, R., Molina, S., Salvador, F. J., & Gimeno, J. (2004). A study of the relation between nozzle geometry, internal flow and sprays characteristics in diesel fuel injection systems. KSME International Journal, 18(7), 1222-1235. doi:10.1007/bf02983297Salvador, F. J., Ruiz, S., Salavert, J., & De la Morena, J. (2012). Consequences of using biodiesel on the injection and air–fuel mixing processes in diesel engines. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 227(8), 1130-1141. doi:10.1177/0954407012463667Basak, N., & Das, D. (2009). Photofermentative hydrogen production using purple non-sulfur bacteria Rhodobacter sphaeroides O.U.001 in an annular photobioreactor: A case study. Biomass and Bioenergy, 33(6-7), 911-919. doi:10.1016/j.biombioe.2009.02.007Salvador, F. J., Romero, J.-V., Roselló, M.-D., & Martínez-López, J. (2010). Validation of a code for modeling cavitation phenomena in Diesel injector nozzles. Mathematical and Computer Modelling, 52(7-8), 1123-1132. doi:10.1016/j.mcm.2010.02.027Andriotis, A., & Gavaises, M. (2009). INFLUENCE OF VORTEX FLOW AND CAVITATION ON NEAR-NOZZLE DIESEL SPRAY DISPERSION ANGLE. Atomization and Sprays, 19(3), 247-261. doi:10.1615/atomizspr.v19.i3.30Salvador, F. J., Hoyas, S., Novella, R., & Martínez-López, J. (2011). Numerical simulation and extended validation of two-phase compressible flow in diesel injector nozzles. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 225(4), 545-563. doi:10.1177/09544070jauto1569Salvador, F. J., Martínez-López, J., Caballer, M., & De Alfonso, C. (2013). Study of the influence of the needle lift on the internal flow and cavitation phenomenon in diesel injector nozzles by CFD using RANS methods. Energy Conversion and Management, 66, 246-256. doi:10.1016/j.enconman.2012.10.011Hiroyasu, H. (2000). SPRAY BREAKUP MECHANISM FROM THE HOLE-TYPE NOZZLE AND ITS APPLICATIONS. Atomization and Sprays, 10(3-5), 511-527. doi:10.1615/atomizspr.v10.i3-5.130Sou, A., Hosokawa, S., & Tomiyama, A. (2007). Effects of cavitation in a nozzle on liquid jet atomization. International Journal of Heat and Mass Transfer, 50(17-18), 3575-3582. doi:10.1016/j.ijheatmasstransfer.2006.12.033Macian, V., Bermudez, V., Payri, R., & Gimeno, J. (2003). NEW TECHNIQUE FOR DETERMINATION OF INTERNAL GEOMETRY OF A DIESEL NOZZLE WITH THE USE OF SILICONE METHODOLOGY. Experimental Techniques, 27(2), 39-43. doi:10.1111/j.1747-1567.2003.tb00107.xOtsu, N. (1979). A Threshold Selection Method from Gray-Level Histograms. IEEE Transactions on Systems, Man, and Cybernetics, 9(1), 62-66. doi:10.1109/tsmc.1979.4310076Payri, R., Tormos, B., Salvador, F. J., & Araneo, L. (2008). Spray droplet velocity characterization for convergent nozzles with three different diameters. Fuel, 87(15-16), 3176-3182. doi:10.1016/j.fuel.2008.05.028DELACOURT, E., DESMET, B., & BESSON, B. (2005). Characterisation of very high pressure diesel sprays using digital imaging techniques. Fuel, 84(7-8), 859-867. doi:10.1016/j.fuel.2004.12.003Yue, Y., Powell, C. F., Poola, R., Wang, J., & Schaller, J. K. (2001). QUANTITATIVE MEASUREMENTS OF DIESEL FUEL SPRAY CHARACTERISTICS IN THE NEAR-NOZZLE REGION USING X-RAY ABSORPTION. Atomization and Sprays, 11(4), 471-490. doi:10.1615/atomizspr.v11.i4.100Desantes, J. M., Payri, R., Garcia, J. M., & Salvador, F. J. (2007). A contribution to the understanding of isothermal diesel spray dynamics. Fuel, 86(7-8), 1093-1101. doi:10.1016/j.fuel.2006.10.011Desantes, J. M., Arregle, J., Lopez, J. J., & Cronhjort, A. (2006). SCALING LAWS FOR FREE TURBULENT GAS JETS AND DIESEL-LIKE SPRAYS. Atomization and Sprays, 16(4), 443-474. doi:10.1615/atomizspr.v16.i4.6

Effects of low reactivity fuel characteristics and blending ratio on low load RCCI (reactivity controlled compression ignition) performance and emissions in a heavy-duty diesel engine

This work investigates the effect of low reactivity fuel characteristics and blending ratio on low load RCCI (reactivity controlled compression ignition) performance and emissions using four different low reactivity fuels: E10-95, E10-98, E20-95 and E85 (port fuel injected) while keeping constant the same high reactivity fuel: diesel B7 (direct injected). The experiments were conducted using a heavy-duty single-cylinder research diesel engine adapted for dual fuel operation. All tests were carried out at 1200 rev/min and constant CA50 of 5 CAD ATDC. For this purpose, the premixed energy was equal for the different blends and the EGR (exhaust gas recirculation) rate was modified as required, keeping constant the rest of engine settings. In addition, a detailed analysis of air/fuel mixing process has been developed by means of a 1-D spray model. Results suggest that in-cylinder fuel reactivity gradients strongly affect the engine efficiency at low load. Specifically, a reduced reactivity gradient allows an improvement of 4.5% in terms of gross indicated efficiency when the proper blending ratio is used. In addition, EURO VI NOx and soot emission levels are fulfilled with a strong reduction in CO and HC compared with the case of the higher reactivity gradient among the low and high reactivity fuel.The authors acknowledge VOLVO Group Trucks Technology and TOTAL for supporting this research.Benajes Calvo, JV.; Molina, S.; García Martínez, A.; Monsalve Serrano, J. (2015). Effects of low reactivity fuel characteristics and blending ratio on low load RCCI (reactivity controlled compression ignition) performance and emissions in a heavy-duty diesel engine. Energy. 90:1261-1271. doi:10.1016/j.energy.2015.06.088S126112719

Surrogate Fuel Formulation to Improve the Dual-Mode Dual-Fuel Combustion Operation at Different Operating Conditions

[EN] Dual-mode dual-fuel combustion is a promising combustion concept to achieve the required emissions and CO2 reductions imposed by the next standards. Nonetheless, the fuel formulation requirements are stricter than for the single-fuel combustion concepts as the combustion concept relies on the reactivity of two different fuels. This work investigates the effect of the low reactivity fuel sensitivity (S=RON-MON) and the octane number at different operating conditions representative of the different combustion regimes found during the dual-mode dual-fuel operation. For this purpose, experimental tests were performed using a PRF 95 with three different sensitivities (S0, S5 and S10) at operating conditions of 25% load/950 rpm, 50%/1800 rpm and 100%/2200 rpm. Moreover, air sweeps varying ±10% around a reference air mass were performed at 25%/1800 rpm and 50%/1800 rpm. Conventional diesel fuel was used as high reactivity fuel in all the cases. Moreover, commercial 95 RON gasoline was used as reference to compare the different TRFs. The engine settings were managed to adjust the rate of heat release to that found with 95 RON gasoline. To do this, a quality index imposing a maximum deviation of 5% point-to-point between the HRR curves from both fuels was defined. The results suggest that PRF 95 with S0 has the most similar behavior compared to conventional 95 RON gasoline whatever the engine load. As the engine load increases, the sensitivity effect is more noticeable and iso-HRR operation was only possible for S0. At low and medium load, the TRFs present similar engine-out emissions with equal fuel consumption. At full load, the NOx emissions are increased with respect to the reference 95 RON gasoline without fuel consumption benefits. The results from the air variation for the different octane numbers demonstrated that the greatest differences are obtained for low air mass (i.e, higher EGR). In addition, the decrease of the octane number limits the maximum air increase due to the pressure gradients, requiring modifications in the engine settings that increase the soot formation.The authors thanks VOLVO Group Trucks Technology and ARAMCO Overseas Company for supporting this research. The authors also acknowledge FEDER and Spanish Ministerio de Economía y Competitividad for partially supporting this research through TRANCO project (TRA2017-87694-R) and the Universitat Politècnica de València for partially supporting this research through Convocatoria de ayudas a Primeros Proyectos de Investigación (PAID-06-18). The author R. Sari acknowledges the financial support from the Spanish ministry of science innovation and universities under the grant ¿Ayudas para contratos predoctorales para la formación de doctores¿ (PRE2018-085043).Benajes, J.; García Martínez, A.; Monsalve-Serrano, J.; Lago-Sari, R. (2020). Surrogate Fuel Formulation to Improve the Dual-Mode Dual-Fuel Combustion Operation at Different Operating Conditions. SAE International. 1-13. https://doi.org/10.4271/2020-01-2073S11