13th International Colloquium Fuels - September 2021 155 Thermodynamic Potential and Emission Characteristics of an Oxygen-containing Sustainable Fuel fulfilling EN 590 and RE- DII-standards Dipl.-Ing. Lukas Nenning University of Technology, Graz, Austria Dipl.-Ing. Gabriel Kühberger University of Technology, Graz, Austria Prof. Dipl.-Ing. Dr. Helmut Eichlseder University of Technology, Graz, Austria Dipl.-Ing. Michael Egert AVL LIST GmbH, Graz, Austria Dipl.-Ing. Thomas Uitz OMV Downstream GmbH, Vienna, Austria Summary This study deals with the thermodynamic potential of an oxygen-containing fuel in a compression ignition (CI) engine. To fulfill future CO 2 -fleet-emission targets with conventional powertrains in the EU, besides an increasing amount of hybridization of the powertrain also the efficiency of the internal combustion engine itself must be optimized. Thus, this work in hand pursues the approach to reduce CO 2 emissions by using a 100% renewable fuel on the one hand, and to exploit specific engine hardware adaptations enabled by this fuel to further increase the engine efficiency and reduce emissions. Therefore a trinary blend (HVO, ethers and alcohol) with an oxygen content of about 10%, which fulfills EN 590 and RED-II legislation, was tested thoroughly on a CI single cylinder research engine (SCRE). The oxygen-content of the fuel leads to a significant smoke reduction and thus a drastically improved NOx-smoke trade-off compared to conventional diesel. It is shown that this advantage can be successfully converted into an improved engine efficiency by applying a distinct increase of compression ratio (CR) with a redesigned combustion chamber and adapted combustion process. Furthermore, the impact of this sustainable fuel on a EU7 capable exhaust aftertreatment system (EAS) was investigated on a four-cylinder CI engine in different driving cycles. 1. Introduction The decreasing CO 2 -fleet-emission targets in the EU are a major challenge for all car manufacturers. The large share of newly registered cars with a conventional drivetrain still underlines the importance of a high powertrain efficiency with gasoline and diesel engines. Besides the amount of hybridization, the combustion efficiency must be increased to fulfill future CO 2 targets, as well. Thus, this work in hand pursues two approaches: The use of a renewable fuel with a lower CO 2 potential and fuel-specific engine hardware adaption for efficiency improvement. As shown in Fig. 1, a typical C-class passenger car (PC) in the WLTC needs a cycle-averaged effective efficiency of about 36% with conventional diesel fuel to fulfill the CO2 target with the given average vehicle mass in 2020. In order to meet the CO2 legislation in 2030 with the same drivetrain efficiency, a fuel with a lower CO2 factor must be used (1). The second option (2) to accomplish the target in 2030 with a conventional drivetrain would require a significant increase of the efficiency. However, since these high drivetrain efficiency values are still unrealistic, this research work strives for combining the two described possibilities to achieve a significant CO 2 reduction. Fig. 2 illustrates the CO 2 reduction potential of different fuels compared to conventional diesel fuel on the basis of the physical properties without consideration of Thermodynamic Potential and Emission Characteristics of an Oxygen-containing Sustainable Fuel fulfilling EN 590 and REDII-standards 156 13th International Colloquium Fuels - September 2021 production. Especially short-chain alkanes and alcohols have an appreciable potential. In contrast, oxymethylene ethers (OME) worsen this fuel parameter. This diagram suggests the conclusion that the CO 2 factor of a fuel can be significantly reduced by choosing the right blend components. Fig. 1: Dependence of WLTC averaged drivetrain efficiency on the CO 2 factor of the fuel Fig. 2: Relative theoretical CO 2 potential of different hydrocarbons compared to conventional diesel fuel 2. Methodology 2.1 Fuel definition Based on findings from the literature [1-3], which report a significant smoke reduction due to the oxygen-content in the fuel, a sustainable blend was defined. In order to ensure fleet compatibility and to fulfill future fuel legislation, this trinary blend meets the EN 590 [4] and the Renewable Energy Directive II (RED-II) legislation [5]. Fig. 3: Composition of Blend-3 This “Blend-3” called test fuel consists of hydrogenated vegetable oil (HVO), ethers and alcohols, which are 100% renewable components. Due to the RED-II legislation, which assigns HVO as a blend component of greater importance in the future, Blend-3 has a great share of HVO. The other two components (1-Octanol and OME 2-5 ) are mainly added for their purpose as oxygen-carriers. Fig. 3 depicts the three-component system of Blend-3 and the blending limits due to the EN 590 legislation. Especially the narrow density limitations only allow a low admixing of the used OME mix. The minimum cetane number limits the share of 1-Octanol (1-Oct.). The maximum decrease of the volumetric lower heating value was defined with about 10% and the minimum oxygen content with 10%. Therefore, Blend-3 consists out of 58% HVO, 30% 1-Octanol and 12% OME 2-5 . The fuel data is stated in Table 2 (Appendix). Fig. 4 displays the distillation curves of the used commercial diesel fuel, Blend-3 and the limits of EN 590. The lower boiling points, respectively boiling ranges of the blend components of Blend-3, lead to a lower distillation curve, which nevertheless fulfills the distillation limits of the EN 590. Fig. 4: Distillation curves and EN 590 limits Thermodynamic Potential and Emission Characteristics of an Oxygen-containing Sustainable Fuel fulfilling EN 590 and REDII-standards 13th International Colloquium Fuels - September 2021 157 2.2 Test methodology Fig. 5 shows the comprehensive test methodology for the investigations with Blend-3 in a CI engine. Starting with the thermodynamics, the emission behavior of this fuel blend was researched with a state-of-the-art SCRE. Fig. 5: Methodological approach of the investigations with Blend-3 Subsequently, the CR was increased in order to improve the combustion efficiency. Based on the afore optimized stepped-lip piston bowl with a CR of 15.5 a new combustion chamber for a CR of 20.6 was developed with a smaller bowl volume. In an upfront carried out 1d engine cycle simulation this CR was found for an engine of this cylinder size to be the most advantageous compromise between efficiency improvement and keeping maximum cylinder pressures within a reasonable limit of 200bar, assuming a similar heat release. For the purpose of an analysis of the combustion process when using this renewable fuel blend, the experimental results were analyzed with a 0d engine cycle analysis. In order to investigate the effects of Blend-3 on tailpipe emissions using a cutting-edge exhaust aftertreatment system (EAS) series-relevant approval cycles, such as Worldwide Harmonized Light Vehicles Test Cycles (WLTC), were carried out using a 2.0l multi-cylinder CI engine. Fig. 6: Schematic of the SCRE measurement setup [6] The major part of the experimental investigations was carried out on a SCRE, which is schematically shown in Fig. 6. The engine design allows maximum flexibility with regards to hardware modifications. The swept volume of 0.5l is very common in PC CI engines. In combination with the latest fuel injection equipment and the modern piston bowl design this combustion hardware guarantees series-relevant research results. The technical data of the SCRE is stated in Table 1. Table 1: SCRE specification [6] Type AVL 5402 Bore 85mm Stroke 90mm Displacement 511cm³ Compression ratio 15.5 Number of valves 4 Max. cyl. pressure 200bar Max. speed 4200min -1 Technology Common-rail injection system Bosch CP4.1 fuel pump Bosch CRI 2-25 injector Stepped-lip piston bowl HP-EGR (cooled, with bypass) Variable swirl system The wall heat loss Q W is a significant efficiency loss in an internal combustion engine. As shown in the first law inner gas work and thus is a relevant optimization parameter of a combustion system. Eq. 1: First law of thermodynamics for an instationary and open system As depicted in Fig. 7, the wall heat loss is split up into three parts according to the combustion chamber walls. The piston cooling, which dissipates the main part of the wall heat loss via the piston, was used to measure an indicator of the overall wall heat loss. The temperature difference between the inand the outflow of the piston cooling ΔT OIL is proportional to the heat flux, as Eq. 2 illustrates. Thermodynamic Potential and Emission Characteristics of an Oxygen-containing Sustainable Fuel fulfilling EN 590 and REDII-standards 158 13th International Colloquium Fuels - September 2021 Fig. 7: Thermal energies and enthalpies in a combustion chamber according to Eq. 1 Eq. 2: Heat flux in the piston cooling gallery Fig. 8: Schematic of the piston cooling temperature measurement As shown in Fig. 8, the inand the outflow oil temperatures of the piston cooling gallery were measured. The conventional piston cooling jet was equipped with a thermocouple. In order to measure the temperature in the outflow T OIL,OUT a small tube was modified to collect the oil from the return-flow. Together with the temperature in the inflow T OIL,IN the temperature difference between these two temperatures ΔT OIL , can be calculated. In order to cover a whole engine map with a few stationary load points in the best possible way, two relevant driving cycles for PCs with different vehicle mass were simulated with AVL-CRUISE TM , as shown in Fig. 9. For investigations in low engine load the load point 2000rpm and a break mean effective pressure (BMEP) of 6bar was chosen, which corresponds to an indicated mean effective pressure (IMEP) of 6.7bar (2000/ 6.7bar) in the referenced four-cylinder engine, stated in Table 4. The total injection quantity in this load point with single pilot injection was 19mg, from which 18mg were used for the main injection. Fig. 9: Overview of the investigated load points Investigations in high engine load were carried out at the same engine speed and a BMEP of 16bar, which requires an IMEP of 17.2bar (2000/ 17.2bar). The engine sweet spot with lowest BSFC in the engine map was predicted to be at 2250rpm and an IMEP of 19bar (2250/ 19bar) which results in a BMEP of 18bar presuming an engine friction reduction down to 1bar in this load point. Fig. 10: Distribution of carbonyls in a Diesel exhaust gas [7] In order to take account of future emission legislation, the emission behavior of non-limited emissions such as carbonyls was investigated as well. Formaldehyde (FA) and Acetaldehyde (AD), which together account for a share of nearly 90%, were measured (Fig. 10). In the following results the respective injection strategy is shown in the upper right corner of the diagram by open triangles representing the mainas well as the applied number of pilot injection events (e.g. ^^ ^) 3. Results 3.1 Thermodynamics Fig. 11 shows the comparison of the analyzed combustion parameters using a single injection and no EGR with the researched fuels at constant center of mass fraction burned (MFB 50 ) at an engine speed of 2000rpm and an injection quantity of 18mg (2000/ 18mg). Thermodynamic Potential and Emission Characteristics of an Oxygen-containing Sustainable Fuel fulfilling EN 590 and REDII-standards 13th International Colloquium Fuels - September 2021 159 The higher cetane number of Blend-3 leads to a shorter ignition delay, resulting in an earlier rise of the rate of heat release (ROHR). It is assumed, that the oxygen content of Blend-3 is responsible for the shorter combustion duration. As a consequence, the degree of constant volume (η CV ) of the combustion with Blend-3 rises. The oxygen content in the fuel lowers the lower heating value (LHV). Therefore, these measurement results compare different chemical energies injected into the combustion chamber. Fig. 11: Combustion parameters of the main injection without EGR Fig. 12: Combustion analysis of a single injection without EGR The shorter ignition delay of Blend-3 also causes a lower initial combustion rate compared to Diesel-B7, as Fig. 12 illustrates. The different nitrogen oxide (NO x ) engine-out emissions and IMEPs are a result of the different LHVs. Fig. 13: Loss analyses of the single injections without EGR The loss analyses in Fig. 13 depict the efficiency losses of the engine operated with the two fuels at a constant gas exchange. The higher excess air ratio (EAR) due to the higher oxygen content in the Blend-3 fuel leads to a higher efficiency of the standard air fuel cycle (AFC) with real charge. The loss due to incomplete combustion (IC) is negligible. The shorter combustion duration and therefore high degree of constant volume combustion leads to a lower loss due to real combustion (RC). Despite the higher EAR, the combustion of the trinary blend causes a higher wall heat loss. This result may have several causes. Both, the lower engine load with Blend-3 and a higher combustion temperature, may cause this higher efficiency loss. The gas exchange loss increases due to the measurement at constant pumping mean effective pressure (PMEP). Hence, at constant injection quantity the indicated efficiencies of the compared fuels are the same. Fig. 14: Combustion parameters in the sweet spot without EGR In the sweet spot of the engine, which was found at 2250/ 19bar, the indicated efficiency decreases with Blend-3, as shown in Fig. 14. The longer injection duration required to compensate the lower LHV and higher wall heat losses are the reason. In contrast to the findings in Fig. 11, the ignition delays and combustion durations Thermodynamic Potential and Emission Characteristics of an Oxygen-containing Sustainable Fuel fulfilling EN 590 and REDII-standards 160 13th International Colloquium Fuels - September 2021 are about the same at this high load point. Due to the high rail pressure of 2000bar, the influence of the fuel parameters on the ignition process becomes secondary. The oil temperature measurement in the inand outflow of the piston cooling could confirm the higher wall heat loss with Blend-3. As illustrated in Fig. 15, a significant change of the oil temperature difference over the piston in the sweet spot was measured. Fig. 15: Oil temperature measurement of the piston cooling in the sweet spot without EGR 3.2 Emission behavior In addition to thermodynamics, the emphasis of the investigations with Blend-3 was laid on the emission behavior. Fig. 16 shows the combustion parameters of an EGR sweep at the selected low load point at constant IMEP and constant PMEP. As a consequence of the higher EAR and the shorter combustion duration, the trinary blend has a slightly higher indicated efficiency and a lower exhaust gas temperature. Similar to the findings in Fig. 11, Blend-3 has a shorter ignition delay, which becomes more pronounced at high EGR rates. As shown in Fig. 17, the trinary blend reduces the exhaust emissions significantly. As a result of the higher engine efficiency and the lower CO 2 factor, the CO 2 emissions are reduced due to the use of Blend-3. Furthermore, the oxygen content of this blend causes a more complete combustion and therefore lower carbon monoxide (CO) and lower smoke emissions. Hence, the NO x smoke trade-off is significantly improved. As a result of the higher cetane number and the shorter ignition delay, the combustion noise level (CNL) is improved as well. With Blend-3 the FA emissions increase slightly, but due to the low level the FA emissions are negligible. In the high load point without EGR the use of Blend-3 causes no significant change in the indicated efficiency, which is illustrated in Fig. 18. At high EGR rates, hence low NO x emissions, the more complete combustion with the sustainable blend results in a higher efficiency. Compared to the low load point in Fig. 16, the differences in ignition delay and combustion duration become smaller due to the higher rail pressure. In line with the previous results, Blend-3 improves the emission behavior in the high load point as well, as can be seen in Fig. 19. Even in those conditions, when the indicated engine efficiency is lower, the CO 2 emissions are still reduced due to the better CO 2 factor of the Blend-3 fuel. Furthermore, the NO x -smoke trade-off is slightly improved and Fig. 16: Combustion parameters of the EGR sweep in a low load point Fig. 17: Emission behavior of the EGR sweep in a low load point Thermodynamic Potential and Emission Characteristics of an Oxygen-containing Sustainable Fuel fulfilling EN 590 and REDII-standards 13th International Colloquium Fuels - September 2021 161 lower smokeand/ or NO x emissions could be achieved. The CO emissions and the CNL are about the same. Again, the use of Blend-3 leads to a slight negligible increase of the FA emissions. The significant improvements found in the NOx-smoke trade-off leading to very low smoke levels enable as a next step the increase of the compression ratio (CR). This measure is a well-known way to improve the engine efficiency, however, Fig. 18: Combustion parameters of the EGR sweep in a high load point Fig. 19: Emission behavior of the EGR sweep in a high load point a high CR also deteriorates on the other hand the NOxsmoke trade-off [5, 6]. 3.3 Increase of the CR Fig. 20: Loss analyses of different compression ratios without EGR Fig. 20 illustrates the loss analyses of the different CRs at constant EAR. The increase of the CR causes a higher efficiency of the AFC with real charge. As a consequence of the higher pressure at the end of the compression stroke and therefore shorter ignition delay, the combustion duration increases and deteriorates the real combustion loss. The higher pressure level during the combustion leads also to a higher wall heat loss. But due to the constant PMEP the gas exchange loss decreases with increased CR. Consequently, as a sum of these effects, a higher CR improves the indicated efficiency. Thermodynamic Potential and Emission Characteristics of an Oxygen-containing Sustainable Fuel fulfilling EN 590 and REDII-standards 162 13th International Colloquium Fuels - September 2021 Fig. 21: Comparison of different CRs in a low load point Fig. 21 depicts the EGR-sweep results with an increased CR with Diesel-B7 and Blend-3 in the low load point. In order to compensate the lower LHV of Blend-3 on the one hand, but also to take advantage of shortening the combustion duration to further improve efficiency at higher loads, the related test runs with Blend-3 were carried out with an injector nozzle having a 45% increased hydraulic flow rate, which is stated in Table 3. With conventional diesel fuel the higher CR leads to a higher indicated engine efficiency due to the higher efficiency of the AFC and therefore a lower exhaust gas temperature. The shorter ignition delay due to the higher pressure at the end of the compression stroke causes a worsened initial fuel preparation and hence higher smoke emissions. Likewise, the shorter free fuel jet length deteriorates the mixture preparation as well. This is also reflected by the increase of the CO emissions, which are an indicator of an incomplete combustion. Compared to the results with Diesel-B7, Blend-3 increases the indicated engine efficiency further due to the higher EAR and improved combustion. The oxygen content improves the NO x -smoke trade-off significantly. With Blend-3 and the high CR the trade-off in this low load point nearly meets the one achieved with Diesel-B7 and the lower CR, while the indicated efficiency is appreciably increased. Fig. 22: Comparison of different CRs in a high load point As shown in Fig. 22, an increase of the CR with diesel fuel leads to the same effects in high load as in low load, namely a higher engine efficiency, the deterioration of the NO x -smoke trade-off, a decreased exhaust gas temperature and higher CO emissions. The use of Blend-3 in combination with a high CR and a high flow injector at this high load point could even improve the NOx-smoke trade-off compared to Diesel-B7 with the low CR. The key-outcome shown in these two diagrams is, that Blend-3 enables adaptations to the combustion system, such as the increase of the CR and the increase of the injector flow rate, resulting in a higher indicated efficiency at approximately the same NOx-smoke trade-off to be expected in the entire engine map. In addition to the emission behavior, the effect of the increased CR on the sweet spot with the lowest fuel consumption in the engine map was investigated. Thermodynamic Potential and Emission Characteristics of an Oxygen-containing Sustainable Fuel fulfilling EN 590 and REDII-standards 13th International Colloquium Fuels - September 2021 163 Fig. 23: Comparison of different CRs and fuels in the sweet spot Fig. 23 shows the efficiency increase with the higher CR. The MFB 50 needed to be retarded in order not to exceed maximum cylinder pressure. The higher cylinder pressure level and thus shorter ignition delay lead to a longer burning duration with diesel fuel. Blend-3 in combination with Inj. 2 increases the indicated efficiency due to the higher hydraulic injector flow rate and therefore shorter combustion duration. Furthermore, the influence of the higher cetane number of the trinary blend can be found as well. 3.4 Driving cycles In order to compare the alternative blend with conventional diesel fuel in a dynamic, series-relevant approval cycle, WLTCs were carried out with a four-cylinder CI engine, whose technical data is stated in Table 4. Fig. 24: Emulated WLTC with the EAS architecture The test cycle as well as the used EU7-capable EAS are illustrated in Fig. 24. To comply with the required nitrogen oxide emission legislation limit in all driving situations, an electrically heated catalyst (EHC), located in front of the diesel oxidation catalyst, is used in addition to the loading-based SCR double dosing system. The required heating energy is recovered via load point shifting. Any possible NH 3 slip is oxidized by the ammonia slip catalyst at the end of the whole exhaust gas aftertreatment system. To be able to run the test cycles on a dynamic test bench, the dynamic behavior of a PC was needed to be emulated. Therefore with a longitudinal dynamic simulation the target torque curve of a heavy Sport Utility Vehicle (SUV), which is among the most demanding applications for a 2.0l four-cylinder engine in terms of engine-emission, was determined and used on the test bench. In order to counteract an undesirable shift of the engine operating point in the engine control unit maps due to the lower LHV of Blend-3 and therefore higher injection quantity, the engine maps were adapted to assure similar calibration settings. Fig. 25: Comparison of the EO emissions in the WLTC Fig. 26: Comparison of the TP emissions in the WLTC Fig. 25 depicts the different engine-out (EO) emissions in the WLTC with the investigated fuels. Also in the cumulative cycle emissions it is obvious, that the oxygen Thermodynamic Potential and Emission Characteristics of an Oxygen-containing Sustainable Fuel fulfilling EN 590 and REDII-standards 164 13th International Colloquium Fuels - September 2021 content in the trinary blend causes a more complete combustion and thus significantly lower soot, CO, hydrocarbon (HC) and CH 4 emissions at approximately the same engine-out NO x emissions. As shown in Fig. 26, also the measured tailpipe (TP) emissions are reduced due to the use of Blend-3. As a consequence of the lower CO 2 factor of the trinary blend, the CO 2 emissions are reduced despite a higher volumetric fuel consumption as a result of the lower LHV of Blend-3. Furthermore, the CO and HC emissions are reduced at very low NO x (TP) emissions of about 40mg/ km. The results achieved on the multi-cylinder engine along the WLTC cycle confirm all the main findings gathered during the SCRE tests and confirmed the flawless operation of the EAS also when using the sustainable Blend-3 fuel. 4. Conclusion and outlook The present work investigates the effects of a trinary fuel blend, fulfilling EN 590 and RED-II legislation, on thermodynamics and on the emission behavior in a CI engine of PC size. Since alternative fuels are able to make a major contribution to the decarbonization of transportation and moreover promote the achievement of the CO 2 targets car manufacturers have to fulfill, a trinary blend consisting of HVO, ethers and alcohols was defined. This fuel blend was investigated in various test runs carried out on a state-of-the-art CI SCRE for steady state thermodynamic and emission measurements. In addition WLTC driving cycles were carried out on a four-cylinder CI engine. The oxygen content of about 10% leads to significant NO x smoke trade-off improvements at low as well as high engine loads and reduces unburned exhaust gas emission components. Furthermore, the CNL is improved due to the higher cetane number. As a consequence of the oxygen content, the higher EAR and the shorter combustion duration improve the indicated engine efficiency at low load. At high load the efficiency only increases at higher EGR rates and thus low NO x emissions due to a more complete combustion. The applied temperature measurement equipment in the piston cooling flow indicated a higher wall heat loss with Blend-3 and verified the result of the loss analysis. The significant trade-off improvements enable adaptations to the combustion system to further improve engine efficiency and reduce CO 2 emissions. It is shown that when increasing the CR in combination with an injector with a higher hydraulic flow rate to compensate the lower LHV and reduce the combustion duration, the trinary blend increases the indicated efficiency by about two percent points at approximately the same NO x -smoke trade-off (expected in the entire engine map) over a CI engine fueled with conventional diesel. Hence, the oxygen content in the fuel, which basically reduces smoke emissions, was successfully used to increase the efficiency via engine combustion hardware optimization. In the WLTC Blend-3 nearly thirded the engine-out soot emissions at the same NO x emissions, which were at a low tailpipe level of about 40mg. Besides the lower HC and CO emissions, the CO 2 emissions were decreased due to the lower CO 2 factor of this renewable blend compared to conventional diesel fuel. Due to the high amount of OME in the fuel, it is assumed, that this fuel is not compatible with the current car fleet. Hardware adaption measures, especially sealing materials of the fuel system, are necessary for the use of the trinary blend. Besides the afore shown tank-to-wheel considerations, a well-to-wheel analysis of this promising fuel will illustrate the importance of the production process of the renewable blend components to reduce the total CO 2 emissions even further. 5. Acknowledgements This study is part of the research project “RC-LowCAP”, which is a publicly funded project by the Austrian Research Promotion Agency (FFG) with partners from the industry AVL, OMV (Downstream), Vitesco Technologies Emitec and Heraeus. References [1] Zubel, M., Bhardwaj, O. 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Appendix Table 2: Test fuel properties [6] Fuel property Unit Diesel-B7 Blend-3 Cetane number - 42 61.5 Density (15°C) kg/ m³ 838.7 824.7 LHV MJ/ kg 42.66 38.72 H/ C Ratio - 1.89 2.22 Stoichiometric Air Demand kg/ kg 14.52 12.99 Carbon content % 85.9 75.0 Hydrogen content % 13.6 14.0 Oxygen content % 0.9 10.7 Total aromatics content % 19.9 0.2 Viscosity (40°C) mm²/ s 2.80 2.58 Flash point °C 67 71 T 10 °C 207.2 188.4 T 50 °C 274.4 234.7 T 90 °C 338.1 287.5 CO 2 factor g/ MJ 73.8 71.0 Table 3: Diesel injectors Abbrevation Hole diameter Flow rate Injector 1 108µm 620ml/ min Injector 2 130µm 900ml/ min Table 4: Four-cylinder engine specification Bore 84mm Stroke 90mm Displacement 1995cm³ Compression ratio 16.5 Number of valves 4 Max. cyl. pressure 150bar Rated speed 4000min -1 Technology Common-rail injection system Bosch CP4.1 fuel pump Bosch CRI 2-20 injectors VNT turbocharger Variable oil pump HP-EGR (cooled, with bypass) SCR with double injection 7. Abbreviations, Symbols and Indices AFC Standard air fuel cycle ASC Ammonia slip catalyst BMEP Break mean effective pressure CNL Combustion noise level CO Carbon monoxide CO 2 Carbon dioxide CA Crank angle CH 4 Methane CI Compression ignition CR Compression ratio CYL Cylinder DIST Distillation DOC Diesel oxidation catalyst EAR Excess air ratio EAS Exhaust aftertreatment system EGR Exhaust gas recirculation EHC Electrically heated catalyst EO Engine-out HC Hydrocarbon HP High-pressure HVO Hydrated Vegetable Oil ID Ignition delay IMEP Indicated mean effective pressure LHV Lower heating value MCE Multi-cylinder engine MFB Mass fraction burned NOx Nitrogen oxide OME Oxymethylene ethers PC Passenger car PMEP Pumping mean effective pressure RED Renewable energy directive RME Rapeseed methyl ester ROHR Rate of heat release SCR Selective catalytic reduction SCRE Single cylinder research engine sDPF SCR-coated diesel particulate filter SN Smoke number SUV Sports Utility Vehicle TC Turbocharger TP Tailpipe UF Under-floor VOL Volumetric WLTC Worldwide harmonized light vehicles test cycle c Specific heat capacity H, h Enthalpy Thermodynamic Potential and Emission Characteristics of an Oxygen-containing Sustainable Fuel fulfilling EN 590 and REDII-standards 166 13th International Colloquium Fuels - September 2021 m Mass p Pressure Q Energy T Temperature U Internal energy W Work Δη IC Imperfect combustion loss Δη GE Gas exchange loss Δη RC Real combustion loss Δη WH Wall heat loss η Efficiency η CV Degree of constant volume χ Heat capacity ratio λ Stoichiometric air to fuel ratio μ Mass fraction ρ Density φ Angle 20 Charge air 21 Intake manifold 31 Engine-out 32 Damping vessel e Effective i Indicated