7635 FACTA UNIVERSITATIS Series:Mechanical Engineering Vol. 20, No 2, 2022, pp. 321 - 339 https://doi.org/10.22190/FUME210329049B © 2022 by University of Niš, Serbia | Creative Commons License: CC BY-NC-ND Original scientific paper ASSESSMENT OF THE QUADRUPLE INJECTION STRATEGY OVER TRIPLE INJECTIONS TO IMPROVE EMISSIONS, PERFORMANCE AND NOISE OF THE AUTOMOTIVE DIESEL ENGINE Sanjoy Biswas1, 2, Achintya Mukhopadhyay1 1Department of Mechanical Engineering, Jadavpur University, India 2Engineering, Tata Motors Ltd, India Abstract. The present study aims at investigating effectiveness of the quadruple (early- pilot-main-after [epMa]) injection strategy over three different triple [early-main-after (eMa), early-pilot-main (epM) and pilot-main-after (pMa)] injection scheduling in terms of emissions, performance [brake specific fuel consumption (BSFC), torque, brake thermal efficiency (BTE) and fuel economy] and noise. The experimentation was carried out on a heavy-duty BS-IV diesel engine with 45% EGR fraction and fixed main injection (Crank-angle) scheduling at eight different RPMs and three loads of engine (20%, 60% and 100%) using design of experiments(DOE). This comprehensive study showed that the quadruple injection strategy provides optimum results in both performance and emissions compared to the promising three triple injection strategy. The quadruple injection strategy exhibits the best BTE at all operating conditions and best BSFC at medium to high-speed zone around 0.5–1% inline to reduce combustion noise (CN) level, especially at low speeds and low to medium load of 0.2–2.2 dBA. Among triple injections, the pMa shows the best performance in BSFC, BTE, smoke and THC emissions. The epM is the best in the CO emissions and torque performance in the low-speed zone. Smoke value is marginally higher for the epMa at low to medium speed than the pMa, although average smoke emissions were the best. Taken together, the overall PM emission level was marginally better than Triple Injections, due to the impact of double pilots in combination with post-injection. In addition, NOx emissions were improved (around 3–6%) significantly with quadruple than with triple injections. The epMa injection scheduling also showed improvement in constant speed fuel economy and in pass-by-noise at the vehicle. Key Words: Quadruple Injections, Emission, Brake Specific Fuel Consumption, Pass- by-noise, Constant Speed Fuel Economy, Brake Thermal Efficiency Received March 29, 2021 / Accepted June 15, 2021 Corresponding author: Sanjoy Biswas Department of Mechanical Engineering, Jadavpur University, Kolkata-700032, India E-mail: s.biswas.me@gmail.com 322 S. BISWAS, A. MUKHOPADHYAY 1. INTRODUCTION Automotive engine out-emissions, noise and fuel economy have a significant impact on environmental pollution. Thus, the challenges are multi-fold for an engine developer/engineer (R&D), especially for the diesel engine as he needs to deal with stringent emissions norms in line with mandated fuel economy norms as per applicability [for example, heavy-duty fuel economy (HDFE) or constant speed fuel economy (CSFE) or corporate average fuel efficiency/economy (CAFE)]. Fuel economy norms are targeted to CO2 emissions reduction (in gm/km) to control global warming. Currently, the diesel engine combustion noise (CN/radiation) has gained significant attention as it is associated with the passengers and pedestrians’ discomfort along with noise pollution. Therefore, the fuel injection strategy plays a key role in the simultaneous reduction of emissions and CN without penalizing fuel economy due to the better control of the combustion process. The fuel injection strategy in combination with the common rail direct injection (CRDI) technology and heavy or high EGR is also promising low-temperature combustion (LTC) methodology [1]. The CRDI technology provides flexibility to experiment with various injection strategies based on the parameters such as injection pressure, fuel quantity and injection timing, which are linked to the engine combustion management. Furthermore, engine with a turbocharging system enables power augmentation with improved fuel efficiency at particular brake mean effective pressure [2]. A five-dimensional study has been carried out on the modern diesel engine to simultaneously improve the performance (especially fuel economy and CN) and emissions. Several studies [3-7] are focused on the effect of pilot injection (single or double/twin) or post-injection on emissions, combustion or CN. Some groups are focused on the impact of injection parameters (fuel injection pressure (FIP), injection rate, injection timing and fuel quantity) on combustion characteristics and emissions [8-9]. The influence of alternative fuel on performance, combustion and emissions has also been explored [10-11] with variation in injection parameters or injection strategies. On the other hand [12-14], the predictive model was developed based on quasi-dimensional (1D) or phenomenological and multi-dimensional (i.e., CFD) approach and validated for combustion and emissions of DI diesel engine with single and multiple injections (double, triple). A recent study [15-18] assessed the impact of multiple injections on the performance, CN, and emission characteristics of the modern diesel engine. The selective outcomes of these studies have been discussed subsequently. Mendez et al. [15] examined the impact of multiple (double, triple and quadruple) injections on a low Compression-Ratio diesel engine with high EGR%. The study concluded that the multi-injections strategy is beneficial along with high rate EGR (~46%) to accept ignition delay with improvement in the emission level, CN and trade- off of fuel economy. D’Ambrosio et al. [16] concluded that the pilot-pilot-main-after (ppMa) strategy could improve in engine out-NOx emissions and trade-off among BSFC- NOx EGR curve compared to both the pilot-pilot-main (ppM) and pilot-main-after (pMa) strategies at mid-range loads and speeds. In addition, it reduces CN significantly compared to both triple injections. In a previous study [17], the impact of epMa injection was assessed with respect to the performance, emissions and CN level of CRDI engine with variables, such as variable main injection timing and eight different speeds and loads, for better and smoother torque, BSFC and reduced CN than baseline pMa-E. In another study [18], the superiority of epMa injection over triple (pMa) and double (pM) Assessment of Quadruple Injection Strategy over Triple Injections to Improve Emissions... 323 injections was assessed with respect to noise, performance and emissions level with fixed main injection time. Currently, only limited literature is available on the quadruple injection strategy consisting of a double pilot and one post-injection event combined with high EGR on the heavy-duty diesel engine. Studies of the influence of multiple injection strategies upon vehicle level fuel economy and noise performance have not been reported yet. Considering this research gap, we have focused on the comprehensive assessment of four types of multiple injections, including the newest quadruple injection (Fig. 1). In the present study, the potentialities of quadruple injection schedules are evaluated over three triple injections on a classic six-cylinder heavy-duty CRDI engine at three different operating loads and eight speeds (low-to-high) using design of experiments (DOE) approach. The results of emissions (nitrogen oxides (NOx), particulate matter (PM), smoke and total hydrocarbons (THC) levels) and performance (torque, BSFC and BTE) and CN (radiated) with fixed EGR% and main injection timing were compared at various engine working conditions. The study also elucidated the impact of these injection strategies on vehicle level pass-by-noise (PBN) and CSFE. The current literature provides an insight in terms of in-cylinder characteristics. Fig. 1 Schematic representation of quadruple and three triple injection strategies In Fig. 1 the following is represented: epM, eMa and pMa-triple injections; epMa- Quadruple injections; TDC-Top dead centre; CA-Crank angle; Ai-Main injection advanced w.r.t TDC; AiE-Early injection advanced w.r.t TDC; AiP-Pilot injection advanced w.r.t TDC; AiA-After injection w.r.t TDC; DtA-after/post-injection Dwell; p- Pilot or Pilot injection 2; e-Pilot injection 1 or early injection; qm-quantity of fuel at main injection; qpf/qaf-Quantity of fuel at pilot/early and after/post-injection. 324 S. BISWAS, A. MUKHOPADHYAY 2. EXPERIMENTAL SETUP AND METHODOLOGY 2.1. Experimental Setup The experiment was conducted on a heavy-duty BS-IV diesel engine containing a cooled EGR and CRDI system. The external cooling system (turbocharged intercooler) is attached to the engine. Table 1 shows the specification of a typical engine. Table 1 Specification of Experimental Engine Parameters Value Engine type BS-IV 6 cylinder inline, Turbocharged Total displacement volume 5.67 L Max power 130 PS @ 2400 rpm Max torque 485 Nm @ 1500 rpm Max speed and Min speed (idle) 2750 rpm and 700 rpm Compression ratio 17.5:1 Injection system CRDI, Bosch–EDC 17 Injection pressure 120–170 MPa EGR type Short route cooled EGR No. of holes at injector and tip angle 8 no. and 148° Combustion chamber type Shallow bowl/semi-quiescent Boost pressure @ max power 214 kPa Fig. 2 Schematic layout of the experimental setup for performance and smoke emissions Assessment of Quadruple Injection Strategy over Triple Injections to Improve Emissions... 325 Fig. 3 Schematic layout of nearby noise test at Rig In Test rig, the engine is propelled by an Eddy current dynamometer using a drive shaft. A 6-speed transmission is mounted with the engine. The driveshaft is connected in between the dynamometer and the transmission/gearbox. Properly conditioned and metered air and fuel were used during experiments as shown in the setup and data acquisition system (Fig. 2) for emissions and performance. Inside the testbed, engine-radiated noise was measured according to the schematic in Fig. 3, following the IS: 10399 guidelines [19]. 2.2. Experimental Methodology The typical engine has EGR for in-cylinder NOx reduction and Bosch-make CRDI system. It also has a definite fuel-mass torque cycle (FMTC) where the broad outline of fuel demand for any particulate torque and speed was mapped. Calibration, diagnostics and validation activities were monitored using INCA software. The permittable smoke limit for the base engine has been outlined for partial as well as full load application with pMa injection schedule. Fuel mass (FM) and engine speed are functions of fuel injection pressure (FIP). Therefore, FIP varies within 120–170 MPa based on the FM and engine speed (RPM). In the present study, EGR% was the same as the typical production diesel engine (Table 2). Herein, the key focus was on the comparative study and understanding the effect of four different multiple injection strategies on performance (mainly BSFC) and exhaust emissions trade-off and CN. The base engine also had pMa triple injection schedules (Ai variable 6 to -3° CA BTDC, AiP -19.9° CA BTDC, DtA 1350 ms), which meets BS-IV norms. To adopt all four injection strategies (i.e., epMa, pMa, eMa and epM), delta optimization was carried out at the base level calibration to reduce variable factors in experimentation and complexity. After-treatment arrangement was carried out similarly as in production/base engine during the experiments. In this test bed, the clutch, gearbox, external cooling/intake system and engine mounts adapted from production models were used in a typical engine. The DOE method used in this study for a systematic approach of testing was based on the inputs presented in Table 2. The experiments were conducted as per the DOE matrix shown in Table 3 for performance and emissions. The data were captured at a steady-state condition, considering an average of 20 cycles for each dataset. To deal with uncertainty in measurement data, especially for the sensitive fuel economy and emissions, NBL-141 guidelines (Issue 2, Amendment No. 3, 2000) were followed in the laboratory. The emission tests were based on European stationary cycle (ESC) with a European load response (ELR) 326 S. BISWAS, A. MUKHOPADHYAY for smoke trial and European transient cycle (ETC) standards to verify the results in reference to regulatory norms. Radiated noise/CN of engine was measured based on the IS: 10399 [19] standard on noise measurement methodology of a stationary vehicle. During the noise trial, the microphone was placed as shown in Fig. 3. Test data were acquired only after stabilization of exhaust gas temperature. Furthermore, the ambient noise of the test rig was measured before the start of the trials. PBN trial was conducted as per IS: 3028 [20] to understand the vehicle level impact. CSFC or CSFE performance of vehicle was measured based on AIS-149 [21] to evaluate the real-time effect. This standard provides the guidelines to calculate the target CSFC at 40 kmph and 60 kmph speed based on engine specification, driveline configuration (e.g., 4×2) and vehicle GVW. Table 2 DOE matrix inputs: factors, level, and value Factors Level Value Triple Injection1 A epM Triple Injection 2 B eMa Triple Injection 3 C pMa Quadruple Injection D epMa Load (%) L1, L2, L3 20, 60, 100 Speed (rpm) N1, N2, N3, N4, N5, N6, N7, N8 1100, 1300, 1500, 1700, 1900, 2100, 2300, 2500 Fixed Factors EGR Ai AiP AiE DtA 45% 2 °CA BTDC 19 °CA BTDC 39 °CA BTDC 1100 ms Table 3 DOE matrix for performance and smoke emissions tests Trial Combination Speed (RPM) N1 N2 N3 N4 N5 N6 N7 N8 epM AL1 AL1N1 AL1N2 AL1N3 AL1S4 AL1N5 AL1N6 AL1N7 AL1N8 AL2 AL2N1 AL2N2 AL2N3 AL2S4 AL2N5 AL2N6 AL2N7 AL2N8 AL3 AL3N1 AL3N2 AL3N3 AL3S4 AL3N5 AL3N6 AL3N7 AL3N8 eMa BL1 BL1N1 BL1N2 BL1N3 BL1S4 BL1N5 BL1N6 BL1N7 BL1N8 BL2 BL2N1 BL2N2 BL2N3 BL2S4 BL2N5 BL2N6 BL2N7 BL2N8 BL3 BL3N1 BL3N2 BL3N3 BL3S4 BL3N5 BL3N6 BL3N7 BL3N8 pMa CL1 CL1N1 CL1N2 CL1N3 CL1S4 CL1N5 CL1N6 CL1N7 CL1N8 CL2 CL2N1 CL2N2 CL2N3 CL2S4 CL2N5 CL2N6 CL2N7 CL2N8 CL3 CL3N1 CL3N2 CL3N3 CL3S4 CL3N5 CL3N6 CL3N7 CL3N8 epMa DL1 DL1N1 DL1N2 DL1N3 DL1S4 DL1N5 DL1N6 DL1N7 DL1N8 DL2 DL2N1 DL2N2 DL2N3 DL2S4 DL2N5 DL2N6 DL2N7 DL2N8 DL3 DL3N1 DL3N2 DL3N3 DL3S4 DL3N5 DL3N6 DL3N7 DL3N8 Assessment of Quadruple Injection Strategy over Triple Injections to Improve Emissions... 327 3. RESULTS AND DISCUSSION The experimental data are presented in tabular and graphical form. In the current study, three major tests were conducted to evaluate performance, emissions and noise sequentially. The data of comparative trials of BSFC and torque among the strategies are shown below. The measured data points have been mentioned on the epMa curve or chart for clarity. 3.1. Rig Level Tests 3.1.1. BSFC, Torque and BTE Performance Performance test data are plotted in graphical format for each load and speed combination as per the DOE strategy (Table 3). Torque (Tr in Nm) and fuel flow rate (FFR in kg/h) were directly measured during experimentation. BSFC (g/kWh) value was calculated using equation (1), where N is engine speed in RPM. )( )35.95491000( NT FER BSFC r   = (1) The average BSFC performance was the best for the quadruple injection strategy among the schemes at 100% load, although at few speeds, pMa performed better (Fig. 4). In addition, the BSFC curve was smoother with the quadruple injection strategy than triple injections, while epM and eMa strategies are the bottom two performers in BSFC. The quadruple injection displays the optimum torque performance among the injection strategies (Fig. 5). Conversely, epM shows the best torque performance in 1200–1800 RPM zone. Herein, the torque performance of pMa strategy was second optimum, and the eMa strategy was the poorest in torque performance at 100% load at almost all speeds. Fig. 4 Comparative BSFC graphs at 100% load 328 S. BISWAS, A. MUKHOPADHYAY Fig. 5 Comparative torque graphs at 100% load At 60% load, epMa exhibits an optimum BSFC performance but is the best between 1800 and 2500 RPM compared to the other three multiple injection strategies (Fig. 6). The pMa injection strategy performed the best <1700 RPM and thus, deemed as the second best. On the other hand, the epM strategy was the poorest in BSFC performance, and the BSFC pattern/curve of epMa was smoother than that of other injection schedules. Similarly, the quadruple epMa injection shows the optimum torque performance among the injection strategies (Fig. 7). However, epM shows the best torque performance from 1100 to 1700 RPM. The second optimal torque performance was assessed using the pMa injection strategy. The eMa is the worst in torque performance at almost all speeds (Fig. 7). Fig. 6 Comparative BSFC graphs at 60% load Assessment of Quadruple Injection Strategy over Triple Injections to Improve Emissions... 329 Fig. 7 Comparative torque graphs at 60% load At a partial load of 20%, the BSFC performance among the four multiple injection strategies could not be distinguished, especially between 2200 and 2500 RPM from the line chart (Fig. 8). The BSFC of the pMa is the best in the zone of 1100–1900 RPM but the BSFC curve is not smooth. On the other hand, the BSFC performance curve was smoother for the epMa and marginally better than the pMa considering the average BSFC level. The epM and eMa injections are the bottom-level performers in BSFC (Fig. 8). Similarly, the torque performance is also mixed in nature at a partial load of 20% (Fig. 9). The quadruple (epMa) injection provides the optimum torque performance among the injection strategies (Fig. 9), although it is the third-best in the 1100–1400 RPM zone. The epM also shows the best torque performance between 1100 and 1500 RPM. The second optimum torque performance was detected with the pMa injection strategy, and the eMa showed the most inadequate torque performance from 1100 to 2000 RPM engine speed. Fig. 8 Comparative BSFC graphs at 20% load 330 S. BISWAS, A. MUKHOPADHYAY Fig. 9 Comparative torque graphs at 20% load BTE is calculated based on the measured torque (Tr), engine speed (N) and FFR. The calorific value (CV) of BS-IV diesel fuel based on the standardization report was 42.8 MJ/kg (termed LHV). The FER was fuel flow rate in kg/h. Then, brake power (BP) was calculated using the torque and speed data. CVFER BP BTE   = 3600 (2) where: 35.9549 NT BP r  = (3) Fig. 10 Average BTE at different loads and overall average BTE of injection strategies Assessment of Quadruple Injection Strategy over Triple Injections to Improve Emissions... 331 Fig. 10 shows the trends of average BTE at different loads and the overall average BTE of each injection strategy. The average and overall average BTE was the best for epMa, while the epM was the worst. The overall average BTE of pMa was the best among triple injections, although the average BTE was the worst at 20% load. Indirectly, this study presented the combustion efficiency of each injection strategy with fixed main injection time and EGR%. 3.1.2. Emission Tests NOx, THC and CO emissions data have been captured following the sampling method of exhaust gases and analyzing using the Horriba Analyser. The measured smoke data are represented in terms of filter smoke number (FSN), and this parameter was measured using AVL Smoke Meter (Fig. 2). In addition, regulatory emission tests were carried out following the ESC with ELR and ETC standards. The measured regulatory test data among the multiple injection strategies were tabulated for comparative analysis of the results. Smoke test as per ELR: The measured smoke data are shown in the scatter chart format (Fig. 11, 12 and 13). The soot concentration (St in mg/m3) could be calculated further using the below imperial equation 4. Similarly, several correlations were available to predict the particulate matter (PM) as the summation of soot and hydrocarbons (HCs) with multiplication factors. 405.0 95.4 38.0 FSN t eFSN S   = (4) The smoke (FSN) emission is the highest with epM among the multiple injection strategies at 100% load (Fig. 11). On the other hand, the epMa shows the best performance from medium to high speed, whereas the pMa is the best in smoke reduction from 1100 to 1500 RPM. At 60% load, the smoke (FSN) emission pattern is similar to 100% load except for the values (Fig. 12). Herein, the epMa displays the best smoke emission from 1700 to 2500 RPM zone, whereas the pMa is the finest in smoke reduction from 1100 to 1500 RPM, and the epM is the worst in smoke performance with a marginal difference. At 20% partial load, the smoke (FSN) emission is the highest with the epM among the multiple injection strategies but has a narrow margin at maximum speeds (Fig. 13). On the other hand, the pMa is the best except at few random speeds and optimum in smoke emission, wherein the quadruple injection exhibits the second-best smoke performance. 332 S. BISWAS, A. MUKHOPADHYAY Fig. 11 Smoke test results at 100% load Fig. 12 Smoke test results at 60% load Fig. 13 Smoke test results at 20% load Assessment of Quadruple Injection Strategy over Triple Injections to Improve Emissions... 333 The average smoke curves (Figs. 14 and 15) indicate that the epMa injection strategy is optimum and the best in the smoke reduction for a wide speed zone except from 1100 to 1500 RPM. Herein, the high fuel-air mixture and diffusive combustion duration play a vital role in smoke or soot formation. Post-injection pulse also has a major impact on soot oxidation, which helps in smoke/soot reduction. Thus, the epM injection strategy is found the worst, while the pMa is the best in average smoke reduction from 1100 to 1500 RPM at low and medium loads. Fig. 14 Average smoke results with varying speeds Fig. 15 Average smoke results with varying loads Regulatory Emission Tests: The emission tests have been carried out according to the ESC and ETC standards for each injection strategy. The measured data are presented in Tables 4 and 5, and the units are in g/kWh. Table 4 ESC Test Results epM eMa pMa epMa BS-IV Limits BS-V Limits PM 0.019 0.018 0.015 0.014 0.020 0.020 NOx 3.208 3.312 3.278 2.971 3.500 2.000 THC 0.068 0.056 0.043 0.051 0.460 0.460 CO 0.053 0.087 0.077 0.061 1.500 1.500 334 S. BISWAS, A. MUKHOPADHYAY Table 5 ETC Test Results epM eMa pMa epMa BS-IV Limits BS-V Limits PM 0.026 0.025 0.021 0.019 0.030 0.030 NOx 3.263 3.501 3.291 3.014 3.500 2.000 THC 0.092 0.084 0.056 0.063 0.550 0.550 CO 0.065 0.090 0.087 0.051 4.000 4.000 The epMa injection comprising of twin pilots and one post-injection pulse produces optimum emissions compared to the other three triple injection strategies (Tables 4 and 5). (1) The epMa injection strategy consisted of both advanced and retreaded pilot injection events combined with a high EGR rate producing the lowest NOx emission due to low burn gas temperature, early termination of the first injection event and controlled heat release rate. The epM shows the second-best performance due to its similar double pilot feature. The eMa is the third in NOx emissions due to early injection and prolonged duration between early injection and main injection schedule that causes the lower bulk gas temperature inside the combustion chamber compared to the pMa. (2) The double pilot-injection strategies gave rise to higher THC emissions due to the rich fuel mixture during the ignition delay period than the single pilot (or early) injection combustion. In addition, the ignition delay has a significant impact on THC that compensates for the overall results. Hence, the THC formation of these injection strategies in ascending order is pMa