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Abstract

A multicylinder turbocharged common rail direct injection engine was tested at part load (62.4 Nm) and high load (156 Nm) to determine the optimum combination of injection pressure (IP) and injection timing (IT) for AB20 blended fuel. IP and IT were varied from default settings, that is, 9.2° before top dead center (BTDC), 45 MPa at part load; 9.8° BTDC, 95 MPa at high load, as specified in the calibration map of the engine. As a result of the experimental results, brake thermal efficiency (BTE) increased up to 5.36% when IP increased from 35 MPa to 45 MPa and 0.72% when IP increased from 45 MPa to 55 MPa under the part load condition. At high load, the maximum BTE of 38.22% was attained at 105 MPa IP and 9.8° BTDC IT. At this condition, nitrogen oxide (NOx) emission was noted as 1353 ppm, which is 12.28% higher than the NOx noted for diesel fuel at the default IP and IT conditions. When IP increases from 35 to 55 MPa at part load and 85–105 MPa at high load, cylinder pressure, heat release rate, and rate of pressure rise increase at all tested ITs. At high load, the condition of retarded IT (8.8° BTDC) and default IP (95 MPa) shows (a) 2.35% higher BTE and (b) almost similar NOx and improved HC, CO, and smoke emissions for the AB20 blend. Moreover, at the same experimental conditions, premixed heat release for the AB20 blend was noted to be 70.16 J/Deg./C.A, with heat release rate peak at 6° ATDC.

Keywords

Injection pressure injection timing CRDI engine combustion argemone biodiesel

Introduction

One of the main contributors to greenhouse gas (GHG) emissions is the transportation sector, which is one of the most carbon-intensive, leading to the introduction of renewable energy sources, including biofuels.^1,2 Biodiesel is currently regarded as the most promising way to replace fossil diesel fuel in compression ignition engines among the various biofuels due to its relatively comparable physiochemical properties.³ To reduce GHG emissions, every liter of diesel substituted with biodiesel is equivalent to a 2.67 kg reduction in CO₂ emissions.⁴ Therefore, biodiesel is emerging as a promising renewable fuel for the future.⁵ Additionally, biodiesel is biodegradable, nontoxic, sulfur-free, highly lubricating, and safe to store and operate.⁶ Accordingly, worldwide biodiesel production will rise to 39 billion m³ in 2024 from 29.7 billion m³ in 2014.⁷ According to a recent report, the global market for biofuels and biodiesel would expand by around 5.48% from 2018 to 2026.⁸ For biodiesel production to satisfy future demands, more diversified feedstocks will need to be researched.

Edible and nonedible oil are the two primary sources of biodiesel production.⁹ The oil of Argemone mexicana has garnered the most attention of the various edible and nonedible oil feedstock investigated so far.^10–12 It can be used to reduce the production cost of biodiesel, increase the farmer's income, and reduce the adulteration of the A. mexicana oil with edible mustard oil. It has been shown that even 1% adulteration of mustard oil with A. mexicana oil causes clinical disease. Moreover, it can grow on nonfertile land with very little water and does not decrease the global food supply.¹³ In light of these benefits, researchers have been motivated to boost biodiesel production from A. mexicana oil to reduce GHG emissions and eliminate edible oil adulteration. Pramanik et al. measured the engine run time when A. mexicana biodiesel was used as a fuel when producing biodiesel from A. mexicana oil.¹² According to their experiment results, A. mexicana biodiesel was found to be a potential fuel to replace the use of diesel fuel in compression ignition (CI) engines because it increases fuel efficiency and reduces GHG emissions.

To illustrate the impact of biodiesel on internal combustion engines, three parameters were considered: combustion characteristics, performance characteristics, and emission characteristics. A time-consuming and expensive laboratory study on internal combustion engines was needed to achieve these parameters. A variety of approaches (i.e. ANN, ANN-GA, ANN coupled RSM, etc.) should therefore be developed and applied to study diesel engines powered by biodiesel without the need to conduct a series of laboratory experiments.¹⁴ Nevertheless, many research studies have been conducted on diesel engines fueled with biodiesel blended at a 20% ratio, and they found that the thermal efficiency and exhaust emissions (HC, CO, CO₂, and smoke) of diesel engines improved significantly.^15,16 Hoang et al. evaluated the application of biodiesel derived from rice bran oil in CI engines based on performance, combustion, and emission characteristics.¹⁷ They suggest that the mixture of 20% rice bran oil biodiesel and 80% petro-diesel fuel, both by volume, could be the most effective composition when considering the technological and economic aspects of CI engines. In addition, diesel fuel with higher biodiesel content provides comparable engine performance to fossil diesel fuel in short-term use. However, some problems include the reduction in performance, excessive smoke emissions, and tribocorrosion phenomena.^18–20 The low calorific value, density, and viscosity of biodiesel may lead to poor air and fuel mixing rates, resulting in poor performance and high smoke emissions. Researchers have also reported an increase in NOx emissions from blending biodiesel (produced from different feedstock) with diesel.^15,21

The higher NOx could be controlled by either lowering the IP or retarding the injection timing (IT).²² The negative effect of high density and viscosity could be controlled by increasing the injection pressure (IP) and advancing the IT. High IP improved fuel atomization, and advanced IT improved fuel-air mixing due to higher ID, resulting in improved engine performance.²³ However, if the IT is over-advanced, an early rise in heat release rate (HRR) may increase the negative work during the compression stroke and result in lower thermal efficiency.^24,25 High IP improved fuel atomization, and advanced IT improved fuel-air mixing due to higher ID, resulting in improved engine performance. Advanced IT and high IP result in early combustion, and retarded IT and low IP result in late combustion.²⁶ Both too early and too late combustion can deteriorate the engine's performance. Thus, it is necessary to find the optimum combination of IT and IP to operate the diesel engine on different types of fuel. Khandal et al. found in their study on the common rail direct injection (CRDI) engine that brake thermal efficiency (BTE) increased with an increase in IP and attained its maximum value at 900 bar IP; they report a slight decrease in BTE when IP is increased further.²⁷ They also mentioned that at high IP, droplet size reduces remarkably and result in the shortfall of O₂ and incomplete combustion. The ECU in modern diesel engines provides the benefit of operating the engine at different IP, IT, and BPr depending upon the operating condition of the engine. The high boost pressure, along with a higher number of holes in the injector nozzle, allows the engine to operate at high IP (350–1500 bar) without any disadvantage of over-penetration of fuel spray.²⁸

From the above discussion, it is clear that the optimum combination of IP and IT depends upon the type of fuel used (diesel, biodiesel, diethyl ether, etc.), the type of engine (CRDI, IDI, and DI, etc.), and more precisely, on the operating condition of the engine (i.e. low load, part load, and high load). The optimum combination of IP and IT for biodiesels made from karanja,²⁹ jatropha,³⁰ mahua,³¹ and castor³² are available in the literature. However, no study has been conducted so far to find the optimum combination of IP and IT for A. mexicana biodiesel (AGB) (feedstock used in present work). The production of biodiesel from A. mexicana oil,¹² its oxidation and storage stability,¹² its effect on combustion stability,³³ and its utilization in a diesel engine ³⁴ have been studied. Even some of the previously conducted studies exhibit that the blending of AGB in diesel fuel (especially 20% blending) improves the performance of the engine with the penalty of higher NOx emissions.^35,36 Therefore, the present work has been conducted to find the optimum combination of IP and IT for the AB20 blend at part load and high load conditions that will improve the engine's performance without imposing any penalty for higher NOx emissions.

Material and method

Experimental setup

The setup consists of a 4-cylinder, 4-stroke, 1.9L, turbocharged engine equipped with a CRDI system, an electronic control unit ([ECU]-Medhaavi-MCP4-i7) and many other sensors and actuators as shown in a schematic diagram of the engine (refer Figure 1). The detailed specifications of the engine setup and the detail of instruments have been shown in Tables 1 and 2, respectively. The ECU controls the duty cycle of various actuators such as injectors, pressure control valve (PCV), volume control valve (VCV), and boost pressure actuator (BPA) to meet the desired operating condition of the engine by using the “NIRA rk Nap” software. The timing of fuel injection has been controlled by the ECU with the combination of a crankshaft position sensor (CKP) and a cam position sensor (CMP). The CKP determines the engine speed and position of the crankshaft.

Figure 1.

Schematic diagram of engine.

Table 1.

Detailed specifications of the experimental setup.

Engine make/model	International Tractors Ltd (ITL)/G2 Series
No of cylinders	4
Cylinder bore/stroke (mm)	84.45/88.95
Capacity	1.9 L
Compression ratio	17.5:1
Number of valves/cyl.	02
Firing order	1-3-4-2
Turbocharger	Variable geometry ECU controlled Turbocharger
Fuel injection	Common rail direct injection
Maximum power (kW)	67 kW–4000 rpm
Maximum torque	207 Nm–1750 rpm
Fuel injection pressure (bar)	1400 (max)
Cooling	Water cooled

Table 2.

Detail of experimental instruments.

Sensor name	Type/make	Resolution
Crank position sensor 1	Hall effect type (5V)	± 0.1°
Crank position sensor 2	Optical encoder	± 1°
Cam position sensor	Hall effect (12 V)	± 0.1°
Rail pressure sensor	Piezoelectric	0.1 MPa
Vacuum modulator	Maximum vacuum consumption 30 l/h (rated voltage 12 V)	_
Dynamometer	Eddy current	_
Load cell	Strain gauge	1 kg
Temperature and manifold pressure sensor (TMAP)	Negative temperature coefficient (NTC), 5V	0.1°/1 kPa
Fuel temperature	Negative temperature coefficient (NTC), 5V	1°
Temperature sensor (T1, T2, T3, T4, T5, and T6)	Thermocouple type K	0.1°
Actuators/components
Boost pressure actuator	Solenoid type vacuum operated	_
Pressure control valve	Solenoid type, electronically operated	_
Volume control valve	Solenoid type, electronically operated	_
Vacuum pump	Lucos - Tvs	_
High-pressure pump	Siemens (1500 bar max.)	_

The camshaft sensor (integrated to the camshaft itself) is used to synchronize the position of the crankshaft and camshaft so that the ECU can differentiate between compressions TDC and exhaust TDC of the piston.

Experimental methodology

In the present work, experimentation was performed on a CRDI engine to find the optimum combination of IP and IT for the AB20 blend. In their previous study, the authors speculated in detail how biodiesel was produced in two steps, esterification and transesterification.³⁷ The important properties of AGB/diesel are shown in Table 3. The part (24 kg) and high engine load (60 kg) are equivalent to 62.4 Nm and 156 Nm engine loads, respectively. The engine testing has been performed in two test modes; mode I part load (62.4 Nm) and mode II high load (156 Nm), at a constant speed of 2000 rpm. In each mode, IP and IT were varied from their default values, as shown in Table 4. The boost pressure was not changed during the experimentation to investigate the effect of varying IP and IT. In all experiments, the temperatures T1 to T6 were allowed to settle before recording the data. The data was recorded using the data acquisition system (DAQ) connected to the computer via KC lab soft. Based on in-cylinder pressure data, HRR is calculated according to the following equation:

H R R = \frac{γ}{(γ - 1)} P \frac{d V}{d θ} + \frac{1}{(γ - 1)} V \frac{d P}{d θ}

(1)

where HRR = heat release rate, J/deg.CA, γ = 1.35, V = instant cylinder gas volume, m³, P = instant cylinder gas pressure, Pa,

Table 3.

Properties of diesel/argemone biodiesel blends.

Property	Diesel	AB20	AB100	ASTM D6751
Density at 15 °C (kg/m³)	830	835.4	857	_
Kinematic viscosity 40 °C (Cst)	2.8	3.612	4.38	1.9–6
Calorific value (MJ/kg)	44.5	43.1	37.5	_
Flash point (°C)	65.5	91	193	93 (min)
Surface tension at 15 °C³⁷	26.1	26.55	28.36	-
Latent heat of vaporization (kJ/kg)³⁷	310	319.26	356.34	-
Copper strip corrosion test	_	Passed	Passed	_

Table 4.

Test matrix.

Test mode I: Part load (24 kg), speed 2000 rpm			Test mode II: High load (60 kg), speed 2000 rpm
S. No	Injection pressure (MPa)	Injection timing (° BTDC)	S. No	Injection pressure (MPa)	Injection timing (° BTDC)
1	35	8.2	1	85	8.8
2	45		2	95
3	55		3	105
4	65		4	115
5	35	9.2*	5	85	9.8^†
6	45*		6	95^†
7	55		7	105
8	65		8	115
9	35	10.2	9	85	10.8
10	45		10	95
11	55		11	105
12	65		12	115

^*Default IP and IT at part load; † Default IP and IT at high load.

The data of emissions HC, CO, and NOx were measured by AVL 4000 Di gas analyzer, and smoke emissions were noted with AVL-437 smoke meter. The results of experiments present errors and uncertainty, neither of which can be resolved entirely. However, they can be reduced to some extent by selecting the appropriate instruments and ensuring that the measurements are conducted under ideal conditions. The authors presented a detailed analysis of mathematical uncertainty calculation methods in the previous study.^38,39 Supplementary Table 1 summarizes the measurement parameters, range, and resolution of the AVL-4000 Di gas, as well as uncertainty analysis for calculated parameters (namely BP, BTE, and BSFC).

During experimentation, each experimental value was noted three times, and an average value was used for plotting the graphs to avoid error in experimentation. For plotting the combustion graphs, an average of 50 engine cycles has been used to avoid cyclic variations during investigation.

Results and discussion

Performance and emission characteristics of the engine

BTE and brake-specific fuel consumption

The authors have found in their previous investigation that the favorable properties of the AB20 blend (high lubricity, higher oxygen content) result in improved performance (BTE, BSFC) and emission characteristics (HC, CO, smoke) of the engine in comparison to diesel fuel when tested with the default calibration map.³⁷ However, this improved engine performance came with a penalty of high NOx emissions, especially under high load conditions. Therefore, in the present work, IP and IT were varied to find their optimum combination for the AB20 blend that provides lower NOx and higher performance of the engine. The effect of varying the IP and IT on the performance and emission characteristics of the engine at part load is shown in Figure 2(a) to (f). It was observed that at part load, the default IT of 9.2° before top dead center (BTDC) gave higher BTE, lower BSFC, and lesser exhaust emissions (HC, CO, and smoke) at all IPs (35, 45, 55, and 65 MPa) for AB 20 blend, when compared with retarded and advanced IT of 8.2° and 10.2° BTDC, respectively (Figures 2(a) to (f) and 4(a) and (b)). The ignition delay is shorter at retarded IT (Figure 6(a) and (b)), leading to a slower burning rate, causing less heat loss to be used to produce useful work, and resulting in lower BTE. Zhang and Kook⁴⁰ and How et al.⁴¹ too found lower engine performance with retarded IT; the reasons cited were lower cylinder pressure (CP), HRR, and slower combustion rate that demand the high fuel supply to attain the same torque as generated at advanced IT. A higher rate of heat release before TDC results in poor performance at advanced IT of 10.2° BTDC since the piston is unable to move upward during the compression stroke due to the increased HRR.^41,42

Figure 2.

(a–f) Effect of injection pressure and injection timing on performance and emission characteristics of engine at part load of 24 kg equivalent to 62.4 Nm.

Figure 2(a) and (b) shows that both the BTE and BSFC are improving with an increase in IP from 35 MPa to 55 MPa. The increase in BTE at default IT (9.2° BTDC) for the AB20 blend was up to 5.36% when IP increased from 35 MPa to 45 MPa and 0.72% when IP increased from 45 MPa to 55 MPa. Moreover, at default IP and IT, the BTE found for the AB20 blend is 31.93%, which is 3.87% higher than the BTE noted for diesel fuel. BTE improved with an increase in IP because an increase in IP produces better fuel atomization, which leads to enhanced air-fuel mixing.⁴³ Interestingly, an additional increase in IP from 55 MPa to 65 MPa reduces the BTE by 0.83% and increases the specific fuel consumption. The higher penetration length of the fuel jet increases with high IP, resulting in fuel impingement on cool surfaces, reducing mixing rates, and deteriorating engine performance.^44,45 Moreover, the high irreversible energy losses in compressing the fuel at high IP due to an increase in HRR before TDC with an increase in IP²² is also one of the probable reason for lower thermal efficiency of the engine at higher IP.

When the engine is operated at high load (156 Nm), the engine's thermal efficiency is higher compared to part load conditions (62.4 Nm), indicating a higher combustion efficiency (Figure 3(a)). The results show that at high load condition, the default IT of 9.8° BTDC shows improved BTE and BSFC among retarded (8.8° BTDC) and advanced (10.8° BTDC) ITs (Figure 3(a) and (b)). Increasing the IP from 85 to 95 MPa at default IT of 9.8° BTDC increases the BTE by 2.7%. Further increasing the IP from 95 to 105 MPa at all ITs of 8.8°, 9.8°, and 10.8° BTDC, gave no significant improvement in BTE. Moreover, a further increase in IP from 105 to 115 MPa at all ITs lowers the BTE for the corresponding IT. At a default IT of 9.8° BTDC (Figure 3(a)), the AB20 blend shows BTE of 37.16%, 38.19%, 38.22%, and 37.56% at IPs of 85, 95, 105, and 115 MPa, respectively.

Figure 3.

(a–f) Effect of injection pressure and injection timing on performance and emission characteristics of engine at high load of 60 kg equivalent to 156 Nm.

Exhaust gas temperature

Exhaust gas temperature increases with an increase in load (Figures 2(c) and 3(c)) due to more fuel burned with an increase in load. However, higher exhaust gas temperature (EGT) at the same load means more heat losses that result in lower BTE.^46,47 In the present work also, it was observed that the test conditions corresponding to higher BTE show lower EGT (Figures 2(a) and (c) and 3(a) and (c)). At part load, the lowest EGT was noted at 55 MPa IP and 9.2° BTDC IT, where maximum BTE and minimum BSFC were observed. Similarly, at high load, the lowest EGT and maximum BTE were observed at default IP (105 MPa) and IT (9.8° BTDC).

HC and CO emissions

Both HC and CO emissions are the result of incomplete combustion and, therefore, follow the same trend. At part load, HC and CO emissions decrease with an increase in IP up to 55 MPa. After that, a slight increase in their values was observed (Figure 2(e) and (f)). The maximum HC and CO emissions were observed at low IP and advanced timing (35 MPa and 10.2° BTDC) condition, and their minimum values were noted at 55 MPa IP and 9.2° BTDC IT. Furthermore, an increase in IP up to 65 MPa shows a slight increase in HC and CO emissions at all ITs. It is believed that this is due to the under-penetration of liquid fuels at low IP and the over-penetration of fuels at high IP, which reduces the mixing rate of air and fuel^47,48 and hence increases the HC and CO at both the low IP (35 MPa) and high IP (65 MPa) conditions. Similarly, at high load, HC and CO decrease with an increase in IP up to 105 MPa. After that, an increase in HC and CO emissions was observed with a further increase in IP from 105 to 115 MPa (Figure 3(e) and (f)).

In addition, HC and CO emissions increased with an increase in IT from the default IT at both low and high engine loads. A possible explanation could be that advances in IT have caused increased ignition delay, which leads to fuel being over mixed and oxidizing more slowly.⁴⁹

Smoke emissions

The formation of smoke is the result of incomplete burning of the liquid fuel and partially reacted carbon content in the liquid fuel.⁵⁰ The default map condition at part load (45 MPa IP, 9.2° BTDC IT) and full load (95 MPa IP, 9.8° BTDC IT) shows lower smoke emissions for the AB20 blend compared to diesel fuel. The reason might be a higher oxygen content in biodiesel, which can improve the local diffusion combustion phase and lead to lower smoke emissions.⁵¹ The results of the present work show that the smoke emissions decrease with an increase in IP for all ITs at both the part-load and high-load conditions (Figure 4(a) and (b)).

Figure 4.

(a, b) Effect of injection pressure and injection timing on smoke emissions.

Higher IP reduces the droplet size of the fuel, which promotes the fuel atomization and air-fuel mixing rate and leads to rapid premixed combustion; hence, lower smoke emissions were observed. Smoke emissions also decrease with the advancement in IT at all tested IP conditions at both part-load and high-load conditions. Advancing the IT leads to a high premixed combustion phase and high in-cylinder temperature that promote the oxidation of soot particles and result in lower smoke emissions.⁵²

NOx emissions

NOx emissions increase with an increase in IP and advancement in IT at both the part load and high load conditions (Figures 2(d) and 3(d)). The advancement in IT and an increase in IP result in earlier ignition and rapid burning of the air-fuel mixture.²⁶ Consequently, the CP peak becomes higher and shifts nearer to TDC, which results in a higher cylinder temperature, which promotes the thermal or zeldovic NOx formation mechanism.^41,53 In the present work also, high NOx emissions were noted when CP was high ((Supplementary Figures 1(a) to (c) and 2(a) to (c)). Moreover, at part load, the lowest NOx was observed at retarded IT of 8.2° BTDC and an IP of 35 MPa, where minimum in-cylinder pressure and temperature were noted (Figures 2(d) and 5(a); Supplementary Figure 1(a)). Unfortunately, these conditions of 8.2° BTDC IT and 35 MPa IP show the lowest BTE. However, an increase in IP up to 45 MPa increases NOx but simultaneously improves the BTE. Additional increases in IP lead to a higher increase in NOx emissions without any significant improvement in BTE. The comparison of diesel fuel and the AB20 blend at default IP and IT conditions (9.2° BTDC and 45 MPa) shows that the AB20 blend has higher BTE and lower exhaust emissions (HC, CO, and smoke), almost similar NOx emissions. According to Balasubramanian et al.,⁵⁴ B20 (20% waste cooking biodiesel + 80% diesel) blended fuel would be best suited for the test engine with a reduction of 17% in HC, 30% in CO, and 16.46% increase in NO_X. Therefore, the condition of default IP and IT at part load seems beneficial for the AB20 blend.

Figure 5.

Effect of injection pressure and injection timing on in-cylinder temperature.

At high load, the maximum NOx emissions were noted at 115 MPa IP, and 10.8° BTDC IT and the minimum NOx was observed at 85 MPa IP, and 8.8° BTDC IT (Figure 3(d)). The thermal efficiency noted at the condition (85 MPa IP and 8.8° BTDC IT) where minimum NOx was noted is 4.68% lower than the BTE noted at the default IP and IT conditions (Figure 3(a) and (d)). Also, the other exhaust emissions, such as HC, CO, and smoke, are higher at lower IP (85 MPa) relative to 95 MPa IP for all tested IT conditions (Figure 3(e) and (f) and 4(b)). On the other hand, the condition of default IP (95 MPa) and retarded IT (8.8° BTDC) for AB20 blend shows 2.24% lower BTE, lower NOx, slightly higher HC, CO, and smoke in comparison to default IP and IT condition. However, the BTE, NOx, HC, CO, and smoke noted for AB20 blend at retarded IT (8.8° BTDC) and default IP (95 MPa IP) were improved in comparison to diesel fuel at default IP and IT. Therefore, the condition of retarded IT (8.8° BTDC) and default IP (95 MPa) was found to be suitable for AB20 blend at a higher load (156 Nm) with the benefit of 2.35% higher BTE and almost similar NOx emissions compared to diesel fuel tested at default IP and IT.

Combustion characteristics of the engine

Effect of IP and IT on ignition delay and CP

Ignition delay is an essential parameter in combustion analysis of diesel engines as many other parameters such as CP, HRR, rate of pressure rise (ROPR), and combustion duration (CD) greatly depend on it.⁵⁵ Ignition delay is defined as the crank angle interval between SOI and SOC, and it can be further elaborated as physical and chemical ignition delay. The physical part of ID includes mixing of fuel/air, atomization of fuel jet, and vaporization of fuel droplets, and the chemical part is related to the properties of the fuel.⁵⁶ In the present work, it was observed that ignition delay increases with the advancement in IT and reduces with an increase in IP at both the part-load and high-load condition (Figure 6(a) and (b)). It results in the poor vaporization of fuel droplets at advanced IT, which leads to higher physical ID due to the lower temperature and pressure of the combustion chamber than at later IT.^57,58 High IP results in finer droplets of fuel, which promotes the atomization of the fuel jet and vaporization of the fuel droplets that results in lower physical ignition delay.⁵⁹ The maximum value of ID was noted as 8.2° and 5.8° at part load (10.2° BTDC IT and 35 MPa IP) and high load (10.8° BTDC IT and 85 MPa IP) conditions, respectively. High IP (85–115 MPa), high boost pressure (160 k Pa), and higher charge temperature at high load promote the early burning of the fuel, leading to lower ID values at high load compared to low load.

Figure 6.

(a, b) Effect of injection pressure and injection timing on ignition delay.

The CP at IT of 8.2°, 9.2°, and 10.2° BTDC with varying IP (35 to 65 MPa) at the condition of part load (62.4 Nm) is shown in Supplementary Figure 1(a) to (c). The results show that with an increase in IP from 35 to 55 MPa at all ITs, the CP increases, and the cylinder pressure peak (CPP) shifts nearer to TDC, as shown in Supplementary Figure 1(a) to (c). It has already been discussed that higher IP causes higher atomization, vaporization, and spray development of fuel, resulting in higher CP, regardless of lower ID. This enhancement in CP was observed up to 55 MPa IP. Furthermore, an increase in IP up to 65 MPa at all ITs brings CPP lower, and its position gets closer to TDC, which shows that the effect of lower ID is more dominating at a higher IP of 65 MPa.

The retarded IT (8.2° BTDC) exhibits lower CPP, and the position of CPP shifts away from TDC at all IPs (35, 45, 55, and 65 MPa), in comparison to the default IT condition (9.2° BTDC). The reason might be less accumulation of air-fuel mixture due to shorter ID (Figure 6(a) and (b)) that results in lower CPP, and the position of CPP shifting away from TDC. Advanced IT (10.2° BTDC) increases the CPP and brings it nearer to TDC compared to the CPP found at default IT of 9.2° BTDC for all IPs. With the advancement in IT, the ID increases (Figure 6(a) and (b)); as a result, more air-fuel mixtures accumulate, resulting in a higher CPP with the position shifted toward TDC.⁶⁰ The maximum CP was observed at 55 MPa IP, 10.2° BTDC IT with CP_max noted as 81.68 bar at a crank angle of 8° ATDC. However, this condition of maximum CP does not correspond to maximum thermal efficiency (Figure 2(a); Supplementary Figure 1(c)); rather, the maximum BTE was observed at the condition of 55 MPa IP and 9.2° BTDC IT with CP noted as 81.68 bar @ 8° ATDC. Unfortunately, this condition of maximum thermal efficiency exhibits higher NOx emissions. Therefore, the condition of 45 MPa IP, 9.2° BTDC has been preferred at part load, as discussed in section 3.1.5.

At the condition of high load, the maximum CP was noted as 112.08 bar at 105 MPa IP, 10.8° BTDC IT ((Supplementary Figure 2(a) to (c)). The values of CP were found to be higher at advanced IT (10.8° BTDC) and lower at retarded IT (8.8° BTDC) in comparison to the default IT condition of 9.8° BTDC at all tested IPs (85, 95, 105, and 115 MPa). The early rise in CP at advanced IT was observed at both high and part load conditions, which probably explains the lower BTE at advanced IT.³⁸ At retarded IT, the CPP shifts away from TDC with values lower than the values of CP noted at default IT condition; as a result, lower thermal efficiency was noted at the retarded timing conditions. The minimum value of CP was noted as 103.74 bar at retarded timing of 8.8° BTDC and 85 MPa IP. An increase in CP values was noted when IP increased from 85 to 105 MPa. After that, a further increase in IP from 105 MPa to 115 MPa, lowers the CPP but brings the CPP closer to TDC. High IP leads to more fuel wall-wetting effects that deteriorate the fuel's burning rate and results in low CPP.⁶¹

Effect of IP and IT on HRR and ROPR

The HRR and ROPR follow an almost similar trend as that of CP, that is, HRR and ROPR increase with an increase in IP up to a specific value (55 MPa at a part load and 105 MPa at a high load); after that, further increases in IP lower the HRR and ROPR (Supplementary Figure 2(d) to (i)). Moreover, it was observed that the premixed HRR increases with the advancement in IT ((Supplementary Figures 1(d) to (i) and 2(d) to (i)). This is because early IT fuel enters into the combustion chamber at a comparatively lower temperature, resulting in an inefficient vaporization of the fuel, leading to an increase in ID and a rise in premixed combustion.⁶² The maximum value of HRR (107.42 J/Deg./C.A.) and ROPR (13.17 Bar/C.A.) at part load was noted at 55 MPa IP and 10.2° BTDC. At high load, the maximum value of HRR and ROPR was noted as 90.39 J/deg./C.A and 11.1 bar/C.A, respectively, at 105 MPa IP and 10.8° BTDC IT.

The lower premixed HRR at high load is due to the high boost (160 kPa) available at high load compared to low load. The greater boost improves the air-fuel mixing rate and results in a gradual increase of CP,²³ which lowers the ROPR and premixed heat release phase at high load compared to low load conditions. At high load, the AB20 blend shows higher CP, HRR, and ROPR than diesel fuel when tested at default IP and IT, which results in higher thermal efficiency and higher NOx emissions. As discussed in section 3.1.5, the condition of 95 MPa IP and retarded IT (8.8° BTDC) seems favorable for the AB20 blend with improved performance and emission characteristics of the engine. The premixed heat release for the AB20 blend was noted to be 70.16 J/Deg./C.A, with HRR peak at 6° ATDC.

Effect of IP and IT on CD

Supplementary Figure 3(a) and (b) shows the effect of IT and IP on CD. CD is defined as the crank angle interval between the start of combustion (10% fuel burnt) and the end of combustion (90% fuel burnt).⁶³ Supplementary Figure 3(a) and (b) shows that the CD decreases with an increase in IP up to a specific value (55 MPa, part load; 105 MPa, high load). A decrease in CD is likely caused by an increase in the rapid premixed combustion phase due to an increase in IP. However, the slight increase in CD at high IP (65 MPa, part load; 115 MPa, high load) is attributed to low ignition delay as well as a low premixed HRR that results in a slower burning rate and higher CD. The advancement in IT lowers the CD at both part-load and high-load conditions, as an increase in IT increases the ID, resulting in more air-fuel mixture accumulation. Therefore, higher premixed HRR and lower CD were observed with the advancement in IT.

Conclusions

The present work elucidates the effect of IP and IT on a multicylinder CRDI engine fueled with an AB20 (20% A. mexicana biodiesel, 80% diesel) blend. Experimentation shows that both the IT and IP are the vital factors that persuade the engine's performance, emission, and combustion characteristics. Based on the experimental observations, the following conclusions could be drawn:

At part load, an increase in IP from 35 MPa to 55 MPa improves the BTE. The maximum value of BTE (32.16%) was noted at 55 MPa IP, 9.2° BTDC IT. Since NOx emissions are high (597 ppm) at this condition; therefore, the default condition of 45 MPa IP and 9.2° BTDC was preferred with BTE = 31.93% and NOx 463 ppm for part-load operation of the engine with AB20 blend.

The maximum BTE was 38.22% at 105 MPa IP and 9.8° BTDC IT at high load. The NOx emission at this condition was 1353 ppm, which is 12.28% higher than the NOx emission at the default IP conditions and IT conditions. Therefore, retarded IT (8.8° BTDC) and default IP (95 MPa) have been preferred for AB20 blends at high engine load with the following benefits: (a) 2.35% higher BTE (37.35%), (b) similar NOx, (c) improved HC, CO, and smoke emissions when compared with diesel fuel at default IP and IT.

CP, HRR, and ROPR increased when IT was advanced from 8.2 to 10.2° BTDC and 8.8 to 10.8° BTDC at part load and high load conditions, respectively. Though the maximum values of CP, HRR, and ROPR at part load and high load were obtained at advanced IT (10.2° BTDC at part load; 10.8° BTDC at high load) and high IP (55 MPa IP at part load, 105 MPa IP at high load), these conditions neither correspond to maximum BTE nor minimum emissions. Thus, it can be concluded that the higher value of combustion attributes (CP, HRR, and ROPR) is not always beneficial. Moreover, the peak position of CP, HRR, and ROPR is also very important, as both the early and late IT can deteriorate the thermal efficiency of the engine.

This paper aims to provide insight into the effects of boost pressure combined with optimized fuel IT on the spectral behaviors of cycle-to-cycle fluctuations in combustion parameters of a multicylinder diesel engine fueled with AB20 with constant combustion phasing, which is a part of the work's future scope.

Supplemental Material

sj-docx-1-pie-10.1177_09544089221146165 - Supplemental material for An investigation of optimum control of injection timing/injection pressure for a multicylinder common rail direct injection engine fueled with AB20 blend

Supplemental material, sj-docx-1-pie-10.1177_09544089221146165 for An investigation of optimum control of injection timing/injection pressure for a multicylinder common rail direct injection engine fueled with AB20 blend by Mandeep Singh, Prem Kumar and Sarbjot Singh Sandhu in Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iDs

Mandeep Singh

Prem Kumar

Supplemental material

Supplemental material for this article is available online.

Abbreviations

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