Effects of rail pressure control on fuel consumption, emissions and combustion parameters in a turbocharged diesel engine

Figures & data

Figure 1. Scheme of tested engine with HP and LP EGR circuits (Zamboni, 2018)

Table 1. Engine specifications

Cylinders	4, inline
Displacement [cm^3]	1248
Bore × stroke [mm]	69.9 × 82
Compression ratio	16.8
Valves for cylinder	4
Maximum power [kW]	70 @ 4000 rpm
Maximum torque [N m]	200 @ 1500–3000 rpm
Fuel injection system	Common rail with solenoid injectors, maximum pressure 1650 bar
Turbocharging system	Borg Warner single stage, variable nozzle turbine, intercooler
EGR system	Standard high pressure circuit, cooled + prototype low pressure circuit, cooled

Table 2. Measured parameters, instrumentation, characteristics and uncertainties

Measured quantity	Instrument	Range	Accuracy	Relative uncertainty [%]
Engine speed	Inductive pick-up	0–5000 rpm	± 10 rpm	0.4
Engine torque	Eddy current dynamometer	0–250 N m	± 1.25 N m	1.0
Fuel mass flow rate	AVL 733S dynamic measuring equipment	0–37.5 kg/h	0.81% for a measured value of 5 g, 0.42% for 10 g, 0.2% for 25 g	Dependent on measured value
Air mass flow rate	Hot wire air flow meter	0–1000 mg/stroke	± 5 mg/stroke	1.0
Exhaust smoke	AVL 415 variable sampling smoke meter	0–10 FSN	± 0.1 FSN	2.0
NOX concentration	Rosemount 951 CLA analyzer	0–250 ppm 0–1000 ppm	± 1.25 ppm ± 5 ppm	1.0
Intake and exhaust CO2 concentration	Beckman 864 NDIR analyzers	0–2.67% 0–16%	0.0267% 0.16%	Dependent on measured concentration
Temperatures (intake circuit, lubricant, etc.)	4-wire RTD	0–350°C	0.15°C + 0.002 × measured value	Dependent on measured value
Temperatures (exhaust and EGR circuits)	K type TC	0–1200°C (class 2)	± 2.5°C or ± 0.75% × measured value (class 2)	Dependent on measured value
Pressures	Strain gauge	−1 to 0.6 bar 0–2.5 bar	< ± 0.2% × full scale	Dependent on measured value
In-cylinder pressure	Kistler 6125B	0–250 bar	< ± 0.5% × full scale	Dependent on measured value
	Kiag Swiss 5001 charge amplifier		< ± 1% × full scale
Fuel pressure	Kistler 4067A2000	0–2000 bar	< ± 0.5% × full scale	Dependent on measured value
	Kistler 4618A2 amplifier		< ± 0.2% × full scale

Table 3. Estimated maximum relative uncertainties (in [%]) for brake-specific fuel consumption (bsfc), NO_x (bsNO_X) and soot (bsS) emissions

	Operating condition ID = n × bmep [rpm × bar]
	1500 × 2	2000 × 5	2500 × 8
bsfc	1.4	1.3	1.2
bsNOx	1.7	1.8	1.8
bsS	3.2	3.1	2.9

Table 4. Controlled sub-systems and variables

Engine sub-system	Control variables/components	Control scheme	Related engine operating parameters
HP EGR	Relative air–fuel ratio	Closed loop	HP EGR mass flow rate (MHP EGR) LP EGR mass flow rate (MLP EGR) Overall EGR mass flow rate (MEGR) EGR rate (fEGR) Charge Dilution Index (CDI) Low pressure proportion (LP proportion)
LP EGR	LP EGR valve opening Exhaust throttle valve position	Open loop
Variable nozzle turbine	VNT duty-cycle	Open loop	Variable nozzle turbine opening degree (AVNT)
	Intake pressure	Closed loop
Fuel injection equipment	Rail pressure (prail)	Closed loop	Injection pressure

Table 5. Schedule of experimental activities

Operating condition ID = n × bmep [rpm × bar]	Fixed variables	Control variables	Rail pressure [bar]
No. 1 = 1500 × 2	Rel. AFR = 2.62 TV position = 2	DCVNT = 80% and 86% (AVNT = 16.5% and 9.5%)	345 (−6.75%) 370 (standard level) 395 (+6.75%) 420 + 13.5%
No. 2 = 2000 × 5	Rel. AFR = 1.80 DCVNT = 82% (AVNT = 17%)	Exhaust throttle valve position = 1 and 3	544 (−7.5%) 588 (standard level) 632 (+7.5%) 676 (+15.0%)
No. 3 = 2500 × 8	Rel. AFR = 1.60 TV position = 0	Intake pressure = 1.520 and 1.570 bar	747 (−8.0%) 812 (standard level) 877 (+8.0%)

Constant operating parameters (ECU standard calibration levels): pilot, pre and main start of injection. Pilot and pre injected quantity.

Figure 2. In-cylinder pressure diagram, curve of pressure first derivative and related parameters

Figure 3. Rate of heat release curve and main combustion parameters

Figure 4. Influence of rail pressure on in-cylinder pressure diagrams

Figure 5. Influence of rail pressure on the first derivative of in-cylinder pressure

Figure 6. Influence of rail pressure on heat release rates

Figure 7. Trade-offs between fuel consumption, emissions, turbocharger speed and combustion noise indicator

Table 6. Investigation steps

Operating condition	No. 1 = 1500 × 2	No. 2 = 2000 × 5	No. 3 = 2500 × 8
Step 1 (reference condition)	Relative AFR = 2.90 (standard HP EGR) fEGR = 22.6% AVNT = 1.4% prail = 370 bar	Relative AFR = 1.80 (standard HP EGR) fEGR = 28.1% AVNT = 7.6% prail = 588 bar	Relative AFR = 1.60 (standard HP EGR) fEGR = 15.6% pi = 1.520 bar prail = 812 bar
Step 2 + LP EGR	Relative AFR = 2.62 fEGR = 42.4% LPproportion = 0.561	fEGR = 37.1% LPproportion = 0.591	fEGR = 21.9% LPproportion = 0.574
Step 3 + VNT control	AVNT = 16.5% fEGR = 42.7% LPproportion = 0.676	AVNT = 14.0% fEGR = 30.7% LPproportion = 0.922	pi = 1.570 bar fEGR = 22.2% LPproportion = 1.0
Step 4 + prail control	prail = 420 bar	prail = 676 bar	prail = 877 bar

If not shown, values are equal to those of the previous step.

Figure 8. Link between rail pressure and combustion parameters (first group)

Figure 9. Link between rail pressure and combustion parameters (second group)

Figure 10. Link between rail pressure and combustion parameters (third group)

Figure 11. Link between rail pressure and soot emission

Zamboni, G. (2018). A study on combustion parameters in an automotive turbocharged diesel engine. Energies, 11(10), 2531. doi:10.3390/en11102531

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