Impact of Electrically Assisted Turbocharger on the Intake Oxygen Concentration and Its Disturbance Rejection Control for a Heavy-duty Diesel Engine
<p>Schematic of the electrically assisted turbocharger (EAT)-assisted diesel engine. The nomenclature for all the symbols can be found in Nomenclature section.</p> "> Figure 2
<p>Schematic of experimental platform.</p> "> Figure 3
<p>Test bench for diesel engine with EAT.</p> "> Figure 4
<p>Validation of the GT-SUITE model over a segment of the hot start FTP-75 drive cycle in terms of boost pressure, pre-turbine pressure, and compressor mass flow rate [<a href="#B27-energies-12-03014" class="html-bibr">27</a>].</p> "> Figure 5
<p>Engine fuel efficiency improvement and <span class="html-italic">X<sub>oim</sub></span> surplus.</p> "> Figure 6
<p>Volumetric efficiency improvement and in-cylinder composition change.</p> "> Figure 7
<p>Comparison of three performance variables with NOx concentration.</p> "> Figure 8
<p>Correlation between NOx concentration and three performance variables.</p> "> Figure 9
<p>Regulations of three actuators during the transient process.</p> "> Figure 10
<p>Tip-in test for the nominal system without assist.</p> "> Figure 11
<p>Tip-in test for the EAT system</p> "> Figure 12
<p>Control structure of the OADRC controller.</p> "> Figure 13
<p>OADRC validation with step changes of desired intake oxygen concentration.</p> "> Figure 14
<p>Comparison between OADRC and PID controller with step changes of intake oxygen concentration.</p> "> Figure 15
<p>Disturbance rejection performance comparison with step change of <span class="html-italic">N<sub>T.</sub></span></p> "> Figure 16
<p>Disturbance rejection performance comparison with step change of variable-geometry turbocharger (VGT) vane.</p> "> Figure A1
<p>Experimental validation of oxygen concentration observer.</p> ">
Abstract
:1. Introduction
- (1)
- Improved boost response allows enhanced engine torque response [12,13], and enables down-speeding and downsizing [14,15]. Improvements of fuel economy (FE) can also be achieved mainly by reduced pumping losses. In a drive cycle simulation by Zhao et al. [16], a 6.44% fuel-saving was reported for a Hybrid electric vehicle equipped with EAT assisted diesel engine.
- (2)
- Better utilization of exhaust enthalpy during regen mode via energy recuperation from turbocharger (TC) braking.
- (3)
- Lower pre-turbine pressure () and thereby lower pumping loss can be achieved through reduced VGT throttling during assist mode. This improves the thermal efficiency of the engine [17].
- (4)
- Proper use of assist and regen modes allows the TC to operate in optimal efficiency region [14].
- (5)
- Improved regulation of intake oxygen concentration (Xoim). Compared to the conventional variable geometry turbocharger-exhaust gas recirculation (VGT-EGR) system, EAT offers additional control degree of freedom and therefore brings a direct result of improved manipulations of and . This helps to improve EGR inert quality and reduce transient soot/Nitrogen Oxides (NOx) emissions [18].
2. Experiment Setup and Simulation Platform
3. Experimental Assessment on the Benefits from Using Xoim as Control Output Variable
3.1. Steady-State Investigation
- When the VGT vane open is less than 22%, the electrical regeneration (E-regen) mode is turned on to brake the turbine in order to avoid over-boost. The electrical power in regeneration is about 0.46 kW at the cost of 45 kPa increase in , compared to the nominal system. Consequently, 12.1% increase in fuel consumption is seen with E-regen compared to the nominal system.
- When the VGT vane is greater than 37% open, there is Xoim surplus even though the HP-EGR valve (the blue triangle curve) is already 100% open. This is a direct effect of reduced caused by wide VGT vane open, which limits the HP-EGR flow capability.
- For VGT vane ranging from 22% to 37%, with increasing VGT vane position, the assist power increases (from 0 kW to 0.78 kW) to compensate for the turbine power deficit in order to maintain the boost pressure. Consequently, the pumping loss (indicated by ) decreases (from 4.22 kW to 0.86 kW) due to reduced . Lower p3 and unchanged p2 elevates the thermodynamic efficiency () of the engine (8.5% improvement) through pumping loss reduction. This allows less fuel injection to maintain the desired torque, relative to the nominal system.
- With VGT vane increasing from 22% to 37%, the incremental benefit in fuel economy decreases, since gradually converges when the VGT open approaches 37%. The fuel saving with VGT vane 37% open is 7.8%, relative to the nominal system. Note that here the electrical energy is assumed to be free in the driveline electrical regeneration during vehicle braking. Therefore, the cost for the electrical power is neglected when evaluating the fuel economy.
- It should be noted that equivalent brake-specific fuel consumption (Eq_BSFC), as defined in Equation (2), can also be used to evaluate the efficiency of the system when the cost of assist power has to be taken into consideration [3]. In Equation (2), t0 and tf are the time stamps of the start and end of the current test respectively, is the engine work output, and are defined as and respectively. In terms of Eq_BSFC, the fuel economy benefit from using EAT is 5.9% relative to the conventional VGT-EGR engine.
3.2. Transient Results Analysis
4. Theoretical Analysis of the Impact of EAT on Xoim Control
- Enhanced air response through the term , since PTMEG increased the compressor power.
- HP-EGR flow deficit when the pressure differential across the HP-EGR valve is insufficient as illustrated by , as PTEMG affects the upstream pressure of the EGR valve.
- EGR gas dilution due to increased engine mass flow rate from elevated volumetric efficiency as indicated by , since PTEMG leads to increased fresh air flow and reduces the fuel consumption.
5. Xoim Controller Development
6. Simulation Validation of the Proposed Xoim Controller
6.1. Intake Oxygen Concentration Step Response Test
6.2. Disturbance Rejection Capability Test
7. Conclusions
- (1)
- At 265 Nm engine load and 1400 rpm engine speed condition, up to 7.8% FE benefit can be achieved with the assist function of EAT(assuming the electrical energy is free in the driveline electrical regeneration during vehicle braking), through the reduction of pumping loss from wider VGT vane open, relative to the nominal system. Further FE benefit is limited by the HP-EGR deficit from over-reduced p3 (low HP-EGR flow capability).
- (2)
- Transient boost response with EAT assist is improved by 52.1% relative to the nominal system. The new dynamics of p2 introduced by EAT must be considered to avoid intake oxygen concentration overshoot and NOx spike. The EGR requirements should be reconsidered because of the excess fresh air from a fast boost response.
- (3)
- The EGR flow-based control objective should be transformed into the intake oxygen concentration-based control objective, which aligns well with the EAT system and the associated control design. EAT assist improved the volumetric efficiency of the engine (by up to 13.6% with 1.01 kW E-assist power at 265 Nm engine load and 1400 rpm engine speed in this paper), thereby increased the engine mass flow rate. This leads to HP-EGR gas dilution. EGR dilution and enhanced boost response makes the conventional EGR rate-based air system control not applicable to EAT system. Experimental results confirmed that Xoim works better as the control output for EAT system than EGR rate for NOx control.
- (4)
- In order to attenuate the disturbances from EAT on Xoim, a disturbance rejection based controller was proposed and validated in a high-fidelity GT-SUITE model. Results showed over 36% improvement in settling time and over 43% improvement in recovery time, relative to the conventional PID controller.
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
Nomenclature
Symbols | |
Rotational inertia | |
Mass flow rate | |
Power | |
Ideal gas constant | |
Temperature | |
Volume | |
Oxygen concentration in the air | |
Oxygen concentration at the outlet of intake manifold | |
Oxygen concentration in the cylinder after combustion | |
Oxygen concentration at the exhaust port | |
Oxygen concentration in the recirculated exhaust gas | |
Efficiency | |
EGR rate | |
Cross-sectional area | |
Specific heat capacity of air | |
Specific heat capacity of exhaust gases | |
Subscripts | |
Compressor | |
Engine | |
High pressure exhaust gas recirculation | |
Turbine | |
Turbocharger shaft mounted electrical motor/generator | |
Turbocharger | |
Volumetric | |
Pre-compressor | |
Post-compressor | |
Pre-turbine | |
Post-turbine | |
Maximum value | |
Intake manifold | |
Exhaust manifold | |
Cylinder | |
Desired value |
Appendix A
Appendix A.1. Lyapunov-Based Observer Design
Appendix A.2. Xoim Observer Validation
Test Case | Fuel Injection Rate | uHP-EGR | uVGT | Xoim | Xoegr | ||
---|---|---|---|---|---|---|---|
Avg. Xerror | Max. Xerror | Avg. Xerror | Max. Xerror | ||||
- | mg/cycle | % | % | % | % | % | % |
Case 1 | 18 | 25→15 | 30 | 0.23 | 2.53 | 0.86 | 3.15 |
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Variable | Value |
---|---|
Displacement (liter) | 6.7 |
Cylinders | V8 |
Compression ratio | 16.2 |
Maximum injection pressure (MPa) | 200 |
Bore (mm) | 99 |
Stroke (mm) | 108 |
Bore/Stroke Ratio | 0.92 |
Maximum torque (Nm)/speed (rpm) | 1166/2600 |
Rated power (kW)/speed (rpm) | 328/2800 |
Variable | Value |
---|---|
Operating voltage (V) | 200~400 |
Maximum power (kW) | 17 kW in continuous mode and 23 kW in intermittent mode |
Shaft speed (krpm) | 0~140 |
Type of cooling | water and oil cooling |
Num | Device | Specifications | |
---|---|---|---|
1 | AVL INDYS22 AC electric dynamometer | Max speed/power | 8000 rpm/200 kW |
2 | AVL 735S/753 C fuel mass flow meter | Max measuring fuel consumption | 125 kg/h |
Max measuring frequency | 20 Hz | ||
3 | KWELL EVS-80-800 Battery Simulator | Max output voltage | 800 V |
Rated power | 80 kW | ||
4 | Bosch LSU 4.9 oxygen sensor | Measuring range | lambda 0.65–∞ |
5 | Continental SNS14 NOx sensor | Measuring accuracy | ±10% from 100 ppm to 1500 ppm |
Variable | GT-SUITE Model |
---|---|
p2 | 1.8% points has error > 5 kPa |
p3 | 2.9% points has error > 10 kPa |
3.3% points has error > 0.01 kg/s | |
Xerror = 6.7% |
Test case | NEng | TEng | p2 | Xoim | uVGT | uHP-EGR | PTEMG |
---|---|---|---|---|---|---|---|
- | rpm | Nm | bar | % | % | % | kW |
Case1 | 1400 | 265 | 1.24 | 15.5 | Sweep from 15% to 55% open | Closed-loop control to maintain Xoim | Closed-loop control to maintain p2 |
Test Case | NEng | TEng | uVGT | uHP-EGR | PTEMG |
---|---|---|---|---|---|
- | rpm | Nm | % | % | kW |
Case1 | 1200 | 120→260 | 56→36 | 24→14 | 0 |
Case2 | 1200 | 120→260 | 56→36 | 24→14 | Closed-loop control to trace NT |
Item | OADRC | PID | Improvement with OADRC |
---|---|---|---|
Average TS (s) | 1.21 | 2.07 | 41% |
Maximum TS (s) | 1.5 | 2.35 | 36% |
Average ESS (%) | 0.05 | 0.05 | 0 |
MP (%) | 0 | 0 | 0 |
Item | OADRC | PID | Improvement with OADRC |
---|---|---|---|
Average MP (%) | 0.24 | 0.31 | 22.6% |
Maximum MP (%) | 0.27 | 0.32 | 15.6% |
Average TR(s) | 1.96 | 3.47 | 43.5% |
Maximum TR(s) | 2.48 | 4.5 | 44.9% |
Item | OADRC | PID | Improvement with OADRC |
---|---|---|---|
MP (%) | 6.18 | 6.19 | 0.2% |
TR (s) | 1.58 | 2.02 | 21.8% |
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Wu, C.; Song, K.; Li, S.; Xie, H. Impact of Electrically Assisted Turbocharger on the Intake Oxygen Concentration and Its Disturbance Rejection Control for a Heavy-duty Diesel Engine. Energies 2019, 12, 3014. https://doi.org/10.3390/en12153014
Wu C, Song K, Li S, Xie H. Impact of Electrically Assisted Turbocharger on the Intake Oxygen Concentration and Its Disturbance Rejection Control for a Heavy-duty Diesel Engine. Energies. 2019; 12(15):3014. https://doi.org/10.3390/en12153014
Chicago/Turabian StyleWu, Chao, Kang Song, Shaohua Li, and Hui Xie. 2019. "Impact of Electrically Assisted Turbocharger on the Intake Oxygen Concentration and Its Disturbance Rejection Control for a Heavy-duty Diesel Engine" Energies 12, no. 15: 3014. https://doi.org/10.3390/en12153014