CMC INDIA Paper ASHOK LEYLAND

Speakers Information- Controls, Measurement & Calibration Congress

Virtual and Experimental Optimization of In-Cylinder Residuals with Modified Cam using Gas Exchange Analysis J.Balaji, S.Palanikumar, L.Navaneetharao, M.V.Ganesh Prasad Ashok Leyland Ltd, India

ABSTRACT This study deals with the measurement and optimization of in-cylinder residuals for NOx reduction on a six cylinder, turbocharged intercooled, off-road diesel engine using a modified cam with secondary lift. One dimensional thermodynamic simulation model was developed using AVL Boost. Experimental setup was developed with instrumentation for performance, emission and indicating measurements along with temperatures and pressures. Incylinder residuals were estimated by AVL GCA module (Gas-exchange and Combustion Analysis) which uses intake, exhaust port and in cylinder pressure inputs primarily. A reduced thermodynamic model created from AVL Boost was coupled with GCA module. Various other operating point specific parameters such as air flow, fuel flow, bmep etc. were measured by test bed automation system. Experiments were conducted with modified cam and in the first iteration a secondary lift of 13% to that of main lift was tried and found the trapped residuals were in excess for the emission target.

Based on the gas exchange measurements an optimum configuration of 11% secondary lift was chosen which was meeting the emission limits. Thus the optimum cam was chosen with in few no of iterations in a short time with the aid of AVL Gas exchange analysis.

INTRODUCTION Stringent emission regulations for off-road, CEV (Construction Equipment Vehicles) diesel engines in India (BS-3 emission norms) calls for major engine design changes to achieve a drastic reduction (>50%) in NOx and PM (Particulate Matter) as compared to BS-2 emission levels. When it comes to diesel emissions the trade-off between NOx and total particulate emissions, forms one of the major challenges that face manufacturers in meeting the ever tightening emission norms. Hence independent treatments are needed for both NOx and PM produced in diesel combustion. In CEV engines limits for NOx emissions are stringent and becomes the driving factor in development. Figure 1 show the progression of emission limits for off-road engines in India [1].

Figure 1. Off-road emission limits in India Nitric oxide (NO) and nitrogen dioxide (NO2) are usually grouped together as NOx emissions. Nitric oxide is the predominant oxide of nitrogen produced inside the cylinder. There are two basic approaches in diesel engine NOx control 1) In-cylinder NOx control such as pilot injection, injection rate shaping, water emulsification of the fuel and Exhaust Gas Recirculation (EGR) and 2)Exhaust gas after treatment systems such as Selective Catalytic Reduction (SCR) or Lean

NOx Trap (LNT) etc. The above NOx control technologies are complex and need high initial and running cost. A relatively simple, cost effective and durable technology is a requirement of Indian CEV sector. One such technology is internal EGR (iEGR) where the exhaust residuals are trapped in the cylinder by modified valve operation with eliminated problems of external EGR. Internal EGR has a great potential in reducing NOx emissions in diesel engines, shown earlier by researchers. Internal EGR has been used in Diesel, Gasoline and Natural gas and even in HCCI engines and also serves different purposes[2][3][4][5].

There are different methods of internal EGR trapping [6] i.e. secondary intake valve opening, secondary exhaust valve opening, late exhaust valve opening, early exhaust valve opening and early exhaust valve phasing. Previous studies have used various actuating mechanisms to achieve internal EGR i.e. Variable Valve Timing (VVT) [3], Compression Release Retarder (CRR) [7], CRR with on/off valve [8], special camshaft with control valve, increased exhaust back pressure control, active valve train control and cam phaser. These mechanisms were controlled by electronic control systems by programmed look-up tables mapped during development stage. These systems eventually offset the cost of external EGR components. A simple cost effective approach to achieve internal EGR would be a fixed secondary valve event achieved by mechanical camshaft. Fixed secondary valve opening has limitations on control of internal EGR rates. Also meeting the emission targets on a mobile engine application is challenging. Hence the main objective of the present work is to develop an optimum internal EGR valve event for off-road engine based on 2EVO and 2IVO strategies.

THERMODYNAMIC SIMULATION USING AVL BOOST A 1-Dimensional thermodynamic simulation model has been developed using commercial software called AVL BOOST V.10 [9] by linking various sub models such as air cleaner, turbocharger, intercooler, cylinder and pipes. Simplified turbocharger model was used with target boost pressure ratios. The thermodynamic state of the cylinder was estimated considering the interactions such as piston work, fuel heat input, wall heat losses, blow-by losses, and enthalpy of in/out flowing masses. AVL MCC combustion model was used for heat release, performance and NOx prediction. Injection rate was calculated using measured nozzle end pressure, in-cylinder pressure and nozzle dimensions such as hole diameter, no of holes and flow coefficients using Bernoulli flow equation. The fuel quantity input to the model was measured from the baseline experiments. Intake port swirl ratio and flow coefficients were measured on cylinder head using paddle wheel swirl rig at each valve lift. NOx prediction in Boost is based on the model developed by Pattas et al [10] based on the Zeldovich mechanism. Schematic diagram of the thermodynamic model are shown in Fig.2.

Figure 2. 1D Thermodynamic model Secondary intake lift strategy was studied in simulation and found 13% secondary intake lift to that of main lift was found suitable to meet the target internal EGR residuals of 10-12%.

EXPERIMENTAL SETUP ENGINE - A six cylinder 4 stroke turbocharged intercooled diesel engine with a displacement of 0.96 liter/cylinder and producing a rated bmep of 10.2 bar has been chosen for this study. This direct injection diesel engine is fitted with an inline fuel injection pump with multiple hole injector. Detailed engine specifications are given in table 1.

Table 1. Engine Configuration Type Bore x Stroke No. of Cylinders Compression Ratio Injection System Rated Power Max Torque Turbocharger

4- Stroke, Water Cooled 104(mm) x 113(mm) 6 Cylinder 17.5:1 Inline Pump 160 HP @ 2400 rpm 570 Nm @ 1200 – 1800 rpm Pulse Turbocharger

TEST CYCLE - A steady state 8 mode test cycle according to ISO 8178 part-4 (1996) [11] (fig 3) for certifying the emissions of non-road diesel engine had been used for result validation.

Figure 3. ISO 8178, C1 8 Mode Cycle

TEST SETUP - Engine was coupled to an AVL alpha 350 eddy current dynamometer by a propeller shaft. Torque measurement was carried out by a strain gauge load cell and for speed measurement an inductive pulse pick up was used. Figure 4 shows the experimental set up. Engine was instrumented with AVL Indiset Advanced plus which has piezoelectric transducer for measuring cylinder pressure, strain gauge transducers to measure injection line pressures at pump side and injector side to estimate the injection rate. Gaseous exhaust emissions were measured using a Horiba 7000 series Exhaust gas analyser capable of measuring all the legal pollutants ie CO, THC, NOx. Particulate matter emission was measured using an AVL 472 smart sampler partial flow particulate measurement device.

Figure 4. Experimental set up AVL’s Gas Exchange & Combustion Analysis (GCA) [12] was done additionally for internal EGR rate estimation. GCA is a software tool based on AVL BOOST combining the measurement and simulation to allow assessment of non-measurable

in-cylinder parameters i.e. internal EGR rate. Measured signals are the input for reduced thermodynamic simulation model, which calculates the mass flow rates across valves and thereby estimates the internal EGR rate. Engine cylinder head was drilled and tapped to mount the Intake and exhaust port pressures sensors on the ports. For intake port pressure GH12D air cooled piezoelectric sensor and for exhaust port pressure GU21C water cooled piezoelectric sensor were used. Figure 5 & 6 shows the gas exchange analysis setup.

Figure 5. Gas exchange analysis set up

Figure 6. Intake and exhaust pressure sensor instrumentation

RESULTS AND DISCUSSION Experiments were conducted at full loads and 8 modes of ISO 8178 C1 test cycle modes. Experiments with base camshaft showed at full loads both intake and exhaust pressures reduce as the speeds reduce from rated speed to max torque speed. Correspondingly calculated instantaneous mass flows show a reduction wrt speed. Part loads at C1 test cycle showed a lower exhaust flow rates at the part loads than at full loads. The negative exhaust flow in the suction stroke is due to the reverse flow of exhaust during valve overlapping period. Refer figures 7 to 12 for base camshaft results. An internal residual level of 3 to 4% with the base camshaft observed which is correlating to simulation (fig 13).

Intake & Exaust Pressures at full load

Intake & Exaust flow at full load

3.5

0.3 Mass flow Kg/s

3 Pressure, bar

2.5 2

0.1

1.5

0 -400

1 -400

0.2

-300

-200

-100

0

100

200

300

Crank angle deg CA 2400_100%_Int 2200_100%_Exh 1500_100%_Int

2400_100%_Exh 1700_100%_Int 1500_100%_Exh

2200_100%_Int 1700_100%_Exh

Figure 7. Intake & Exhaust pressures at full load

-300

-200

400

-100

0

100

200

300

400

-0.1 Crank angle deg CA 2400_100%_Int 2200_100%_Exh 1500_100%_Int

2400_100%_Exh 1700_100%_Int 1500_100%_Exh

Figure 8. Intake & Exhaust flow at full load

2200_100%_Int 1700_100%_Exh

Intake & Exhaust Pressures at 2200 rpm

Intake & Exhaust flow at 2200 rpm

3.5

0.25 0.2 Mass flow kg/s

Pressure, bar

3 2.5 2

0.15 0.1 0.05 0

1.5

-400

-300

-200

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2200_100%_Int 2200_75%_Exh

-100

0

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Crank angle deg CA 2200_100%_Exh 2200_50%_Int

300

2200_75%_Int 2200_50%_Exh

2200_100%_Int 2200_75%_Exh

Mass flow kg/s

2

Pressure, bar

2200_75%_Int 2200_50%_Exh

0.15

1.8 1.6 1.4

0.1 0.05 0

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1.2 1 1500_100%_Int 1500_75%_Exh

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-100

300

Intake & Exhaust flow at 1500 rpm

2.4

-200

200

2200_100%_Exh 2200_50%_Int

2.6

-300

100

Figure 10. Intake & Exhaust flow at 2200 rpm

Intake & Exaust Pressures at 1500 rpm

-400

0

-0.1 Crank angle deg CA

400

Figure 9. Intake & Exhaust pressures at 2200 rpm

-0.05

0

100

200

1500_100%_Exh Crank angle deg CA 1500_50%_Int

300

400 1500_100%_Int 1500_75%_Exh

1500_75%_Int 1500_50%_Exh

Figure 11. Intake & Exhaust pressures at 1500 rpm

-0.1 Crank angle deg CA 1500_100%_Exh 1500_50%_Int

1500_75%_Int 1500_50%_Exh

Figure 12. Intake & Exhaust flow at 1500 rpm

% Mass Basis

Residual EGR % of Base Camshaft Experimental vs Simulation 6 4 2 0 0

2

4

6

8

Mode no Simulation

Experiment

Figure 13. Residual EGR % of base camshaft Secondary intake opening strategy (2IVO) with 1.6mm lift was selected at first. A new turbocharger was matched based on simulation results which increases the intake boost pressures by 30% which can be clearly seen in pressure and flow measurements of camshaft with 1.6mm lift at rated speed. Intake mass flow showed a negative trend during the beginning of exhaust stroke which traps the residuals at intake manifold. With 1.6mm 2IVO an internal EGR residuals of 12% observed in the 6 high weightage modes of C1 test cycle. With 1.6mm lift NOx reduction of 32% with huge increase in soot emission which was mainly due to insufficient fresh air charge at mid speed. Hence 12% iEGR levels with the present 1.6mm 2IVO camshaft were estimated to be too high to maintain the fresh air charge levels at mid speed. In order to increase the fresh air charge levels and reduce smoke levels further, secondary lift was reduced to 1.30 mm. An instantaneous mass flow reduction of 12% observed with 1.3mm lift and an overall internal residual reduction of 2-4%

observed compared to 1.6mm lift (fig 20). Results show a good improvement in air excess ratio and improved smoke levels of the engine with 8-9% iEGR rate. Especially at lower speeds intake manifold pressure increased upto 0.2 bar.

With 1.3mm secondary lift NOx reduction was found to be 18% and PM increase was only 22% which is well within the limits. C1 cycle results of NOx and PM (table 2) were close to the legal limits with 1.30 mm 2IVO and show a direction to achieve the targets. Further tuning of combustion parameters can reduce the emissions to meet the BS3 CEV limits.

Intake & Exhaust Pressures with Secondary intake lifts

Intake & Exhaust flow at with secondary intake lifts

4.5

0.4 0.3

Mass flow, kg/s

Pressure, bar

4 3.5 3 2.5 2

0.2 0.1 0

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1.5

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-0.2 Crank angle deg CA 2400_100%_Int 2400_100%_1.3_Int 2400_100%_1.6_Int

Crank angle deg CA 2400_100%_Int 2400_100%_Exh 2400_100%_1.3_Int 2400_100%_1.3_Exh 2400_100%_1.6_Int 2400_100%_1.6_Exh

2400_100%_Exh 2400_100%_1.3_Exh 2400_100%_1.6_Exh

Figure 14. Intake & Exh pressures with 2IVO at 2400 rpm Figure 15. Intake & Exh flow with 2IVO at 2400 rpm Intake & Exhaust Pressures at Secondary intake lifts

Intake & Exhaust flow with secondary intake lifts

4

0.3

Pressure, bar

3.5

0.2 Exhaust flow kg/s

3 2.5 2 1.5

0.1 0 -400

-300

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Crank angle deg CA

2200_100%_Base_Int 2200_100%_1.3mm_Int 2200_100%_1.6mm_Int

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-0.2 Crank angle deg CA 2200_100%_Base_Int 2200_100%_Base_Exh 2200_100%_1.3mm_Int 2200_100%_1.3mm_Exh 2200_100%_1.6mm_Int 2200_100%_1.6mm_Exh

2200_100%_Base_Exh 2200_100%_1.3mm_Exh 2200_100%_1.6mm_Exh

Figure 16. Intake & Exh pressures with 2IVO at 2200 rpm Figure 17. Intake & Exh flow with 2IVO at 2200 rpm Intake & Exhaust Pressures at Secondary intake lifts

Intake & Exhaust flow with secondary intake lifts

3

0.2 Exhaust flow kg/s

Pressure, bar

2.5 2 1.5

-400

1 -400

-300

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-100

0.15 0.1 0.05 0 -300

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Crank angle deg CA 1500_100%_Base_Int 1500_100%_Base_Exh 1500_100%_1.3mm_Int 1500_100%_1.3mm_Exh 1500_100%_1.6mm_Int 1500_100%_1.6mm_Exh

400 -0.1 Crank angle deg CA 1500_100%_Base_Int 1500_100%_Base_Exh 1500_100%_1.3mm_Int 1500_100%_1.3mm_Exh 1500_100%_1.6mm_Int 1500_100%_1.6mm_Exh

Figure 18. Intake & Exh pressures with 2IVO at 1500 rpm Figure 19. Intake & Exh flow with 2IVO at 1500 rpm

400

% iEGR Residuals

% iEGR Residuals 14 12 10 8 6 4 2 0

11.8 8.8 3.5

11.4 9.3

12

10.6 9.4

11.9

8.8

4.8

4.1

2200

100%

75%

2200

1500

1.6 mm

3.9

1500

1500

75%

50%

50% 100% Engine Speed / Load% Base

9

8.4 3.3

2.9

2200

11.7

1.3 mm

Figure 20. % iEGR residuals on ISO 8178 C1 test cycle Table 1. Emission Results Base Engine

1.60 mm 2IVO

1.30 mm 2IVO

BS3 CEV Limits

CO(g/kWh) NOx+HC (g/kWh)

0.586

2.276

0.794

4.500

5.47

3.700

4.490

3.800

PM(g/kWh)

0.132

0.502

0.162

0.270

Results

CONCLUSION Thus the new camshaft with 2IVO valve event has a good potential of storing internal EGR residuals and NOx reduction.

Internal EGR rates were estimated using Gas Exchange and Combustion analysis with a good accuracy level. NOx and PM results were close to the legal limits with new camshaft and show a direction to achieve the targets.

REFERENCES 1.

2.

3.

4.

5.

6.

7.

8.

9.

G.S.R. (General Statutory Rules) 276 (E) dated 10th April 2007, Emission limits for Construction Equipment Vehicles (CEV).

Benajes, JB., E Reyes. and JM Lujan. “Intake Valve Pre-Lift Effect on the Performance of a Turbocharged Diesel Engine.” SAE Paper No 960950 (1996).

Pourkhesalian, A.M., Shamekhi, A.H. and Salimi K.N. “NOx Control Using Variable Exhaust Valve Timing and Duration”, SAE Paper No 2010-01-1204 (2010).

Kawasaki, K., Hirota, K., Nagata, S., Yamane, K., Ohtsubo, K. And Nakazono, T. “Improvement of Natural-gas HCCI Combustion by Internal EGR by Means of Exhaust Valve Re-opening”, SAE Paper No 2009-32-0079 (2009).

Aleiferis P. G., Charalambides A. G., Hardalupas Y., Taylor A. M. K. P. and Urata Y. “Modelling and Experiments of HCCI Engine Combustion with Charge Stratification and Internal EGR”, SAE Paper No 2005-01-3725 (2005).

Edwards, S.P., Frankle, G.R., Wirbeleit, F. and Raab, A., “The Potential of a Combined Miller Cycle and Internal EGR Engine for Future Heavy Duty Truck Applications”, SAE Paper No 980180 (1998).

Meistrick, Z., Usko, J., Shoyama, K., Kijima, K., Okazaki, T. and Maeda, Y. “Integrated Internal EGR and Compression Braking System for Hino's E13C Engine”, SAE Paper No 2004-01-1313 (2004).

Schwoerer, J., Dodi, S., Fox, M., Huang, S. and Yang, Z. “Internal EGR Systems for NOx Emission Reduction in Heavy-Duty Diesel Engines”, SAE Paper No 2004-01-1315 (2004).

AVL BOOST User Guide, Version 2010.

10. Pattas K,. Haefner G,. “Stickoxidbildung bei der ottomotorischen Verbrennung”. Motortech Zeits 1973; 34(12):397–

404 (1973).

11. ISO 8178-4:1996, Reciprocating internal combustion engines -- Exhaust emission measurement -- Part 4: Steady-

state test cycles for different engine applications 12. AVL Gas Exchange and Combustion Analysis V4.1, Product Guide.

CONTACT J.Balaji Manager, Engines – Product Development Ashok Leyland Ltd, Technical Centre Vellivoyal Chavadi, Chennai – 600 103 Ph: +91 44 2560 6616 Email: jb.alh1@ashokleyland.com Email: Balaji.J@ashokleyland.com

DEFINITIONS, ACRONYMS, ABBREVIATIONS 2EVO Secondary Exhaust valve Opening 2IVO

Secondary Intake Valve Opening

ATDC after Top Dead Centre BS

Bharat Stage

BTDC before Top Dead Centre CEV

Construction Equipment vehicle

CRR

Compression Release Retarder

DI

Direct Injection

ECE

European Council for Emission

ECU

Electronic Control Unit

EGR

Exhaust Gas Recirculation

HCCI

Homogeneous Charge Compression Ignition

iEGR

Internal Exhaust Gas Recirculation

LNT

Lean NOx Trap

PM

Particulate Matter

SCR

Selective Catalytic Reduction

SOI

Start of Injection