Virtual and Experimental Optimization of In-Cylinder Residuals with Modified Cam using Gas Exchange Analysis

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 % 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 % 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- emission norms) calls for major engine design changes to achieve a drastic reduction (>5%) in NOx and PM (Particulate Matter) as compared to BS- 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 show the progression of emission limits for off-road engines in India []. Figure. Off-road emission limits in India Nitric oxide (NO) and nitrogen dioxide (NO) 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 ) In-cylinder NOx control such as pilot injection, injection rate shaping, water emulsification of the fuel and Exhaust Gas Recirculation (EGR) and )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[][][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) [], 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 EVO and IVO strategies. THERMODYNAMIC SIMULATION USING AVL BOOST A -Dimensional thermodynamic simulation model has been developed using commercial software called AVL BOOST V. [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 [] based on the Zeldovich mechanism. Schematic diagram of the thermodynamic model are shown in Fig.. Figure. D Thermodynamic model Secondary intake lift strategy was studied in simulation and found % secondary intake lift to that of main lift was found suitable to meet the target internal EGR residuals of -%. EXPERIMENTAL SETUP ENGINE - A six cylinder 4 stroke turbocharged intercooled diesel engine with a displacement of.96 liter/cylinder and producing a rated bmep of. 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.

Table. Engine Configuration Type 4- Stroke, Water Cooled Bore x Stroke 4(mm) x (mm) No. of Cylinders 6 Cylinder Compression Ratio 7.5: Injection System Inline Pump Rated Power 6 HP @ 4 rpm Max Torque 57 Nm @ 8 Turbocharger Pulse Turbocharger rpm TEST CYCLE - A steady state 8 mode test cycle according to ISO 878 part-4 (996) [] (fig ) for certifying the emissions of non-road diesel engine had been used for result validation. Figure. ISO 878, C 8 Mode Cycle TEST SETUP - Engine was coupled to an AVL alpha 5 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 7 series Exhaust gas analyser capable of measuring all the legal pollutants ie CO, THC, NOx. Particulate matter emission was measured using an AVL 47 smart sampler partial flow particulate measurement device. Figure 4. Experimental set up AVL s Gas Exchange & Combustion Analysis (GCA) [] 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

Pressure, bar Mass flow Kg/s 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 GHD air cooled piezoelectric sensor and for exhaust port pressure GUC water cooled piezoelectric sensor were used. Figure 5 & 6 shows the gas exchange analysis setup. Figure 5. Gas exchange analysis set up RESULTS AND DISCUSSION Figure 6. Intake and exhaust pressure sensor instrumentation Experiments were conducted at full loads and 8 modes of ISO 878 C 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 C 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 for base camshaft results. An internal residual level of to 4% with the base camshaft observed which is correlating to simulation (fig ). Intake & Exaust Pressures at full load.5.5 Intake & Exaust flow at full load....5 4_%_Int 4_%_Exh _%_Int _%_Exh 7_%_Int 7_%_Exh 5_%_Int 5_%_Exh -. 4_%_Int 4_%_Exh _%_Int _%_Exh 7_%_Int 7_%_Exh 5_%_Int 5_%_Exh Figure 7. Intake & Exhaust pressures at full load Figure 8. Intake & Exhaust flow at full load

% Mass Basis Pressure, bar Mass flow kg/s Pressure, bar Mass flow kg/s Intake & Exhaust Pressures at rpm.5.5.5 _%_Int _%_Exh _75%_Int _75%_Exh _5%_Int _5%_Exh Intake & Exhaust flow at rpm.5..5..5-4 - - - -.5 4 -. _%_Int _%_Exh _75%_Int _75%_Exh _5%_Int _5%_Exh Figure 9. Intake & Exhaust pressures at rpm Figure. Intake & Exhaust flow at rpm Intake & Exaust Pressures at 5 rpm.6.4..8.6.4. 5_%_Int Crank angle 5_%_Exh deg CA 5_75%_Int 5_75%_Exh 5_5%_Int 5_5%_Exh Intake & Exhaust flow at 5 rpm..5..5 -.5 -. 5_%_Int 5_%_Exh 5_75%_Int 5_75%_Exh 5_5%_Int 5_5%_Exh Figure. Intake & Exhaust pressures at 5 rpm Figure. Intake & Exhaust flow at 5 rpm 6 4 Residual EGR % of Base Camshaft Experimental vs Simulation 4 6 8 Simulation Mode no Experiment Figure. Residual EGR % of base camshaft Secondary intake opening strategy (IVO) with.6mm lift was selected at first. A new turbocharger was matched based on simulation results which increases the intake boost pressures by % which can be clearly seen in pressure and flow measurements of camshaft with.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.6mm IVO an internal EGR residuals of % observed in the 6 high weightage modes of C test cycle. With.6mm lift NOx reduction of % with huge increase in soot emission which was mainly due to insufficient fresh air charge at mid speed. Hence % iegr levels with the present.6mm IVO 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. mm. An instantaneous mass flow reduction of % observed with.mm lift and an overall internal residual reduction of -4%

Pressure, bar Exhaust flow kg/s Pressure, bar Exhaust flow kg/s Pressure, bar Mass flow, kg/s observed compared to.6mm lift (fig ). 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. bar. With.mm secondary lift NOx reduction was found to be 8% and PM increase was only % which is well within the limits. C cycle results of NOx and PM (table ) were close to the legal limits with. mm IVO and show a direction to achieve the targets. Further tuning of combustion parameters can reduce the emissions to meet the BS CEV limits. Intake & Exhaust Pressures with Secondary intake lifts 4.5 4.5.5.5 4_%_Int 4_%_Exh 4_%_._Int 4_%_._Exh 4_%_.6_Int 4_%_.6_Exh Intake & Exhaust flow at with secondary intake lifts.4... -. -. 4_%_Int 4_%_Exh 4_%_._Int 4_%_._Exh 4_%_.6_Int 4_%_.6_Exh Figure 4. Intake & Exh pressures with IVO at 4 rpm Figure 5. Intake & Exh flow with IVO at 4 rpm Intake & Exhaust Pressures at Secondary intake lifts 4.5.5.5 _%_Base_Int _%_Base_Exh _%_.mm_int _%_.mm_exh _%_.6mm_Int _%_.6mm_Exh Intake & Exhaust flow with secondary intake lifts... -. -. _%_Base_Int _%_Base_Exh _%_.mm_int _%_.mm_exh _%_.6mm_Int _%_.6mm_Exh Figure 6. Intake & Exh pressures with IVO at rpm Figure 7. Intake & Exh flow with IVO at rpm Intake & Exhaust Pressures at Secondary intake lifts.5.5 5_%_Base_Int 5_%_Base_Exh 5_%_.mm_Int 5_%_.mm_Exh 5_%_.6mm_Int 5_%_.6mm_Exh Intake & Exhaust flow with secondary intake lifts..5..5 -.5 -. 5_%_Base_Int 5_%_Base_Exh 5_%_.mm_Int 5_%_.mm_Exh 5_%_.6mm_Int 5_%_.6mm_Exh Figure 8. Intake & Exh pressures with IVO at 5 rpm Figure 9. Intake & Exh flow with IVO at 5 rpm

% iegr Residuals 4 8 6 4 % iegr Residuals.8.4.9.7.6 8.8 9. 9.4 8.8 8.4 9.5 4. 4.8.9..9 5 5 5 % 75% 5% % 75% 5% Engine Speed / Load% Base.6 mm. mm Figure. % iegr residuals on ISO 878 C test cycle Results Table. Emission Results Base Engine.6 mm IVO. mm IVO BS CEV Limits CO(g/kWh).586.76.794 4.5 NOx+HC (g/kwh) 5.47.7 4.49.8 PM(g/kWh)..5.6.7 CONCLUSION Thus the new camshaft with IVO 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. G.S.R. (General Statutory Rules) 76 (E) dated th April 7, 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 9695 (996).. Pourkhesalian, A.M., Shamekhi, A.H. and Salimi K.N. NOx Control Using Variable Exhaust Valve Timing and Duration, SAE Paper No --4 (). 4. 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 9--79 (9). 5. 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 5--75 (5). 6. 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 988 (998). 7. Meistrick, Z., Usko, J., Shoyama, K., Kijima, K., Okazaki, T. and Maeda, Y. Integrated Internal EGR and Compression Braking System for Hino's EC Engine, SAE Paper No 4-- (4). 8. 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 4--5 (4). 9. AVL BOOST User Guide, Version.

. Pattas K,. Haefner G,. Stickoxidbildung bei der ottomotorischen Verbrennung. Motortech Zeits 97; 4():97 44 (97).. ISO 878-4:996, Reciprocating internal combustion engines -- Exhaust emission measurement -- Part 4: Steadystate test cycles for different engine applications. AVL Gas Exchange and Combustion Analysis V4., Product Guide. CONTACT J.Balaji Manager, Engines Product Development Ashok Leyland Ltd, Technical Centre Vellivoyal Chavadi, Chennai 6 Ph: +9 44 56 666 Email: jb.alh@ashokleyland.com Email: Balaji.J@ashokleyland.com DEFINITIONS, ACRONYMS, ABBREVIATIONS EVO Secondary Exhaust valve Opening IVO Secondary Intake Valve Opening ATDC after Top Dead Centre BS Bharat Stage BTDC before Top Dead Centre CEV CRR DI ECE ECU EGR HCCI iegr LNT PM SCR SOI Construction Equipment vehicle Compression Release Retarder Direct Injection European Council for Emission Electronic Control Unit Exhaust Gas Recirculation Homogeneous Charge Compression Ignition Internal Exhaust Gas Recirculation Lean NOx Trap Particulate Matter Selective Catalytic Reduction Start of Injection