Increasing Low Speed Engine Response of a Downsized CI Engine Equipped with a Twin-Entry Turbocharger A. Kusztelan, Y. F. Yao, D. Marchant and Y. Wang
Benefits of a Turbocharger Increases the volumetric efficiency of the engines combustion chamber Creates a higher mass flow rate enhancing the brake mean effective pressure acting upon the piston crown www.engineerography.com
Research Objective The emphasis today is to provide feasible engineering solutions to create more economical engines whilst still maintaining a high specific power output One solution is pressure boosting, allowing automotive manufacturers to adopt smaller displacement engines, commonly known as engine downsizing A common problem that occurs when turbocharging downsized diesel engines is the response of the turbine at low engine speeds The application of a twin-entry turbocharger suggests that the pulsating energy of the exhaust gas is better utilized providing an increased turbine response at lower RPM ranges. www.borgwarner.com/turbodriven
Twin-Entry Turbocharger Configuration In contrast to a single-entry turbochargers, a twin-entry turbine housing will better utilize the pulsating energy of the exhaust gas [1] Potential benefits for downsizing applications: Increased turbocharger response at low engine speeds Reduced turbocharger delay time i.e. lag providing improved vehicle drivability Disadvantage: Cost of castings for complex twin-entry geometry www.modified.com [1] Aghaali H. and Hajilouy-Benisi A. (2008). Experimental modelling of twin-entry radial turbine. Iranian Journal of Science & Technology, Transaction B, Engineering, Vol. 32, No. B6, pp 571-584
Ricardo Wave 1D Simulation 1D simulation software accurately replicates an engine using different configurations and operating conditions Quickly and precisely change variables Initial engine cell testing procedures performed using software Identify any initial problems early in the design and testing stages Viable validation source Time saving Cost saving Development Tool Research Tool Our research based on a Down sized Renault 1.5 DCi Engine
1.5 DCi K9K Engine 1.5 DCi frequently cited as a bases for down sized CI engine development Engine Technology International [2] Fitted as standard with a BorgWarner single-entry Turbocharger www.renault.com [2] Weissbaeck M. (2011). Diesel Downsizing, Engine Technology International, January, p. 26
1D Simulation Model Simulation based on the Wiebe combustion model [3] and a series of user defined parameters taken from the original engine. Bore Stroke Exhaust Valve Lift Inlet Valve Lift 76 mm 80.5 mm 8.6 mm 8.0 mm Compression Ratio 17.9 : 1 Firing Order 1-3-4-2 No. Of Cylinders 4 No. Valves Per Cylinder 2 Inlet Manifold Temp ~ 120 C Exhaust Manifold Temp ~ 800 C [3] Ricardo Wave 8.3 User Manual
Compressor: BorgWarner KP 35 A suitable flow map [4] for the compressor needs to imported within the software to create the correct turbocharger operating conditions: Volumetric Flow Rate m3/s Default Ricardo extrapolation methods are used to create operating conditions not originally presented (or available) from manufacturer flow maps. [4] BorgWarner compressor flow map (http://corsaclub.forumcommunity.net/?t=32167079 (2010). (Accessed: December 2010)
Engine Boundary Conditions For the purpose of this research the model is based on a steady state simulation cycle (1000 5000 RPM) Transient simulation models based on the current Euro Drive Cycle are planned Identical compressor geometry was used for both the single and twin-entry models Variables defined using {x} then set within the constant table at each RPM stage Further typical parameters include: Fuel/Air ratio {FA} Turbocharger shaft speed {CRPM}
Single-Entry Configuration Model: 4 into 1 manifold geometry: Strong flow interactions and turbulent mixing of the pulsating exhaust gases within manifold Energy transfer from exhaust gas to turbine impeller are therefore not optimised
Twin-Entry Configuration Model: Using the standard firing order of 1-3-4-2 the manifold can be tailored to keep the varying exhaust gas pulses separate [5] Both models were run using the same boundary conditions for 100 simulation cycles [5] Hiereth, H. and Prenninger, P. (2003) Charging the internal combustion engine. Springer: New York
Simulation Model Validation Data provided by Renault: Peak engine power 45 Kw @ 4000 RPM Fuel consumption (26.7 mpg) Turbocharger type (BorgWarner KP 35) Bore and stroke dimensions Calculated parameters: Adiabatic combustion temperature (2440 C) Torque @ 4000 RPM (107.98 Nm) BMEP @ 4000 RPM (9.046 Bar) Volumetric efficiency @ 4000 RPM (1.2) Ensure engine model is creating the correct power and torque output using pre defined parameters and BorgWarner compressor flow map at 4000 RPM Accurate correlation between known and calculated data
Power (Kw) Validation Results Power as indicated from Renault is 45 Kw @ 4000 RPM Results show good correlation between given and simulated power output 50.00 45.00 40.00 Renault Indicated Power Value (45Kw) 35.00 30.00 25.00 20.00 15.00 10.00 5.00 1000 1500 2000 2500 3000 3500 4000 4500 Engine RPM
Torque (Nm) Calculated Results Validation Torque was calculated using engine speed specified at maximum power (108 Nm) The calculated value was then compared to the simulated results (108.06 Nm) 120.00 110.00 100.00 90.00 80.00 70.00 60.00 50.00 40.00 1000 1500 2000 2500 3000 3500 4000 4500 Engine RPM
BMEP (Bar) Calculated Brake Mean Effective Pressure (BMEP) 10.00 Calculated BMEP @ 4000 RPM is 9.046 Bar Simulated recorded value @ 4000 RPM (9.30 Bar) 2.7 % Improvement 9.00 8.00 7.00 6.00 5.00 4.00 1000 1500 2000 2500 3000 3500 4000 4500 Engine RPM
Simulation Results A series of comparison plots were created using the simulation results to indicate a potential change in engine performance when using the twin-entry geometry turbocharger: Turbocharger shaft speed - indication as to whether impeller spool increases at low engine speeds (1000-3000 RPM) Power and torque variations - through improved turbocharger performance BMEP and volumetric efficiency - through improvements in compressor pressure ratio Correlation between turbine and compressor performance using plotted engine drive lines
Shaft Speed (RPM) Twin and Single entry Comparison Results Due to a potential improvement in energy transfer caused by the twin-entry turbine housing and subsequent manifold design the shaft speed is increased. Clear increase across the engine speed range of 1000-3500 RPM, but greatest percentage improvement of 31.7% visible at 2500 RPM 240000 220000 200000 180000 160000 140000 120000 Twin-Entry Single-Entry 100000 80000 60000 40000 1000 1500 2000 2500 3000 3500 4000 4500 Engine RPM
Power (Kw) Torque (Nm) Power and Torque Improvements An increase in power and torque is also clearly visible within the speed range of 1000-3500 RPM indicating improved engine speed performance due to the adoption of twin-entry turbocharger Twin-Entry 50.00 45.00 120.00 110.00 Single-Entry 40.00 35.00 30.00 25.00 20.00 15.00 10.00 100.00 90.00 80.00 70.00 60.00 50.00 5.00 1000 1500 2000 2500 3000 3500 4000 4500 Engine RPM 40.00 1000 1500 2000 2500 3000 3500 4000 4500 Engine RPM Greatest increase of 28.1% at 2500 RPM for both the power and torque results
Volumetric Efficiency Air Flow (Kg/Hour) Volumetric Efficiency Improvement An increase in the compressor speed would normally result in an improved air flow rate into the engine This in-turn will theoretically create a higher volumetric efficiency as verified by the simulation results 1.50 1.40 1.30 350 300 250 1.20 1.10 1.00 0.90 0.80 200 150 100 50 Twin-Entry Single-Entry 0.70 1000 1500 2000 2500 3000 3500 4000 4500 Engine RPM 0 1000 1500 2000 2500 3000 3500 4000 4500 Engine RPM Both VE and Air flow indicate an increase of 23.1% at 2500 RPM showing a clear improvement during low engine speed conditions
BMEP (Bar) Compressor discharge pressure (Bar) Brake Mean Effective Pressure (BMEP) A similar trend is illustrated by the increase in BMEP and compressor discharge pressure due to the increased air mass flow rate 10.00 2.20 9.00 2.00 8.00 1.80 7.00 1.60 6.00 1.40 5.00 1.20 4.00 1000 1500 2000 2500 3000 3500 4000 4500 Engine RPM 1.00 1000 1500 2000 2500 3000 3500 4000 4500 Engine RPM
Effect of increased engine performance on turbocharger Using simulated PR and M two drive lines are plotted representing both the single/twin entry geometry This clearly indicates what effect the changed turbine geometry has on the compressor performance Twin-Entry Single-Entry Volumetric Flow Rate m3/s The increased flow rate produced by the compressor due to the twin-entry turbine geometry is clearly visible. Drive line (twin-entry) shifted into higher efficiency areas indicating increased compressor performance
Simulation Outcomes and Observations Application of a twin-entry volute design clearly effects engine performance during low RPM conditions Twin-entry geometry indicates a greater energy transfer to the turbine impeller from the split pulse exhaust gases Improved compressor performance providing better torque and power characteristics during low engine speed conditions The drive line locations on the compressor map moved to higher efficiency zones due to the increase in air flow rate Reducing turbocharger delay time due to faster impeller spooling time Increasing engine response during 1000-3000 RPM engine speed conditions Potential cost reductions over currently available designs e.g. turbo-compounding and 2-stage turbocharging
Improvement Percentage within the 1000-3500 RPM Range Power 15.1 % Torque 15.1 % BMEP 15.1 % Volumetric Efficiency 13.1 % Mass Air Flow 13.0 % Shaft Speed 16.2 % Comp. Discharge Pressure 7.25 % Clear improvement in engine and turbocharger performance due to the use of a twin-entry turbocharger
Future Simulation Validation The dynamometer facilities at Kingston University London are capable of performing transient drive cycle tests using the 1.5 DCi Renault engine Using recorded test cell data to validate the 1D simulation results Apply recorded data taken from dyno test to create more accurate boundary conditions for the simulation model Application of 3D CFD Use CFD resources to demonstrate the effect of twin-entry geometry on flow conditions using both simulated and experimentally acquired boundary conditions Determine the flow conditions at very low engine speed conditions i.e. 1000-1500 RPM within the compressor housing
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