!"" #$!%& Development of a Double Variable Cam Phasing Strategy for Turbocharged SIDI Engines GMPT Europe, Engine Development & Simulation Vincenzo Bevilacqua, Jany Krieg, Roland Maucher, Raymond Reinmann 1
Contents Introduction Synergies between different engine technologies Cam Phasing Optimization Comparison between simulation and experiments Summary 2
Contents Introduction Synergies between different engine technologies Cam Phasing Optimization Comparison between simulation and experiments Summary 3
Introduction Turbo Diesel Engines Turbocharged diesel engines gained persistently increasing market shares in the European Market in the last decade. This success can be explained with the high low-end torque output power comparable with the competitor SI engines low fuel consumption Tough challenge for SI engines developers! 4
Introduction SI Engines Compete against turbo diesel engines represents a tough challenge for SI engine developers and require a sophistication of the engine concept: Dual Variable Cam Phasing optimizes the volumetric efficiency and improves fuel consumption at part load; Direct Injection allows the downsizing of the engine and consequently improves fuel consumption; Turbocharger increases the specific torque and power, and, eventually, allows lean stratified operating condition at part load; Full factorial experimental approach is too time consuming to optimize the system 5
Synergies between different engine technologies Introduction Synergies between different engine technologies Cam Phasing Optimization Comparison between simulation and experiments Summary 6
Synergies between different engine technologies By combining the proprieties of different technologies, synergies can be achieved: LOW END TORQUE A high degree of scavenging can be provided by the cam phasing. This increases the VE and the efficiency of the turbo. Thanks to DI no fuel is lost. FUEL CONSUMPTION The variable cam phaser can be used to shift compression work from engine to thecompressor and improve system efficiency (versus wastegate control) Brake Torque [Nm] MAXIMUM TORQUE PLATEAU Engine Speed [rpm] 7
Synergies between different engine technologies FUEL CONSUMPTION Making the engine work with lower volumetric efficiency an higher boost pressure is required to fulfill the target. The positive pumping work is then increased. Brake Torque [Nm] Engine Speed [rpm] 8
Contents Introduction Synergies between different engine technologies Cam Phasing Optimization Comparison between simulation and experiments Summary 9
Cam Phasing Optimization With the help of the cam maps, the cam position can be optimized for each operating point, to achieve: the maximum performance potential the minimum fuel consumption In the diagram (as example) the point at 1800 rpm is shown. Overlap Width Overlap position 10
Cam Phasing Optimization - Performance VOLU METRIC EFFICIENCY The VE is maximized by maximum overlap PMEP Positive PMEP is increased advancing exhaust cam. The trade off depends on engine speed: low rpm: high scavenging high rpm: low neg. PMEP MANIFOLD PRESSURE The manifold pressure (index of performance potential) shows a minimum in a intermediate region. Low High Maximum Performance Potential Cam Timing 11
Cam Phasing Optimization - Performance VOLU METRIC EFFICIENCY The VE is maximized by maximum overlap PMEP Positive PMEP is increased advancing exhaust cam. The trade off depends on engine speed: low rpm: high scavenging high rpm: low neg. PMEP MANIFOLD PRESSURE The manifold pressure (index of performance potential) shows a minimum in a intermediate region. Low High Maximum Performance Potential Cam Timing 12
Cam Phasing Optimization - Consumption PERCENT BURNED MASS The content of residual gas is an index of the COV of Torque and the knock intensity. A limit of 3% has been chosen. BSFC In the BSFC cam map the Minimal Consumption Cam Timing can be located. Low High 13
Contents Introduction Synergies between different engine technologies Cam Phasing Optimization Comparison between simulation and experiments Summary 14
Comparison with experiment In order to validate the outcome of the numerical optimization experimental test have been carried out. Both maximum performance potential and minimal consumption timings have been tested. Due to cam phaser authority, cam phasing has been slightly modified (dotted lines). 15
Comparison with experiment MANIFOLD PRESSURE Maximum performance potential timings allows to reach the target torque with a significant lower boost pressure. BSFC Minimal consumption timings allows a reduction of BSFC up to 7.5%. 7.5% 16
Contents Introduction Synergies between different engine technologies Cam Phasing Optimization Comparison between simulation and experiments Summary 17
Summary The cam phasing for a turbocharged GDI engine has been analyzed with 1-dimensional simulation. The analysis provide a deep insight of the cam phasing effect and in particular permit to highlight two strategies: maximum performance potential minimal consumption Increasing the compressor work, fuel consumption can be improved Experiments confirmed the outcomes of the simulation work showing potential in fuel economy (cam phasing vs. waste gate) 18
GM Powertrain Europe Thank you for the attention! 19