Downsizing Capability Evaluation of Active Control Turbocharger (ACT)

This study aims to evaluate the downsizing capability of active control turbocharger (ACT) by means of computer simulation approach. One dimensional simulation package was used to model a commercial 13L diesel engine equipped with variable geometry turbocharger (VGT) and a 10L diesel engine equipped ACT. The 10L ACT engine delivered up to 34.42% of higher brake power than 13L VGT engine at 1000RPM and below, but for the higher engine speed, 13L VGT engine delivered higher brake power (up to 14.5%) than 10L ACT engine. Introduction Turbocharging has been recognized as the most significant enabler in engine downsizing [1-3]. Figure 1 depicts the downsizing trends for the three most influential regions in the world. It can be observed that for the next 10 years to come, average engine displacement in the US will reduce from 3.6L to 2.9L as automotive manufacturers move from V8 and V6 engine blocks to 4 cylinders. In Europe, which has a mature turbo market, 4 cylinders will remain the architecture of choice, but with the improving turbo technologies, the engine displacement will further reduce from an average 1.8L to 1.4L or even smaller. In China, where the turbo experience is more recent, will see a move of engines sizes from 1.8L to 1.6L. By 2015, it is predicted that up to 50 percent of all turbocharged engines in China will be 1.7L or smaller [2]. Figure 1: Engine Downsizing Trend for USA, China, and Europe [2] Currently, the Variable Geometry Turbocharger (VGT) is the most widely used boosting options, and it has overcome many of the conventional turbocharging problems such as turbolag and engine speed matching. However, VGT does not completely address the pulsating nature of the exhaust pulse. An advanced turbocharging technique called Active Control Turbocharger (ACT) was proposed to overcome the shortcoming of the VGT. ACT is a turbocharger system with system and method of operation, which regulates the turbine inlet area throughout each engine exhaust gas period, thereby actively adapting to the characteristics of the high frequency, highly dynamic flow. ACT is essentially an improved version of the conventional VGT [4]. This paper evaluates the downsizing capability of the ACT by means of 1D simulation approach by comparing the performance of a 10L commercial diesel engine equipped ACT to a 13L VGT engine. 13L VGT Engine Modelling and Validation One dimensional simulation package, AVL boost was used to model commercial 13L and 10L, inline six cylinders, 4 strokes diesel engine equipped with VGT. The engine geometrical data and is depicted in Table 1: Table 1: Engine geometrical data Engine parameters 13L 10L Bore [mm] 135 125 Stroke [mm] 150 140 Compression Ratio 16.5:1 16.5:1 Valves/Cylinder 4 4 Engine Displacement [L] 12.88 10.3 Speed Range [RPM] 800-2000 800-200 The turbine performance maps were obtained through cold flow experiments at the Imperial College London. During the simulation, a UDF was used to alter the VGT rack position at different engine speed to obtain the optimum performance for the engine. The simulation results were compared with engine manufacturers at F/A=0.057, and the result is shown in Figure 2. It can be seen that simulation results matched very well with the manufacturer’s data for both brake power and torque at F/A=0.057. Figure 2: Brake power between comparison between actual and simulated VGT engine ACT Simulation for 10L Diesel Engine In ACT operating mode, the instantaneous position of the turbine rack is given by, [4]: = , + 1 − sin (ωt) sin(ωt) (1) Where, = , − , = − , (2) On the other hand, the frequency of the exhaust pulse emitted into turbine is given as: