Optimized Air Intake for a Turbocharged Engine Taking into Account Water-Cooled Charge Air Cooler Reflective Properties for Acoustic Tuning 2013-01-0575

Unsteady intake wave dynamics have a first order influence on an engine's performance and fuel economy. There is an abundant literature particularly for naturally aspirated SI engines on the subject of intake manifolds and primary runner lengths aimed to achieve a tuned intake air line. A more demanding design for today's engines is to increase efficiency to meet the requirements of lower fuel consumption and CO2 emissions. Today's tendencies are downsizing the engine to meet these demands. And for drivability purposes, the engine is combined with a turbocharger coupled with a charge air cooler. However, when the engine's displacement is reduced, it will be very dependent on its boosting system. A particularly interesting point to address corresponds to the engine's operation in the low speed range and during transients where the engine has large pumping losses and poor boost pressure. This operation point can be optimized using acoustic supercharging techniques. The proposed solution for a turbocharged engine is through an optimized air intake system from the compressor outlet to the intake valves. In this paper such a dedicated line is experimentally proposed on a four cylinder Diesel engine. First the reflective properties of a water-cooled charge air cooler are highlighted and compared to a traditional air charge cooler. This was done experimentally on an engine test bench using wave decomposition techniques through forward and backward components. Secondly this reflection is put to use by employing an adequate pipe length between the intake manifold and the charge air cooler aimed to improve low end torque and transient response. A series of pipe lengths were investigated and a final one is shown to give the greatest pressure wave amplitudes upstream of the intake valves for a low rpm range where the compressor provides little work. As a result it is shown that acoustic tuning is still possible on a turbocharged engine with a reduced plenum volume thus keeping costs low. Finally a GT-Power model of the engine is built where the exhaust and intake lines were correctly modeled. Then, the dynamics of intake system were replaced by an artificial excitation boundary which can be controlled independently and would correctly interact with the intake valves. Thus the optimized pressure waves obtained from the experimental measurements are fed directly into the intake of the model. The latter calculates the mean value of pressure only. Therefore rendering possible the prediction of the CO2 gain obtained from such an optimized line.