Improvement of Transient Response on a Downsized 4 Cylinder Engine for Automobile Application

Ever since mainstreaming of automobiles, engineers are focusing on making the vehicles better by means of making them more efficient, powerful and less polluting. In this study, venues of improving low end torque via improvement in volumetric efficiency as well as proper selection of turbochargers is done. An in-depth analysis of gas dynamics with respect to valve timing is studied along with the AVL Boost 1D simulation. It was found that volumetric efficiency starts to improve when there is a reduction in exhaust - exhaust valve overlap. There is an improvement found in the fresh air ratio (lambda) as the residual gas content is reduced. After the selection of valve timing, turbocharger optimization is done with comparison between two turbine sizes. Along with turbocharger comparison, technology comparison is also done namely between normal electronic VGT (Variable Geometry Turbo) (bigger turbine) and electronic VGT coupled with waste gate (smaller turbine). Dynamic as well as static performance is compared on vehicle level as well as testbed level. Time to torque (TTT) value was measured for the turbos and performance was compared for different lambda limits. A MATLAB tool was programmed to predict the vehicle level performance from the TTT values. The performance was validated on vehicle level as well. In summary, better low-end response was observed with smaller turbine size with 5% improvement in low end volumetric efficiency and similar efficiency at rated power.