Methodology for Optimization of VVT and LP-EGR Strategies in Gasoline Turbocharged Direct Injection Engine to reduce Fuel Consumption

At the moment, downsizing is the research main focus on SI engines, decreasing their displacement and using a turbocharging system to compensate the loss in performance due to the engine size reduction. Knocking continues to be a key problem for SI engines, especially in those heavily downsized. A good solution to address this problem is using exhaust gas recirculation (EGR). The EGR reduces the reactivity of the mixture reducing the risk of knocking, leading to a better combustion phasing, and it also decreases pumping losses and heat losses and, therefore, improving fuel economy. This paper presents a study of the variable valve timing (VVT) optimization using cooled EGR in a SI Gasoline Turbocharged Direct Injection Engine (GTDI) to reduce fuel consumption that will improve the understanding on this subject. Two steady engine operating conditions were investigated, 10 bar at 2000 rpm and 10 bar at 3000 rpm. The VVT parameters optimization is performed since the original configuration does not have a low pressure EGR system installed and the VVT parameters are not optimize for this conditions. A 1D engine model was used to optimize the VVT parameters for the two mentioned operating conditions. The 1D engine model was validated at the maximum EGR rate for the both operating conditions. The model was used to perform parametric simulations in order to study the effect of the VVT on the pumping losses, heat losses and internal exhaust gas recirculation (IGR). The optimization was based on minimizing the pumping losses, heat losses and IGR, in order to obtain an optimum setup for the VVT parameters. The final VVT parameters configuration obtained by simulation was compared to VVT parameters optimization performed on the dyno test cell using a Design of Experiment (DOE). Promising results were seen, validating the developed methodology using the 1-D model as tool to optimize the VVT parameters. The specific fuel consumption improvement for the 10 bar BMEP at 2000 rpm operating conditions was around 4 g/kWh, and for the 10 bar BMEP at 3000 rpm operating conditions was around 4 g/kWh.