A review of parallel and series turbocharging for the diesel engine

Abstract

Several turbocharger units can be used for engine boosting in series or parallel arrangements in which they are phased in and out according to the operating conditions of the engine. This technology has the potential to facilitate downsizing of automotive engines in order to yield benefits in terms of their transient performance, the fuel consumption and emissions output. This review investigates the benefits and drawbacks of series and parallel turbocharging arrangements. Since the effectiveness of using the boosting technology crucially depends on the control scheme applied, developments in the modelling and control approaches used in single-stage, series and parallel turbocharging are also examined. In comparison with single-stage turbocharging, using several turbochargers in series or parallel can provide a faster transient response without compromising the fuel consumption, while also having the potential to provide higher boost pressures. Novel non-linear and robust control approaches have demonstrated improvements in performance and robustness over traditional approaches used in commercial engine control relying on separate control loops for the different engine variables.