Variable geometry turbocharging for lower emissions and improved torque characteristics

Abstract

Currently, 80 per cent of European diesel passenger cars are turbocharged and, as emission standards become more stringent, this figure is expected to approach 100 per cent in the near future. One major focus that has emerged for the high-speed diesel engine is the application of variable geometry turbocharging (VGT). An extensive steady state experimental investigation has been undertaken on a prototype 1.8 L direct injection (DI) diesel engine to compare the potential benefits of VGT relative to the standard build of the engine with a wastegated fixed geometry turbocharger (FGT). Under part load operation, where emission production is significant in the European drive cycle, independent control of both VGT vane position and exhaust gas recirculation (EGR) valve position was used to optimize emission levels. A reduction in the levels of nitrogen oxides (NO x) of up to 45 per cent was observed at discrete operating points without compromising FGT levels of fuel consumption or smoke. Under limiting torque conditions a 10 per cent improvement was achieved with the VGT over and above the figures of the baseline FGT build within the limiting criteria set for maximum cylinder pressure, smoke level and pre-turbine temperature.