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.

Non-axisymmetric flow characteristics in centrifugal compressor

“…When the compressor is close to the choke point, the static pressure along the flow direction in the volute decreases. References [1,3,9,11,14] investigated the static pressure circumferential distribution of the diffuser and the volute of the centrifugal compressor by either experimental test or steady numerical calculation method with the conclusion that the variation of the static pressure is consistent with the above discussion. Fig.4 presents the time-averaged static pressure distribution on the intermediate longitudinal section of the volute with two different operating conditions.…”

“…This asymmetric structure of the volute has significant effects on the flow field of the diffuser and impeller [1,2] . It affects the distribution of the pressure and the velocity at the circumferential direction inside the volute.…”

Electric Boosting and Energy Recovery Systems for Engine Downsizing

“…Variable nozzle devices have two principal types, namely, pivoting vanes and moving sidewall [48], and can provide (amongst other benefits) improved transient performance [54] and low speed boost [57]. By using a variable nozzle turbocharger fitted to 1.8 L direct injection diesel engine, Hawley et al [58] increased the torque in the entire engine speed range compared with an equivalent fixed geometry unit. Wijetunge et al [17] and Matsura et al [54] believed that variable geometry turbochargers rely on the build-up of exhaust gas energy and thus do not completely solve the problem of transient response, particularly at low engine speeds.…”

Research and development on transonic compressor of high pressure ratio turbocharger for vehicle internal combustion engines

“…The compressor is driven by the turbine extracting energy from exhaust gases. Compared to a naturally aspirated engine, the benefits of a turbocharged engine are power increasing, lower fuel consumption and emission reduction [2].…”