Turbocharging Perspective

Auszug

Turbocharging is used first and foremost to boost the specific torques of internal combustion engines; a patent for it was granted to Alfred Büchi in 1905. This is also precisely why the turbocharger has found its way into almost all modern diesel and gasoline engines over the last 20 years. Short term, a turbo share of around 70 % is expected for new registrations in Europe, while the share of the US automotive market is expected to grow from around 30 % at present to around 50 % over the next five years. A similar trend can also be seen in China. As a continuous flow machine connected to the combustion engine while in transient operation, the turbocharger is always lagging behind spontaneous power demand. Avoiding the so-called turbo hole requires wide-ranging charging concepts, such as smaller turbochargers with high speed, multi-stage charging and/or combining with mechanical or electrically driven auxiliary compressors. The electrification of the vehicle drive system, from 48-V systems to full hydride, raises the complex question of which charging concepts will make sense in future. Increasing hybridization may help eliminate the need for a rapid build-up of boost pressure, since the electric motor provides sufficient driving dynamics. Cost reasons preclude the use of turbochargers in certain hybrid drive concepts. With that in mind, it is impossible to foresee a general solution for using turbochargers, the further development of which will primarily determine future emission limit values and an increase in durability. In particular, media and customer attention require systems that meet the requirements in terms of emissions, fuel consumption and drivability and not just in prescribed test cycles. For diesel engines, this means increasing the pressure ratios or boosting pressures to compensate for the high EGR rates required. At the same time, the rapid heating of the exhaust gas aftertreatment and setting sufficient temperatures for functional aftertreatment are becoming more and more important. Multi-stage charging systems, which are increasingly likely to prevail in future, are at a disadvantage here. Even so, rapid pressure build paves the way to reducing particle emissions. For the gasoline and diesel engines used in passenger cars, the trend is still towards higher specific outputs. Unlike in commercial vehicle engines, usable engine speed bands are extended, which also increases the spread of the mass flow at the turbine. An additional electric compressor is recommended for multi-stage turbocharging systems with a pure internal combustion engine drive. Combining an exhaust gas turbocharger with an electrically driven booster compressor opens up further scope to reduce the displacement of the internal combustion engine. This reduces internal engine friction as a means of cutting CO₂ emissions without sacrificing engine performance. Using the exhaust gas turbocharger thus offers excellent prospects for the future. …