Forced-induction spark-ignition engines for passenger cars have
undergone rapid development in just a few years. The development
steps towards reducing consumption, improving response and
increasing durability have required considerably less time than in
the case of the naturally aspirated engine. Forced-induction
engines currently employ exhaust gas turbo-charging almost
exclusively. By this means the required quantities of air can be
supplied with acceptable size, weight and efficiency, together with
the advantage of good acoustic characteristics. In step with the
combustion engine, the turbo-charger is also undergoing continuous
further development.
The paper describes the individual development steps, which can
be divided into four stages. Particularly good results can be
obtained with forced-induction engines incorporating four valves
per cylinder.
Compared with naturally aspirated engines, forced-induction
spark-ignition engines place significantly greater demands on the
engine ancillary systems. The higher output levels necessitate the
use of inter-cooling, sophisticated ignition and injection systems,
heat resistant materials and more efficient cooling, all of which
make turbo-charged engines more expensive. The most suitable
applications are thus primarily in the performance car category, or
for fast touring saloons.