Future Transportation Systems - Decreasing Fuel Consumption and Exhaust Gas Emissions in Transportation - page 261

compressor compressor belt drive

magnetic
coupling

throttle

charged air
cooler

fresh air

crank-
shaft

waste gate

exhaust
gas

air filter flap ventilation

turbo-fill catalyst

Fig. 17.2 Use of a positive displacement compressor in a four-cylinder spark ignition engine

required high temperature resistance in turbines constructors use nickel-based steel
alloys [ 5 ].
Further devices are valves and pressure regulators for flexibly steering the
charging air and the additional use of a compressor with an electric booster pro-
viding compressed air from the air reservoir.

17.1.1.4 Compressor Technology

Turbochargers can be started only when the engine produces sufficient exhaust gas.
The turbo lag in the first seconds of start is an unfavorable side effect of this
technology. Positive displacement compressors improve the engine response
without significant delays or turbo lags. They need a direct drive, which is taken
off at the crankshaft; see Fig. 17.2 .
Positive displacement compressors usually run up to 2,000-2,400 rpm; the
turbocharger starts at higher rpm. Future compressors will need high temperature-
resistant materials, in the air intake as well, because they will operate with a higher
number of revolutions and therefore at a higher charge air temperature. Monitoring
emissions will become more important to achieve improved inspection and

maintenance under extremely raw operation conditions [ 6 ].
Engine performance due to fully loaded and optimized compressor technology has
increased by about 15% in the last years. However, the use of compressors also has
disadvantages, such as the higher fuel consumption and the delayed start of the
catalyst. The operation temperature of the exhaust gas after treatment system is higher
compared to the turbocharged system and an early aging of the catalyst is possible.
The combined use of a turbocharger and a compressor needs less space than
two turbochargers usually placed above the engine, because the turbocharger and
the compressor can be put between the cylinder heads. This construction has a
lower temperature in the engine compartment compared to two turbochargers.
A lower temperature with better aerodynamics partly compensates for the higher
fuel consumption.