The charging can occur through the pressure of the exhaust gas flow (turbo charger), a mechanical connection with the crankshaft, a compressor (Roots blower and a G-supercharger), or direct contact of the exhaust gases with the fresh gases and control by mechanical connection (comprex charger). The high temperatures caused by the compression make air-to-air cooling, or cooling of the air heat-exchanger between compressor and engine-air collector, absolutely necessary for the efficiency.
Charging is mostly more favourable than increasing the displacement
Basically, charging means more air, and with it, more oxygen, is pumped into the cylinders instead of being sucked in, and thereby the filling is improved. The engine power and the torque also increase in the important lower RPM range without increasing the cubic capacity. In addition, both fuel consumption and emission are lowered. This however, mostly only in comparison to a conventionally aspired engine with the same performance but having a larger displacement. In comparison to a conventionally aspired engine with the same displacement, these values rise slightly. There are exceptions, if, e.g., the charging is not used to increase the performance of the diesel engine, rather, e.g., for the exhaust gas improvement, only more air flows through the engine.
Charging means, first and foremost, always a little higher power loss. Also the turbocharger does not receive the driving energy gratis due to the back pressure increase in the exhaust gas system. With the compressor however, more performance is certainly diverted. Properly used within the engine management, these losses can even be converted into profits, e.g., the motor driven geometrical compression caused by very late closing of the intake valve, is clearly lowered and is compensated by the charging. This can lower, by quickly withdrawn boost pressure, operational loss through needlessly high compression under certain working conditions. It is important that through this regulation, a conformance to the compression of the petrol-engine knock-limiting is possible under various working conditions.
If one wants to divert only a relatively small amount of performance for the charging, one would rather choose turbo-supercharging. High adjustment speeds, e.g., with VTG-chargers and small construction units reduce the most essential disadvantage, the delayed response characteristic (turbo-lag) of turbochargers. The more suitable candidate for charging, still seems to be the diesel engine, maybe because hardly anything disturbs the free path of the air to the combustion chambers. With the petrol engine one has the impression that the compressor is asserting itself. Also here there are already vehicles with a VTG-charger. However, smaller vehicles with especially low consumption, will remain, also for economic reasons with conventionally aspired engines.
The charger is looked at by some experts in the motor technology field, as a second engine. An interesting theory, particularly because apparently Ferrari had this, even with fuel injection in the compressor. Then, e.g., the turbocharger becomes a real gas turbine, which then shares the work with the pistons.As you can see, the charging confusion plays quite a bit of havoc with the doctrines of motor technology. One of them is, that there is no substitute for cubic capacity. Also the established compression limits from 9:1 to 12.5:1 for petrol engines, are no longer valid because one can use a boost-pressure which is graded for various operating conditions. Nowadays, apart from the geometrical,- a dynamic compression is also available. And, if you think about it, apparently there have been boost pressures of up to 5 bar in racing engines which have exceptionally short-lives... 03/08
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