Scavenging (automotive)
Under Scavenging (English dispel ) is the operation of an internal combustion engine, in which the opening times of the intake and exhaust valve partially overlap. Characterized flushed a part of the cold fresh air sucked in the cylinder, the hot exhaust gas in the exhaust manifold, whereby the filling substantially improved compared to the conventional operation.
Due to the increased mass flow in the exhaust system to improve the responsiveness of the turbocharger especially at low engine speeds. In addition, the high oxygen supply favors the afterburning of the exhaust gases. Scavenging is thus helping to reduce the so-called " turbo lag ".
Requirements
Prerequisite for the utilization of the scavenging effect are variable valve timing, direct fuel injection and high-temperature resistant materials for exhaust manifold and turbocharger.
Variable control times are necessary, since the scavenging effect is desired only at low engine speeds. At higher speeds, the exhaust amount is enough even without this effect, to bring the turbocharger to the desired speed. The variable valve timing is achieved by the cam phase converter which reduce the overlap of the timing of the rotational speed increases. They are controlled by the engine electronics.
The direct injection ensures that the fresh gas is not mixed when entering the cylinder with fuel, as would be the case with petrol engines or engines with manifold injection. This results in no undesired scavenging losses, so the leakage of unburned gasoline into the exhaust manifold.
In the afterburning of the exhaust gases, temperatures up to 1000 ° C. Therefore, the exhaust manifold and the turbocharger must be made of materials that can withstand these temperatures permanently.
Effects
The scavenging effects two desirable effects: For one, the afterburning of the exhaust gases leads to fresh air to better emission values , on the other hand, the increase of the turbocharger speed (due to the increased exhaust gas enthalpy ) at low engine speed to a higher charge pressure and thus to a better filling of the cylinder with fresh gas, wherein reducing the tendency to knock. This increases the efficiency of combustion and hence the torque and the power of the engine.
Meaning in the English language
In English, scavenging has another, original meaning in engine technology: It denotes the gas exchange in the cylinders of an internal combustion engine generally, notably the flush of a two-stroke engine with fresh gas.
External links and sources
Alfa Romeo is in the 1.8 TBi engine for the first time scavenging method a, ATZ online 12 May, 2009
- Internal combustion engine