Turbocharging and Turbulence

Turbochargers as per Michael Mayer's "Abgasturbolader"

fig. 1 Pulse turbocharging scheme
One of the main objectives of the development of diesel engines with turbochargers for trucks and buses, is to provide high torque even at low revs. Pulse turbocharging has become the most improved method for commercial vehicles with diesel engines (Fig. 1). Much smaller manifolds than those used in turbochargers with constant pressure, allow almost complete utilization of the kinetic energy of the exhaust gas.

Pressure in the pipes is constant for a short time, that is why only in multi-cylinder engines it is possible to combine the exhaust pipe of these cylinders in which the pistons are not moving opposite to one another during the cycles of filling and discharge. In the six-cylinder engine, two groups of three cylinders are connected to the turbine. Exhaust gases from each group of cylinders power the turbine wheel (twin turbine).

Single exhaust manifolds and single entry turbines are mainly used in cars and exhaust gas pulses attenuation is achieved by use of compact piping system. Pulses are the impermanence of the exhaust gas pressure in the exhaust manifold. It fluctuates because strokes of release in the individual cylinders do not coincide in time and are also short. The more cylinders the engine has, the more pulses are smoothed because strokes overlap.

fig.2 Car turbocharger features 
In constant pressure turbo engines the pulse pressure attenuation is achieved by use of relatively large manifolds, so at higher engine speed more exhaust gases at lower pressure can enter the turbine. Fuel consumption is reduced while the engine is able to throw the exhaust for less reciprocating pressure. This type of solution disadvantage is significantly less torque achieved at low rpm. For this reason, constant pressure turbocharging is mostly used in engines operating at a steady mode, i.e. those that do not need a torque increase by acceleration (such as large marine engines, generators and industrial engines). Operating mode of the turbocharger is illustrated mostly by graphics (Fig. 2).

You can download the file here.