Mazda intake system 3.
Boosting the engine in the case of a diesel engine results not only from improving performance or power, but also from the basic laws of physics and chemistry.. Burning fuel requires a specific amount of oxygen. Diesel oil needs much more of it than in the case of gasoline engines, because the calorific value of the fuel is much higher. Burning one diesel molecule requires approx 15 oxygen particles (30 atoms). We then talk about complete combustion. If there is no air (oxygen) then the engine starts smoking (incomplete combustion – instead of CO2, only C) but this involves a limitation of the power obtained. So you need to add a little more to the engine “oxygen into the lungs”. In the engine “ordinary” (without turbine) air enters through simple suction, but this is no longer sufficient for effective combustion in diesel. Therefore, charging systems are used – compressors of various types (compressor, comprex, turbine).
The most popular supercharging system in the world is a turbine driven by a stream of exhaust gases, although for many years the Mercedes company has been installing Roots compressors simply driven by a belt (just like the alternator).
The turbine sucks in air and compresses it (the compressed air pressure is usually approx. 0,85-1,2 only – in the case of DiTD – pressure starts from 0,35 and grows slowly to 0,85). A side effect is an increase in air temperature, because passing through the turbine blades it cools it and the compression itself produces heat (like a bicycle pump). The air is usually cooled in a radiator called an intercooler (abbreviated as IC), which uses several physical phenomena – but the most important thing is this, that more cold air can fit in the same unit of volume than heated air. So more oxygen flows into the cylinder – combustion can be complete in a larger volume, so the power increases (almost for free) and the smoking significantly decreases. Only advantages, before the turbine (usually) the pneumothorax hose is connected (removal of oil vapors from the engine). Turbine “they had” also these oil vapors (and if it is very worn, it also adds fresh oil from under its own seals) and it is all pushed under pressure into the inlet manifold. And at that moment everything would be great, if it weren't for two elements, which after some time (in every TDI, DiTD, TDVI, D4D, TDCI etc.) have nasty side effects.
The system becomes clogged from the IC to the valves. This is influenced by two phenomena:
– Worn out turbine or something like that, which is not cooled on its axis (when switching off) “turns brown” oil residues, which, after restarting the engine, squeezes under the seals in the form of carbon deposits. Over time, they push outwards and run through the air, clogging the IC (it looks like sand, it is very insoluble and seals the channels perfectly, difficult to fall asleep). “Frying the oil” is called for larger engines and turbines – coking on the shaft and is a classic occurrence of this type of solutions.
– presence of EGR – valve, which is intended to re-burn exhaust gases (the ecology): after leaving the engine, exhaust gases contain 10-15% oxygen, so they are directed back to the intake manifold – so they carry not only oxygen but also soot. The soot alone would be survivable, if not for this, that when mixed with oil vapors, they form a compact mass and settle in the form of a nasty slime on the walls of the intake manifold. At high mileage, they can almost completely clog the air supply to the cylinder (which ends with the engine seizing up). Intake system obstruction (most are the IC and the collector) or its leakage (system or it is catching air from somewhere before, next to the filter or compressed air escapes through the sides) causes a drop in power, smoke, increased fuel consumption (not always!) and other strange phenomena. A stuck EGR valve also causes smoke and often a loss of power. This also results in characteristic results in CR motorcycles “scratching” in terms of 1600-2000 rpm.