 Diesel engine 2
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The basic technology of direct injection has been known for a very long time. There are drawings by Rudolf Diesel that envisage injecting diesel fuel directly into the combustion chamber. It just couldn't be implemented
because the force of the pressure increase of the fuel already burning during injection was simply too great.
It was not until a good half a century later that the MAN company succeeded in creating a direct injection system using the 'center sphere process' (picture above). What is striking in their description is the measures taken
to limit the problem described. The fuel was largely distributed over the wall of the ball in the piston. There it was supposed to burn as slowly as possible.
Only part of the fuel was distributed through the air so that combustion could take place. For military use it was even further developed into a multi-fuel engine. With a type of spark plug it was now given the name 'FM' for
externally-supplied ignition. The development that began in the 1940s was crowned by series production that began only 15 years later.
Those who were able to avoid the losses caused by pressure in the secondary combustion chamber were rewarded with, among other things, higher efficiency. However, extensive modifications were also required. This
initially affected the injection pump, which now worked at a much higher pressure. Measures were also taken to swirl the intake air, initially as a welded-on sheet metal part on the valve.
At Mercedes, one of the first trucks with direct injection was called the 1620 in 1963, its predecessor the 334. The power increased slightly from 147 kW (200 hp) to 154 kW (210 hp). My father had one of these in his small
fleet and was unhappy about the frequency of repairs. This shows that the introduction of direct injection was by no means without difficulties.
kfz-tech.de/PME115
Giving a truck engine a boost with turbocharging, mainly of course its torque, has a very long tradition, as can be clearly seen in the Ford V8 two-stroke engine above. So before the additional fuel-saving use of
turbochargers began in trucks, they had long since conquered the world of large engines. This meant that the truck engine was pretty much complete.
The car, on the other hand, was already running as a diesel with turbocharging, but without direct injection, torque and power development were still pretty much lacking. It was only when the VW Group, initially led by Audi,
introduced direct injection in cars that its triumph began.
This type of injection was initially implemented with a radial instead of an axial piston pump because the latter could not withstand the high pressure. Then the entire group switched to the pump-nozzle solution. We don't
want to spend too much time on this because VW was the only one to do this and they finally abandoned it for trucks too.
Typical for the pump nozzle is the lack of a central high-pressure pump. The pressures are created where there used to be only injection valves. The required force comes from the camshaft(s), which are given an
additional cam. This naturally puts additional strain on the valve train. The delivery rate is, however, controlled electrically. The cylinder head must be redesigned for the system.
The pump nozzle was noticeable at the time because of the somewhat rough engine running. However, it finally died due to the fact that injection is only possible during the cam lift, which significantly restricts post-
injection, for example. A master of almost unlimited possibilities in this case is Common Rail, which has now also become established in trucks.
Pressure is generated centrally here, although not always the 2,500 bar that is often mentioned. Since something like this costs energy, one has learned very precisely which pressure is useful in which operating ranges.
This can also be less than 400 bar when starting. Together with an electric internal tank pump, the system is complete except for numerous sensors and actuators.
The many possible injections during a complete injection process are very important from the very first. Bosch says there are up to eight, but of course that also depends at least on the engine speed. But here we have it
again, the problem of taking away the active force from the diesel engine during injection. However, new requirements have long been added regarding the exhaust emissions of such an engine.
The one problem is to avoid soot, especially when accelerating. The particle filter has been doing this for some time, although it probably needs to be serviced after a long period of use. But it does its job excellently. The
diesel scandal forced manufacturers of cheaper cars to solve the second problem.
But it is also difficult because whenever the diesel engine is running at its most efficient level, its combustion gets quite hot and it therefore emits a lot of nitrogen oxides. However, if you install an SCR catalytic converter,
you can get the problem somewhat under control. However, it requires AdBlue and this liquid is usually not enough for the time between inspections.
The truck has had to catch up quickly in everything, which has almost doubled the installation space of its engine. The dilemma of the diesel engine: At the very moment when it has practically reached its highest quality in
terms of range, exhaust quality, torque, power and, above all, CO2 consumption, it has to disappear.
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