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  Physics - Air 1



Humans need air, admittedly at much shorter intervals than water, but water also more often than solid food. What about the internal combustion engine? Of course, it also needs air first and foremost, almost more frequently than humans and above all in larger quantities. If necessary, it could do without water altogether; it even produces it mostly in the form of steam.

Of course, the car can't do without air in other ways either, even if the cooling system has been largely converted to water or coolant in the meantime. There are the tyres, where one occasionally sees modest attempts to replace air with small, firm springs, for example. Or air as an element of the suspension, mainly in luxury cars.

And then there are the brakes of heavy trucks, which also need a certain amount of energy in case of need. Even if you wanted to switch the brakes to hydraulics, you would again need a fixed volume of air to maintain the pressure. This is where the wonderful property of the continuous compressibility of air comes into play.

We have probably forgotten applications, but we would like to slowly focus on air for the combustion engine. First of all, cooling, because that is dealt with more quickly. No, we won't deal with the actual air cooling now, there are many more or less wonderful pages on the internet about this, if you want to deal with the VW Beetle and its engine alone.

Almost unnoticed, a change has taken place here. Cooling by and through air is actually relatively common, just think of charge air and/or exhaust gas recirculation. But even a generator is usually air-cooled, the starter rather not, but that is precisely why it cannot tolerate longer operating times. If so, then the various oil coolers on the engine and, for example, the automatic transmission are also worth mentioning.


And where is the change now hidden? Quite simply explained by the intercooler, its presence was characterised by a tangle of pipes, from the compressor around the engine forward to the air-to-water cooler underneath for air through air and then back to the engine intake. Actually, one could already guess the resistances at that time, although some of the pipes were of quite large cross-section.

Above all, one suspected an even more delayed response. In any case, this arrangement is mostly old news. Now the coolant comes to a much shortened connecting line to cool the pressurised air column via a heat exchanger. Even the exhaust gas recirculation system is now equipped with such an additional system.

However, this is not necessarily without problems. BMW is currently struggling with a quite considerable recall. Inside such a heat exchanger, the hot exhaust gases ignited the antifreeze, causing entire cars to catch fire. Nevertheless, we maintain that air is still needed for cooling in a few areas of the combustion engine.

The situation changes completely when we consider the air used for combustion. It used to be called intake air, but those days are long gone. We don't have any statistics at hand, but we suspect that the supercharged engines are by far the majority, just by looking at their dominance in the Diesel sector.

What times were those when the only agony of choice was whether to let the engine suck in cool and thus oxygen-rich air or preheated air. The latter in winter, of course, but perhaps less warm as the operating temperature increased. This was also managed, for example, by thermostatically controlling a flap between the two intakes.

Thus the air reached the mostly sheet metal air filter relatively quickly. This by no means always consisted of a paper mesh, but could also contain oil-soaked metal wool or even a centrifuge, The latter, of course, only when operated in a particularly dusty environment. And that was it. At some point, the allocation to the various cylinders came, either before several carburettors or after just one.

Intake valve and then the air was at its destination. For the later course of history, it is perhaps worth mentioning that even then, of course, air escaped past the pistons into the space of the crankcase. crankcase. Don't worry, this air was usually deprived of its oil entrainment somewhere as high up as possible by a primitive spring and then released into the open air, not without still containing a certain amount of residual oil.

No, a brake booster of today's kind did not exist at that time, very rarely, e.g. a mechanically acting one at Rolls-Royce. Customers were expected to exert greater pedal forces and the self-reinforcement of the drum brakes at the front did the rest. The first pneumatically acting brake boosters were even set to boost so much that customers first had to practise on secondary routes in order not to scare off following traffic.

Since the introduction of this type of boosting, the area to look for the cause in case of secondary air has to be rethought. You know, false air, the scourge of sensible operation of internal combustion engines. They then do whatever comes to mind. Idle sometimes high, sometimes too low. A little more or less shaking, throttle response at random. An engine like that is a lot of fun.

As you can see, the pneumatic brake booster represents the first significant expansion of the area in which the air necessary for combustion or its remnants can be found. If air is sucked in, it can affect the booster itself or the line leading to it, and in extreme cases even a brake pedal that has not been adjusted correctly. At this point, please get into the habit of pushing the system limits as far as possible.








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