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 Turbocharger
kfz-tech.de/PDM60
Such a truly awesome device, we'd like to open this extremely important chapter with it. Please don't leave it too early, because we have one more highlight in store for you at the end that you absolutely cannot miss. This is
where the diesel will finally contract a certain affinity with a modern F1 engine.
Historically, it all began quite innocently. Engineers interested in racing used such a device to extract incredible performance from racing engines. Among the many possible examples, BMW's F1 engine (pictured below)
was just one of it, built from 'hung' (a term used in the butcher's trade) cast iron engine blocks from the BMW 1500. Obviously, they had to be used and of a certain age to withstand the strains BMW intended for them.
It was the era of qualifying engines that were so thoroughly tuned that they clearly couldn't last a full race. They were used only to secure the best starting position, to secure the most favorable starting position for the race.
It's hard to believe, but BMW's racing department allegedly boosted this engine with up to 5 bar of pressure. It's a miracle that it even managed a full lap.
Overall, the turbocharger didn't have a good reputation at the time. While its design was simple, the more power an engine developed with it, the more pronounced turbo lag became. Simply put, this means a delay
between accelerating and the increase in torque; the lower the engine speed, the worse it becomes. Imagine how difficult it is to control the accelerator pedal with this delay when you want to ease off the throttle before a
corner and accelerate through it.
This behavior isn't quite as detrimental for a diesel engine, because even back then, they didn't have a throttle valve, which could have caused a blockage in the compressor section of the turbo and caused the engine
speed to drop significantly. Turbochargers are generally phlegmatic, rather reserved when it comes to instantaneous power. And so the turbocharger conquered the truck engine market. One prerequisite for this was the
wastegate (pictured below), a valve that opens the pressure side of the turbocharger to the exhaust system, which, incidentally, had already been around for some time.
The innovation was to virtually oversize the turbocharger, giving it much more charging capacity than the engine needs. And to prevent it from self-destructing, the wastegate reduces boost pressure above a certain level.
Since then, the torque curves have no peak, but rather a horizontal line extending over a wider speed range. For example, 2000 Nm at 1200-1700 rpm was now specified.
Thanks to this new control system, the increased torque is now exactly where it's needed. However, such a diagram doesn't indicate the time delay with which it is generated. You determine this on the test bench, so you
essentially bring the engine speed to 1200 rpm and try to maintain it by gradually increasing the throttle, while demanding more and more torque from the engine through a kind of brake. Finally, you note the torque at 1200
rpm at which the engine can just barely maintain the speed at full throttle.
As you can see, there's no mention of response time here; turbo lag doesn't appear in a normal power or torque diagram. But you're probably also aware that such a huge engine in a heavy truck, with as much
displacement per cylinder as a diesel car in total, reacts relatively sluggishly anyway, especially when it's towing a total of 40 tons. With a truck like this, it's not so much about acceleration, but rather about maintaining
speed and thus the gear on the beginning of a hill for as long as possible.
So, multiple gears might also make sense for regular long-distance trucks. What did the turbocharger initiative lead to? You could call it the first downsizing, which means that the six-cylinder engines are now among
themselves, effortlessly delivering performance previously considered only achievable with V8 engines, and with significantly lower fuel consumption. Incidentally, as is often the case, the Americans had achieved a leading
position in multi-cylinder engines. I had the honor of getting to know a Peterborough with two six-cylinder engines side by side in US, with two crankshafts, mind you. The owner/driver said the fuel consumption wasn't all
that high.
So, downsizing perhaps made the engines a bit more "lively" despite the turbo lag. And, of course, with a workhorse, one shouldn't forget the now more favorable payload-to-unladen weight ratio. And once the difficulties
with the significantly higher pressure in trucks were overcome, the idea of applying this principle to cars began. Cars had just adopted direct injection, already quite belatedly, and turbocharging was now being explored
there as well.
However, the problems with turbo lag become more apparent here. Modern cars maintain speed on (highway) hills even if the owner hasn't chosen the most powerful engine. But accelerating, for example, when
overtaking, is something a car should be able to do instantly. The familiar period of suffering follows, which actually continues to this day. When testers bring up this point, you have to listen very closely to still detect a hint of
criticism. But it's still there.
At least the variable turbine geometry does represent a small leap in quality. Instead of a wastegate, boost pressure is adjusted directly in the turbine section using adjustable guide vanes. The inline six-cylinder engine is
also suddenly popular because an entire battery of turbochargers (pictured below) can be mounted on its intake side. Just one small one isn't enough with a displacement of three liters. So, a small one and a large one,
and the paths are cleverly opened up so that the large one, with its certain inertia, only comes into play when the airflow is higher. Or split into two smaller ones for three cylinders each. Or one with two compressor
chambers. It will probably end with three turbochargers for the time being.
kfz-tech.de/PDM56
Gasoline engines that want to benefit from this principle and the fuel-efficiency advantage combine a turbocharger and a supercharger. Unfortunately, the Comprex supercharger (pictured below) hasn't been further
developed. It would certainly have provided an answer to the problem of turbo lag. To date, it hasn't been reliably eliminated. And now, when everyone would prefer to abolish the diesel engine, there's suddenly hope, albeit
only in the form of a prototype.
For the second time, Formula 1 has paved the way with an additional electrically driven turbocharger. If its electric motor can overcome the enormous heat problems, it could be a hit, assuming anyone is still interested in
further developing the diesel engine. In principle, it doesn't matter whether the engine runs on 48 volts or a higher voltage. But if not only a diesel engine is currently struggling to overcome its turbo lag due to insufficient
exhaust pressure, then an electric motor rapidly driving the connecting shaft could provide enormous pressure in the truest sense of the word.
The problem with this electric motor is the enormous amount of heat it generates.
kfz-tech.de/PDM57
Borg Warner hopes to achieve even more: not leave the reduction of the often six-figure engine speed to the charger itself, but use it to generate electricity through recuperation. The turbine can now be made larger again,
resulting in a wider power range with the same basic engine. The possibilities for ventilating the engine independently of exhaust pressure and improved interaction with exhaust gas recirculation are still open.
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