In this series we will talk about forced refueling and the development of internal combustion engines.
He is a prophet in the car tuning scriptures. He is the savior of the diesel engine. Gasoline engine designers neglected this phenomenon for many years, but today it is becoming ubiquitous. This is a turbocharger ... More advanced than ever.
His brother, a mechanically driven compressor, has no plans to leave the stage either. Moreover, he is ready for an alliance that will lead to perfect symbiosis. Thus, in the turmoil of modern technological rivalry, representatives of two prehistoric opposing currents have united, proving the maxim that the truth remains the same regardless of the difference in views.
Consumption 4500 l / 100 km and a lot of oxygen
The arithmetic is relatively simple and based solely on the laws of physics ... Assuming that a car weighing about 1000 kg and hopeless aerodynamic drag overcomes 305 meters from standstill in less than 4,0 seconds, reaching a speed of 500 km / h at the end. on the site, the engine power of this car must exceed 9000 hp. The same calculations show that inside the section, the rotating crankshaft of an engine rotating at 8400 rpm will only be able to turn about 560 times, but this will not prevent the 8,2-liter engine from absorbing about 15 liters of fuel. As a result of another simple calculation, it becomes clear that, according to the standard rate of fuel consumption, the average consumption of this car is more than 4500 l / 100 km. In a word - four thousand five hundred liters. In fact, these engines do not have cooling systems - they are cooled by fuel ...
There is nothing fiction in these numbers ... These are great, but quite real values from the world of modern drag racing. It would hardly be correct to classify cars participating in races with maximum acceleration as racing cars, since surreal four-wheeled creatures, shrouded in blue smoke, are incomparable even with the cream of modern automotive technology used in Formula 1. Therefore, we will use the popular name "dragsters". - Undoubtedly interesting in their own way, unique cars, delivering unique sensations both to fans outside the 305-meter track, and to pilots, whose brain, at a fast acceleration of 5 g, probably takes the form of a color two-dimensional image on the back wall of the skull
These dragsters are arguably the most famous and most impressive variety of popular motorsport in the United States, belonging to the controversial Top Fuel class. The name is based on the extreme performance of the nitromethane chemical that hellish machines use as fuel for their engines. Under the influence of this explosive mixture, the engines operate in overload mode and in just a few races turn into a heap of unnecessary metal, and because of the propensity of fuel to continuous detonation, the sound of their operation resembles the hysterical roar of a beast counting the last moments of your life. Processes in engines can only be compared with absolute uncontrollable chaos, bordering on the pursuit of physical self-destruction. Usually one of the cylinders fails by the end of the first section. The power of the engines used in this crazy sport reaches values that no dynamometer in the world can measure, and the abuse of machines really exceeds all the limits of engineering extremism ...
But let's get back to the heart of our story and take a closer look at the properties of nitromethane fuel (blended with a few percent balancing methanol), which is without doubt the most powerful substance used in any form of car racing. activity. Each carbon atom in its molecule (CH3NO2) has two oxygen atoms, which means that the fuel carries with it most of the oxidant required for combustion. For the same reason, the energy content per liter of nitromethane is lower than per liter of gasoline, but with the same amount of fresh air that the engine can suck into the combustion chambers, nitromethane will provide significantly more total energy during combustion. . This is possible because it itself contains oxygen and therefore can oxidize most of the hydrocarbon fuel components (usually non-combustible in the absence of oxygen). In other words, nitromethane has 3,7 times less energy than gasoline, but with the same amount of air, 8,6 times more nitromethane can be oxidized than gasoline.
Anyone familiar with combustion processes in a car engine knows that the real problem with squeezing more power out of an internal combustion engine is not to increase the flow of fuel into the chambers - there are enough powerful hydraulic pumps for that. achieving extremely high pressure. The real challenge is to provide enough air (or oxygen) to oxidize hydrocarbons and ensure the most efficient combustion. That is why nitrogen is used in the fuel of dragsters, without which it would be absolutely unthinkable to achieve results of this order with an 8,2 liter engine. At the same time, cars operate with fairly rich mixtures (under certain conditions, nitromethane can begin to oxidize), due to which part of the fuel is oxidized in the exhaust pipes and forms impressive magic lights above them.
Torque 6750 Newton meters
The average torque of these engines reaches 6750 Nm. You have probably already noticed that there is something strange in all this arithmetic ... The fact is that in order to reach the specified limit values, every second an engine operating at 8400 rpm must suck no more, no less than 1,7 XNUMX cubic meters of fresh air. There is only one way to do this, and that is force filling. The main role in this case is played by a huge classic mechanical unit of the Roots type, thanks to which the pressure in the collectors of the dragster engine (based on prehistoric Chrysler Hemi Elephant) reaches a staggering 5 bar.
To better understand what loads are involved in this case, take as an example one of the legends of the golden age of mechanical compressors - the 3,0-liter racing V12. Mercedes-Benz W154. The power of this car was 468 hp. with., but it should be borne in mind that the compressor drive took a whopping 150 hp. with., not reaching the specified 5 bar. If now we add 150 thousand to the account. with., we come to the conclusion that the W154 really had an incredible 618 hp for its time. You can judge for yourself how much real power the engines in the Top Fuel class achieve and how much of it is absorbed by the mechanical compressor drive. Of course, using a turbocharger in this case would be much more efficient, but its design could not cope with the extreme heat stress from the exhaust gases.
Start of contraction
For most of the history of the automobile, the presence of a forced ignition unit in internal combustion engines has been a reflection of the latest technology for the corresponding stage of development. This was the case in 2005 when the prestigious award for technological innovation in the automotive industry and sports, named after the founder of the magazine, Paul Peach, was presented to the head of VW engine development Rudolf Krebs and his development team. application of Twincharger technology in a 1,4-liter petrol engine. Thanks to the combined forced filling of the cylinders using a synchronous system of mechanics and a turbocharger, the unit skillfully combines the uniform distribution of torque and the high power typical of naturally-aspirated engines with a large displacement with the economy and economy of small engines. Eleven years later, VW's 11-liter TSI engine (with slightly increased displacement to compensate for its efficient contraction due to the Miller cycle used) now features much more advanced VNT turbocharger technology and is again nominated for a Paul Peach Award.
In fact, the first production car with a petrol engine and turbocharged variable geometry, Porsche The 911 Turbo was released in 2005. Both compressors, developed jointly by Porsche R&D engineers and their colleagues at Borg Warner Turbo Systems, VW use the well-known and long-established idea of variable geometry in turbodiesel units, which has not been implemented in gasoline engines due to a problem with higher (about 200 degrees compared to diesel) average exhaust gas temperature. For this, heat-resistant composite materials from the aerospace industry were used for gas guide vanes and an ultra-fast control algorithm in the control system. Achievement of VW engineers.
The golden age of the turbocharger
After the 745i was discontinued in 1986. BMW for a long time they firmly defended their own constructive philosophy in the creation of gasoline engines, according to which the only "orthodox" way to achieve more power was to run the engine at high speeds. No heresies and flirting with mechanical compressors a la Mercedes (C 200 Kompressor) or Toyota (Corolla compressor), no bias towards VW or turbocharged turbochargers Opel... Munich engine builders favored high-frequency filling and normal atmospheric pressure, the use of high-tech solutions and, in extreme cases, a larger displacement. Compressor experiments based on Bavarian engines were almost completely transferred to the "fakirs" by the tuning company Alpina, which is close to the Munich concern.
Today BMW no longer produces naturally aspirated gasoline engines, and the turbocharged four-cylinder is already part of the diesel engine lineup. Volvo uses a combination of mechanical and turbocharging, Audi created a diesel engine with a combination of an electric compressor and two cascade turbochargers, Mercedes - a gasoline engine with electric and turbocharger.
However, before talking about them, we will go back in time to find the roots of this technological transition. We learn how in the XNUMXs American manufacturers tried to use turbo technology to compensate for the engine displacement caused by the two oil crises, and how they failed in those attempts. We will tell you about Rudolf Diesel's unsuccessful attempts to create a compressor engine. We will remember the glorious era of compressor engines in the 20s and 30s, as well as the long years of oblivion. Of course, we will not miss the appearance of the first production turbocharger models after the first major oil crisis of the 70s. Or for the Scania Turbo compound system. In short - we will tell you about the history and evolution of compressor technology ...
Text: Georgy Kolev