What is a turbocharger?
Ever heard of the word turbochargers? Sound familiar?
You likely did so when you were having a discussion about sports cars or race cars! Turbochargers can also be found in large diesel engines. The basic purpose of a turbocharger is to increase the vehicle’s horsepower by a notable amount but without adding excess weight to the whole car itself.
We already know that the lighter the car, the faster it will move, and a turbocharger does just that. Its benefits have made it hugely popular over the years. A turbocharger basically compresses the air flowing into a cylinder. This translates to the engine pushing in more air to the cylinder.
More air, in turn, means that more fuel can be added, which means we can generate more power with each explosion inside a single cylinder. Overall there is an increase in power, this is how turbochargers work.
They use the exhaust flow from the engine and spin a turbine which spins an air pump, in turn, it is stated by the ideal gas law that that if all the variables are constant the pressure is directly proportional to the temperature. Hence when the air is then compressed and the pressure increases, the temperature does too. This is one of the flaws turbochargers have which results in a significant rise in temperature.
The heat and the spin
Diving deeper we have seen that turbo peaks between 80,000 and 200,000 RPM!
It depends on a variety of factors such as the size of the turbine, the weight of the rotating parts as well as the boost pressure developed and the compressor design. Most of them use fluid bearings because it is impossible for standard ball bearings to bear the high rotational speeds generated by the turbine.
A layer of free-flowing oil which is acquired from the engine oil suspends and cools the moving parts down. This layer of oil needs coolant before being passed through the engine. Some of the turbochargers use staggeringly precise ball bearings which are dunked in fluid dampened cavities.
Because of very low friction, the turboshaft can be made with light materials which in turn reduces the boost lag or the turbo lag. Water-cooled turbocharges are also available in the market. The future of turbocharging includes foil bearings which totally eliminates the need for cooling systems we discussed previously.
This will be a huge leap forward as the chances of failure will reduce significantly. As we already know the turbocharger produces a lot of waste heat, this might be a problem for cars that were not designed to handle excess heat. The compression ratio along with the expansion ratio results in a slight fall in thermal efficiency which finally leads to the overall fuel efficiency being impacted negatively.
There have been many innovations in this regard, for example, the 2.0L FSI turbo engine from Audi brings in a lean and burn direct injection technology which can save fuel in low load conditions. The airflow management is achieved through a very complex system that includes mobile parts and sensors inside the chamber itself which allows it to use a stratified charge and amazing atomization. The direct injection system also consists of a charge cooling effect which enables it to use higher compression ratios and boost pressures than a typical port injection turbo engine.
Diesel and Turbos
Diesel engines nowadays and turbocharging go hand in hand with each other. We can find turbocharged diesel engines in common automobiles such as trucks and locomotives for heavy machinery applications. Non-turbo charged diesel engines hardly exist in the market anymore and might become obsolete in the near future. Some of the reasons for which diesel engines are particularly suitable for turbocharging are:
- The power to weight ratio in a naturally aspirated diesel engine is lower than gasoline engines. Turbocharging increases the power to weight ratio.
- Diesel engines are already built-in with a robust fashion because they run at high compression ratios and high temperatures beforehand. Thus, they need only a little bit of modification to handle a turbocharger. Gasoline engines, on the other hand, need a lot more modification compared to diesel engines.
- The engine speeds in diesel engines have a narrower band in which they operate making the operating characteristics of a turbocharger over the rev range a much better bargain than that of gasoline-powered engines.
- During cylinder charging, diesel engines blow only air into the cylinders and squirt fuel only when the intake valve is closed and the compression has begun. In gasoline engines, both the fuel and air come simultaneously during the intake cycle and are both compressed during the compression cycle. Forced induction engines have higher intake charge temperatures, which reduces the compression possible in gasoline engines. Diesel engines are not sensitive to this.
Turbocharging has a whole history which started from when it was invented by Alfred Buchi, who had been working on steam turbines. Post that, this technology has been taken forward to amazing feats ranging from ships to aircraft.
Racing cars have been inspired by technology and it is simply astonishing to see how a simple thought has translated into complex technologies that have benefited us hugely. The few flaws which the technology has got have brought researchers to create systems to eliminate them as much as possible. They have gone to great heights at succeeding to control temperatures generated at 200,000 RPM, which exactly shows how far we have come forward.
Turbos surely have a place in the future and it will be really interesting to see what the future brings to us!