What is a Supercharger
Before learning about supercharger let us first understand the factors on which power output of an engine depends.
The power output of a naturally aspirated engine depends on following things.
- Amount of air inducted into the system
- Extent of utilization of inducted air
- Speed of the engine
- Quality of fuel used
- Thermal efficiency of the engine
From the above factors which govern power output of an engine we can find that quality of fuel used and thermal efficiency is largely independent things.
Quality of fuel is set by a country wide standard and increasing thermal efficiency of engine is not that easy. All we can do to increase power output of an engine is to consider first three factors.
Every fuel needs oxygen to burn. Same is the case with the fuel which is burnt inside the automotive engine.
Higher the amount of oxygen available for burning better will be the combustion. This will result in better fuel efficiency and more power availability to the power train.
Most of the engines we see in our daily life are naturally aspirated. It means the air available to them for burning, comes to engine at ambient pressure.
Since the time available for air suction is very less for a modern day high speed engine. It generally happens that the air inlet valve closes before the engines breaths to its full capacity. It results in less air available for combustion. Which ultimately produces inefficient fuel burning.
The breathing efficiency of an engine is the ratio of actual air available for combustion and the actual volume of engine cylinder.
Breathing efficiency = (actual air available for combustion)/ (actual volume of engine cylinder)
Naturally aspirated engines generally have poor breathing efficiency. To solve the problem of poor breathing efficiency, scientists and engineers came up with a solution which is economical and suitable of normal engines.
The solution was turbocharger.
A turbocharger is a device which increases breathing efficiency of engines by sending compressed air to it.
A turbocharger is a combination of turbine and blower. Turbine takes power from exhaust gases and gives that power to blower. Blower uses that power to send compressed (dens) air to the engine.
A turbocharger is a very economical solution for increasing breathing efficiency of an engine. Since it derives power from the exhaust gases.
Turbochargers are good for normal engines, like our routine cars, trucks and buses. But they are not efficient for racing cars. The main reason is that they derive power from exhaust gases and that power is not sufficient for racing cars.
For racing cars, we need a dedicated air compressor which derives its operating power from an electric motor or directly from the engine.
The device which performs the above functions is known as supercharger.
- Variable ratio supercharger
Supercharging of an engine can be summarized as
- Supercharging increases power output of an engine without increasing fuel consumption.
- Certain amount of power generated by the engine goes for the compression of air but overall power output is more.
- The engine which is to be used with a supercharger is made to withstand higher forces due to supercharging.
- Due to increased pressure and temperature of the combustion process, tendency of detonation increases. Therefore, fuel with better antiknock quality should be used.
Advantages of supercharging
- Higher power output
- Greater induction of charge mass
- Better atomization of fuel
- Better mixing of fuel and air
- Better scavenging products
- Better torque characteristics over whole range
- Quick acceleration of vehicle
- Complete and smooth combustion
- Even fuel with poor ignition quality can be used
- Improved cold starting
- Reduced exhaust smoke
- Reduced specific fuel consumption
- Increased mechanical efficiency
- Smooth operation and reduction in diesel knock tendency
Disadvantages of supercharging
- Increased detonation tendency in SI engines
- Increased thermal stress
- Increased heat loss due to increased turbulence
- Increased gas loading
- Increased cooling requirements of the engine
Attribution: By DVespremi – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=60188885