Turbo charger’s
Operating principle
Otto and diesel cycle engines rely on the downward stroke of a piston to create a low-pressure area (less than atmospheric pressure) above the piston in order to draw air through the intake system. With the rare exception of tuned induction systems, most engines cannot inhale their full displacement of atmospheric density air. The measure of this loss or inefficiency in four stroke engines is called volumetric efficiency. If the density of the intake air above the piston is equal to atmospheric, then the engine would have 100% volumetric efficiency. Unfortunately, most engines fail to achieve this level of performance. This loss of potential power is often compounded by the loss of density seen with elevated altitudes. Thus, a natural use of the turbocharger is with aircraft engines.As an aircraft climbs to higher altitudes the pressure of the surrounding air quickly falls off. At 5,486 m (18,000 ft) the air is at half the pressure of sea level, which means that the engine will produce less than half-power at this altitude.also automobiles used in hills or high altitude.
The objective of a turbocharger, is to improve an engine's volumetric efficiency by increasing the intake density. The compressor draws in ambient air and compresses it before it enters into the intake manifold at increased pressure. This results in a greater mass of air entering the cylinders on each intake stroke. The power needed to spin the centrifugal compressor is derived from the high pressure and temperature of the engine's exhaust gases. The turbine converts the engine exhaust's potential pressure energy and kinetic velocity energy into rotational power, which is in turn used to drive the compressor.
A turbocharger may also be used to increase fuel efficiency without any attempt to increase power. It does this by recovering waste energy in the exhaust and feeding it back into the engine intake. By using this otherwise wasted energy to increase the mass of air it becomes easier to ensure that all fuel is burnt before being vented at the start of the exhaust stage. The increased temperature from the higher pressure gives a higher carnot efficiency.
Division of turbocharger
All turbocharger applications can be roughly divided into 2 categories, those requiring rapid throttle response and those that do not. This is the rough division between automotive applications and all others (marine, aircraft, commercial automotive, industrial, locomotives). While important to varying degrees, Turbo lag is most problematic when rapid changes in engine performance are required.
Turbo lag
Turbo lag is the time required to change speed and function effectively in response to a throttle change. For example, this is noticed as a hesitation in throttle response when accelerating from idle as compared to a naturally aspirated engine. Throttle lag may be noticeable under any driving condition, yet becomes a significant issue under acceleration. This is symptomatic of the time needed for the exhaust system working in concert with the turbine to generate enough extra power to accelerate rapidly
How to reduce turbo lag
1. by lowering the rotational inertia of the turbocharger; for example by using lighter, lower radius parts to allow the spool-up to happen more quickly. Ceramic turbines are of benefit in this regard and or billet compressor wheel.
2. by changing the aspect ratio of the turbine.
3. by increasing the upper-deck air pressure (compressor discharge) and improving the wastegate response; this helps but there are cost increases and reliability disadvantages that car manufacturers are not happy about.
4. by reducing bearing frictional losses; by using a foil bearing rather than a conventional oil bearing. This reduces friction and contributes to faster acceleration of the turbo's rotating assembly.
5. Variable-nozzle turbochargers greatly reduce lag.
6. by decreasing the volume of the upper-deck piping.
7. by using multiple turbos sequentially or in parallel.
(FOR BETTER UNDERSTANDING REFER VIDEO)
(FOR BETTER UNDERSTANDING REFER VIDEO)
Categories:
automobile,
mechanical