Closing Remarks on Turbo-charging

P M V SubbaraoProfessor

Mechanical Engineering Department

New Ideas with Turbo-charging….

Turbine Sizing

• The selection of the turbine size is a bit simpler than the sizing of the compressor.

• Important to note that the turbine size effects boost threshold, turbo lag and fuel consumption .

• Boost threshold is the engine speed at which there is sufficient exhaust gas flow to generate positive (intake) manifold pressure, or boost.

• This is the time between the demand for an increase in power and the turbocharger(s) providing increased intake pressure, and hence increased power.

• The selection is basically just a balancing act.

• There are no complicated maps or processes used to select the turbine size.

Large Turbine

• Larger turbines, conversely, allow much more airflow through the compressor and reduce back pressure.

• Demands less enthalpy exhaust in manifold .

• Leads to higher boost thresholds and larger turbo lag.

Small Turbine

• Smaller turbines will provide lower boost thresholds and better turbo response.

• Able to create limited airflow through the compressor.

• Demands higher enthalpy exhaust in manifold.

• Leads to lower turbine exit pressure.

Selection of Turbine Exducer bore

Lower Limit

Higher Limit

Geometrical Design of Casing for Turbine

Steps in Geometrical Design

Geometric Parameter : Casing for Turbine

The A/R ratio of the turbine is the ratio of the housing discharge area to the radius of the center of the discharge area to the center

of the turbine blades

Guide for selecting a turbine A/R ratio

Lower Boost ThresholdH

igh

Pow

er E

ngin

e

7.0R

A

4.1R

A

Performance Studies on Turbocharged Engine

The Breathing Effectiveness

Engine Power Rating

Engine Compactness

Engine Fuel Economy

Strange Thinking/Understanding for Future

• Turbocharged modes were found to match or exceed the capabilities of typical larger bore normally aspirated engines found in passenger vehicles.

• Case studies showed that A normally aspirated engine could be readily matched with the smaller turbocharged unit, with a 66% reduction in engine capacity.

• It is possible to achieve 22% reduction in fuel consumption and CO2 emissions, including a reduction of 62% at idle conditions.

Advanced Turbo-charging Systems

• Higher volumetric efficiency is achieved through increased pressure @ IVC.

• Go back to Era of Otto or Diesel.

• Compression ratio has a great impact on fuel consumption of an engine.

• Generally, the bigger the compression ratio is, the lower the fuel consumption can be reached.

• Knock limit constrains the compression ratio increase of SI engines.

• It is known to all that any effort resulting in intake air temperature decreasing will extend the knock limit.

• Attainment of higher volumetric efficiency with lower Tivc is the theme of advanced turbo-charging methods.

Scheme of the turbo-cooling system

T-s & p-v Diagrams for ATCS

Effect of Turbo-cooling

Cold Air for Higher CR

Base Engine

ATC: Boost pressure before HX

ATC: Exit of Air Turbine