Matching of Turbo-charger with I.C. Engine

P M V SubbaraoProfessor

Mechanical Engineering Department

A Tuning Among Heterogeneous Devices is A Must….

Three constraints on Compressor Sizing

• Generation of required Boost Pressure (ratio).• Isentropic efficiency must be better than 60%.• Mass flow rate must be higher than average engine

mass flow rate at Full load.• Flexible parameters:• Compressor geometry : radial to Mixed.• Compressor Speed : low to high.

Engineering Shape of A Compressor

65000rpm

75000rpm90000rpm

105000rpm

120000rpm

130000rpm

hrm / 699.1 3

Engine in the House of Compressor

Closure on Thermodynamics of Compressor Sizing

The Power Consumed by Compressor

The Turbine to Drive the Compressor

ТC

1

2 3

4P1, T1

P2, T2P3, T3

P4, T4

Engine

Irreversible Adiabatic Flow Through Turbine : SSSF

h

s4iso

Ideal work wiso = h03 –h04iso

Actual work wact = h03 – h04act

Internal Efficiency of a turbine

iso

actturbineiso hh

hh

,0403

,0403,

4actual

actwV

hV

h 22

24

4

23

3

3

actwhh 0403

iso

actturbineiso TT

TT

,0403

,0403,

Thermodynamics of Turbine Sizing

1

03

0403,04

p

pTT iso

1

03

04,03,04 11

p

pTT turbneisoact

Turbine Sizing

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

• The fact is that the turbine size effects boost threshold, turbo lag and fuel consumption .

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

• It is basically just a balancing act.

• Smaller turbines will provide lower boost thresholds and better turbo response but only be able to create limited airflow through the compressor and will create a lost of back pressure and heat in the exhaust manifold.

• Larger turbines, conversely, allow much more airflow through the compressor and reduce back pressure and heat in the exhaust manifold at the expense of higher boost thresholds and larger turbo lag.

Small Turbine Vs Large Turbine

Tuning of Compressor, Turbine & Engine

• The airflow through the compressor is directly related to the boost pressure the compressor creates.

• Therefore larger airflow through the compressor means higher boost pressures.

• Back pressure in the exhaust manifold can lead to reversion, which is when the pressure is so high in the exhaust manifold that exhaust gases are forced back into the cylinder when the exhaust port opens during the exhaust stroke.

• This obviously not good and hurts engine power.

• These opposing concerns must thus be balanced against each other.