What does a compressor map look like?
What are the efficiency lines on a compressor map?
The blue curved lines. Greater efficiency closer to the centre. Efficiency is a measure of the pressure increase to the temperature increase.
What is the choke line?
On the right of a compressor map
Can’t go below it otherwise too much air is going through and air starts to become supersonic
What is the surge line?
The maximum pressure for a given flow rate
Where the pressure ratio is too great and the mass flow rate too small. This causes unstable flow in the turbocharger
What does the waste gate do?
Allow some of the exhaus gas to by pass the turbocharger to prevent chocking
What is constant pressure turbocharging?
The exhaust gases of all cylinders are piped into a common receiver, so that the pressure pulses are smoothed out.
The exhaust gas flows to the turbine at practically constant pressure.
The degree of reaction of the turbine blades can be chosen freely.
What is pulse turbocharging?
- Pressure and velocity fluctuations are generated in individual exhaust pipes of comparatively small diameter, into which flow the exhaust gas of a number of cylinders with suitable timing.
- The exhaust energy is transported to the turbine mainly in the form of pressure energy, so that there is a back pressure of varying magnitude, which affects the exhaust work done by the piston, even though the kinetic energy is only a small fraction of the total energy.
Used in cars
What is the relationship between the mass flow rate through the compressor and the turbine?
What is the difference in design between a compressor and a turbine?
The exhaust turbine is made for lots of low pressure air. The compressor produced less high pressure air.
What numbers are different parts of the turbocharging process denoted by?
What is a basic equation for the mass flow rate through a turbine?
α is the flow pulse factor and between 0.9 and 1 for pulsating flow
How do you find the density of a gas?
R=287 for air
What is η1?
Around 1 third for petrol engines
What is λc?
The volumetic efficiency. Greater than 1 if you push air in.
What is compressor isentropic efficiency?
What is turbine isentropic efficiency?
What is the first basic equation of exhaust turbocharging?
Cpg is the specific heat capacity of the exhaust gas
Cpa is the specific heat capacity of the air
What equation gives the energy avaliable in the exhaust gas?
What are the advantages and disadvantages of pulse turbocharging?
What are the advantages and disadvantages of constant pressure turbocharging?
What is f?
ratio of exhaust gas to air
- 03 for diesel engines
- 07 for gasoline engines
What is Vs?
The total displacment
What are all the terms in the basic turbo exhaust temperature equation
What does the parameter β represent, and how should its value be selected in practice?
The energy pulse factor. A coefficient to take into account pulsating flow rate.
List 4 requirements for mating a turbo and an engine?
Can’t go into surge or choke
Balance the power of the turbine and compressor