Turbocharging of I.C. Engines P M V Subbarao Professor Mechanical Engineering Department Going for Artificially Breathing Engines….

A Turbocharged Engine The Primary Objective:

Matching of Turbocharger with Engine I.C. Engines are semi-control volumes. Can accept or deliver flow across the boundary intermittently. Turbocharger is a combination of two pure control volumes. They need to continuously accept and deliver flow across boundary. Demands a special engineering art called as tuning. An art of tuning CVs with CM. –Fluid Dynamic Turning. –Thermodynamic Tuning.

Turbocharger Compressor :A device to increase microscopic kinetic energy of intake air. Turbine :A device to utilize waste microscopic kinetic energy of exhaust gasr.

Practical Implementation of Duty of A Compressor

Thermo-fluid Dynamics of Impeller Radial Flow Impeller Mixed Flow Impeller

Flow Through Compressor

Gas Dynamics of An Impeller riri rere

s T T 01 p 0i T 0ce =T 0e p 0ce =p 0e Thermodynamic View of an isentropic Compressor pepe p ce Only Impeller can consume Power !!! pipi

Power input factor,  Typical values for the power input factor,  : – Power Input to An Irreversible Impeller

Irreversible Compressor p 0ce =p 0e T 0es =T 0e s T Overall Losses Impeller Losses T 0i p 0i

Work consumed by A compressor = Increase in Stagnation Enthalpy of gas For an irreversible compressor of given pressure rise, the actual temperature rise is more than isentropic temperature rise. Define, isentropic Efficiency of A Compressor:

The Problem of Fluid Dynamic Tuning Т C i ceti te p i, T i p ce, T ce P ti, T ti P te, T te Engine

Turbocharged engine with Reservoirs

Thermodynamic Tuning Т C A BC D P a, T a P b, T b P c, T c P d, T d Engine

Compressor Sizing A compressor is sized based on two pieces of information, boost pressure and airflow. The minimum boost pressure needed to achieve the required volumetric efficiency is to be evaluated. The airflow is directly related to the engine speed and is thus calculated based on what part of the speed range is desired to experience a power increase. Once the boost pressure and airflow are known, they are used to size the compressor. A compressor works best at a particular combination of airflow and boost pressure.

A comparison of this optimal combination of boost pressure and airflow for a given compressor to the Engine anticipated combination of boost pressure and airflow determines the suitability of the compressor for the system. The First Law of Tuning

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 75000rpm 90000rpm rpm rpm rpm

Engine in the House of Compressor

The Power needs of Compressor

The Turbine to Drive the Compressor Т C i ceti te p i, T i p ce, T ce P ti, T ti P te, T te Engine

Irreversible Adiabatic Flow Through Turbine : SSSF h s te iso Ideal work w iso = h 0ti –h 0teiso Actual work w act = h 0ti – h 0teact Internal Efficiency of a turbine te actual ti

Thermodynamics of Turbine Sizing

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.