Volumetric efficiency

• Volumetric efficiencies above 100% can be reached by using forced induction such as supercharging or turbo charging.

• With proper tuning, volumetric efficiencies above 100% can also be reached by naturally aspirated engines.

• The limit for naturally aspirated engines is about 137%; these engines are typically of a DOHC layout with four valves per cylinder.

Double Overhead Camshaft (DOHC)

Double or Dual Overhead Camshaft (DOHC)

SOHC

VALVE TIMING DIAGRAM

Valve events

Intake valve opening160 BTDCLow pressure in cylinder

Intake valve closing 550 ABDCCylinder pressure is effected by timing

Exhaust valve opening 550 BBDCResidual pressure helps movement of exhaust gases

Exhaust valve closing 160 ATDCLow pressure in exhaust port draws air in

Best thermal efficiency estimates for various Power Plants

Power plant type

• Spark-ignited, port-injected, stoichiometric • Direct-injected. spark-ignited,

stoichiometric• Direct-injected. spark-ignited, lean, early

injection • Indirect-injected diesel • Direct-injected, spark-ignited, lean, late

injection

Efficiency (%)

• 31.5• 33

• 34.5

• 35.5• 38

WHY DIESEL GIVES BETTER MILEAGE

• On average, 1 gallon (3.8 L) of diesel fuel contains approximately 155x106 joules (147,000 BTU), while 1 gallon of gasoline contains 132x106 joules (125,000 BTU)

• This along with the high efficiency of diesel engines, explains why diesel engines get better mileage than regular petrol engines

THERMAL EFFICIENCY

Engine thermal efficiency is the relation between the power produced and the energy in the fuel burned to produce that power. Some of the heat produced by combustion is carried away by the engine lubricating and cooling systems. Some heat is lost in the hot exhaust gases as they leave the cylinder.

THERMAL EFFICIENCY

These heat (thermal) losses reduce the Thermal efficiency of the engine. The engine uses the remaining heat to produce power. Thermal efficiencies of spark-ignition engines may be below 20 %. They are seldom above 25 %. Some diesel engines have thermal efficiencies of 35 % or higher.

Best thermal efficiency estimates for various power plants

Power plant type

• Gas turbine • High-speed, direct-injected diesel• Heavy-duty. direct-injected diesel (HDDI) • Fuel cell• Turbo compounded, HDDI diesel

Efficiency (%)

• 38• 43• 46• 52• 54

INTERNAL COMBUSTION ENGINES

Advantages• MECHANICAL SIMPLICITY• IMPROVED THERMAL

EFFICIENCY• DON’T NEED AUXILLARY

EQUIPMENT• SHORT START AND STOP

TIME• LOW INITIAL COST• EFFICENT PERFORMANCE

Disadvantages• FUEL COST

• WORKING FLUID ONLY LIQUID OR GASEOUS AT GIVEN SPECIFICATIONS

• VIBRATION PROBLEMS

AUTOMOTIVE FUEL NEEDS

ENGINE SYSTEMS

ENGINE SYSTEMS

• COOLING SYSTEM• EXHAUST SYSTEM• LUBRICATION SYSTEM• FUEL SYSTEM• IGNITION SYSTEM

AIR INTAKE