I C Engine and Gas Turbines
Topic: Introduction to IC Engines
Lecture - 1
Disclaimer:
The study materials/presentations are solely meant for academic purposes and they
can be reused, reproduced, modified, and distributed by others for academic purposes
only with proper acknowledgements.
MEC 502
National Institute of Technology Durgapur
Dr Sirshendu Mondal
I C Engine and Gas Turbines
Course Outcomes:
CO1  Mechanism of internal combustion engines
CO2  Knowledge of IC engine fuel
CO3  Pollution from internal combustion engines
CO4  Mechanism of gas turbines
CO5  Outlines of alternative fuels
Topics covered:
Introduction, Fuel and Thermochemistry, Fuel metering, Combustion
MEC 502
National Institute of Technology Durgapur
Dr Sirshendu Mondal
I C Engine and Gas Turbines
References and acknowledgement:
• Internal Combustion Engine – V. Ganesan (Tata McGraw-Hill)
• Internal Combustion Engine Fundamentals – John B. Heywood (McGraw-Hill)
MEC 502
National Institute of Technology Durgapur
Dr Sirshendu Mondal
I C Engine and Gas Turbines
Internal Combustion Engines (I C Engines):
• The purpose is to produce mechanical power from the chemical energy contained in the
fuel.
• IC engines mainly refer to spark-ignition (SI) and compression-ignition (CI) engines.
• In internal combustion engines, the energy is released by burning or oxidizing the fuel
inside the engine.
• In this operation, the actual working fluids are the fuel-air mixture before combustion and
burned products after combustion.
• For internal combustion engines, the work transfers occur directly between working fluids
and mechanical components of the engine.
MEC 502
National Institute of Technology Durgapur
Dr Sirshendu Mondal
I C Engine and Gas Turbines
• By this definition, gas turbines are also internal combustion engines. However, the term
“IC engines” are conventionally used for SI and CI engines.
• These two types of engine have found wide application in transportation (land, sea, and air)
and power generation.
MEC 502
National Institute of Technology Durgapur
Dr Sirshendu Mondal
I C Engine and Gas Turbines
• There are many different types of internal combustion engines. A few ways to classify IC
engines are:
 Basic engine design: 1. Reciprocating engine, 2. Rotary engine
 Working cycle: 1. Four stroke cycle, 2. Two stroke cycle
 Fuel: 1. Petrol engine, 2. Diesel engine, 3. Duel fuel engine
 Method of ignition: 1. Spark ignition (SI), 2. compression ignition (CI).
 Method of cooling: 1. Water cooled, 2. Air cooled, and 3. uncooled (natural convection and
radiation)
• We follow ‘method of ignition’ as the primary classifying feature. Therefore, SI (spark
ignition) and CI (compression ignition) engines will be studied in detail.
• Let us first look at different components of a generic reciprocating engine.
MEC 502
National Institute of Technology Durgapur
Dr Sirshendu Mondal
I C Engine and Gas Turbines
Basic geometry of a reciprocating engine
Exhaust manifold: Exhaust
valve to exhaust system
Intake manifold: intake
system to inlet valve
Gudgeon pin
Connecting rod
Combustion chamber
Cylinder
Piston
Crank pin
Crank
Crank shaft
MEC 502
National Institute of Technology Durgapur
Dr Sirshendu Mondal
I C Engine and Gas Turbines
• In reciprocating engines, the piston moves back and forth (or up and
down) in a cylinder and transmits power.
• The piston comes to rest at the top-center (TC) and bottom-center
(BC) when the cylinder volume is a minimum or maximum,
respectively. (Also called TDC/IDC and BDC/ODC)
• The inner diameter of the cylinder is called bore, and the maximum
distance travelled by the piston is called stroke.
• The minimum cylinder volume is called the clearance volume 𝑽𝒄 .
• The volume swept out by the piston is called the displaced or swept
volume 𝑽𝒅 . This is the difference between the maximum or total
volume 𝑉𝑡 and the clearance volume 𝑉𝑐 ,
MEC 502
National Institute of Technology Durgapur
Dr Sirshendu Mondal
I C Engine and Gas Turbines
• The ratio of maximum volume to minimum volume is the
compression ratio 𝒓𝒄 .
• Typical values of 𝑟𝑐 are 8 to 12 for SI engines and 14 to 22 for CI
engines.
• The majority of reciprocating engines operate on the four-stroke
cycle.
• A complete cycle which consists of four strokes of its piston or two
revolutions of the crankshaft produces one power stroke.
• This four-stroke cycle is used by both SI and CI engines.
MEC 502
National Institute of Technology Durgapur
Dr Sirshendu Mondal
I C Engine and Gas Turbines
• The four-stroke cycle comprises a) an intake stroke, b) a compression stroke, c) a power
stroke, and d) an exhaust stroke.
MEC 502
National Institute of Technology Durgapur
Dr Sirshendu Mondal
I C Engine and Gas Turbines
• An intake stroke starts with the piston at TC and ends with the piston at BC
• During this stroke, fresh air or fuel-air mixture is drawn into the cylinder.
• To increase the mass inducted, the inlet valve opens shortly before the stroke
starts and closes shortly after it ends.
• A compression stroke starts with the piston at BC and ends at TC.
• The mixture inside the cylinder is compressed to a small fraction of its initial
volume.
• Toward the end of the compression stroke, combustion is initiated and the
cylinder pressure rises more rapidly.
MEC 502
National Institute of Technology Durgapur
Dr Sirshendu Mondal
I C Engine and Gas Turbines
• A power stroke or expansion stroke starts with the piston at TC and ends at BC.
• The high-temperature, high-pressure gases push the piston down and force the
crank to rotate. About five times as much work is produced during the power
stroke as consumed during compression.
• As the piston approaches BC, the exhaust valve opens to initiate the exhaust
process and drop the cylinder pressure to close to the exhaust system pressure.
• In an exhaust stroke, the piston moves from BC to TC.
• The remaining burned gases exit the cylinder: first, because the cylinder pressure may
be significantly higher than the exhaust pressure; second, these gases are swept out by
the piston as it moves toward TC.
• As the piston approaches TC the inlet valve opens and just after it reaches TC the
exhaust valve closes. The cycle then repeats.
MEC 502
National Institute of Technology Durgapur
Dr Sirshendu Mondal
I C Engine and Gas Turbines
• The four-stroke cycle requires two crankshaft revolutions for each power stroke.
• To obtain a higher power output from a given engine size, and a simpler valve design, the twostroke cycle was developed. The two-stroke cycle is applicable to both SI and CI engines.
MEC 502
National Institute of Technology Durgapur
Dr Sirshendu Mondal