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Internal Combustion Engines

Lecture-3

Ujjwal K Saha, Ph.D.Department of Mechanical Engineering

Indian Institute of Technology Guwahati

Prepared underQIP-CD Cell Project

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Background

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Classifications

1. Engine Cycle

Four Stroke Cycle Experiences 4 strokes of the Piston movements over 2 revolutions of the crankshaft

Two Stroke Cycle Experiences 2 strokes of the Piston movements over 1 revolution of the crankshaft

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Using volatile fuels like gasoline, alcohol, kerosene

Using gaseous fuels like natural gas, biogas

Using solid fuels like charcoal, powdered coke (converted to gaseous fuel outside the engine in a gas producer)

Using viscous fuels like diesel

Using dual fuel – methanol (suction stroke) + diesel (comp. stroke) – CI Engine– gasoline + alcohol (gasohol)

Classifications – Contd.2. Fuel Used

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Fuel Used - at a Glance

GasolineDiesel Gas, Natural gas, Methane Liquid Petroleum GasAlcohol, Methanol

HydrogenDual Fuel

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Classifications – Contd.

3. Method of IgnitionSpark Ignition: An SI engine starts the

combustion process in each cycle by use of a spark plug. In early engine development, before the invention of the electric spark plug, many forms of torch of torch holes were used to initiate combustion form an external flame.

Compression Ignition: The combustion process in a CI engine starts when the air-fuel mixture self-ignites due to high temperature in the combustion chamber caused by high compression.

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Classifications – Contd.

4. Position & Number of CylindersSingle CylinderInline Cylinders V EngineOpposed Cylinder EngineW EngineOpposed Piston EngineRadial Engine

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(a) (b) (c)

(d) (e)

(f) (g)

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Single cylinder: Engine has one cylinder and piston connected to the crankshaft.

In-Line: Cylinders are positioned in a straight line, one behind the other along the length of the crankshaft. Number of cylinders may vary from 2 to 11 or even more. In-line four-cylinder engines are very common for automobiles. In-line engines are also referred to as straight such as straight six or straight eight.

Cylinder Arrangement

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V Engine: Two banks of cylinders at an angle with each other along a single crankshaft. The angle between the banks of cylinders is usually within 60-90. V engines have even numbers of cylinders ranging from 2 to 20 or more. V6 and V8 are the common engines with six and eight cylinders respectively.

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Opposed Cylinder Engine: Two banks of cylinders opposite to each other on a single crankshaft. These are mostly used in small aircraft and some automobiles with an even number of cylinders from two to eight or more. These engines are also called flat engines such as flat four.

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W Engine: Similar to that of V engine except with three banks of cylinders on the same crankshaft. This type of arrangement has been used in some racing cars.

Opposed Piston Engine: Two pistons in each cylinder with the combustion chamber located centrally between the pistons. A single-combustion process causes two power strokes at the same time, with each piston being pushed away from the center and delivering power to a separate crankshaft at each end of the cylinder Engine output is either on two rotating crankshafts or on one crankshaft incorporating a complex mechanic linkage.

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Radial Engine: Engine with pistons positioned in a circular plane around the central crankshaft. The connecting rods of the pistons are connected to the crankshaft through a master rod. A bank of cylinders on a radial engine always has an odd number of cylinders ranging from 3 to 13 or more.

Many medium-and large-size propeller-driven aircraft use radial engines. For large aircraft, two or more banks of cylinders are mounted together, one behind the other on a single crankshaft, making a powerful and smooth engine.

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Cylinder Arrangement

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Single Cylinder Engine

Single-cylinder engine gives one power stroke per crank revolution (360 CA) for 2 stroke, or every two revolutions for 4 stroke.

The torque pulses on the crank shaft are widely spaced, and engine vibration and smoothness are significant problems.

Used in small engine applications where engine size is more important

180 CA0 CA(TC)

720 CA(TC)

540 CA360 CA(TC)

180 CA

4-stroke

2-stroke

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Multi-cylinder Engines

Multi-cylinder engines spread out the displacement volume amongst multiple smaller cylinders. Increased frequency of power strokes produces smoother torque characteristics.

Most common cylinder arrangements are in-line 4 and V-6:

Engine balance (inertia forces associated with accelerating and decelerating piston) better for in-line versus V configuration.

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V-6 Engine

Air intakemanifold

Inlet runner

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Classifications – Contd.5. Valve Locations

Valves in head (overhead valve), also called I-head engine.

Valves in block (flat head), also called L-head engine. Some historic engines with valves in block had the intake valve on one side of the cylinder, and the exhaust valve on the other side. These were called T-head engines.

One valve in head (usually intake) and one in block, also called F-head engine.

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(a) (b)

(c) (d)

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Classifications – Contd.6. Air Intake process

Naturally Aspirated: No intake air pressure boost system.

Supercharged: Intake air pressure increased with the compressor driven off the engine crankshaft.

Turbocharged: Intake air pressure increased with the turbine-compressor driven by the engine exhaust gases

Crankcase Compressed: Two-stroke cycle engine that uses the crankcase as the intake air compressor.

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Air Intake

Aftercooler

Turbine CompressorAir Intake

Exhaust

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Where the turbocharger is located in the car

Where the turbocharger is located in the car

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How a turbocharger is plumbed (including the charge air cooler)

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Roots Blower Vane CompressorScrew Compressor

Axial compressorRadial compressor

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Classifications – Contd.

7. Method of Fuel supply for SI Engines

Carbureted

Multi Point Fuel Injection - One or more injectors at each cylinder intake.

Throttle Body Fuel Injection - Injectors upstream in intake manifold.

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Fuel

Float

Vent

FloatChamber

Throttle

Fuel dischargenozzle

Fuel meteringjet lip, h

Choke

Air

InletValve

Fuelfromsupply

Carbureted System

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Multi Point Fuel Injection System

Throttle Body Injection System

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Classifications – Contd.8. Combustion Chamber Design

Open chamber (disc, wedge, hemispherical, bowl-in-piston)

Divided chamber (small and large auxiliary chambers like swirl chamber, pre-chambers)

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Classifications – Contd.

9. Type of CoolingAir CooledLiquid Cooled/Water Cooled

R adia tor

C ylinder

P iston

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The cooling system in most cars consists of the radiator and water pump. Water circulates through passages around the cylinders and then travels through the radiator to cool it off.

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Classifications – Contd.

10. Applications

Car, buses, two-wheelers, trucksLocomotivesStationary Marine Light AircraftPortable Power SystemsLawnmowers

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Technologists, Addison Wisley.3.3. Fergusan CR, Fergusan CR, andand Kirkpatrick ATKirkpatrick AT,, (2001), Internal Combustion Engines, John

Wiley & Sons.4.4. Ganesan VGanesan V,, (2003), Internal Combustion Engines, Tata McGraw Hill.5.5. Gill PW, Smith JH, Gill PW, Smith JH, andand Ziurys EJZiurys EJ,, (1959), Fundamentals of I. C. Engines, Oxford

and IBH Pub Ltd. 6.6. Heisler H,Heisler H, (1999), Vehicle and Engine Technology, Arnold Publishers.7.7. Heywood JB,Heywood JB, (1989), Internal Combustion Engine Fundamentals, McGraw Hill.8.8. Heywood JB, Heywood JB, andand Sher E,Sher E, (1999), The Two-Stroke Cycle Engine, Taylor & Francis.9.9. Joel R, Joel R, (1996),(1996), Basic Engineering Thermodynamics, Addison-Wesley.10.10. Mathur ML, and Sharma RP,Mathur ML, and Sharma RP, (1994), A Course in Internal Combustion Engines,

Dhanpat Rai & Sons, New Delhi.11.11. Pulkrabek WW,Pulkrabek WW, (1997), Engineering Fundamentals of the I. C. Engine, Prentice Hall.12.12. Rogers GFC, Rogers GFC, andand Mayhew YRMayhew YR, (1992), Engineering Thermodynamics, Addison

Wisley. 13.13. Srinivasan S,Srinivasan S, (2001), Automotive Engines, Tata McGraw Hill.14.14. Stone R,Stone R, (1992), Internal Combustion Engines, The Macmillan Press Limited, London.15.15. Taylor CF,Taylor CF, (1985), The Internal-Combustion Engine in Theory and Practice, Vol. 1 & 2,

The MIT Press, Cambridge, Massachusetts.

References

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