Internal Combustion Engines Power & Energy 3201
Outline • Internal Combustion Engines • Types of motion • Four Stroke Cycle Engines • Two Stroke Cycle Engines • Rotary Engines • Diesel Engines
Internal Combustion Engine • Internal combustion heat engines • Are a category of engines that burn fuel internally to produce power.
Types of Motion • Internal combustion engines produces mechanical motion in one of three ways: 1. Reciprocating • Back and forth motion. Ex: Piston engines 2. Rotary • Turning motion. Ex: Turbines and rotary engines 3. Linear • Motion in a straight line. Ex: Jet/Rockets and Potato gun.
Gasoline Piston Engines • There are two types of gasoline piston engines: 1. Four Stroke Cycle 2. Two Stroke Cycle
Gasoline Piston Engines • Stroke – the movement of the piston from the top of the cylinder to the bottom. • Cycle – A complete set of piston movements that are needed to produce a power stroke.
Gasoline Piston Engines • Both operate with a piston moving up and down in a cylinder. • The difference is in the number of strokes each piston makes per engine cycle.
History • The principle of four stroke cycle engine was developed in 1862 by Beau de Rochas of France. • The first four stroke cycle engine was built in 1876 by a German mechanical engineer called Nicholas Otto (Otto cycle).
History • In 1893 two American brothers named Duryea built and operated the first gasoline automobile.
Four Stroke Gasoline Engines • In four stroke engines there are four separate piston strokes: 1. Intake 2. Compression 3. Power 4. Exhaust
Four Stroke Principles of Operation • Intake stroke • The intake valve opens. • The piston moves down the cylinder creating a partial vacuum. • A mixture of air and fuel is sucked into the cylinder through the intake valve.
Four Stroke Principles of Operation • Compression stroke • When the piston reaches BDC, both valves are closed. • This seals the cylinder and prevents the air-fuel mixture from escaping. • The piston begins to move up the cylinder and compresses the mixture.
Four Stroke Principles of Operation • Power stroke • The piston rises until it reaches TDC. • At that moment a high voltage spark is created by the spark plug.
Four Stroke Principles of Operation • Power stroke • This spark causes the compressed air-fuel mixture to ignite and burn rapidly. • The force of this contained explosion forces the piston down in the cylinder producing power.
Four Stroke Principles of Operation • Exhaust stroke • As the piston nears BDC the exhaust valve opens. • As the piston rises back up, it pushes the burned gases out of the exhaust valve.
Four Stroke Principles of Operation • Exhaust stroke • Once the exhaust stroke is completed, the four strokes of operation begin all over again.
Four Stroke Principles of Operation • Four stroke Video • Four stroke engine basics
Two Stroke Gasoline Engines • Two stroke engines operate on the same basic operating principles as the four stroke engine. • However, it completes the intake, compression, power and exhaust strokes in only two movements of the piston, as opposed to four.
Two Stroke Gasoline Engines • Each time the piston moves up, it completes the intake and compression stroke. • Each time the piston moves down, it completes the power and exhaust stroke.
Two Stroke Principles of Operation • Intake/Compression Stroke • As the piston moves up the cylinder the intake and exhaust ports are covered. • The air/fuel/oil mixture above the piston is compressed.
Two Stroke Principles of Operation • Intake/Compression Stroke • At the same time a new air/fuel/oil mix is drawn into the crankcase of the engine through a reed valve connected to the carburetor.
Two Stroke Principles of Operation • Intake/Compression Stroke • The reed valve is a special valve that permits air/fuel/oil to move in one direction only.
Two Stroke Principles of Operation • Power/Exhaust Stroke • At the top of the stroke the spark plug ignites the compressed mixture. • The burning of the mixture pushes the piston downward producing power.
Two Stroke Principles of Operation • Power/Exhaust Stroke • The downward motion of the piston pressurizes the air/fuel/oil mixture in the crankcase and forces the reed valve to close.
Two Stroke Principles of Operation • Power/Exhaust Stroke • As the piston reaches BDC, the intake and exhaust ports are opened. • The exhaust gases are expelled out of the engine and at the same time the air/fuel/oil mixture is forced into the cylinder through the intake port.
Two Stroke Principles of Operation • Power/Exhaust Stroke • The rush of air/fuel/oil into the cylinder helps push out the exhaust gas and is ready to be compressed by the upward movement of the piston. • The cycle now begins again.
Two Stroke Advantages • Advantages • Requires fewer moving parts to accomplish the same amount of output as four stroke engines. • Cheaper to maintain than four stroke engines. • Smaller and simple in construction than four stroke engines. • Can work in any orientation.
Two Stroke Disadvantages • Disadvantages • Less fuel efficient than four stroke. • Quicker wear of the engine’s moving parts. • More polluting than four stroke engines since oil is burnt with the fuel and air mixture.
Rotary (Wankel) Engine • Designed in 1958 by a German scientist named Felix Wankel. • Wankel engines do not use pistons.
Wankel Engine • The wankel engine uses a triangular shaped rotor housed in an oval shaped cylinder. • As the rotor is rotated it moves around the cylinder producing the four basic functions to produce a power stroke.
Wankel Engine Principles of Operation • Intake Stroke • The production of power begins with the rotor at point A. • The intake port is uncovered allowing a new air/fuel mixture to enter the combustion chamber.
Wankel Engine Principles of Operation • Compression Stroke • As the rotor rotates the combustion chamber is reduced in size compressing the mixture.
Wankel Engine Principles of Operation • Power Stroke • At the highest point of compression the air/fuel is ignited. • The hot expanding gases push on the rotor causing it to rotate.
Wankel Engine Principles of Operation • Exhaust Stroke • The continued rotation of the rotor uncovers the exhaust port allowing the exhaust gas to escape. • The cycle then repeats when a new air/fuel mixture is permitted to enter the combustion chamber.
Wankel Engine Advantages • Advantages • Less vibration than piston driven engines. • A two rotary engine is as powerful as a six cylinder piston engine. • Power output can be increased by adding additional rotors to the engine.
Wankel Engine Disadvantages • Disadvantages • Sealing the rotor in the odd shaped cylinder is very difficult requiring costly maintenance. • Construction cost are high for this engine. • Shortages of trained mechanics to service this engine type.
Diesel Engines • This engine was invented in 1892 by a German mechanical engineer named Rudolph Diesel. • At first this engine was known as the compression engine but later was named Diesel after its inventor.
Diesel Engines • Diesels come in two stroke and four stroke versions and operate much like the gasoline driven engines. • Diesels have a greater compression ratio than gasoline engines. • Diesel 16:1 – 23:1 • Gasoline 6:1 – 12:1
Diesel Engine Principles of Operation • Intake Stroke • The intake valve opens. • The piston moves downward. • Only air is pulled into the cylinder or pumped in using a turbo charger (fan).
Diesel Engine Principles of Operation • Compression Stroke • The upward movement of the piston compresses the air increasing the temperature to approximately 538 degrees Celsius.
Diesel Engine Principles of Operation • Power Stroke • As the piston reaches the top, fuel is injected at just the right moment and ignited by the heat, forcing the piston back down.
Diesel Engine Principles of Operation • Exhaust stroke • The piston moves back to the top and pushes the burned gases out of the exhaust valve or port.
Diesel VS Gasoline Engines • Different type fuel (Diesel fuel). • Diesel engines operate at a much higher compression ratio. • Diesel engines do not use spark plugs. • Glow plugs are used to help get the engines going on very cold days.
Diesel Engine Advantages • Advantages • Greater fuel economy (25% more efficient than gasoline engines). • Produces more power. • Requires less maintenance.
Diesel Engine Disadvantages • Disadvantages • Must be constructed heavier to withstand the higher pressures. • Shortage of qualified mechanics in some areas.