INTERNAL COMBUSTION ENGINE CHAPTER 1
ENGINE CLASSIFICATION • An engine is a machine that converts a form of energy into mechanical force. • External combustion engine is an engine that generates heat energy form the combustion of a fuel outside the engine. Ex. Steam engine • Internal combustion engine is an engine that generates heat energy from the combustion of a fuel inside the engine. Ex. Gasoline engine
ENGINE CLASSIFICATION • Small engine is an internal combustion engine that converts heat energy from the combustion of a fuel into mechanical energy generally rated up to 25 horsepower. • Classified further by ignition, number of strokes, cylinder design, shaft orientation and cooling systems.
IGNITION • Spark ignition or compression ignition engines are based on how fuel is ignited. • Spark ignition engines commonly use gasoline • Compression engines use diesel fuel. • Both engines are available in 4-stroke or 2-stroke cycle engine.
NUMBER OF STROKES • Small engines are classified as either 4-stroke or 2-stroke engines. • 4-stroke engine utilizes four strokes to complete one operating cycle of the engine. • 2-stroke engine utilizes two strokes to complete one operating cycle of the engine.
NUMBER OF STROKES • Both engines complete five distinct events during a cycle. • 1. intake • 2. compression • 3. ignition • 4. power • 5. exhaust
CYLINDER DESIGN • Small engine typically contain one or two cylinders. • Cylinder orientation can be- • Vertical • Horizontal • Slanted depending on the axis of the cylinder
CYLINDER DESIGN • In multiple cylinder engines can be “V”, horizontal opposed, or in-line configuration. • Usually cylinder orientation are selected for its power and application. • Horizontal opposed engines have low profile produces a low degree of vibration. • All engines provides ease of manufacturing but requires more space.
SHAFT ORIENTATION • Shaft orientation is the axis of the shaft. • Vertical shaft engines commonly are used in push lawnmowers. Blade is directly attached to the shaft and rotates parallel to the ground. • Horizontal shaft engines commonly are used with generators, tillers, pumps, augers, etc. Power is transfer to a driven component.
COOLING SYSTEM • In a combustion engine approximately 30% of the energy released is converted to useful work. • Remaining energy is lost in the form of heat to: • cooling air(30%) • Exhaust systems(30%) • Radiation & friction (10%)
HISTORY • 1680 - Christain Huygens developed the first internal combustion engine. • Next 100 years, inventors focused on steam engines. • 1801- Eugene Lenoir developed the first internal combustion engine using coal gas with electric ignition. • 1859- Etienne Lenoir mixed coal gas and air together
HISTORY • 1862 – Nikolaus Otto developed the first successful gasoline engine. • 1892 – Rudolf Diesel patented a new type of internal combustion reciprocating engine that ignited the fuel by high compression. Today is is known as the Diesel engine. • 1920 – Briggs and Stratton Corporation introduced a portable Model P engine operating at 2200 rpm and developed 1HP.
HISTORY • 1931 – B&S produced a low-profile L-head ½ HP Model Y engine used under washing machine tubs. • 1953 – B&S produced the first die-cast aluminum block small engines. First 50 million engines produced between 1924-1967. • Took only 8 years to produced the next 50 million. Today, B&S engines are widely used in agricultural applications.
ENERGY CONVERSION PRINCIPLES • All internal combustion engines exhibits and convert different forms of energy. • Energy is the resource that provides the capacity to do work. • Potential energy is stored energy • Kinetic energy is energy of motion (Ex. Converts the potential engine in gasoline into kinetic energy of a rotating shaft.
ENERGY CONVERSION PRINCIPLES • The operation of an internal combustion engine is based on basic energy conversion principles. • All internal combustion engines operate by utilizing basic principles of: Heattorquechemistry Forcework Pressurepower
HEAT • All matter is composed of atoms and molecules that are in a constant state of motion. • Heat is kinetic energy. • Heat added to a substance causes molecule velocity to increase causing an increase in internal energy. Heat removed from a substance causes an decrease of internal energy. Ex. Events occurring during compression and power stroke of an engine.
HEAT TRANSFER • Three methods of heat transfer; • Conduction • Convection • radiation
HEAT TRANSFER • Conduction is heat transfer that occurs atom to atom when molecules come in direct contact with each other, and through vibration, kinetic energy is passed from one to the other. • Heat conduction occurs in small engines through the medium of lubricating oil. Oil comes in direct contact with engine parts that have a much high temperature than the oil. The oil conduct the heat away from the part and into the crankcase.
HEAT TRANSFER • Convection is heat transfer that occurs when heat is transferred by currents in a fluid. • Heat transfer by convection occurs in a liquid-cooled engine radiator. Warm liquid from the engine is pumped into the top of the radiator. The liquid gives up its heat to air as it passes through the radiator. Cooler liquid is then drawn from the bottom and returned to the engine.
HEAT TRANSFER • Radiation is heat transfer that occurs as radiant energy without a material carrier. • Radiant energy waves move through space without producing heat until it comes in contact with a opaque object. Heat radiation occurs in small engines as the engine block, cylinder head and other components have heat passed through them into the atmosphere.
TEMPERATURE • Temperature is the measurement of degree or intensity of heat. • A common unit for quantity of heat measurement is the Btu (British Thermal Unit) • Btu is the amount of heat energy required to raise the temperature of 1 pound of water 1 degree F. • Calorie is the amount of heat energy required to change the temperature of one gram of water 1 degree C.
Temperature Scales • Temperature is commonly expressed in the small engine industry using the Fahrenheit or Celsius scale. • Freezing points / boiling points– • 32° F freezing & 212° F boiling • 0° C freezing & 100° C boiling
Temperature Scales • Formulas • °C = °F – 32 1.8 °F = (1.8 X °C) + 32
FORCE • Force is anything that changes or tends to change the state of rest or motion of a body. A body is anything with mass. • Force is measured in pounds(lbs) or in newtons(N)
PRESSURE • Pressure is a force acting on a unit of area. Area is the number of unit square equal to the surface of an object. • When force and area are known, pressure is found by applying the formula. P=pressure(psi); F=force(in lb); A=area(sq in.) P = F A
PRESSURE Example: What is the pressure exerted if a 60 lb force is applied to an area of 4 sq. inches? P = F P = 60 = 15 psi A 4
TORQUE • Torque is a force acting on a perpendicular radial distance from a point of rotation. It is equal to force times radius. • When force and radius(distance) are known, torque is found by applying the formula: T = F x r T = torque (in. lb or ft. lb) R = force (in. lb) R = radias (distance)
TORQUE • What is the torque developed if a 60 lb. force is applied at the end of a 2-foot lever arm? T = F x r T = 60 x 2 T = 120 ft. lbs • Lever is a simple machine that consists of a rigid bar that pivots on a fulcrum(pivot point) with both resistance and effort applied.
Levers • Lever is a simple machine that consists of a rigid bar that pivots on a fulcrum(pivot point) with both resistance and effort applied. • The purpose is to obtain mechanical advantage to overcome a large resistance with reduced effort. • This principle is used on several rigid and semi-rigid components in a small engine. Example-Crankshaft
WORK • Work is the force applied through a parallel distance causing linear motion. Work occurs only when the force results in motion. • When force and distance are known, work is found by applying the formula: • W = F X D • W = work • F = force (lb) • D=distance (ft)
WORK • Example of work: What is the amount of work performed if a horse pulled a container that weighed 330 lbs 100 feet? • W = F X D • W = 330 X 100 • W= 33,000 lbs-ft
POWER • Power is the rate at which work is done. • Power adds in a time factor. • Therefore, power is work divided by time. • Power can be expressed in several ways—force, distance and speed. • Examples: Power ratings include horsepower, watt or kilowatt. Both horsepower and watt measure how fast work is done.
POWER • When force and distance are known, power is found by applying the formula: • P = W T P= power (ft.lb/min W= force x distance (ft.lb) T= time (minutes)
POWER • Example: What is the power output of an engine that performs 100,000 ft lbs of work in 6 minutes? • P = W T • P = 100,000 6 • P = 16,666.67 ft.lbs/minute
HORSEPOWER • Horsepower (HP) is a unit of power equal to 746 watts or 33,000 ft lbs. per minute. • Horsepower is commonly used to rate and rank the power produced by an engine based on a finite engine speed. • Note: The evolution of HP as a measurement used today goes back to the history of the combustion engine. James Watt realized that a steam engine produced more power than anyone human. He needed a reference point to compare the power of his new steam engine. He selected a horse and determined that a horse could move/lift 33,000 lbs on a linear plane, 1 foot per 1 minute. This was the basis for the standard used today.
HORSEPOWER • Horsepower is found by applying the formula: • HP = W . T x 33,000 • HP = horsepower • W = work (force x distance) (ft.lb) • T = time (minutes) • 33,000 = HP contant (ft lb)
Determining Horsepower • What is the horsepower of an engine that produces 5,940,000 ft lbs in 10 minutes? • HP = _____W . T x 33,000 • HP = 5,940,000 10 x 33,000 • HP = 5,940,000 330,000 • HP = 18 horsepower
QUESTION? • What is the horsepower rating of an engine that produces 412,500 ft lbs in 2-1/2 minutes? • ANSWER? _________________________
CHEMISTRY • All internal combustion engines utilize some form of fossil (hydrocarbon) fuel as a source of energy. Combustion chemistry involves the combining of hydrocarbon fuel with oxygen from the atmosphere. • C8H18 + 12½02 + 47N2 = Air-fuel mixture Gasoline + oxygen + nitrogen • 8CO2 + 9H2O + 47N2 = Exhaust gases carbon dioxide + water +nitrogen