Chapter 1 Internal Combustion Engines Engine Classification • Small Engine Development • Energy Conservation Principles • Small Engine History

Competencies Explain the classification “small engine” and discuss the main small engine types. Describe types of cylinder design and cooling systems. Explain small engine development history. Explain energy conversion principles that apply to small engines. Explain heat transfer. List the common energy conversion calculations. Explain the chemistry of fuel combustion in small engines. Describe the small engine industry.

Small Engines internal combustion engine converts heat energy from the combustion of fuel into mechanical energy rated up to 25 horsepower (HP) spark ignition or compression four-stroke or two-stroke cycle A small engine is an internal combustion engine, generally rated up to 25 horsepower (HP), that converts heat energy from the combustion of a fuel into mechanical energy. Figure 1-1. Based on how the fuel is ignited, a small engine is either a spark ignition (using an electrical spark to ignite an air-fuel mixture) or compression engine (igniting fuel by compression). Both spark ignition and compression ignition engines are available as either four-stroke or two-stroke cycle engines. A four-stroke cycle engine is an internal combustion engine that utilizes four distinct piston strokes to complete each operating cycle. A two-stroke cycle engine is an engine that utilizes two strokes to complete one operating cycle of the engine. Figure 1-2.

Engine Design one, two, or four cylinders cylinder orientation vertical, horizontal, or slanted cylinder configuration V, horizontally-opposed, or in-line air-cooled or liquid-cooled Small engines typically contain one or two cylinders but can have as many as four cylinders. Cylinder orientation is vertical, horizontal, or slanted, depending on the axis of the cylinder. Cylinder configuration in multiple cylinder engines is V, horizontally-opposed, or in-line. The cooling system on a small engine removes heat using air or liquid. An air-cooled engine is an engine that circulates air around the cylinder block and cylinder head to maintain the desired engine temperature. A liquid-cooled engine is an engine that circulates coolant through cavities in the cylinder block and cylinder head to maintain desired engine temperature.

Development History gunpowder engine steam engine coal gas internal combustion gasoline power diesel engine In 1680, Christian Huygens developed a gunpowder engine. During the next hundred years, Savery, Newcomen, and Watt all designed steam engines to pump water from underground mines. Figure 1-4. Eugene Lebon and Etienne Lenoir developed internal combustion engines that used coal gas. In 1862, Nikolaus Otto developed the first successful gasoline engine and in 1876, developed the four-stroke cycle engine. Figure 1-7. In 1892, Rudolf Diesel patented a new type of internal combustion reciprocating engine, to be known as the diesel engine, that ignited fuel by high compression.

Energy Conversion Principles small engines convert potential energy into kinetic energy all internal combustion engines operate utilizing basic principles of heat, force, pressure, torque, work, power, and chemistry All internal combustion engines exhibit and convert different forms of energy. Potential energy is stored energy a body has due to its position, chemical state, or condition. Figure 1-10. Kinetic energy is energy of motion. Small gasoline engines convert the potential energy in gasoline to the kinetic energy of a rotating shaft that is used to do work. All internal combustion engines operate by utilizing basic principles of heat, force, pressure, torque, work, power, and chemistry. Heat is kinetic energy caused by atoms and molecules in motion within a substance. Heat added to a substance causes molecule velocity and internal energy to increase; heat removed from a substance causes molecule velocity and internal energy to decrease. The internal combustion engine operates by means of these increases and decreases of heat. Figure 1-11.

Heat Transfer conduction is heat transfer from atom to atom via molecules in direct contact convection is heat transfer by currents in a fluid radiation is heat transfer that occurs as radiant energy without a material carrier Three methods of heat transfer are conduction, convection, and radiation. Figure 1-12. Conduction is heat transfer that occurs from atom to atom when molecules come in direct contact with each other, and through vibration when kinetic energy is passed from atom to atom. Heat conduction occurs in small engines through lubrication oil. 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. Radiation is heat transfer that occurs as radiant energy without a material carrier. Heat radiation occurs in small engines as the engine block, cylinder head, and other metal engine components have heat passed through them into the atmosphere.

Energy Conversion Calculations temperature is the intensity of heat °C = (°F – 32) ÷ 1.8 °F = (1.8 × °C) + 32 pressure is a force acting on a unit of area pressure = force ÷ area Temperature is the intensity of heat and is commonly measured using the Fahrenheit or Celsius scale. Force is anything that changes or tends to change the state of rest or motion of a body and is applied in different ways to produce pressure, torque, or work. Pressure is a force acting on a unit of area.

Energy Conversion Calculations torque is a force acting on a perpendicular radial distance from a point of rotation torque = force × radius work is the movement of an object by a constant force work = force × distance Torque is a force acting on a perpendicular radial distance from a point of rotation. It is equal to force times radius. Figure 1-16. A lever is a simple machine that consists of a rigid bar which pivots on a fulcrum (pivot point) with both resistance and effort applied for the purpose of obtaining mechanical advantage. Figure 1-17. Work is the movement of an object by a constant force. Figure 1-18.

Energy Conversion Calculations power is the rate at which work is done power = work ÷ time horsepower (HP) is a measure of power equal to 76 watts or 33,000 lb-ft per min HP = work ÷ (time × 33,000) Power is the rate at which work is done and is measured in watts or horsepower. Horsepower is equal to 746 watts or 33,000 lb-ft per min (550 lb-ft per sec). Figure 1-19.

Combustion Chemistry combining of hydrocarbon fuel with oxygen a chemical reaction between the hydrocarbon molecule and atmospheric oxygen combining at ignition temperature causes an exchange of elements that releases heat energy Combustion chemistry involves the combining of hydrocarbon fuel with oxygen from the atmosphere. When the ignition of the air-fuel mixture occurs in an engine, a chemical reaction between the hydrocarbon molecule and atmospheric oxygen causes an exchange of elements that releases heat energy. Figure 1-20.

Small Engine Industry outdoor power equipment manufacturers service technicians Briggs & Stratton MST program Outdoor power equipment manufacturers use small engines to produce products for the consumer lawn and garden care, commercial turf care, golf course maintenance, and gasoline powered hand-held equipment markets. Figure 1-21. New products and new technology have created a growing need for trained service technicians in the small engine industry. A benchmark of small engine service technician competency is the Briggs & Stratton Master Service Technician (MST) program based on successful completion of an exam.

Chapter 1 Review In a typical small engine, approximately what percent of the energy released is converted into useful work? Approximately 30% of the energy is converted into useful work. What is horsepower? Horsepower is a unit of power equal to 33,000 lb-ft per min. When fuel is oxidized (ignited providing combustion) in a typical small engine, approximately 30% of the energy released is converted into useful work. Horsepower is a unit of power equal to 746 watts or 33,000 lb-ft per min (550 lb-ft per sec).