Small Gasoline Engines

Engine “A machine for converting energy into mechanical force and motion.”

Heat Engine An engine which uses heat to convert the chemical energy of a fuel into mechanical force and motion

Two general categories based on design. External combustion engine Internal combustion engine

Internal Combustion Engines

Internal Combustion--Intro Many different designs are used for internal combustion engines. Engines can be classified by: 1.Size 2.Ignition system 3.Strokes per cycle 4.Crankshaft orientation 5.Control system

Engine Size Industry definition: “A small engine is an internal combustion engine generally rated up to 25 horsepower.” Engines are available in a wide range of sizes.

Largest The Wartsila-Sulzer RTA96-C turbocharged two-stroke diesel engine is the most powerful and most efficient prime-mover in the world today. The cylinder bore is just under 38" and the stroke is just over 98". Each cylinder displaces 111,143 cubic inches (1,820 liters) and produces 7,780 horsepower. Total displacement comes out to 1,556,002 cubic inches (25,480 liters) for the fourteen cylinder version.

Smallest Not much bigger than a stack of pennies, the "mini engine" is the first engine of its size to deliver power on a continuous basis. Currently will produce 2.5 watts of electricity ( hp). Uses 1/2 fluid ounce of fuel per hour

Engines are further classified by ignition, number of strokes, cylinder design, shaft orientation and cooling system. (pg. 2 & 3)

Ignition Spark ignition Compression ignition

Number of Strokes Four stroke Two stroke

Cylinder Design Small engines usually have one or two cylinders, but may have as many as four. Three Common Cylinder Orientations For Single Cylinder Engines Vertical Horizontal Slanted

Cylinder Design-cont. V Horizontally opposed In-line Three common cylinder configuration in multiple cylinder engines:

Horizontal Vertical Small gas engines use three crankshaft orientations: Cylinder Design-cont. Multi-position

When fuel is oxidized (burned) heat is produced. Only approximately 30% of the energy released is converted into useful work. The remaining (70%) must be removed from the engine to prevent the parts from melting.

Excess heat is removed by: Cooling system Exhaust system Lubrication system Radiation

Additional heat is also generated by friction between the moving parts. This heat must also be removed.

Controls  Traditionally engines are controlled by mechanical means.  Governor  Throttle  Choke  Etc.  Honda has an engine with an electronic control unit (ECU).  ECU - Electronic Control Unit –Monitors and controls engine functions including Throttle, Choke, Ignition Timing, Oil Alert –Offers programmable governor and throttle modes for unprecedented flexibility and diagnostic LED for trouble shooting –Stepper motors precisely control throttle and choke position

Small Engine Development (pg 5) YearEngineDesigner/developer 1680GunpowderChristian Huygens 1698Savery PumpThomas Saverly 1712Newcomen SteamThomas Newcomen 1763Watt Double-acting steamJames Watt 1801Coal gas/electric ignitionEugene Lebon 1802High pressure steamRichard Trevithick 1859Pre-mixed fuel and airEtienne Lenoir 1862GasolineNikolaus Otto 1876Four cycle gasolineNikolaus Otto 1892DieselRudolf Diesel 1953Die-cast aluminum B&S

Physical Principles of Engines

Energy Conversion “All internal combustion engines exhibit and convert different forms of energy.” “Energy is the resource that provides the capacity to do work”. The two forms of energy used in engines are potential and kinetic.

Potential Energy “Stored energy a body has due to its position, chemical state, or condition.”

Examples of Potential Energy Fuels have potential energy based on their chemical state. A compressed spring has potential energy due to its mechanical condition. Water behind a dam has potential energy due to difference in elevation.

Kinetic Energy

Flywheel Water falling over a dam. A speeding automobile

Internal combustion engines operate utilizing the principles of nine (9) physical phenomena. Heat Chemistry Temperature Force Power Pressure Lever Torque Horsepower

Heat “ Kinetic energy caused by atoms and molecules in motion within a substance.”

In a small engine, as the air-fuel charge is compressed, internal energy increases, producing heat. When the charge is ignited and the burning gases expand, internal energy decreases and heat is given up. Engines use heat in two ways

Heat Transfer Heat is always transferred from an object of higher heat to one with lower heat. Transfer is by conduction, convection, and radiation

Temperature Temperature ( o F) is the intensity of heat”. The amount of heat is measured in BTU’s.

British Thermal Unit (BTU) The amount of heat required to raise the temperature of 1 pound of water 1 o F.

Force A force can result in pressure, torque or work, depending on how it is applied. “Anything that changes or tends to change the state of rest or motion of a body.”

PRESSURE The cylinder pressure is not constant. It is highest right after combustion, as much as 2,000 psi, and decreases as the piston moves away from the cylinder head. “A force acting on a unit of area.”

Force In engines the amount of force exerted on the top of a piston is determined by the cylinder pressure during the combustion process.

Torque “A force acting on the perpendicular radial distance from a point of rotation.” To (lb-ft) = Force x Radius

Lever “A lever is a simple machine that consists of a rigid bar”, which pivots on a fulcrum with both resistance and effort applied. Applied force Resultant force

Power is the rate of doing work

Horsepower 1 Hp = 33,000 ft-lb/min A unit of power developed by James Watt to provide a basis for comparing the amount of power produced by horses and other engines.

Chemistry All internal combustion engines utilize some form of fossil fuel. A fossil fuel is composed of carbon and hydrogen. When the hydrocarbon is ignited in the presence of air, the oxygen causes an exchange of elements which release heat energy.

PERFECT COMBUSTION EQUATION Unfortunately, combustion is not perfect---the result is many unwanted gasses and compounds.

The End