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. Size2. Ignition system3. Strokes per cycle4. Crankshaft orientation5. 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.

LargestThe 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 (0.00335 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)

Year Engine Designer/developer1680 Gunpowder Christian Huygens

1698 Savery Pump Thomas Saverly

1712 Newcomen Steam Thomas Newcomen

1763 Watt Double-acting steam James Watt

1801 Coal gas/electric ignition Eugene Lebon

1802 High pressure steam Richard Trevithick

1859 Pre-mixed fuel and air Etienne Lenoir

1862 Gasoline Nikolaus Otto

1876 Four cycle gasoline Nikolaus Otto

1892 Diesel Rudolf Diesel

1953 Die-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

FlywheelFlywheelWater falling over a dam.

A speeding automobile

Internal combustion engines operate utilizing the principles of nine (9) physical phenomena.

HeatChemistryTemperatureForce 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

TemperatureTemperature

Temperature (oF) 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 oF.

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.

Time

“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.

P r e s s u r e

A r e a

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

P=WT

P=F x D

T

.

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

C 8 H 18 + 121

2O 2 + 47N 2 = 8CO 2 + 9H 2 O + 47N 2 + HEAT

Unfortunately, combustion is not perfect---the result

is many unwanted gasses and compounds.

The End