2. Engine Ignition Types

Worksheet: Engine Classification

There are types of ignition, based on how the fuel is ignited. • Spark ignition

– the fuel mixture is ignited with an electrical spark. (spark plug)

– Commonly use gasoline.

• Compression – The fuel mixture is ignited by compressing the fuel mixture

under pressure and heat – Commonly use diesel fuel

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3. Engine Stroke Types

A stroke is one complete travel of the piston from top dead center to bottom dead center or vice versa.

• Two (2) Stroke

– Utilizes two strokes to complete the intake, compression, power (ignition) and exhaust cycle

• Four (4) Stroke

– Utilizes four strokes to complete the intake, compression, power (ignition) and exhaust cycle

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4. Engine Cylinder Design

• Vertical – pistons travel up and down vertically.

• Horizontal - pistons travel back and forth in the horizontal plane

• Slant – pistons are oriented at an angle to the vertical

• V – pistons are divided into two banks at an angle to the vertical forming a v-shape

• Inline – pistons are all oriented in the same direction

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• the cylinders are arranged inline in a single bank that move vertically.

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• also known as horizontally opposed or a boxer

• the cylinders are arranged in two banks on opposite sides of the engine:

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• the cylinders are arranged inline and specifically designed such that the cylinders are inclined at a 30-degree angle from vertical.

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• V - the cylinders are arranged in two banks set at an angle to one another:

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• the cylinders are arranged in a line in a single bank. Can be arranged vertically or slanted.

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5. Shaft Orientation

Vertical

• The shaft extends from the bottom of the engine.

• common applications of a vertical engine include:

• walk-behind rotary lawnmowers

• yard tractors

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Horizontal

• The shaft extends from one side of the engine and rotates parallel to the ground.

• common applications of a vertical engine include:

• Generators

• snow throwers

• water pumps

• pressure washers.

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6. Cooling Systems

• Air Cooled

– Air is circulated around the cylinder block and cylinder head to maintain the desired temperature

• Liquid Cooled

– Liquid is circulated through cavities in the cylinder block and cylinder head to maintain the desired temperature

• Heat is also removed through the exhaust system and radiant heat from the engine components.

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• Most small, single-cylinder engines are cooled by a stream of air developed by fan blades on the flywheel.

• The air stream is deflected around the cylinder and cylinder head by a metal or plastic cover called a shroud.

• Additional engine heat is dissipated through cooling fins around the cylinder.

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• The cooling system on liquid-cooled cars circulates a fluid through pipes and passageways in the engine.

• As this liquid passes through the hot engine it absorbs heat, cooling the engine.

• After the fluid leaves the engine, it passes through a heat exchanger, or radiator, which transfers the heat from the fluid to the air blowing through the exchanger.

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Extra Engine Classifications

• Engine displacement

– Is the volume of space that the piston moves through as it moves from TDC to BDC.

Displacement is measured in cubic inches, cubic centimeters or liters.

– Displacement = (3.14)(d2)(s)(n) ÷ 4

• d = the diameter of the piston.

• s = the length of the stroke.

• n = the number of cylinders/pistons.

– What is the displacement of a chainsaw engine with a cylinder diameter of 5cm and a stroke length of 2.54cm?

• When the piston is at BDC, the cylinder volume is at its largest.

• When the piston is at TDC, the cylinder volume is at its smallest.

Compression Ratio

– Is the ratio of the largest cylinder volume to the smallest cylinder volume.

Example:

• If the cylinder volume measures 6 cu. in. when the piston is at BDC, and 1 cu. in. when at TDC, the compression ratio of the engine is 6 to 1 (6:1).

Small engines can operate on

– Gasoline

– Liquefied Petroleum Gas (LP-gas)

– Natural Gas

– Diesel Fuel

• Gasoline is the most popular of all small engine fuels.

– Provides more horsepower

– Readily Available

– Easily transported

• LP-Gas may be propane, butane or a mixture of both.

– Burns cleanly.

– Emits fewer harmful fumes.

– Requires a different fuel system.

– Often used in warehouses (Fork lifts, generators, compressors).

• Is primarily Methane

• Burns cleanly

• Causes a horsepower loss of around 20% when compared with gasoline.

• Requires a different fuel system.

• Diesel fuel is injected into the cylinder where it is ignited by the heat of compression.

• Diesel engines are much stronger than small gasoline engines.

• Small Diesel engines are not as popular as gasoline engines.