Engines What is an internal combustion engine Internal

Engines

What is an internal combustion engine?

• Internal, in this case , means “inside” or “enclosed”. • Combustion is the “act of burning” • SO: An internal combustion engine burns fuel internally. • ***An internal combustion engine turns heat energy into mechanical energy.

• For this to occur, there must be an exact mix of air and fuel. • The air-fuel mixture expands rapidly while burning and pushes outward. • This push can be used to move a part of the engine, and transmitted to drive the engine.

Elements of an internal combustion engine • • Air, Fuel, and Combustion Reciprocating and Rotary Motion Compression of Air-Fuel Mixture Engine Cycles

Air, Fuel, Combustion • Air is needed to combine with fuel and give it oxygen for fast burning. • Air also: – Will compress – 1 cubic foot of air can be packed into 1 cubic inch or less – Compressed air produces heat

Fuel • Fuel must be readily be mixed with air to ignite easily • 4 types of fuels: – Gasoline – LP gas – Natural gas – Diesel

• Fuels ignite more easily when vaporized. Why is this so?

Combustion • Combustion is the actual igniting and burning of the air-fuel mixture. The oxygen combines with the vaporized fuel to provide the combustion.

• How fast the fuel burns determines the explosiveness needed to get full power from the engine • We control the rate of burning by – How far we compress the air – How much fuel is used – How volatile the fuel is

Engine elements: Reciprocating and Rotary Motion • Reciprocating motion = up and down or back and forth • Rotary motion = a circular motion around a point

• Engines convert reciprocating motion to circular motion • Four parts are needed: – Can you name them?

• • Cylinder Piston Connecting rod Crankshaft

• The piston fits very closely inside the cylinder, with the top of the cylinder being closed off by the cylinder head. • The cylinder head has an extra space at the top (combustion chamber) where the combustion of the air-fuel mixture occurs.

• The connecting rod connects the piston to the crankshaft. • When the piston is forced downward, it pushes the connecting rod down and forces the crankshaft to turn. • This changes reciprocating motion the rotary motion.

• ** The crankshaft contains a section offset from the center line of the shaft. The offset is called the crank or “throw”. • The stroke of the piston (how far it travels in the cylinder) is set by the throw of the crankshaft (how far it is offset).

Engine Elements: Compression of Airfuel mixture • An average gasoline engine works best when 14. 7 parts of air are mixed with 1. 0 parts of fuel, by weight. • 14. 7 pounds of air per 1 pound of fuel • 1361 gallons of air per 0. 16 gallons of fuel

Stoichiometric ratio • 14. 7 – to – 1 air to fuel ratio -- mixture • Under perfect conditions, all of the fuel would be burned and all of the oxygen used up in the combustion process • The stoichiometric ratio can vary and is dependent on octane and additives such at detergents and oxygenators.

Air fuel

• Compression ratio – tells how much the airfuel mixture is compressed by volume • Example: if at the bottom position, the cylinder holds 8 pints, and at the top position, the cylinder holds 1 pint, the compression ration is 8 to 1.

Engine elements: Cycles • Series of events: • 1. Fill the cylinder with a combustible mixture • 2. Compress the mixture into a smaller space • 3. Ignite the mixture, causing it to expand produce power • 4. Remove the burned gases from the cylinder

• In other words: • • Intake (suck) Compression (squeeze) Power (bang) Exhaust (blow) • Thanks Decker!!

• Two stroke engines: Two strokes of the piston (one up and one down) during each cycle • The whole cycle occurs during one revolution of the crankshaft.

• In four-stroke engines, the same 4 events occur (I – C – P – E), but with four strokes of the piston – two up and two down. • The crankshaft will rotate twice to complete the cycle.

• A single cylinder only gives one power stroke every two revolutions of the crankshaft, thus it only produces power one-fourth of the time. • Multiple cylinder engines allow the power stroke to follow much more closely, producing more continuous power.

Fuel systems • • Gasoline LP – gas Natural gas Diesel

Gasoline fuel system • The basic parts: • Fuel tank – stores fuel • Fuel pump – moves fuel to carburetor • Carburetor – atomizes fuel and mixes w/ air

• Fuel supply systems – Gravity feed – has the fuel tank placed above the level of the carburetor. Fuel flows by gravity to the carburetor. – Force feed – fuel tank placed wherever necessary. A fuel pump moves fuel from the tank to the carburetor

LP Gas System • LP is made up mainly of propane and butane that have been liquefied by compressing many gallons of vapor into one gallon of fluid. • The fuel tank must be a closed unit to prevent the vapor from escaping.

• When starting the engine, vapor withdrawal is used because the heat exchanger cannot change liquid fuel to vapor (carb only operates on vapor)

• In the liquid withdrawal system, a heat exchanger converts liquid fuel to vapor by circulating hot water from the engine cooling system around the fuel line. • As the fuel heats up and pressure is reduced, the fuel vaporizes.

Natural Gas Fuel System • Natural gas is gaseous at any temperature above -259 F. It must be stored in a closed container to prevent it from escaping. • Natural gas must be stored as – Compressed Natural Gas (CNG) – Liquefied Natural Gas (LNG)

• LNG is stored in a high-strength insulated fuel tank to maintain the low temperatures.

Diesel fuel system • In a diesel fuel system, fuel is sprayed directly into the engine combustion chamber where it mixes with hot compressed air and ignites. • No electrical spark is used to ignite the mixture.

• Instead of a carburetor, a fuel injection pump and spray nozzle are used. • Major components of a diesel engine – Fuel tank – Fuel transfer pump – Fuel filter – Water separator – Injection pump / high pressure pump – Injection nozzles

• Injection pump engines: the injection pump meters the fuel, puts the fuel under high pressure, then delivers it to each injection nozzle in the proper sequence. • High pressure pump – the high-pressure pump delivers fuel under high pressure to common rail-type systems.

Intake System • The intake system supplies the engine with clean air of the proper quantity, temperature, and fuel to provide the correct mixture for good combustion. • The intake system has these 5 parts: – Air cleaner -- Intake manifold – Carburetor / air inlet -- Intake valves – Supercharger/turbocharger (optional)

• Air cleaners – remove dust and dirt from the air flowing to the intake manifold. A precleaner prevents large particles from plugging the air cleaner • Superchargers – pressurize the intake air. The supercharger can increase horsepower by packing more air (diesel) or air-fuel mix into the engine cylinders than the engine could take in by natural aspiration. Superchargers are gear or belt-driven and gets power from the crankshaft

• Turbochargers - perform a very similar function as the supercharger, but is driven by the engine’s exhaust. • Intake manifold – route the air (diesel) or airfuel mix to the engine cylinder • Carburetor (gas) – mix incoming air with fuel in the proper proportion for combustion, and to control engine speed

• Intake valves – allow air / air-fuel into the combustion chamber. They are opened and closed by mechanical linkage from the camshaft

Exhaust system • The exhaust system collects the exhaust gases after combustion and carries them away. 1. Removes heat 2. Muffles engine sounds 3. Carries away burned and unburned gases

• The exhaust system has 3 parts: 1. Exhaust valves – opens to release burned gases. – operated by the camshaft 2. Exhaust manifold - collects the exhaust gases and routes them away from the cylinder 3. Muffler – reduces the sound of the engine exhaust.

Lubrication system • Responsible for – Reducing friction between moving parts – Absorbing and dissipating heat – Sealing the piston rings and cylinder walls – Cleaning and flushing moving parts – Deadening the noise of the engine

• Lubrication reduces friction between moving parts • Lubrication also conducts heat away from moving parts

• The lubrication system may splash oil on the parts or feed oil under pressure via internal oil passages. • The crankcase is where the oil is stored and cooled. • The crankcase must be vented (back to intake) to prevent pressure from the blow-by gases from the piston

Cooling System • Types: Air Cooling Liquid Cooling

• Air Cooling: – Uses air passing around the engine to dissipate heat – Used mainly on small engines and aircraft – Metal baffles, ducts, and blowers are used to aid in distributing air.

• Liquid cooling – Uses water or water-based solutions to dissipate heat. – The water/coolant circulates around cylinders and cylinder head – A large amount of engine heat is absorbed by coolant, then flows to the radiator. – Air flowing through the radiator removes heat from the coolant then dissipates the heat into the air.

• Water is an adequate coolant, but freezes in the winter • It is mixed with ethylene glycol to prevent freezing.

Compression Ratios • Compression ratio compares the volume of the air in the cylinder before compression with the volume after compression. • Gasoline: 8: 1 • Diesel: 16: 1

Torque • Torque = Twisting Force • Torque = Length of the lever X Force

Engine Measurement and Performance • Cylinder Bore (Diameter) • Piston stroke (Travel)

• Cylinder Bore: • The cylinder bore of an engine is the diameter of the engine’s cylinders.

• Piston Stroke: • Piston stroke is the distance traveled by the piston either from the bottom dead center (bdc) to its top dead center (tdc) or from tdc to bdc.

• Piston stroke: Is determined by the crankshaft – the amount of offset from the centerline. The distance from the centerline of the crankshaft to the center of the rod journal is exactly one-half of the piston’s stroke. -- Also called the crankshaft throw

• Piston stroke:

• Long stroke engines are usually slower, but produce more torque. • Short stroke engines are usually faster because of the smaller orbit path. • Both engines, however, may have the same horsepower.

Displacement • The displacement is determined by the cylinder bore, the length of the stroke, and the number of cylinders. • Expressed in cubic inches, cubic centimeters, or liters

Displacement formula • Piston Area X Piston Stroke X Number of Cylinders • How do you find the piston area? • You multiply the bore x 0. 7854

Example: You have a six cylinder car with a 5. 0 inch bore and a stroke of 4. 4 inches. What is it’s CID (cubic inch displacement)?

Solution (5. 0 X 0. 7854) X (4. 4) X 6 = Piston area 518. 52 cubic inches Stroke # of cylinders

Horsepower Credited to James Watt Determined that a draft horse could pull 330 pounds a distance of 100 feet in one minute 1 horsepower = 33000 pounds/feet of work in one minute

1 hp = 33000 pds/ft in one minute or 1 hp = 550 pds/ft in one second 1 hp = 746 watts

Horsepower formula hp = force (pounds) X Distance (feet) time (minutes) x 33000 hp = force (pounds) X Distance (feet) time (seconds) X 550

Horsepower can also be calculated using a dynamometer with a given torque setting at the flywheel. It can also be calculated using a given number of watts.