Lesson 2b - Heat Engine

Engine

are mechanical devices that convert heat energy of fuels into mechanical energy

External Combustion Engines (ECE)

Internal Combustion Engines (ICE)

Types of heat engine

External Combustion Energy (ECE)

the fuel is ignited and burned outside a cylinder and the heat energy is applied indirectly to a piston by an intermediate medium usually water vapor.

Internal Combustion Engines (ICE)

the fuel is ignited and burned inside a cylinder and the resulting explosion causes an instantaneous application of pressure to a piston.

Internal Combustion Engines

completely replaced the steam engine for all types of agricultural power applications

fuel or combustible fuel

is placed inside the cylinder in a gaseous condition and compressed before it is ignited

Cylinder Block/Engine Block

confines the expanding gases and forms the combustion chamber

Cylinder Head

houses the valves and forms a cover to the cylinder

contains the spark plugs in SI engines and the fuel injectors in CI engines and some SI engines

Cylinder Head Gasket

found between the head and the block

seals the combustion chambers, and water and oil passages

serves as a sealant between the engine block and head where they bolt together

Cylinder

constitute the basic and supporting portion of the engine power unit

its major function is to provide space in which the piston can operate to draw in the fuel mixture or air (depending upon spark ignition or compression ignition), compress it, allow it to expand and thus generate power

Piston

receives and transmits the pressure forces in the combustion chamber to the rotating crankshaft

Crown - Skirt

top piston is called the ___ and the sides are called the ___

Piston Rings

retain compression; reduce cylinder wall contact thereby reducing friction losses and wear

Compression Rings

Scraper

Oil Ring

Three types of piston rings according to function

Compression Rings

The first and second rings

control blowby

Scraper

keeps excess oil from the combustion space

Oil ring

serrated to deliver oil to bore

Piston Pin

also known as Wrist Pin

connecting rod is connected to the piston through the ___

serves to fasten the piston to the upper end of the connecting rod;

Connecting Rod

connects the piston to the crankshaft

transmits the power of combustion from the piston to the crankshaft

Small bearing end - Big bearing end

___ known as small end, and the other end is known as ____

Piston

Piston Rings

Connecting Pin

Connecting Rod

Parts of piston assembly

Crankshaft

converts the rectilinear motion of the piston into rotation

has harmonic balancer, or vibration dampener, mounted on the from where it muffles torsional vibration

Crank Throw or Crank Radius

The offset from the axis of ration is sometimes called ____

Flywheel

keep the engine at uniform speed when the crankshaft is not receiving power from the piston

store energy that keep the engine rotating between power strokes and smooths out engine operation

Valve Train

consists of the valves, camshaft, and other associated parts

Valves

control the flow of the incoming air-fuel mixture and the outgoing exhaust gasses

Larger

intake valves are ___ than the exhaust valves

Timing Gear

connected by chain, gears, or a belt to the crankshaft at one end

ICE - fuel is combusted inside a cylinder

ECE - fuel is combusted outside of the engine system

engine classification based on where combustion occurs

Electric (Spark) ignition engine or Otto Cycle Engine

Compression (Injection) ignition engine or Diesel-cycle engine

engine classification according to the method of ignition

Dr. N. A. Otto

a German who patented the first successful engine operating on four-stroke cycle principle.

Dugald Clerk

an English man, who patented the first two-stroke-cycle engine

Electric (Spark) ignition engine or Otto Cycle Engine

utilizes an electric spark produced by a sparkplug located inside the combustion chamber to ignite the compression air and fuel mixture

gasoline; carburetor

in spark ignition engine, Fuel used is ___ and metering is done by a device called ____

Compression (Injection) ignition engine or Diesel-cycle engine

utilizes the heat of compressed air to ignite the fuel as it is being injected inside the combustion chamber

Diesel; fuel injection system

in compression ignition engine, the fuel used is ___ and metering is accomplished by the ___

Dr. Rudolph Diesel

a German engineer, who patented the first engine designed to operate utilizing the heat produced by high compression for igniting the fuel charge in the cylinder.

Two-stroke cycle engine

Four-stroke cycle engine

Engine Classification according to the number of strokes to complete a cycle

Two stroke cycle engine

completes the cycle in 1 revolution of the crankshaft or two piston strokes

Four stroke cycle engine

completes the cycle in 2 revolutions of the crankshaft or four piston strokes

Intake

Compression

Power

Exhaust

ICPE

the events that occur in a 4SCE

Two stroke engine

is one in which two strokes of the piston are required to complete the necessary series of events required to produce one power stroke

1. Stroke compresses air in the cylinder to ignite the fuel oil

2. the other stroke is produce by the burning gases. it is the power stroke

The two strokes are

Gasoline engine

Diesel engine

engine classification according to the fuel used

Gasoline engine

engine that uses a fuel, represented by octane (C8H18) octane rating

Diesel engine

Engine that uses a fuel, represented by cetane (C16H34) cetane rating

paraffin hydrocarbons or alkanes

Cn H2n+2

general formula for alkanes

Indirect cooling system

Direct Cooling system

engine classification according to method of cooling

Indirect cooling system

also known as water-cooled engine.

water serves as the coolant or the medium which circulates in the water jackets to absorb the heat from the engine.

Direct cooling system

also known as air-cooled engine

Air is directly used as cooling agent. Instead of water jackets, there are metal fins or shrouds that are placed around the cylinders

Small engines

Automotive engines

Marine engines

Engine classification according to number of cylinders

Small engines

used in motorcycles and even small cars

one, two, or three cylinders

Automotive engines

usually have two, four, or six cylinders

Marine engines

have more than 8 cylinders.

Vertical or inline engine

Horizontal Engine

V - engine

Engine classification according to cylinder arrangements

Vertical or in-line engine

cylinders arranged vertically one after the other in the cylinder block

Horizontal engine

cylinder arranged horizontally

V-engine

cylinder arranged in two rows or banks. the block resembles the shape of "letter V"

I-head engine

L-head engine

F-head or T head Engine

Engine classification according to valve arrangements

I-head engine

it has all the intake and exhaust valves placed or installed or mounted in the cylinder head.

these valves are operated by rocker arms actuated directly by camshaft and from the crankshaft.

L-head engine

it has all the intake and exhaust valves located on one side of the cylinder block.

the valves are directly operated by tappets or cam followers.

F-head or T-head engine

the arrangement of the valves follow the letter it represents

low speed

medium speed

high speed

Engine classification according to speed

low speed

below 350 rpm

medium speed

350 to 1000 rpm

high speed

over 1000 rpm

direction injection

indirect injection

Engine classification according injection

direct injection

injects the fuel directly into the combustion chamber

indirect injection

injects the fuel in the pre-combustion chamber

Piston displacement, crankshaft speed

the power output of an engine is largely determine by its ___ and ____

Piston displacement

Pd = A x L

Piston displacement is the space swept through by the moving piston in moving from end of its stroke to the other end and is expressed in cubic unit.

Engine displacement

Ed = Pd x n

provides information as to the relative size of the rngine and is related to its ability to produce power

Compression ratio

is a characteristics of an engine that is related to engine efficiency

is the ratio of the total volume in a cylinder to clearance volume

Clearance volume

is the volume or space within the cylinder above the piston when the piston is at the upper end of its stroke

Thermal efficiency

TE = Bhp/pf

the ratio of the output in the form of useful mechanical power to the power value of the fuel consumed

an indication of the fraction of energy in the fuel that is converted to power at the flywheel

15 to 35%

TE of ICE varies from ___ to ___, depending upon the type of engine, speed, load, design factors

Brake thermal efficieny

is the overall efficiency of the engine in converting fuel power into useful power

Torque (ft.lb)

refers to the turning or twisting effort developed through its crankshaft and applied to the belt pulley or power-transmitting mechanism

Brake mean effective pressure

the pressure which would result in a given brake power output if there were no losses due to friction and driving the engine accessories

Mechanical Efficiency

ratio of brake horsepower to indicated horsepower.

varies from 75-90% depending upon the load, speed, etc.

losses due to friction in the moving parts

losses involved in the induction of the fuel mixture and the exhaust of the residue

principal factors affecting ME of an engine

Specific Fuel Consumption

developed to indicate fuel consumption in relation to the amount of work that is being done by the engine