Small Engines Final
cold cranking amps
(CCA)- the number of amps produced by the battery for 30 seconds at 0 degrees Fahrenheit while maintaining 1.2 volts per cell
746 watts =
1 horspower
governor spring rules
1 replace like for like 2 replace if damaged 3 never modify
Hp range
11-18hp
exhaust head of valve temp
1100-1450?
Diesel engine compression ratio
14:1 25:1
types
2 stroke and 4 stroke
Spark occurs when
20 degrees of crankshaft rotation before TDC Because it needs time to ignite
water boils at
212* F
% of energy required to compress charge before combustion
25% of the energy released during combustion
intake valve angle
30 degrees valve face 31 degree
% of engine energy is used
30%
exhaust valve stem temp
300-800
support service requires how many parts
35,000 parts
intake face temperature
400-700
exhaust valve angle
45 degrees face 46
average dealer age
45 years
safety can shouldn't exceed
5 gallons
usefull life
6 years for walk behinds and rear engine riding mowers 9 years for garden, snow throwers and tillers
head of intake valve temperature
600-800
Small gas engine ratio
6:1 8.5:1
lost to other places not usable bby the engine
70%
how many engines manfactured a year
8,000,000
outdoor power equipment industry
8.5Billion $
U.S AC Voltage
80 Hz
products
8CO2 + 9H2O + 47N2 +heat
exhaust face temperature
900-1450
intake valve stem temperature
<300
common types of valve guides
Aluminum Valve Guides: most common, predictable thermal expansion rate, good performance, low manufacturing cost Brass Valve Guides: greater resistance to wear, abrasive foreign particles, ability to embed abrasive foreign particles Sintered Iron Valve Guides: separate machined from powdered iron compound heated and compressed, highest quality, lubricating, resistance to wear
ANSI
American National Standards Institute Specialize in codes and standards helps identify industrial and public needs for national standards Is the National coordinator of voluntary standards activities Serves as an approval house and clearinghouse for consensus standards Is the US representative at ISO
API
American petroleum institute Primary trade association of US petroleum industry Provides public policy regarding the development of petroleum Also addresses enviro public safety issues
types of horsepower
Brake horsepower friction horsepower indicated horsepower
reactants
C8H18+ 12 1/2 O2+ 47 N2
Advantages of 2 stroke engine
Can be used in any position Light weight Simple Easier to clear out water
3 Ignition
Charge is ignited and rapidly oxidized to release heat
Class D
Combustable Metals star
Compression ratio
Comparison of volume of combustion chamber with piston at BDC VS TDC
Safety Rules
Don't operate engine in disclosed area Work in space with ample room Use approved spark plug tester to check for spark Do not have an open flame or smoke near flamable liquids Don't refuel engine while it's operating Be familiar w/ engine shutoff procedures for quick response in an emergency Do not operate an engine w/o a muffler never leave operating engine unattended
4 power
Hot expanding gasses force piston down Both valves closed to save power and prevent damages
Disads of 2 stroke
Increased fuel consumption Higher emmisions
LAT
Limited Angle Torque
Valve overlap
Most useful at higher speeds Happens during exhaust to bring in and push out air at the same time
NIOSH
National institute for occupational safety and health develop and revise recomended exposure limits for hazardous substances And work to reduce or eliminate these hazards More research
OSHA
Occupational safety and health administration established color code, Requires employees to have safe work environment More enforcement
Class A fire
Ordinary combustables: wood paper trash triangle
crankshaft parts
PTO, PTO journal (on side with gear), Rod Journal/crankpin journal, Magneto Journal, (all are bearing journals) counterweights, crankgear,
Class B
Petroleum products: flamable liquids, chemical square
PCV Valve
Positive Crankcase Vent Vents off extra pressure
Colors
Red: fire, danger, stop Orange: danger(ous parts of machine) (exposed pulleys, gears, rollers, cutting devices) Yellow: caution (power source of machinery, under repair, safety lines) purple: radiation green: first aid/safety Black/White/BW: traffic and housekeeping
SAE
Society of American Engineers Network of people who want to advance engineering Major source of information used in design of small engine powered systems Also have standardized method of testing engine output
5 exhaust
Spent gases are removed and released to atmosphere Exhaust valve open Piston going up
The higher the compression ratio
The more fuel efficient the engine
thermal conductivity
ability of a material to conduct and transfer heat
standard
accepted form or practice
sidedraft
air intake above fuel bowl and parallel to horizontal plane, used on crossover engines
downdraft
air intake above fuel bowl used in horizontal shaft engines
explain or sketch Bernoulli's principle
air moving through restriction increases in speed and creates a low pressure area which draws in fuel [ also the higher pressure area forces fuel up
air vane governor
aka pneumatic, senses engine speed by the amount of air coming off the flywheel, as engine speed decreases, the governor spring pulls the throttle open
wiper ring
aka scraper ring, napier ring, back up compression ring in the middle, provides consistent thickness of oil film to lubricate the running surface of the compression ring most have tapered angle face
DC Current
all sources have a positive and a negative terminal, flows in one direction, all points in circuit have polarity, common source is a battery
valve stem surface treatment purpose
allow reduction in valve stem to valve guide clearance and reduce friction related wear
WOT wide open throttle
allows maximum speed
importance of compression
allows more energy to be released when charge is ignited, heat is produced during compression from work applied by piston
Btu
amount of energy to raise 1 lb of water 1*F
friction horsepower
amount of power required to overcome internal friction of engines moving parts
reserve capacity
amount of time that a battery can produce 25 amps @ 80 degrees Fahrenheit.
brake horsepower
amount of useable power taken from engine
Hardfacing
application of material to an engine component to improve wear resistance from load, heat, and chemical corrosion
magnetism
atomic level force derived from the atomic structure and motion of certain orbiting electrons in a substance
temporary (soft) magnet
can only become magnetic in an external magnetic field
hydrocarbon emissions
caused by incomplete combustion, consist of methane, ethane, acetane, and other hydrocarbons not readily oxidized at normal engine temps
different ways to provide proper mixture for starting in cold weather
choke plate (restricts air flow creating lower pressure and draws up more fuel), primer system (rubber bulb depressed to force fuel into venturi), dry bulb primer system (rubber bulb filled with air connected to fuel bowl, allow atmospheric pressure into fuel bowl depressing it forces fuel into venturi), wet bulb primer system (rubber bulb filled with fuel, when depressed forces that fuel into venturi)
governor droop curve
combination of rpm decrease and maximum brake horsepower (BHP) curves
specific gravity
comparison of the mass of a given sample volume compared to an equal volume of water
circuit
complete path that controls the rate and direction of electron flow on which voltage is applied
Elliptical piston
conform to ever changing dimensions of cylinder bore
lpg gases that qualify and where they are used
consists of propane, propylene, butane, and butylene storage facilities, terminals, forklifts, other material handling equipment because of reduced emissions
crankshaft
converts linear motion of piston into rotary motion
piston ring rotation:
critical to engine durability
piston
cylinder slides back and forth in cylinder bore by forces from combustion process
bore of an engine
diameter of cylinder bore
Piston materials and requirments
die- or gravity-cast aluminum alloy must withstand pressure and tenp
lawn mowers need less precision
due to greater chance of hunting and surging for load variations
Class C
electrical circle
What happens to electrolytes as battery discharges
electrolyte loses sulfuric acid and increases the percentage of water resulting in a decrease in specific gravity
electricity
energy created by flow of electrons in a conductor
mechanical governor
engine speed is sensed by the movement of rotating flyweights in a mechanical governor system
alcohol in gasoline, characteristics, advantages, disadvantages, limitations
enhances octane rating, burns less btu than gas, has richer air fuel mixture, provides more oxygen which increases engine operation temp methanol (an alchohol additive) can deteriorate rubber fuel lines and carburetor components protective sealing, can cause extreme overheating, alcohol's affinity for water can cause water bubbles in fuel tank, cause problems in 2 stroke engines, remove lubricating qualities
cylinder head
fastened to the end of cylinder block farthest from crankshaft, keeps the cylinder sealed, helps cool the engine and holds the spark plug.
advantages of lithium ion batteries
faster charging time, contain less toxic materials, low self discharge rate(1.5% per month)
head gasket
filler material between cylinder block and cylinder head to seal combustion chamber
Current (I)
flow of electrons moving past a point in a circuit, can be alternating or direct, measured in amperes (A), {similar to measurement of water through a pipe gallons per minute}
Hertz
frequency is measured in this, is equal to one cycle per second
governed idle
function that allows engine to accept light to moderate loads w/o stalling the engine @ idle the governor spring applies no tension, so it does not open the throttle plate if the engine is placed under load can be fixed by adding a governed idle spring
a flamable liquid
has a flashpoint below 100 degree
parallel circuit
has two or more paths for current flow, Allows parts to be opened up and the other parts to still work
governor spring
helps pull throttle toward the WOT position
effects of change in altitude
higher altitude thinner air means smaller charge inside cylinder lower altiude thicker air means larger charge inside cylinder
study parts of crankcase
holds crankshaft in place and oil resevour
crankcase
houses and supports crankshaft, anything covering the crankshaft
effects of valve rotation
improved temp distribution, cleans valve interface causes surface wear
when throttle plate is moved toward WOT position, engine torque is
increased
updraft
intake opening below fuel bowl, used on engines with little room for air cleaner assemblies, fuel tanks, and PTO attachments
common clearances for intake and exhaust valves
intake: .002-.003 exhaust: .004-.005
interface angle
intentional deviation from a specification of two mating machine components to improve seating quality after a sufficient break-in period
inherent pressure
internal spring force that expands a piston ring based on the design and properties of the material used requires significant force needed to compress a piston ring to a smaller diameter
magnetic flux
invisible lines of force in a magnetic feild
tight droop
less stable speed control but results in more available power
stroke
linear distance piston travels in cylinder bore from top dead center to bottom dead center
lpg
liquefied petroleum gas
integrally machined valve seat
machined portion of cylinder block, often used for intake valves
governor purpose
maintain engine speed regardless of applied load and conditions
engine governor
maintains engine speed by modifying air fuel mixture in carbuerator
conductor
material that allows the free flow of electrons
valve seat function
mates with valve face to seal combustion chamber/ removes heat from valves
electric dynamometer
measure brake horsepower by converting mechanical energy into electrical energy
eddy current dynamometer
measure engine torque using load produced by magnetic field
throw
measurement from center of crankshaft to the center of the crankpin journal, which is used to determine the stroke of the engine
water dynamometer
measures engine torque using load produced by a water pump
test tool
measures the condition or operation of engine component or system
prony brake
measuring engine torque using brake that exerts preasure on spring scale
carburetor
mixes air fuel mixture
function of the carburetor
mixes and provides required air fuel mixture to combustion chamber based on engine operating speed and load, air is drawn through carburetor as piston moves down and creates low pressure area
electrolyte
mixture of water and sulfuric acid used in lead acid battery
hydrocarbon molecule
molecule held loosely together by bond between hydrogen and carbon atoms, occurs naturally in all fossil fuels
speed sensing device
monitors engine speed and functions to maintain slowest possible engine speed
multiple barrel
more than one venturi, may have common or shared intake, used on bigger engines
gasoline as a fuel source
most common fuel, was originally undesirable by product, was used for lamp fuel and cleaning agent
AC Current
most common, produced by generator (rotating magnet through wire coil) , current changes directions
normal atmospheric air
mostly nitrogen and oxygen
flywheel
mounted at end of crankshaft provides inertia for the engine swings magnet around to build up charge for spark plug cooling fins to cirulate air
piston function
movable end of combustion chamber, creates compression
camshaft
moves and times tappets and valves
radiator
multi-channeled container allows air to pass around the channels to remove heat from liquid within
4 types of carburetor designs and common uses
multiple barrel, sidedraft, downdraft, updraft
piston ring twist:
negative twist in piston ring, creates a seal against the ring land during non combustion strokes
all 3 nitrous oxide compounds that are commonly produced
nitric oxide, nitrogen dioxide, and dinitrogen monoxide
Frequency
number of complete electrical cycles per second (cps)
antiknock index and how it relates to octane numbers
numerical value assigned to gasoline that indicates the ability to eliminate knocking and pinging in an engine, octane quality is indicated by the anti knock index research octane number is octane number that impacts engine knock at low speeds, market octane number at high speeds
lambda excess air factor
numerical value assigned to represent the stoichiometric ratio of atmospheric air to any hydrocarbon fuel small engines usually .6-.8
octane rating
octane is ability to resist engine knock and ping
flo-jet
older style, uses float bowl
valves
opened by tappets and camshaft intake brings in air fuel mixture exhaust releases exhaust gases
resistance
opposition to flow of electrons, measured in ohms
main (high speed) circuit
path from fuel bowl to emulsion tube created by fixed orifice jet in carburetor, helps control engine speed, increases engine performance with better control of fuel entering air stream
1 intake
piston moves down drawing air fuel mixture into combustion chamber, intake valve open
2 Compression
piston moves up compressing the air, both valves closed
Valve Interface
point of contact between valve face and valve seat
low volatility
poor cold weather operation
high volatility
poor hot weather operation
applied pressure
pressure applied from combustion gases to piston ring causing it to expand
vapor pressure
pressure exerted above the surface of the liquid
piston ring rotation
prevents any compression gasses or oil from entering ring land. and wear, maintains acceptable exhaust gas emmission
honing
process using hone with rigid carborundum stones rotated in cylinder bore to remove small surface irregularities and any glazing
adiabatic process
process where heat is derived from process itself heat is produced by work of piston, the increase in temp is proportional to quantity of work applied to compress the charge.
volatility
propensity of a liquid to become a vapor, all liquids have a certain measurable volatility based on the liquid and ambient temperature
valve guide function
provide consistent clearance between itself and the valve stem regardless of operating conditions and removes heat from valve
33000 jobs
provided
Barrel Shape piston
provides smoother transition during direction changes of piston, the piston roll into the cylinder wall when changing direction at the end of a stroke reduces noise, spreads force of directional change across a greater surface, and reduces side loading on the piston skirt
compression ratio
ratio of volume at BDC to volume at TDC small gas engines: 6:1 to 8.5:1
why lead acid batteries need to be recharged
reaction can not continue indefinitely, recharging drives the reaction backwards to store up electrons
bearings
reduce friction , maintain clearance between stationary and rotating components of engine
when throttle plate is moved toward WOT position, level torque is
reduced
Code
regulation or minimum requirment
governed idle spring
removes lost motion between the governor spring and governor linkage to improve governor sensitivity @ low rpm
how lithium ion batteries are used
replace lead acids in vehicular applications
piston ring dynamics
requires presence of oil film between piston ring running surface and the cylinder wall, piston rings should not touch the wall,
Valve Seat Insert
separate machined component pressed into the cylinder block, made from sintered iron
piston windows
series of small holes machined into oil ring groove surface of the piston
tappets/valve lifters
sit under the valves to move them
idle circuit
small hole in throttle plate, allows fuel mixture past throttle plate to prevent stalling at low speeds
Taper piston
smallest diameter of the taper at the piston head compensates for thermal expansion and growth
PPE
snug denim coveralls w/ freedom of movement convenient access pockets that don't snag, long hair secured, jewelry removed, safety glasses, face sheilds, goggles
stoichiometric ratio
specific air-fuel ratio of atmospheric air to fuel at which the most efficient and complete combustion occurs
detonation
spontaneous combustion of significant portion of charge before the spark induced flame front reaches it aka knocking, spark knock pinging causes pressure difference, then shock waves
wide droop
stable speed control but results in less available power
three functions of electrical system
starting engine, spark for ignition at proper time, battery charging system
magneto
stationary magnet that builds up charge for the sparkplug
permanent (hard) magnet
stays magnetic even after magnetizing force is gone
indicated horsepower
sum of brake and friction horsepower total power produced in engine cylinder
engine block
supports and helps maintain allignment of internal and external components/ keeps parts alligned
electronic governor
system that uses a LAT motor in place of the governor spring and speed sensing device provides greater sensitivity and control of engine speed than a mechanical governor
measurement from center of crankshaft to center of crankpin journal
throw
Hazard Diamond
top red: fire hazard right yellow: reactivity bottom white: specific hazard left blue: health hazard
compression ring
top ring, most exposed, transfers combustion chamber heat from piston to cylinder wall
piston rings
top: compression ring- seals combustion chamber middle: wiper ring- further seal and wipe cylinder walls botton: oil ring- wipe cylinder walls
carbon monoxide (char, reason it is produced, etc.)
toxic gas produced by incomplete combustion of gasoline or other HC-based fuels
connecting rod
transfers motion from piston to crankshaft and functions as lever arm
series circuit
two or more components connected so there is only one path for current flow
oil ring
two thin rails, holes cut in the radial center of the ring allow flow of excess oil back to the oil reservoir, highest inherent pressure
pre-ignition
undesirable engine condition, occurs when small portion of combustion chamber component or a particle in the combustion chamber becomes excessively heated and ignites the charge as it enters the combustion chamber
Hysteresis
undesirable motion of governor system components caused by engine vibration and governor system friction characteristics Related to wave physics: resonance, oscillation, etc
Hunting
undesirable quick changing of engine rpm when set at desired speed
Surging
undesirable slow changing of engine rpm in a cyclical pattern when the engine is set at a desired speed
Maverick Air
undesirable unaccounted for air entering engine through leaks caused by worn engine components decreases engine performance and increases exhaust gas temp
diesel engines
use injection pump to deliver pressurized fuel to cylinder at precise intervals heat from compression ignites fuel mixture
pulsa-jet
uses a pump to lift fuel from fuel tank to fuel cup (a resevoir high in fuel tank), more efficient than vacu-jet
magnetron ignition system
uses electrical components in place of breaker point and condenser, provide greater efficiency, and reliability
vacu-jet
uses fuel tank as very large fuel bowl with single pickup tube to fuel supply
breaker point ignition
uses mechanical switch to control timing of ignition, uses induction produced in ignition coil to cause a spark to ignite the charge, point plunger prevents movable points from touching fixed contact surface
induction
using magnetic field to create voltage and current conductor passes through magnetic field
components involved
valves, valve guides, valve seats, pistons, piston rings, and cylinder bore, head gasket, valve train
generators need
very precise speed control
volts (v)
voltage is measured in volts, volt is the unit of measure for electrical pressure difference between two points in a conductor or device
charge
volume of compressed air fuel mixture trapped inside combustion chamber ready for ignition
displacement
volume of stroke =strokeX.5(bore)^2Xpi
dynamometer types
water, electrical, eddy current, prony brake dynamometers test horsepower
preignition
when parts of the combustion chamber become heated and ignite the fuel mixture as it enters the chamber decreases problems, makes noises
WOT
wide open throttle
how is specific gravity checked, what does it indicate?
with a hydrometer, a decrease in specific gravity means a discharged battery