Small Engines Flashcards

Question

What is the function of the compression ring?

Answer 1

Combustion gas pressure forces piston ring against cylinder wall to form seal

Answer 2

Allows excess oil to pass from cylinder bore and return to oil reservoir

Answer 3

- Older design -Has deflector piston -piston dome directs incoming fuel/air up and over -Smooth idle and good low RPM performance -not breathing efficient -high RPM exhaust gasses get left behind -Inexpensive -Gets too hot and can cause pre ignition

Answer 4

-series of 2 or more ports direct the air/fuel into cylinder -better fuel economy -scavenges more completely -Superior engine power

Answer 5

when something inside the combustion chamber ignites the air/fuel mixture before the spark plug Red-hot metal from the piston, cylinder, or cylinder head can cause this

Answer 6

-Reduce friction -support a load a. radial loads b. axial loads

Answer 7

1.Journal bearing: for parts that spin: crankshaft, piston pin, camshaft 2. Guide bearing: for parts that reciprocate: valve guide 3. Thrust bearing: controls side-to-side end thrust (axial load)

Answer 8

*physically compact * low cost * easily replaced * can tolerate greater levels of debris in the lubrication

Answer 9

1. cylindrical roller bearings *used in radial & axial load applications *needle type & tapered rollers are variations of cylindrical rollers 2. ball bearings * designed for radial loads & axial loads * offer lower friction levels than #1

Answer 10

 Cool engine parts by absorbing heat  Clean engine via detergents that are added to the oil  Seal the area between the rings and the cylinder wall to improve combustion  Quiet the engine by separating moving parts

Answer 11

its resistance to flow or rate of flow. * Low viscosity oil = thinner (think baby oil) * High viscosity oil = thicker (think honey)

Answer 12

* grease is oil that has a thickener added to increase its viscosity  lithium is a common thickener * rust and corrosion prevention additives are added * “tackifiers” makes it cling to parts * antifriction additives such as Molybdenum may be added * easier to seal in (and prevent leaks) than oil is * better than oils under heavy loads * it is designed to remain in contact with parts and lubricate as well  without being squeezed out between moving parts  or forced out from gravity or centrifugal force

Answer 13

* the points act as a mechanical switch * they open and close the coil’s primary winding circuit * spark at the plug occurs when the points open

Answer 14

mix air & fuel in the correct proportions (14.7:1)  lower ratios means the carburetor is delivering more fuel for a given amount of air – a rich mixture  colder engines or colder climates require more fuel - a richer mixture  ratios above 14.7:1 indicate that there is less fuel for a given amount of air – a leaner mixture * the carburetor must atomize the fuel * fuel delivery from the carb to the engine is determined by two forces:  atmospheric pressure and...  engine vacuum (which is low pressure)

Answer 15

1. Float bowl style carburetor 2. Suction Feed Carburetor 3. Diaphragm Carburetor – 2 stroke engine 4. Constant Velocity Carburetors 5. Sliding Valve Carburetors

Answer 16

The piston moves downward, the intake valve opens to allow air into the engine cylinder, exhaust valve remains closed. As the piston pushes downward, this creates a partial vacuum inside the cylinder that pulls air molecules in. *only air is drawn into the cylinder – no fuel * the air is not throttled on a diesel * simple – no traditional throttle needed * excellent volumetric efficiency

Answer 17

the ratio of the volume above the piston at BDC compared to the volume at TDC. * The formula for CR is... cylinder volume + combustion chamber volume % combustion chamber volume * typical compression ratios for gasoline engines range from:  8.5:1 up to 12:1 * typical cylinder pressures in gasoline engines range from:  120 psi up to 190 psi

Answer 18

only air is initially introduced into the combustion chamber. The air is then compressed with a compression ratio typically between 16:1 and 24:1. This high compression causes the temperature of the air to rise. *much higher compression pressures than a gasoline engine * compression pressures can range from 400 to 600 psi * higher compression means higher efficiency * air temperature at the end of the compression stroke can reach ≈500°C or higher

Answer 19

towards the end of the compression stroke, diesel fuel is sprayed directly into the combustion chamber under high pressure  fuel pressure ranges from 3000psi to 40,000psi * the high fuel pressure is needed to overcome the pressure of the compressed air, but also to properly atomize the fuel * injection initiates combustion  therefore, injection timing is critical * no separate spark is needed to initiate ignition * air-to-fuel ratios in a diesel can range from:  20:1 for high load to...  70:1 for light loads

Answer 20

the heat of the compressed air ignites the diesel fuel * high pressure develops as the burning gasses expand forcing the piston down & creating torque at the crankshaft * timing of the injected fuel is critical as it is with the timing of the spark in a gas engine * the quantity of fuel injected determines power output & speed of the engine

Answer 21

uses conventional process to push out burnt gases * more heat energy has gone into driving the piston down the cylinder & less is lost to the exhaust stream when compared to a gasoline engine

Answer 22

 direct injection  indirect injection

Answer 23

fuel is sprayed directly into the combustion chamber * “Mexican hat” design eliminates dead air space below fuel injector  this creates maximum turbulence  excellent fuel efficiency and torque levels  the most common design now in use

Answer 24

* Part of the combustion space is in the cylinder head * Fuel is injected into the precombustion chamber * Position & design of the pre-combustion chamber causes air at the end of the compression stroke to enter at very high speeds & creates turbulence * This enhances fuel & air mixing which increases combustion speed thermal efficiency is lower because there is more surface area * part of the air-fuel mixture is burned in the precombustion chamber & some of it is burned in the cylinder * used in all passenger car and light truck diesels until the mid 1990’s

Answer 25

heat the air in the cylinder prior to a cold start

Answer 26

Seriously, go do it

Answer 27

1. Air & Fuel 2. Spark 3. Compression

Answer 28

1. Piston Port *piston skirt controls port opening/closing * usually used with loop scavenged engines * simple, inexpensive design 2. Reed Valve Engine * a pressure sensitive one-way valve * thin spring steel reeds flex during intake stroke to allow AFM to enter cylinder * during power stroke the positive pressure in crankcase closes and prevents fresh AFM from being pushed out of the crankcase 3. Rotary Disc Valve Engine * uses a rotating disc spun by the crankshaft * during the intake stroke, AFM is admitted into the crankcase only when the opening in the rotary valve is in alignment with the crankcase port

Answer 29

* gasoline and oil is premixed and poured into the fuel tank * gas-to-oil mix ratio can range from 25:1 to 50:1 * the ratio is very important!