Chapter 17 Study Quide

IHP

(Indicated Horsepower) The amount of pressure made in the combustion chambers. It is measured with special instruments and varies throughout the four-stroke cycle. Theoretical Measurement

NH

(Net Horsepower) The maximum power available from the engine when all accessories are turned on

Compression ratio of diesel engines

15:1 to over 20:1

Cylinder bores in automobile engines usually range from ?

3.5 - 4 inches

Average engine has how many strokes?

3.5 - 4 strokes

Torque readings are made every

500 rpm

Torque

A TURNING OR TWISTING FORCE; THE MOMENT OF A FORCE; THE MEASURE OF A FORCE'S TENDENCY TO PRODUCE TWISTING OR TURNING AND ROTATION AROUND AN AXIS

One horsepower in terms of work is

Amount of work required to lift 550 pounds 1 foot in 1 second

heat

Another form of energy

Swept Volume Formula

Bore/2 x Bore/2 x Stroke x 3.14 (pi) = Swept Volume OR [3.14 (pi) x B^2 x Stroke] x Number of Cylinders / 4

Formula to determine cylinders displacement

Bore^2 x Stroke x 0.7854

Engines total displacement is determined by multiplying what?

Bore^2 x Stroke x 0.7854 x Number of Cylinders

Heat is measured in

British Thermal Units (Btu). One Btu is the amount of heat required to heat 1 pound of water by 1*F. 1 Btu equals 778 ft - lb

What might be wrong if the compression pressure is low?

Burned valve, a broken piston ring, or a blown head gasket could possibly be causing a leak.

How is the compression pressure measured?

By installing a compression tester into the spark plug hole and cranking the engine through several revolutions

How is the engine size determined?

By the volume of air that its pistons displace in the cylinders.

Chassis dynamometer includes what safety devices?

Carbon monoxide, keeping vehicles secured to rollers, part failure and noise

What lowers the engines effective compression ratio?

Closing the intake valve later

What is the piston or cylinder displacement measured by?

Cubic Inches, cubic centimeters, or liters

Mechanical effeciency

Describes all ways friction is lost in the engine, engine output drivided by engine inout

piston stroke

Distance the piston moves from top dead center (TDC) to bottom dead center (BDC)

What is the Maximum volume of the cylinder and combustion chamber?

Eight times the combustion chambers volume (8:1)

What are the 2 automotive dynamometer power absorption units

Electromagnetic and water brake

What are the characteristics of a oversquare engine?

Faster revving, Lack Low-speed torque

Engine Dynamometer includes what safety devices?

Fire, part failure, and noise

Where is Inertia and energy stored?

Flywheel

What is work measured by?

Foot-Pounds or watts

Formula for work is:

Force x Distance = Work

Gasoline engines of muscles cars from the 50s - 80s had higher or lower compression ratios?

Higher (12:1)

Compression ratio determines?

How much air and fuel is being compressed on the compression stroke. As the piston moves from BDC to TDC in a gasoline engine, the mixture is compressed to about 1/8 of the volume it occupied when the piston was at BDC.

What is compression pressure measured in?

In pounds per square inch (psi) or kilopascals (kPa)

What can a higher compression ratio do?

Increase engines power and fuel economy, produce more exhaust emission.

The compression ratio can have an effect on how much power an engine can produce by?

Increase the thermal efficiency of the engine

Why are the compression ratio on newer vehicles starting to trend upward?

It is trending higher due to improved computer programming and gasoline direct injection

What are some forms of work?

Lifting or Sliding

Effective Compression Ratio of 7:5:1

Maximum for hot street engines or engines with poor intake systems and low volumetric efficiency. Pump gas can be used

Effective Compression Ratio of 7:1

Maximum for street engines with good compression, intake, and exhaust systems. Pump gas can be used

Chassis dynamometer (road horsepower)

Measures the horsepower delivered to the drive wheels. This is always less than brake horsepower because of friction loss through the driveline.

The more the mass the more or less it is effected by Enertia

More

What is work measured by?

Newton-Meters or joules

hub-driven dynamometer

Portable, can be taken to racetracks

What is force measured in?

Pounds or Newtons

gross horsepower

Power produced at the crankshaft

What forms of force are there?

Push,Pull, or lift

Effective Compression Ratio of 8:1 and above

Racing gas and dyno tuning required

thermal effiency

Ratio of how effectively an engine converts a fuels heat energy into usable work

Service specifications chart

Shows specifications of an automobile

What are the characteristics of a undersquare engine?

Slower revving, Good low-speed torque. They make good engines for work trucks.

Torque in an engine is?

The amount of turning force exerted by the crankshaft

When measuring the bore and stroke how are they listed?

The bore is listed first and the stroke is listed last. For example, 4,000 in. X 3.500 in would mean 4 in. bore and 3 1/2 in. stroke

What determines an effective compression ratio?

The closing time of the intake valve

The more you squeeze the mixture into smaller places the more___?

The higher the concentration pressure and increased expansion of the mixture throughout the power stroke

The larger the displacement means?

The larger the engine

What is the piston stroke controlled by?

The length of the throw of the rod journal

net horsepower

The power that remains for use

scavenging

The vacuum behind the moving exhaust stream draws in fresh air and fuel through the open intake valve.

During combustion, what is the potential energy of the air-fuel mixture turned into?

Thermal (heat) energy and kinetic energy

Tightening a bolt is a use of

Torque

Measuring horsepower

Torque x rpm / 5200

Atkinson Cycle Engine

Used on many hybrid vehicles because it can run more efficiently within a relatively narrow rpm band.

Engine Dynamometer

Used to measure the brake horsepower of modern car engines

What is the compression pressure of Gasoline engines?

Usually 125-175 psi

Horsepower is measured in?

Watts

undersquare

When the bore is less than the stroke.

Momentum

a body going in a straight line will keep going the same direction at the same speed if no other forces act on it.

dynamometer (dyno/dyne)

a power absorption device for measuring engine power. the engine must be loaded (braked) to measure the torque it can produce.

Prony brake

a simple friction brake dynamometer

twin roller chassis dynamometer

also called cradle roll, has smaller rollers than chassis dynamometer

Joules

an equivalent value that compares heat energy (Btu) to mechanical energy (ft-lb) 1 Btu = 778 ft. lb

Swept Volume

another means of determining a cylinders displacement.

Force

any action that changes, or tends to change, the position of something

Momentum is the product of

bodys mass and speed

Engine Displacement

determined by multiplying the cylinder displacement by the number of cylinders

bore

diameter of the cylinder

Power

how fast work is done or how fast motion is produced against a resistance

Valve overlap

is a moment where both the intake valve and exhaust valve are open simultaneously for a brief moment

mean effective pressure

is the ratio between the work and engine displacement.

Horsepower

measurement of engines ability to perform work in a specified time. One horsepower equals 33,000 ft-lbs of work per minute.

Crank Throw

one-half of the total piston stroke

Energy

the ability to do work, or ability to produce a motion against a resistance.

Intake stroke

the air-fuel mixture has work done on it to get it into the cylinder

compression pressure

the amount of pressure made by the piston moving up in the cylinder.

Volumetric efficiency

the efficiency with which the engine can move the charge of fuel and air into and out of the cylinders

power stroke

the expanding air-fuel mixture work

watts

the horsepower equivalent in the metric system. One horsepower equals 0.746 kW

Inertia

the tendency of a body to keep its state or rest or motion

Displacement

the volume that the piston displaces the cylinder as it moves from the TDC to BDC.

Oversquare

when an engine has a cylinder bore that is larger than its stroke.

work

when an object is moved against a resistance or opposing force.

compression stroke

work is done as the mixture is compressed

exhaust stroke

work is performed as the exhaust gas is expelled from the engine

GHP

(Gross horsepower) The power available with only the water pump and alternator using power.

BHP

(Brake Horsepower) Usable horsepower at the crankshaft

FHP

(Frictional horsepower) The power lost due to friction. It is the difference between brake horsepower and indicated horsepower. It considers the power needed to compress the air-fuel mixture and friction between engines parts such as piston rings and cylinder walls