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
