The flashcards below were created by user
on FreezingBlue Flashcards.
Name the five processes in an internal combustion engine in order starting with compression
What is the range of power produced by internal combustion engines and what order of power is produced by the vast majority of engines?
- Range: 0.01 kW to 20x10^3 kW
- Order: 10^2 kW
What components of a reciprocating engine have remained basically the same since the later 1800s?
- reciprocating internal combustion engine
- connecting rod
Can both the spark ignition (SI) and compression ignition (CI) engines use the four stroke and the two stroke cycles?
What does knock limit in an Otto cycle engine?
the maximum compression ratio of the Otto cycle engines
What controls the power in a SI engine?
What controls the power in a CI engine?
the amount of fuel injected into the cylinder
What limits the power of a CI engine?
the formation of smoke (forms if there is inadequate mixing of the fuel and air)
Does a diesel or C.I. engine have a throttle?
What is scavenging in a two stroke cycle?
the pushing out of exhaust by the incoming air
What is short circuiting in a two stroke engine?
when some of the air goes straight through the cylinder and out the exhaust port
Why is short circuiting particularly bad for carbureted engines?
Instead of being in the crankcase, there is an air-fuel mixture. So, if short-circuiting occurs, fuel is wasted and there is increased hydrocarbon emissions.
Which is greater, the brake power or the indicated power and why?
Indicated power; due to friction
bsfc is a valid measure of efficiency provided what parameter is held constant?
q_c (the heat of combustion)
Is the volumetric efficiency defined in Ferguson and Kirkpatrick chapter 1 dependent on the atmospheric or intake density?
What is a typical bmep and mean piston speed for an engine, independent of the size?
- bmep = 5 bar
- mean piston speed = 5 m/s
What causes the torque at maximum throttle to decrease as at high engine speeds.
Viscous friction effects
Which occurs at lower speed, maximum torque or maximum power?
intake pressure is greater than exhaust pressure
units of Joule
- # revolutions/cycle
- 2 stroke = 1
- 4 stroke = 2
mean effective pressure
the average pressure acting on the expansion stroke that will produce the same amount of work as is produced by the cycle
goes up when you turbocharge
- specific fuel consumption
- mdot_f/power or m_f per cycle/work per cycle
can only compare engines that use the same fuel
- combustion efficiency
- 99% +
- fraction of heat converted to work
fuel conversion efficiency
e_vi is less than or equal to 1.0
- displacement volume
- units: m^3/cycle
an internal combustion engine, in which fuel intake depends solely on atmospheric pressure
identifies work being produced by the cylinder gases on the piston of the engine
the work measured from the output shaft
- Rod/Crank ratio
- rod length/crank radium (1/2 stroke)
When does r_c apply?
- Otto: 1-2 and 3-4
- Diesel: only 1-2