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1
Q

advantages of v engine

A

▪ Shorter engine compartment
▪ A shorter crankshaft has less bending stress

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2
Q

Opposed Cylinder (or “flat”) Engine advantages

A

Lower height and shorter engine and crankshaft length (vs. straight)

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3
Q

advantages of having more cylinders

A

▪ Smaller diameter – shorter flame travel distance
▪ More power strokes per revolution – smoother engine

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4
Q

disadvantages of having more cylinders

A

▪ More surface area – more friction
▪ More heat loss per cycle – more surface area to volume ratio

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5
Q

Naturally Aspirated

A

Atmospheric pressure intake

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6
Q

Supercharged

A

Intake air pressure increased using external compressor usually power from
crankshaft

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7
Q

Turbocharged

A

Intake air pressure increased with the turbine-compressor driven by the engine exhaust gases

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8
Q

Crankcase Compressed

A

Uses the crankcase as the intake air compressor (common in 2 cycle engines)

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9
Q

Top-Dead-Center (TDC)

A

Position of the piston when it stops at the furthest point away from the crankshaft

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10
Q

Bottom-Dead-Center (BDC)

A

Position of the piston when it stops at the point closest to the crankshaft

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11
Q

Bore

A

Diameter of the cylinder or piston face

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12
Q

Stroke

A

Movement distance of the piston from TDC to BDC and back again

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13
Q

Clearance Volume

A

Minimum volume in the combustion chamber with piston at TDC

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14
Q

Displacement or Displacement Volume

A

Volume displaced by the piston as it travels through one stroke

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15
Q

Wide-Open Throttle (WOT)

A

Engine operated with throttle valve fully open when maximum power or speed is desired

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16
Q

Brake Maximum Torque (BMT)

A

Speed at which maximum torque occurs

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17
Q

Carburetor

A

Venturi flow device which meters the proper amount of fuel into the air flow by means of a pressure differential.

18
Q

Flywheel

A

Rotating mass with a large moment of inertia connected to the crankshaft to store energy and provide a large angular momentum that keeps the engine rotating between power strokes and smooths out engine operation

19
Q

advantages of hybrid

A

o Better fuel economy
o Fewer emissions
o Shuts off IC engine when not needed
o Regenerative braking

20
Q

cons of hybrid

A

o Higher cost
o Higher weight
o Battery disposal environmental impact
o More complicated to manage air conditioning, coolant and other auxiliary systems when engine off

21
Q

Fuel Cell

A

Efficient method with less emissions for converting chemical energy into electricity vs. IC engine

22
Q

advantages of under square engine

A

less heat loss
shorter flame travel distance

23
Q

advantages of over square engine

A

less friction, slower piston speed
shorter cylinder length

24
Q

compression ratio

A

volume at bdc/volume at tdc

can be lowered using superchargers and turbochargers

25
work
fundamental engine output
26
indicated work
work inside combustion chamber (compression and power strokes)
27
pump work
intake and exhaust strokes (negative without super or turbo chargers)
28
brake work
crankshaft output after friction and other loads
29
why is mean effective pressure useful
can compare engines independent of their size and speed
30
torque
indication of ability to do work measured off of crankshaft units of Nm or lbft
31
power
rate of work units of kw or hp
32
dynamometers
measures torque and power over the engine speed and load ## Footnote o Simplest - absorb energy in a mechanical friction (prony) brake o Fluid or hydraulic dynamometers - absorb engine energy in water or oil pumped through orifices or dissipated with viscous losses in a rotor-stator combination ▪ Absorbs large amounts of energy ▪ Attractive for large engines o Eddy current - Disk, driven by the engine being tested, rotating in a magnetic field of controlled strength. The rotating disk acts as an electrical conductor cutting the lines of magnetic flux and producing eddy currents in the disk. With no external circuit, the energy from the induced currents is absorbed in the disk. o Electric - absorbs energy with electrical output from a connected generator ▪ Accurate way of measuring the energy absorbed ▪ Load is easily varied by changing the amount of circuit resistance ▪ Operate in reverse as motor that drives unfired engine for testing mechanical friction losses and air pumping losses, which are hard to measure on a running engine
33
in SI AF ratio higher than ideal
lean
34
in SI AF ratio lower than ideal
rich
35
equivalence ratio
actual ratio of fuel-air to ideal
36
specific fuel consumption
measurement of how much fuel an engine consumes per unit of power output Units: lbm/hp-hr or gm/kW-hr ## Footnote * Trends o Decreases with engine speed (less heat loss) until minimum and then increases (more friction) o Decreases with compression ratio (higher thermal efficiency) o Lowest with equivalence ratio near 1 and increases for higher and lower equivalence ratios o Decreases with engine size (better for larger engines)
37
conbustion efficiency
fraction of fuel that burns
38
volumetric efficiency
actual injected air per stroke vs. the benchmark of filling the displacement volume with atmospheric pressure air every stroke
39
Air-standard Cycle
Idealized engine cycle simplification for more manageable analysis
40
simplifications of air standard cycle
Gas in the cylinders are approximated as air that is treated as an ideal gas with constant specific heats * Closed cycle – exhaust air is recycled to intake air * Combustion modeled as appropriate heat input * Exhaust energy rejection modeled using heat transfer in the closed system * Constant pressure intake and exhaust strokes o Generally atmospheric pressure o Turbo and supercharges – higher constant intake pressure o Partially closed throttle – lower constant intake pressure * Isentropic (frictionless/reversible and adiabatic) compression and power strokes, neglecting these secondary processes: o Piston friction o Gas flow friction Heat transfer * Combustion – constant volume (SI), constant pressure (CI) or combination (CI dual cycle) o SI – fast combustion, piston assumed stationary while heat released o CI – slow combustion (less volatile fuel and no spark), piston expanding during combustion * Exhaust blowout – constant volume heat rejection * All processes reversible
41

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