Engines 2

Question 1

Difference between piston and jet engines

Answer 1

Piston:
Reciprocating parts
Intermittent internal combustion
Heat energy to mechanical energy

Jet:
Rotating parts
Continuous internal combustion
Uses action reaction to produce thrust

Question 2

Stroke definition

Answer 2

Distance of piston motion

Question 3

Swept volume

Answer 3

Volume in cylinder between TDC and BDC

Question 4

Clearance volume

Answer 4

Volume above PISTION at TDC

Question 5

Compression ratio

Answer 5

CR = (swept volume + clearance volume) / clearance volume

Question 6

Bore

Answer 6

Internal diameter of cylinder

Question 7

Firing interval

Answer 7

= number of degrees per cycle / number of cylinders

DA40= lycoming IO-360 m1a. Firing interval is 180

Question 8

Firing order

Answer 8

1324 5768
1 —>
<—2
3<—
—>4

Question 9

Manifold

Answer 9

Ducting talkies fuel from carb to cylinders (induction manifold) and leads exhaust gases from the cylinders to main outlet (exhaust manifold)

Question 10

Manifold pressure

Answer 10

Pressure at any time in the induction manifold

Question 11

Crank angle

Answer 11

Angle between crank and piston

Question 12

Boyle law

Answer 12

pV=C1 (c is temp and constant)

Question 13

Charles law

Answer 13

V= C2T (pressure is constant) volume directly proportional to temp

Question 14

Heat rejection

Answer 14

Loss of energy in heat

Question 15

Valve timing

Answer 15

Exact timing of inlet and outlet valves

Question 16

CamshFt

Answer 16

Controls valves and gear to 1/2 speed of crankshaft
Timing adjusted using tappets and Valve clearance

Question 17

Valve lag

Answer 17

The late closing of the inlet valve to allow for maximum induction due to inertia of mixture (typically 60° of crank angle)

Intake valve open 15° before TDC of induction stroke and closes 60° after BDC to maximise intake

Question 18

Valve lead

Answer 18

Exhaust valve opening before bdc and closing after TDC (typically 55° of crank angle)

Exhaust valve opens 55° before BDC of exhaust stroke and closes 15° after TDC

Question 19

Valve overlap

Answer 19

15° either side of TDC between exhaust and induction strokes both valves open

Scavenging:
Increases intake due to reduction in pressure from open exhaust valve
Increases exhaust effectiveness incoming mixture pushes exhaust out
AIDS internal cooling of cylinder by swirling relatively cool incoming charge

Question 20

Effective crank angles

Answer 20

Top and bottom of rotation less effective (less vertical movement)
First 90° and 3rd 90° cover most volume

Question 21

Most effective con rod thrust

Answer 21

Angle between con rod and crank web is 90°
This occurs with crank angle of 67°
Max torque produced when peak pressure occurs before this angle
Con rod typically 2.5 times crank throw

Question 22

Ignition timing

Answer 22

Finite time for combustion process (.003-.004 seconds)
At 2000 rpm crank turns 15° every .001 seconds

Question 23

Factors that effect combustion timing

Answer 23

FA ratio ccm 1:15 burns the fastest
Temp higher is faster
Frame of fuel : lower grade leads to large increase in flame front speed
CR and manifold pressure: high pressure faster burn
Number of ignition points
Gas turbulence: more swirl faster burning

Question 24

Spark advance

Answer 24

In order to develop peak pressure before 90° crank con rod angle
Ignition initiated 15-40° before TDC (usually 25°)

Question 25

Rpm vs engine power

Answer 25

Higher rpm gives higher engine power until it doesn’t