ME257 revision sheet 1 page 2

Question 1

Explain the term “Gas lag”

Answer 1

the inability of incoming air charge keeping up with the speed of the piston on induction stroke. this lag is more common on naturally aspirated engines

Question 2

Explain the term “Ineffective crank angle”

Answer 2

Is a period at DBC, TDC where the Piston has little to no movement, while the Crankshaft has a large amount of movement

Question 3

Explain the term “Valve overlap”

Answer 3

The period at TDC where both Inlet & Exhaust Vv are open on the exhaust stroke.
This helps
Assist induction
Improve scavenge
cooling on Vv

Question 4

Explain the term “TDC” - and how many are there in a four stroke cycle

Answer 4

The position of the piston, in the cylinder at the top of its upwards travel.
Two TDC- one for compression and one for exhaust stroke

Question 5

What type of fuel lines are fitted and who would you tell if there were to fail?

Answer 5

double walled due to the high pressures, if the first pipe fails, the leak will run down the second pipe wall. into drain to alarm tank. which indicates on the panel of a fuel leak.
there also a leak indicator on fuel pump to know which one has failed.

Question 6

what does H or HL stand for on fuel injectors

Answer 6

Long stem nozzle

Question 7

State the test that are carried out on a fuel injector before it can be installed

Answer 7

1. back leakage
2. set pressure
3. seat tightness
4. spray formation

Question 8

what does FCCAR180M756 on fuel pumps stand for

Answer 8

F = flanged type pump
CC = Pump size ie 15mm stroke
A = Single element
R = Roller trappet type
180 = plunger diameter
m756 = Special features S/M Pp

Question 9

Describe how the valenta fuel rack is adjusted

Answer 9

It is positioned accurately for tuning by use of a slip gauge

Question 10

explain the abbreviation BPF and what type of pump it is

Answer 10

BPF = British pump flanged and it is a single element pump