What is the purpose of a glow plug on a diesel engine?
Glow plug is a heating plug used with some diesel engines for easy starting. They are small electric heater plugs that are fitted to the small combustion chambers of in direct-injection engines. They are used to provide heat during cold starting. 

Whats the difference between an two stroke and four stroke petrol engine?

For presentation

Lubrication 

There are two types lubrication system of two-stroke engine.

Mixed lubrication - lubricating oil mixed with fuel; 

Separate lubrication - use of oil pump to pump the lubricating oil into the crankshaft, etc., then the oil burned with air-fuel mixture inside the cylinder. 

Due to this lubrication system carbon build build inside engine and will stick onto piston rings, causing leaks, or may block the exhaust port, causing power loss, and wear the crank and connecting rod bearing. 

In four-stroke engine lubrication system, there are also two types. 

One is splash lubrication - the oil is splashed up from the oil pan or trays in the lower part of the crankcase by moving components. The oil is thrown up as droplets or fine mist to provide lubrication to valve mechanisms, piston pins, cylinder walls, and piston rings. 

The other type is the combination splash and pressure lubricating system, The lubricating oil circulating through the engine to all moving parts requiring lubrication by an oil pump, it takes oil form the oil pan and forces oil through holes drilled in the engine block and crankshaft to lubricate all moving parts, in this system, cylinder walls are lubricated by splashing oil thrown off from the connecting-rod bearings.

Compare the lubricating system of two-stroke and four-stroke engine, we can see the two-stroke lubricating system is less effective than four-stroke engine. Therefore, the life of most of two-stroke engine only about half of four-stroke engine.

Other:
In two-stroke engine the main thermal parts are the cylinder head, cylinder, piston, 
piston rings and other parts. In four-stroke engine the main thermal parts including the cylinder head, cylinder head cover, cylinder, piston, piston rings and valve timing mechanism.Valve timing mechanism including valves, valve guides, valve seats, valve springs, camshaft, cam belt or chain, cam gear, belt or chain tensioner, rocker arm and other component parts. Two-stroke engine has small size, simple structure, light weight, easy manufacture and maintenance compare to four-stroke engine.
In four-stroke engine, it needs four strokes to complete a work cycle. First, intake air-fuel mixture into the cylinder, then the mixture is compressed, after that, ignite the mixture to generate power, last exhaust out from the cylinder. This intake, compression, combustion and exhaust processes are the four movements for four-stroke engine. Two-stroke engine crank 360 ° to complete a work cycle, that is, crankshaft rotate one revolution to complete the cycle, which is air-fuel mixture intake through the transfer port on cylinder wall, and push the burnt mixture out of exhaust port to complete the intake and exhaust process. but four-stroke engine crank 720 ° to complete a work cycle.Because two-stroke engine rotate one revolution to do a cycle, but four-stroke engine needs rotate twice, so the torque generated by two-stroke engine are more evenly than four-stroke engine. While at the same working speed and the same volume of cylinder and combustion chamber, two-stroke engine should outputs twice much power than the  four-stroke engines but there are power loss during intake and exhausts, and the piston working distance is short than four-stroke, so the output of the two stroke engine only about 50% to 70% more than the four-stroke engine.


Reference:
http://zhidao.baidu.com/question/78387415.html
http://www.doc88.com/p-04866931808.html
http://www.google.com/search?hl=zh-CN&source=hp&biw=1364&bih=597&q=engine+lubricating+system&oq=engine+lubri&aq=0&aqi=g2&aql=&gs_sm=e&gs_upl=19820l22511l0l12l11l0l0l0l0l653l2209l2-2.2.1.1
http://www.britannica.com/EBchecked/media/93029/Typical-gasoline-engine-lubrication-system
http://www.dansmc.com/4_stroke_oilpump.htm

Assignment

Assignment-(Pascals principle, Boyles Law, Charles Law)One page 300-500 words per subject, this must be in TUESDAY 3rd MAY

PASCAL'S PRINCIPLE

Blaise Pascal (1623 1662), France - the famous mathematician and physicist, philosopher and essayist. Main contribution is in physics, discovered PASCAL's law, and his name to be used as pressure units.

Pascal's law (the Principle of transmission of fluid-pressure)

Since the liquidity of liquids, when the pressure of a certain part of static fluid changes in a closed container,will pass this pressure to all directions constantly. 

According to the Pascal's law, when a pressure went on one of the piston in hydraulic system will produce the same pressure on another piston in the system. If the second piston area is the first ten times of piston area, then the forces on the second pistons will increase to first pistons ten times, but the two pressure of the piston still equal.

P1 = P2, F1 ÷ S1 = F2 ÷ S2

P - Pressure  F - Force  S - Area

This law in production technology is very important in the application of the principle. It has many uses, such as hydraulic brake etc.

BOYLE'S LAW

Robert Boyle (1627 ~ 1691) physicist and chemist, was born in January 25 1627.

Boyle's law

Certain quality of gas at constant temperature, the pressure in inverse proportion to the volume.

Certain quality of gas, with constant temperature, The average kinetic energy of gas molecules will not change. If gas reduce volume, the number of gas molecules in unit volume will increase, the number of gas molecules hit the container in unit time will increase, so the pressure will increase; if volume increase, the pressure will decrease. 

When temperature constant: 

P1 x V1 = P2 x V2

P - pressure   V - Volume

LARGER PRESSURE - LESS VOLUME

LESS PRESSURE - LARGER VOLUME

CHARLE'S LAW

Jacques Alexandre Cesar Charles (1746～1823）French physicists and mathematicians and inventor.

Charle's law 

Describe the pressure of quality gas at constant temperature for linear with its volume change rules: V=V0(1+βt)，V0 is the volume at 0℃, t in Celsius temperature, β is gas coefficient of expansion. For the ideal gas, β=1/273.15, V=V0(1+t/273.15), The quality that shall set the volume of ideal gas pressure with thermodynamics is proportional to the temperature.

Certain quality of gas, when its volume is certain, it is proportional to the pressure and temperature.

When volume constant: 

P1 ÷ P2 ＝ T1 ÷ T2 　　

P - pressure   T - temperature

HIGHER TEMPREATURE - HIGER PRESSURE

LOWER TEMPREATURE - LESS PRESSURE

Reference:

http://www.mintye.com/h_brake_system.asp 

http://baike.baidu.com/view/84928.html#sub84928 

http://en.wikipedia.org/wiki/Pascal's_law 

http://www.google.com/imgres 

http://en.wikipedia.org/wiki/Boyle's_law 

http://www.baidu.com/s?wd=%B2%E9%C0%ED+%B6%A8%C2%C9 

http://baike.baidu.com/view/414465.htm#sub414465 

1.What is the firing order of a four stroke engine?
3 cylinders: 1-2-3
4 cylinders: 1-3-4-2 / 1-2-4-3 / 1-3-2-4

5 cylinders: 1-2-4-5-3

6 cylinders: 1-5-3-6-2-4 / 1-6-5-4-3-2 / 1-2-3-4-5-6 / 1-4-2-5-3-6

7 cylinders: 1-3-5-7-2-4-6
8 cylinders: 1-8-4-3-6-5-7-2 / 1-8-7-2-6-5-4-3 / 1-3-7-2-6-5-4-8 / 1-5-4-8-7-2-6-3 / 1-6-2-5-8-3-7-4

10 cylinders: 1-10-9-4-3-6-5-8-7-2 / 1-6-5-10-2-7-3-8-4-9

12 cylinders: 1-7-5-11-3-9-6-12-2-8-4-10

16 cylinders: 1-12-8-11-7-14-5-16-4-15-3-10-6-9-2-13

2.What is the difference between a S.I and C.I engine?
1. Type of cycle: 
 S.I - Otto cycle
 C.I - Diesel cycle
2. Type of fuel:   
 S.I - Petrol
 C.I - Diesel
3. Type of ignition:
 S.I - Ignite by spark plug
 C.I - Self-ignite by high pressure
4. Compression ratio:
 S.I - 6~10
 C.I - 16~20
5. Weight:
 C.I engines are heavier than S.I engines because higher pressure inside the engine.
6. Speed:
 S.I engines run at higher speeds than C.I engines
7. Thermal efficiency:
 C.I engines have higher thermal efficiency than S.I engines due to the higher pressure.


3.Is there any difference between a S.I and C.I piston if so what?
In most C.I engines, the combustion chamber is in the top of the piston,  rather than the S.I engines in the cylinder head. C.I pistons also longer and heavier than S.I pistons.

   C.I piston                        S.I piston


4.What year was the diesel engine invented and by whom?

Diesel engine was invented at 1892 by German inventor Rudolf Diesel.


5.What is the purpose of the oil jet on the connecting rod, and where does it spray?
The oil jet lines up with the oil hole in the crankpin once on each revolution of the crankshaft. When this occurs, a squirt of oil is directed onto the cylinder walls, also lubricates the piston pin.

6.On the connecting rod where is the big end and little end?
 Big end - The crankpin end. Little end - The piston end.

7.What is the purpose of the thrush washers on the crankshaft?
Thrust washers are long-wearing flat bearings to keep crankshaft rotates in position.

8.On a diesel engine whats the difference between direct injection and a indirect injection type?
Direct injection: Fuel is injected directly into the combustion chamber in the piston head.
Indirect injection: Fuel not inject into the main combustion space, instead, the fuel is injected into a small separate chamber.

9.Explan the term valve timing?
Lead - intake valve opens before TDC and exhaust valve opens before BDC.
Lag - intake valve closes after BDC and exhaust valve closes after TDC.

Overlap - intake and exhaust valves are both open for a few degrees around TDC of the exhaust stoke.

10.Why do we have valve clearance?
Because the valve train gets hot when engine is running, needs some clearance to expand, otherwise the valve will not shut properly. May cause a gas leak, or a valve burn.

What is taper and ovality in the bore, how is it caused how do you check it?

Taper - difference between the measurements of A1 B1 C1 and difference between the measurements of A2 B2 C2. 
That caused by the piston rings rubbing on the cylinder walls. 
To measure it, place the cylinder-bore gauge across the cylinder, just below the unworn ring ridge, move the gauge slowly up and down to measure taper at top middle and bottom of the ring travel in cylinder.

Ovality(out-of-roundness) - difference between A1 and A2.
May caused by unequal pressure on the piston.
To measure it, place the cylinder-bore gauge across the cylinder, just below the unworn ring ridge, move the gauge slowly up and down to measure A1, turn the gauge 90° in the cylinder to measure A2. 

What is side clearance on a piston and how is it checked? 
Side clearance  about 0.02mm to 0.05mm.
Using a micrometer, measure the diameter of piston at a point about one-third of the skirt height, and compare to the diameter reading measured from cylinder bore.


How can you tell the difference between a inlet and exhaust valve and why?
Inlet valve always lager or more than the exhaust valve.
Because  lager or more inlet valves reduce intake resistance, allow lager intake passages and freer flow into cylinder.

What sort of tempatures do the inlet and exhaust valves get upto?
Inlet - 150~250°F / 66~121°C
Exhaust - 1000~1500°F / 538~816°C


What temperatures and speeds must the piston be able to cope with?
Temperatures - Around 230°C at the top, and around 100°C at the skirt.
Speeds - Around 16m/s for automobile engines, and around 20–25 m/s for sport automobile engines or motorcycles


Why do we have piston ring end gap clearance ?
Because when engine is running, the piston ring get hot, needs room to expand.

What could the result be if the piston ring end gap is too small?
If the gap is too small, the ring will have no room to expand when it gets hot.



Why do aluminum cylinder heads usually have a steel shim (washer) between the valve spring and the 
cylinder head surface ?
Because the valve spring needs to move up and down lots of times, could damage the aluminum cylinder head, steel has better intensity than aluminum, also shim can adjust the valve length to control the valve seat pressure.


What is meant by the terms S.I and C.I in a four stroke engine?
S.I - Spark ignition 
C.I - Compression ignition 


What is the purpose of the margin on the valve?
If there is not margin or thickness at the edge of valve, will cause the valve head to overheat then the edge will burn.

What is the purpose of a core plug?
It is used to remove sand from the casting when the engine block is cast.

What is end float and run out on a crankshaft, hows is measured?
End float - alignment at the end of crankshaft.
Run out - alignment at the journal of the center bearing.
How to measure refer to the pictures:

                             End Float

                             Run out