With rare exceptions, 4-stroke engines run at substantially
slower rpms than a comparable 2-stroke engine…most in the
under-10,000 rpm range vs. 12,000, 13,000 or more for a
typical 2-stroke of the same size. They are engineered to
deliver maximum power at slower rpms, with bigger props.
What does this have to do with it? One of the main factors
used in determining the proper oil content of fuel is heat.
To use the well-worn term, it doesn’t take a rocket
scientist to figure out that the more slowly an engine
turns, the less heat it generates from friction. If you
don’t believe that, rub your palms together slowly, then as
fast as you can.
It is just becuase in two stroke petrol engines the
crankcase is used to pressurized the Air Fuel mixture into
the combusting chamber and therefore if using the wet sump
system the combustion chamber will be filled with oil and
the spark plug will be coverd by burned oil that is why the
dry sump systerm is used.
we use oil because there is no lubrication facility in case
of two stroke engines as they are double acting and the
fuel has to be mixed in the lubricating oil but in case of
4 stroke engines,they are separated by the moving piston.
2 stroke is much simpler machanism. It has inlet and
exhaust ports. There is no valve mechanism as in the 4
stroke engine. So lubrication in 2 stroke is much simpler
and just add oil into the petrol for lubricating the moving
parts like piston assy. Whereas 4 stroke requires more
machanism and seperate lubrication system.
in two stroke more heat is generated. in order to reduce
heat generation lubrication is needed.there is two power
cycles in when compared to 4 stroke ,more lubrication is
needed.this is the main drawback of 2 stroke .
We are using oil with petrol in two stroke engine because
their are no force feed system to lubrication the
component.Two stroke engine have no inlet and exhaust valve
so no need of lubrication for cylinder head. the air/fuel
mixture follow via crankcase we need to lubricate only
crankcase ( cylinder wall, connecting rod, piston pin etc.)
2 stroke engine lack a dedicated cooling system as in 4 strake engine. the crankcase of 2 stroke engine doesnot contain lubricating oil.
As the mixture of oil and petrol reaches crankcase in 2 stroke ,the petrol gets vaporised and transferred to cylinder for combustion leaving the oil lubricating the parts of crankcase.
The connecting rod uses a roller bearing which requires less lubrication .
In a 4 stroke engine, we have a dedicated system for lubrication. We have lubricating ports which supply the lubricating oil from the sump so that all the parts are thoroughly cooled. But, most small petrol two-stroke engines cannot be lubricated by oil contained in their crankcase and sump, since the crankcase is already being used to pump fuel-air mixture into the cylinder. So while fueling, we mix gasoline with an oil to be distributed throughout the engine for lubrication. The two-stroke oil is ultimately burned along with the fuel. But i=this can contribute to more smoke and distinctive odor.
1. How are voltmeter and am meter connected in the circuit?
2. What is the function of space heaters for motors?
3. What is Ohms law?
4. Enumerate the parts of Main Switchboard
5. Examples of good conductors of electricity.
6. Examples of good insulators.
7. What are to be checked in an induction motor?
8. How many battery discharges?
9. How to find ground in main switchboard?
10. What is the cause of motor not to start?
11. Where can you find space heater lam p and what is its
12. How do you detect earth by lam p?
13. Why the transformer is mostly used aboard the ship?
14. Electrical symbol
15. List the different devices and components of main
16. What are to be checked in an induction motor?
17. How do you detect earth by lam p?
18. How do you reset the circuit breaker?
19. What is the purpose of ventilation in the battery room?
20. What are the usual checks when induction motor is running?
21. Methods to dry up wet induction motors?
22. The unit of resistance?
23. The lowest allowable insulation resistance?
24. What is space heater?
25. What is hertz in electrical system?
26. In electricity, what is commutator? Carbon brush?
27. Draw a parallel circuit with one battery and two
resistors. Derive the formula for resistance?
28. Define earth lamp?
29. What is the use of multi tester?
30. How to check the diode, fuse and bearer switch?
31. What is the formula to determine the speed of induction