INTERNAL COMBUSTION ENGINES QUESTIONS WITH ANSWERS

INTERNAL COMBUSTION ENGINES

Fig. Internal Combustion Petrol Engine

QUESTIONS WITH ANSWERS

1. Define supercharging in IC Engines.

A supercharger is a compressor which compresses air 6 to 8 psi above atmospheric pressure. This gives more oxygen for better burning of fuel. Thus engine produces more power.  Supercharger gets power from the IC engine crankshaft through a belt/chain/gear drive. Air crafts and racing cars use superchargers. Various types of superchargers are roots-type supercharger, centrifugal –type supercharger and scroll – type supercharger.

     2. What is the difference between a turbocharger and a supercharger?

The function of both is same to pre-compresses air going into the engine for the fuel burning. But the main difference is the source of energy for their working.  A turbine run by exhaust gases runs a turbocharger.  The super charger gets power from the crankshaft of the engine by a belt/chain/gear drive.

Q3. Describe the aims of supercharging in internal combustion engines.

A.

1. Reduces the weight of an engine per kW developed as in racing cars.

2. Overcomes the effect of altitude (low pressure) as in case of air crafts and vehicles in hilly areas.

3. Increases power output from a certain engine.

4. Decreases the size of the engine to produce certain power.

Q4.  What is a delay period in internal combustion engines?

A.

The time interval between the starting of fuel injection and starting of combustion of the fuel. Delay period is in terms of crank angle. The delay period in case of SI engines is of the order of 0.001 sec. Due to delay period, there is knocking in the engine. Knocking is more pronounced in SI engines.

STEPS TO REDUCE THE DELAY PERIOD in internal combustion engines

1. Using a high Cetane number fuel

2. Increased compression ratio

1. Fine atomization and increased rate of injection

Q5. Give the cause of governing quantitatively for SI engine and  qualitatively CI engines?

A.

Governing means to keep speed constant during all conditions of loading on the engine. SI engines have constant Air fuel ratio but the quantity is varied as per load on the engine. In CI engines, Change air fuel ratio is as per load in CI engines.

Q6. Explain thrust and thrust power of jet propulsion systems.

A.

Thrust is a mechanical pushing force (k N). It moves the aircraft( in the direction of motion) and missile in the air. The thrust moves the submarine under water. It is the force (reaction) to the propulsive force. This propulsive force is due to the acceleration of the gas because of heat of combustion. The accelerated fuel comes in the form of a jet. The thrust overcomes the drag of an aero plane and weight of the rocket. Thrust power is multiple of  thrust and speed.

Q7. What are air injection and solid injection systems in internal combustion engines?

In air injection method, inject fuel into the cylinder with  compressed air. It needs a multi compressor system which increases the weight as well as the cost. It is no longer in use today. In solid injection, a pump along with a nozzle, injects fuel in the combustion chamber. Injected fuel is in the form of very tiny droplets. Presently this method is in common use. It does not use any compressed air.

Q8. Compare liquid and solid propellants in internal combustion engines.

ANS.

Table: Comparison between liquid and solid propellants

Sr. No.	Property	Liquid propellant	Solid Propellant
1.	Calorific value	High	Low
2.	Ease of handling	Easy	Difficult being bulky
3.	Storage required	Less	More
4.	Density	High	Less
5.	Stability	Less stable	More stable
6.	Thrust produced	Produces less thrust for a certain size rocket. Thrust is controllable.	Produces more thrust for a certain size rocket. Produces a fixed thrust.
7.	Corrosiveness	More	Less
8.	Examples	Alcohol, liquid hydrogen, Hydrazine and Hydrides of Boron, methyl nitrate	Poly butadiene and Acrylic acid, aluminum perchlorate
9.	Control over thrust	Controllable, thrust is variable	Not controllable only fixed thrust

Both types of propellants have advantages and disadvantages over one another. Hence for some purposes solid fuel rockets are more advantages while for other applications liquid propellants rockets are more advantageous.  A space shuttle use both types of fuels. Solid propellants are in the boosters which help the shuttle to propel into the orbit. The main engines use hydrazine and liquid oxygen. It gives much better control over the movement of the shuttle in space.

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