Reciprocating Machines Viva Questions
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Multiple Choice Questions
Q.1. Define Bore.
Ans. The inside diameter of the cylinder is known as the bore.
Q.2. What do you mean by swept volume?
Ans. The volume between the TDC and BDC is known as swept volume.
Q.3. What is Engine Speed?
Ans. This is measured in terms of revolutions of crankshaft per minute. It is represented by rpm (revolution per minute).
Q.4. Define Dead Centres.
Ans. The extreme position of the piston travel is known as the dead centres. There are two positions of the dead centres. For vertical engines, they are Top Dead Centre (TDC) and Bottom Dead Centre (BDC). In the case of horizontal engines, they are Outer Dead Centre (ODC) and Inner Dead Centre (IDC).
Q.5. Write the classification of Compound Steam Engines.
Ans. The compound steam engines are generally classified as:
- Tandem compound steam engines
- Cross-compound steam engines.
The cross-compound engines are further divided as
- Woolfe compound steam engines
- Receiver type compound steam engines.
Q.6. What do you mean by compression ratio?
Ans. It is the ratio of total volume (V1) to the clearance volume (VC)
r_{c}=\frac{v_{1}}{v_{c}}=\frac{v_{c}+v_{s}}{v_{c}}=\frac{1+v_{s}}{v_{c}}Q.7. Define Diagram Factor.
Ans. The ratio of the area of the actual indicator diagram to the area of the theoretical indicator diagram is known as the diagram factor.
Q.8. What do you mean by clearance volume (Vc)?
Ans. The space between the cylinder cover and the piston dead centre is known as the clearance volume or volumetric clearance.
Q.9. What is governing? What are the types of governing which are commonly used?
Ans. The automatic control on the steam supply according to the variation of the load is known as governing and the equipment used for this purpose is known as Governor. The following are the two types of commonly used governing in steam engines:
- Cut-off governing
- Throttle governing
Q.10. Define Brake Horse Power.
Ans. The power available at the shaft is less than that developed inside the cylinder due to various frictional losses. This power is known as the Brake Power of the engine.
Q.11. What is meant by external combustion and internal combustion engines?
Ans. If the combustion of the fuel takes place outside the working cylinder, the engine is called an external combustion engine.
If the combustion takes place inside the working cylinder, the engine is called an internal combustion engine.
Q.12. What are the reasons for using I-C engines in mobile units?
Ans. High efficiency and the absence of cumbersome auxiliary equipment, such as furnaces, boilers and condensers make the internal combustion engine relatively lighter and compact. For its output, I-C engines are very popular where space or weight consideration is important; hence these are very commonly used in mobile units such as motorcycles, motor cars, tractors.
Q.13. What are the advantages of internal combustion engines over external combustion engines?
Ans. Internal combustion engines (petrol engine, diesel) compared to external combustion (steam engines) are compact, highly efficient and need less maintenance, operating cost and auxiliary equipment, like furnace, boiler, condenser etc. However, in external combustion engines, cheaper fuel like coal is utilized.
Q.14. How are I.C. engines classified?
Ans. I.C. engines are classified as:
- (a) Diesel Engine (b) Petrol Engine (c) Gas Engine.
- (a) Air-cooled Engine (b) Water-cooled Engine
- (a) Single Cylinder Engine (b) Multicylinder Engine
- (a) Spark ignition (b) Compression ignition Engine (c) Hot spot ignition.
Q.15. What is a Diesel engine?
Ans. The diesel engine is an engine that uses low-grade oil for fuel and ignites this fuel by the heat of air compression.
Q.16. What creates the heat in the cylinder of a C.I. Engine?
Ans. Air is compressed until it attains a temperature high enough to ignite the fuel.
Q.17. What is a two-stroke cycle engine?
Ans. A two-stroke cycle engine is one in which two strokes of the piston are required to complete the necessary events to create one power stroke.
Q.18. What is meant by the power stroke?
Ans. The power stroke is the stroke of the piston produced by the expanding gases; it is the working stroke of the engine.
Q.19. What happens when the piston has completed its power stroke in a four-stroke cycle engine?
Ans. The piston starts on the return stroke, forcing out the burned gases.
Q.20. What is a cycle?
Ans. A cycle is a series of events that are repeated in regular order to bring about the operation of an engine.
Q.21. What is scavenging?
Ans. Clearing a cylinder by forcing through it a current of air to make it ready for clean air for the next compression.
Q.22. What is meant by a double-acting engine?
Ans. A double-acting engine is one that operates similarly to a single-acting engine, except that pressure producing the power strokes is exerted first on one side of the piston, then on the other end, which makes each piston stroke a power stroke.
Q.23. How two-stroke cycle engine is less efficient than a four-stroke cycle engine?
Ans. During scavenging in the two-cycle engine, some of the fresh char is also lost with the combustion products which reduces the efficiency of the engine.
Q.24. Why carburettor is necessary for petrol engine?
Ans. Because air and petrol have to be mixed in correct proportion,
Q.25. What methods are used for injecting fuel into the cylinders?
Ans. Two basic methods are used,
- Air injection
- Airless or solid injection.
Q.26. Explain heat supply process in case of petrol and diesel engine.
Ans. In the case of petrol engine heat supply takes place at constant volume and also the combustion, while in a diesel engine the combustion takes place at constant pressure.
Q.27. What is the charge?
Ans. The charge is a material that enters through the inlet during suction stroke. In the case of the S.I. engine, a mixture of air and fuel serves as the charge. While in a C.I. engine only air forms the charge.
Q.28. In a cycle, the air is compressed to a high-pressure fuel is then injected into air, which is at a temperature above ignition point, and burns at nearly constant pressure. Isentropic expansion of the products of combustion is followed by exhaust and suctions of fresh air. Which is this cycle?
Ans. It is Diesel Cycle.