Question Set 26 – Mechanical Engineering

# Question Set 26

Question No. 1

Explain Otto cycle.

Otto cycle can be explained by a pressure volume relationship diagram. It shows the functioning cycle of a four stroke engine. The cycle starts with an intake stroke, closing the intake and moving to the compression stroke, starting of combustion, power stroke, heat exchange stroke where heat is rejected and the exhaust stroke. It was designed by Nicolas Otto, a German engineer.

Question No. 2

Why iso-octane is chosen as reference fuel for S.I. engines and allotted 100 values for its octane number?

Iso-octane permits highest compression without causing knocking.

Question No. 3

Why thermal efficiency of I.C. engines is more than that of gas turbine plant?

In I.C. engine maximum temperature attained is higher than in gas turbine.

Question No. 4

Which are the reference fuels for knock rating of S.I. engines?

n-heptane and ISO-octane.

Question No. 5

What will be the position of Piston Ring?

In 180 degree angle the Top ring, Second ring and Oil ring are fixed. Position the ring approximately 1 inch gap below the neck.

Question No. 6

What is Heat rate of a Power plant?

Heat rate is a measure of the turbine efficiency. It is determined from the total energy input supplied to the Turbine divided by the electrical energy output.

Question No. 7

When effect of variations in specific heats is considered then how do maximum temperature and pressure vary compared to air standard cycle?

Temperature increases and pressure decreases.

Question No. 8

Quantities like pressure, temperature, density, viscosity, etc. are independent of mass. What are these called?

Intensive properties.

Question No. 9

Why we do not use same technology to start both SI /CI engine?

The S.I. or spark ignition engine uses petrol as a fuel and the C.I. or compression ignition engine uses diesel as a fuel. Both the fuels has different compression ratio. In SI engine the compression ratio is 8-12:1. In CI engine the compression ratio is 16-22:1. So in case of SI engine, the compression ratio is not sufficient for fuel to burn so a spark plug is used, whereas in CI engine, the compression ratio is so high that due to its internal heat the fuel is combusted so there is no need for a spark plug. So the technology used in SI engine is different from CI engine.

Question No. 10

What VVTi written on new cars of Toyota stands for?