Which is not the material for automobile pistons?
Aluminium alloys
Cast iron
Cast steel
Steal forgings
Piston compression rings are made of
Cast iron
Brass
Aluminium
Spring steel
The minimum number of rings in a piston are
Two
Three
Four
Six
A slow speed diesel engine theoretically operates on the principle of
Heat addition at constant volume and heat rejection at constant volume
Heat addition at constant pressure and heat rejection at constant volume
Heat addition at constant pressure and heat rejection at constant pressure
Heat addition at constant volume and heat rejection at constant pressure
Which of following processes is not associated with diesel cycle?
Constant volume
Constant pressure
Isothermal
Adiabatic
A compression ignition engine working on an air standard diesel cycle has the following particulars
1. Cylinder bore=15 cm
2. Stroke = 25cm
3. Clearance volume =400 cm3
The fuel injection takes place at a constant pressure
for 5% of the stroke. The cut off ratio will be about
0.82
1.55
2.1
12.0
The german Mercedes ‘190D’ car possesses a four stroke cylinder-in-line diesel engine with compression ratio 21:1 and expression ratio 10.5:1
the cut off ratio will be
the air standard efficiency will be about
0.5, 25%
1.3, 32%
2.0, 49%
2.7, 65%
(1,c) and (2,d)
The compression ratio for a practical diesel engine usually lies in the range
3-5
6-8
10-15
16-22
The fitting of a turbocharger with diesel engine does suggest that the engine
Works on four-stroke cycle
Is meat for operation at high altitudes only
Is supplied air at a pressure and density higher than the atmospheric
Will run at high speed
The petrol engines are usually not supercharaged as that results in
Power loss
Increased specific fuel consumption
Drop in volumetric efficiency
Increased knocking
What is not true in the context of supercharging of I.C. engines?
Air is supplied to the engine at a pressure and density greater than atmospheric
Compensates the power loss at higher altitudes due to rarified atmosphere
The engine structure is heavy
The specific fuel consumption of the supercharged engines is more
More favourable with diesel engines than with petrol engines
Which of the followings is a false statement in the context of combustion in spark ignition engines?
Spark is provided some crank degrees before the piston reaches the end of compression stroke
Number of degrees before t.d.c. position at which ignition occurs is called the angle of advance
Actual combustion of fuel commences only after certain preflame reactions heat the fuel to its self ignition temperature
High peak pressures ae attained at t.d.c. where the combustion ends
In combustion process, the effect of dissociation is to
Reduce the flame temperature
Reduce the proportion of carbon monoxide is gases
Separate the products of combustion
Reduce the use of excess air
Velocity of flame propagation in the SI engine is maximum for air-flame mixture which is …………..stoichiometric
10% to richer than
Equal to
More than 10% richer than
10% leaner than
Delay period refers to the period that elapses between providing a spark and the commencement of actual combustion of fuel. An increase in which of the following factors increases the delay period?
Self ignition temperature of fuel
Intake temperature
Inlet pressure
Compression ratio
The delay period in a petrol engine is or the order of
0.001 sec
0.002 sec
0.01 sec
0.05 sec
Detonations is said to take place in the engine when
Sudden acceleration is imparted to the engine
Temperature rise is too high
High pressure waves are setup
Combustion of fuel takes place without spark provided to it
All of the following factors promote detonation in spark ignition engines, except
Increase in inlet pressure and temperature of charge
Higher compression ratio
High self ignition temperature of fuel
Advanced spark timing
In a petrol engine, the tendency of detonation increases with
Supercharging
Retarded spark timings
Running the engine at high speeds
Increasing the cooling rate
Consider the following statements:
Detonation in the SI engine can be suppressed by
retarding the spark timing
increasing the engine speed
using 10% rich mixture
Which of these statements are correct?
1 and 3
2 and 3
1 and 2
1, 2 and 3