Question { TATA, 38210 }

What is the cause of major loss in efficiency of an IC
engine?

Answer

the energy in an IC engine is produced by the burning of
fuel in each power stroke..inefficiency is created in many
steps..
much of this heat energy is lost with exhaust gas,by
convection,conduction and radiation from the cylinder..only
some of it is converted to useful energy i.e in pushing the
piston down rapidly..this is the major cause of inefficiency
in IC engines.. after ehich various mechanical losses like
friction comes in...

Question { TATA, 28025 }

why petrol engine gives more power than diesel engine
eventhough diesel engine has high compression ratio?

Answer

sorry guys i won't agree to u guys...
i would say the question itslef is incomplete as normally
diesel engine is more efficient than a petrol
engine(surprise!!??)

yes..diesle engines do require a lot of maintenance due to
its his vibration and operating temperature etc.. if not
maintained the efficiency goes well below that of a petrol
engine..
at same cc.. a diesel engine has more efficiency..infact its
efficiency can be made a lot better still by adding
turbochargers annd VVT and using CRDi etc..

the reason is that in diesel engines better combustion
occurs(higher compression+more air)..
take care..

Question { 8937 }

whether a spehrical ballon rises faster or a cylindrical
ballon?

Answer

assuming both baloons to be having same volume..then both
will have same bouyantic force acting on them..now again as
u know a cylnder of same volume has more surfce area, the
weight of rubber used for a cylinderical baloon would b
higher(assuming same thicknes for both baloons), so
spherical will weigh lesser..now assuming again that the
same amount of rubber is used for both,then just drag
decides..and drag is decided by the configuration in which
the balon is rising..even a cylindircal baloon can rise
faster(assuming it to be going up length wise) if its
properly configured and left..assuming again no disturbing
forces in air..

Question { 20067 }

Why do 4 stroke engine uses valves while 2 stroke engine uses
ports ????

Answer

in 2 stroke engines too valves can be designed and also
there are 2 stroke diesel engines with valves..
but common 2 stroke engines like that of a kinetic honda
engine don't have valves bcos it simplifies the construction
a lot and by arranging the ports in such a manner it
achieves the purpose..bt then it creates a lot of
inefficiency and waste of lubricant.. so no valves are used
where these can be compromised or minimised by other methods..

Question { RRB, 26894 }

What are the causes of turbine vibration

Answer

yeah right..every rotor howmch ever care taken cannot be
properly placed or properly balanced..it could be minimised
by adjusting the mounting and mass distribution at a given
configuration dynamically by operating it at its maximum
speed..at its natural frequency it still vibrates high..
so the main causes of turbine vibration are
unbalancing,fluid flow instabilities & mounting problems..
fluid flow problems effect greatly the axial vibrations..

Question { 11892 }

what is capillarity?
in case of 'water' why capillary rise & in case of 'Hg' why
capillary depression

Answer

capillarity is the rise or fall of a liquid inside a
tubular(open) structure thts placed on the surface of a
liquid... the amount of rise or fall depends on many
factors..if it rises or falls is dependent on the angle of
contact of the liquid with the material of the tube..this is
actuallya term thts dependednt on whether adhesive forces or
cohesive forces dominate at the given interface..it is
physically the angle of the meniscus made by the liquid with
the tube..for water,with glass,it has an acute angle..
u just refer any XI physics text u will get the equations
regaring this..its basicaly just balancing all the
forces..surface tension,weight..etc etc.. a term cos alpha
comes..where alpha is the angle of contact..

Question { 12045 }

What is the difference between safety valve and relief valve?

Answer

safety valve and relief valve
the terms are used interchangeably in the industry..

some differences which i have noted in my company are..
safety valves are connected invariably to the output of a
flow creating equipment(exmple a pump or a compressor)..its
purpose is to protection frm flow restriction ahead(or any
other source of high pressure in the fluid)...
now relief valves are used everywhere where there is the
need for a pressure reduction to a set value..a sort of
pressure control valve(PCV) job can be done by a relief valve..

Question { L&T, 35009 }

what is the effect of clearance volume in performance of air-
compressor???

Answer

clearance volume of a compressor actually should be minimum
enought 2 avoid piston from striking the head(thermal
expansion and valve clearance should be given)..it should
be minimum bcos greater the clearance more compressed gas
tht left in the cylinder after each compression stroke, so
tht leads to energy loss and lower efficiency..(volumetric
efficiency goes down)..

Question { 13134 }

Purpose of governer in automobile?

Answer

yes governors are used in automobiles..especially in diesel
engines..petrol engines can also have governors to limit its
speed..or if used for constant speed applications..
what it basically does is to keep the engine speed constant
or at a desired level when the load varies.. that is
governor controls the throttle taking engine speed as input...

Question { Nagarjuna Construction, 24412 }

DRAW SFD & BMD OF SIMPLY SUPPORTED ,CANTILEVER, UNIFORMLY
DISTRIBUTED BEAMS

Answer

SFD is shear force diagram and BMD is bending moment diagram..

u draw a free body diagram of the required situation and
just balance the forces and bending moments at an arbitary
crossection..

u can refer any text on solid mechanics to get more details..

Question { 4879 }

which kind of force act when the piston slides inside the
cylinder?and how to calculate that force or stress
theoritically.

Answer

the stress and force on what when piston slides insides a
cylinder??
is it tht on piston rod? piston?? or crankshaft or cylinder
block??
please b a bit more specific.. well anyway the basis of all
these calculations start off with the evaluation of the
pressure distribution inside the swept volume with crank
angle...u get an idea of tht or atleast the avg pressure
inside the volume with crank angle, u can calculate all
these ,assuming u know the material properties of these
components..

Question { L&T, 25424 }

How to calculate per kW how much fuel conssume in DG set?

Answer

it would be actually "how mch kwhr/litre of fuel" u might be
asking..as kwhr is the unit of energy and not kw...i
supposeethe answer is straight forward...just like u
calculate the mileage of ur car..
you can put a known load across it.. and run genset from
full tank to empty.. calculate the time it took... multiply
it to the load(power in kw of the load) .. u get the
electrical energy produced from a full tank of fuel by the
DG.. divide the energy by quantity of fuel.. u get ur answer..