IC Engines 1

IC engines is a scoring area, there are usually straightforward questions from engine testing, carburetion or diesel injection, emissions, knocking etc. So, good returns on specific minimal effort. No need for PhD in engines.Below, I have taken up numericals first because 1.they are the scoring areas and need immediate attention., 2.they can be understood even with general sense of engines. Books usually put them in end. By that time, we know much about engines, but we run out of energy to push thru these tedious procedural questions.

Please feel free to give your inputs/corrections/suggestions on any topic or any solved question below. Do quote the Q no. ex 2015A3b20 or topic name while doing so. Cheers!

General
Difference between External combustion engine and Internal combustion engine

Basic engine parts, nomenclature, materials used, dimension terms

Classification of engines

4 stroke and 2 stroke engines, valve timings, differences






Engine testing numericals
ip, bp, n-ith, n-bth, n-m, n-v, isfc, bsfc, F/A, A/F
Balance sheet on minute basis

2015A3b20 Petrol engine, 4S, 9cyl, D=14.5cm, L=18cm, r=7, bp 350kW @ 2000rpm, when mix is 15% weak with 82.5%C ad 14.8% H2,  CV=47MJ/kg , vol eff=0.76 at 15degC, 1 bar, (eta-m)=0.9, R=0.287kJ/kgK, to find: (eta-ith)
Ans: Now, bp=350kW so, ip =bp/(eta-m)=350/0.9 =388.9kW
(eta-ith)=ip/(mf x CV) and (eta-v)= ma /( rho x pi D^2 L /4 x N/120 x n)
now that catch in the question is to get air mass rate ma and then A/F, then mf and hence eta-ith
so, ma= (eta-v) x RT/p x pi D^2 L /4 x N/2 x n
ma= 0.76 x 287 (273+15) /10^5 x pi x 0.145^2 x 0.18 /4 x 2000/120 x 9 = 0.28 kg/s
in above, i have used rho =RT/p gas eqn, vol of cyl =pi D^2 L/4, cycles per sec=N/(2x60), n=9 cyls
Now, consider 100kg fuel, mixed in stoichiometric ratio then
(82.5/12)C + (14.8/2)H2 +(aO2 + 79.1a/20.9 N2) -->bCO2 +dO2 + eN2 +fH2O
so, b=6.875, d=0 no excess air, a=d+b+f/2 = 0+6.875+7.4/2=10.575 kmoles(air required for stoichio)
So for 15% weak mix, air required =0.85 x 10.575 kmoles=8.98875 kmoles
so, ma=(ax32 + 79.1a/20.9 x28)= (32 + 79.1/20.9x28)x8.98875=1241.57kg/s when mf=100kg/s
or A/F=ma/mf=12.4157, so for ma=0.28 kg/s, mf=0.28/12.4157=0.02255 kg/s
(eta-ith)=388.9kW/(0.02255 kg/s x 47000 kJ/kg) = 0.367


Emissions related theory and numericals
Apparatus for measuring exhaust emissions

Gasoline engine emission control


Diesel smoke and control



Air standard cycles
Carnot

Stirling 1816

Ericsson
Lenoir

Constant volume or Otto


Diesel cycle

Dual cycle


Atkinson

Joule or Brayton cycle

Fuel air cycles and actual cycles(no numericals from here, don't break your head over them)
Assumptions made in fuel air cycle


Loss due to variation of specific heat on p-v diagram


Effect of disassociation on temperature at different mixture strength, and on power


Effect of variable on p, T in cylinder
1.compression ratio

2.F/A ratio
   -on efficiency
   -on max power
   -on max temp
   -on max pr
   -on exhaust temp
   -on mep

Losses in an actual cycle
-Time losses
-Direct heat losses
-Exhaust blowdown loss
-Pumping losses
-Rubbing friction loss


Combustion in SI engines
Stages

Effect of engine variables on ignition lag
-fuel
-mixture ratio
-initial p,T
-electrode gap
-turbulence

Effect of engine variables on flame propagation
-F/A ratio
-compression ratio
-intake p,T
-engine load
-turbulence
-engine speed
-engine size

p-theta for different rates of combustion

Abnormal combustion

Detonation/knocking

Effects of detonation

Theories of detonation


Factors affecting detonation

Control of detonation

knock evaluation in cfr engine(Philips knock meter)

Abnormal combustion knock(surface ignition)
-wild ping, rumble etc

CC design principles

CC desings
-T head
-I head
-F head

Combustion in CI engines
Stages

A/F ratio in CI engines

Delay period or ignition lag

Variables affecting delay period

Diesel knock

Methods of controlling diesel knock(reduce delay period)

Methods of generating swirl

M-chamber

Cold starting

SI vs CI engines, comparison


Fuels and additives
Fuel desirable properties
Refining process

Volatility and effect on engine performance
-cold and hot starting
-vapour lock
etc

Knock rating
-HUCR
-octane number
-RON, MON
-PN
Effect of fuel structure on knocking

Diesel fuels
-flash point, fire point, viscosity, cloud point, pour point
Cetane number

Diesel index
Aniline point
API gravity


Additives
-antiknock


Fuels for gast turbines and jet engines
ATF


Alternative fuels
Methanol, Ethanol

Volumetric efficiency
factors affecting
-inlet air temp
-inlet and exhaust pr
-inlet mach number
-piston speed and engine size
-induction heat transfer
-valve timing




Carburetion
-A/F for max power, max sfc

Automotive engine operation F/A ranges
-idling and low loadm cruising, max power

Simple carburettor(no need to look at variants)
Theory and formula for simple carb

Exact analysis, considering compressibility

Electronic fuel injection--features, compare with conv carburetion

Altitude compensation


Diesel injection
Heat release diagram


Types of injection systems(no need for details, only overview)

Numericals on quantity of fuel per cycle, nozzle orifice size




Ignition, Lube system, cooling system



Supercharging
objective, p-v diagram compare

Effect on engine performance
-on power output


-on mechanical efficiency

-on fuel consumption


Gas turbine cycle
p-v and efficiency calcs