Cycle calculations show that as the equivalence coefficient exceeds one, the efficiency decreases due to lack of oxygen.

$($TRUE or FALSE$)$

In spark ignition engines, the aftergas ratio is minimum at idle. $($TRUE or FALSE$)$

Which of the following statements is incorrect? Crankshaft rotation speed of internal combustion engines,

$[$a$]$ increases with engine size.

$[$b$]$ It is limited due to inertial forces.

$[$c$]$ In rotary piston engines, it is higher than in reciprocating engines.

$[$d$]$ Decreases with increasing engine displacement.

$[$e$]$ Limited due to the linear speed of the piston.

To obtain mechanical energy from the chemical energy in the fuel

$[$a$]$ The fuel must undergo hydrocracking at the refinery.

$[$b$]$ The fuel needs to be decarbonized.

$[$c$]$ A reversible process is required.

$[$d$]$ Combustion and gases must expand within the cylinder.

$[$e$]$ An adiabatic and irreversible process is required.

Multistage mixed engines

$[$a$]$ They can work with leaner mixtures

$[$b$]$ They are compression ignition engines.

$[$c$]$ They use carburetors.

$[$d$]$ They use more than stoichiometric fuel.

$[$e$]$ They are a kind of rotary $($WANKEL$)$ type engines

The thermal efficiency of compression ignition engines is higher than spark ignition engines because,

$[$a$]$ The combustion process is more efficient.

$[$b$]$ They use heavier hydrocarbons.

$[$c$]$ It has higher compression ratios.

$[$d$]$ The equivalence coefficient of the mixture is higher.

Combustion in a spark ignition engine is generally

$[$a$]$ Started at top dead center.

$[$b$]$ Started before top dead center

$[$c$]$ Started after top dead center

$[$d$]$ It starts $10$ degrees after the exhaust valve closes.

Compression ratio of a modern truck engine

$[$a$]$ is between $7-9$

$[$b$]$ Between $12-24$

$[$c$]$ is over $40$

$[$d$]$ Varies depending on the type of fuel used.

$[$e$]$ It is a function of speed.

Which of the following statements is incorrect?

$[$a$]$ In spark ignition engines, the aftergas ratio varies from $20\%$ at light loads to $7\%$ at full throttle.

$[$b$]$ In some engines, a portion of the exhaust gas is mixed into the fresh mixture in order to control hydrocarbon emissions.

$[$c$]$ Up to $30\%$ of exhaust gas can be recycled.

$[$d$]$ During compression, the rate of burnt gas may increase up to $30\%-40\%.$

Which of the following statements is incorrect?

$[$a$]$ Flame is a combustion reaction that can travel at subsonic speed.

$[$b$]$ Flames are unstable in spark ignition engines.

$[$c$]$ In a conventional spark ignition engine, the flame is pre$-$mixed and moves at laminar speed.

$[$d$]$ The combustion process in diesel engines is largely a sudden, turbulent diffusion flame.

Which of the following statements is incorrect?

$[$a$]$ Internal combustion engine fuels are mostly iso$-$octane and norma$-$heptane mixtures.

$[$b$]$ Hydrocarbons in internal combustion engine fuels are paraffins, naphthas, olefins, acetylenes and aromatics.

$[$c$]$ In a stoichiometric mixture, there is only enough oxygen to convert the fuel into fully oxidized gases.

$[$d$]$ In fuel$-$rich mixtures, the composition of burned gases cannot be determined by mass equalization alone.