Internal Combustion Engines _I_C_ Engines — Part 2 MCQs with Explanations

In a four stroke cycle diesel engine, the compression Starts at 40° after bottom dead center and ends at 10° before top dead center

In a four stroke cycle petrol engine, the compression Starts at 40° after bottom dead centre and ends at 30° before top dead centre

In a four stroke cycle diesel engine, the inlet valve Opens at 20° before top dead center and closes at 40° after bottom dead center

In a four stroke cycle petrol engine, the inlet valve Opens at 20° before top dead center and closes at 40° after bottom dead center

In order to eliminate knocking in compression ignition engines, there should be short delay period. - Add 1% of ethyl nitrate or any nitrate to accelerate the combustion of fuel. This process is known as “Doping” and reduce delay period considerably and hence prevent diesel knock. - For spontaneous ignition of the fuel, we require much higher temperature this can be achieved by raising the compression ratio.

The normal heptane (C 7 H 16 ) is given a rating of 0 octane number.

In order to mix air and petrol in the required proportion and to supply it to the engine during suction stroke, then carburettor is employed.

The increase in intake temperature of internal combustion engines will decrease efficiency.

During idling, a petrol engine requires rich mixture.

The camshaft is either chain or gear driven from the crankshaft. Because the engine is a four stroke, the camshaft will rotate at half the speed of the crankshaft. The cam shaft of a four stroke I.C. engine running at 1500 rpm will run at 750 rpm

Polymerization is a chemical process in which molecules of a compound become Larger Polymerization that occurs through the coupling of monomers using their multiple bonds is called addition polymerization. The simplest example involves the formation of polyethylene from ethylene molecules.

The theoretically correct mixture of air and petrol is 15 : 1

An hmh flame speed is obtained in diesel engine when air fuel ratio is About 10% of rich mixture. The flame speed is the measured rate of expansion of the flame front in a combustion reaction. Whereas flame velocity is generally used for a fuel. Combustion engineers differentiate between the laminar flame speed and turbulent flame speed. Flame speed is typically measured in m/s, cm/s, etc.

A stoichiometric air-fuel ratio is Chemically correct mixture. Air–fuel ratio (AFR) is the mass ratio of air to a solid, liquid, or gaseous fuel present in a combustion process. If exactly enough air is provided to completely burn all of the fuel, the ratio is known as the stoichiometric mixture, often abbreviated to stoich.

The temperature of interior surface of cylinder wall in normal operation is not allowed to exceed 180°C

A two stroke cycle engine gives two the number of power strokes as compared to the four stroke cycle engine, at the same engine speed.

The fuel air ratio in a petrol engine fitted with suction carburettor, operating with dirty air filter as compared to clean filter will be Higher. For proper combustion of fuel, engine require oxygen, and this oxygen is supplied to engine by atmospheric air. The ratio of mass of air sucked by engine to mass of fuel injected is air-fuel ratio.

Diesel engine can work on very lean air fuel ratio of the order of 30 : 1. A petrol engine can also work on such a lean ratio provided cannot work as it is impossible. - For cold starting (simply when your engine parts are not warmed) - 9 : 1 (rich of fuel) - For Idling (when you stop at signal without turning off engine) - 12 : 1 (rich mixture) - For cruising (when you run engine at constant medium/economy speed) - 16 : 1 (lean mixture) - When you accelerate bike/car - 13 : 1 (rich mixture but require less fuel than idling)

cc stands for cubic centimeters, a unit of volume. This number basically is approximately the displacement volume of the engine i.e. the volume covered by the stroke of the piston multiplied by the number of cylinders the engine has.

Diesel is in principle easier to refine than gasoline, however it contains more pollutants that must be extracted before it can reach the same levels of emissions as petrol. Per litre, diesel contains more energy than petrol and the vehicle’s engine combustion process is more efficient, adding up to higher fuel efficiency and lower CO 2 emissions when using diesel.

Diesel as compared to petrol is More difficult to ignite

Fuel consumption of diesel engines is not guaranteed at one quarter load because at such low loads The small difference in cooling water temperature or in internal friction has a disproportionate effect

The magneto in an automobile is basically D.C. generator. A magneto is an electrical generator that uses permanent magnets to produce periodic pulses of alternating current. Unlike a dynamo, a magneto does not contain a commutator to produce direct current. It is categorized as a form of alternator, although it is usually considered distinct from most other alternators, which use field coils rather than permanent magnets.

The purpose of testing an internal combustion engine is: - To determine the information, which cannot be obtained by calculations - To conform the data used in design, the validity of which may be doubtful - To satisfy the customer regarding the performance of the engine

The knocking in spark ignition engines can be reduced by - Retarding the spark -Increasing the engine speed

The two reference fuels used for cetane rating are Cetane and alpha-methyl naphthalene

For the same power developed in I.C. engines, the cheaper system is Supercharged

As compared to air standard cycle, in actual working, the effect of variation in specific heats is to Reduce maximum pressure and maximum temperature

The expansion of fuel in a four stroke cycle diesel engine Starts at 15° after top dead center and ends at 30° before bottom dead center

The fuel valve in a four stroke cycle diesel engine Opens at 15° before top dead center and closes at 20° after top dead center

In a typical medium speed, 4-stroke cycle diesel engine Fuel injection starts at 10° before top dead center and ends at 20° after top dead center

The exhaust valve in a four stroke cycle petrol engine Opens at 50° before bottom dead center and closes at 15° after top dead center

For the same compression ratio Otto cycle is more efficient than the Diesel

The ratio of the brake power to the indicated power is called Mechanical efficiency

a four stroke cycle, the minimum temperature inside the engine cylinder occurs at the Beginning of suction stroke

There are different valves used in a diesel engines. Now it depends on which valve numbers you want to know. Inlet valves - inlet valves generally allow the intake air to enter into the combustion chamber. These may generally vary from 1 to 2 per cylinder in numbers depending on air quantity and open timings. Exhaust valves - likewise they allow the exhaust gas to allow burnt out gas from chamber to exhaust manifold. They are also 1 to 2 per cylinder in numbers.

The pressure inside the cylinder is above the atmospheric pressure during the exhaust stroke.

The specific fuel consumption of a petrol engine compared to diesel engine of same H.P. is more. A fuel consumption of 1 litre per 100 km corresponds to approximately 26.5 g CO 2 /km for diesel and 23 g CO 2 /km for petrol, depending on the exact composition of the fuel.

The pressure and temperature at the end of compression stroke in a petrol engine are of the order of 6 - 12 kg/cm 2 and 250 - 350°C.

The brake power is the power available at the crank shaft. The brake power (briefly written as B.P.) of an I.C. Engine is the power available at the crankshaft. The brake power of an I.C. engine is, usually, measured by means of a brake mechanism (prony brake or rope brake).