Internal Combustion Engines (I.C. Engines) MCQ Questions & Answers | Mechanical Engineering

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.

In this system of governing, the quality of charge (i.e. air-fuel ratio of the mixture) is kept constant. But the quantity of mixture supplied to the engine cylinder is varied by means of a throttle valve which is regulated by the centrifugal governor through rack and pinion arrangement.

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 CO₂/km for diesel and 23 g CO₂/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/cm² 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).

The flywheel's weight is primarily determined by the engine's firing frequency, which is related to the number of power strokes per minute. Since the two-stroke diesel engine has the lowest number of power strokes per minute (750 r.p.m.), it will experience larger fluctuations in torque between power strokes, necessitating a heavier flywheel to smooth out these fluctuations.

The heavier flywheel is required for engines with lower firing frequencies (lower RPM) to help smooth out power delivery and reduce vibration. Since both Options C and D have the same RPM (750 r.p.m.), we need to consider the type of engine.

The two-stroke diesel engine tends to have more vibration compared to a four-stroke engine due to its firing frequency and fewer cycles to absorb the power strokes. Therefore, the two-stroke diesel engine (Option C) will likely require a heavier flywheel compared to the four-stroke diesel engine (Option D).

Hence, the correct answer is: Option C: 30 kW two-stroke diesel engine running at 750 r.p.m.

In a typical medium speed 4-stroke cycle diesel engine the inlet valve Opens at 20° before top dead center and closes at 35° after the bottom dead center

- 2-stroke engine can run in any direction
- In 4-stroke engine, a power stroke is obtained in 4-strokes
- Thermal efficiency of 4-stroke engine is more due to positive scavenging