Isooctane is supplied to a fourcylinder sparkignition engine

Isooctane is supplied to a four-cylinder spark-ignition engine at 2 g/s. Calculate the air flow rate for stoichiometric combustion. If the engine is operating at 1500 rev/min, estimate the mass of fuel and air entering each cylinder per cycle. The engine displaced volume is 2.4 liters. What is the volumetric efficiency?

Solution

1. Air Flow rate for stoichiometric combustion:-

for Stoichiometric combution,

mass of air/mass of fuel = 15:1

So

Flow rate of air = 15 * mass of fuel supplied ..............(mass of fuel supplied = 2 g/s)

Flow rate of air = 2 *15 = 30 g/s

Flow rate of air = 30 g/s

2. Mass of fuel and air entering each cylinder per cycle:-

Now

mass of fuel supplied = 2g /s

Mass of air supplied = 30 g/s

Above mass supplied to all four cylinders per second

Engine is operating speed = 1500 rev/min = 1500/60 = 25 rev/ s

For Four Stroke engine 1 cycle completes in 2 revolutions

So number of cycles per second = 25/2 = 12.5

Mass of Fuel entering per cycle to all four cylinder = 2/12.5 = 0.16 g /s

Mass of fuel entering per cycle per cylinder = 0.16/4 = 0.04 g/s

Mass of Air entering per cycle to all four cylinder = 30/12.5 = 2.4 g/s

Mass of Air entering per cycle per cylinder = 2.4 /4 = 0.6 g/s

3. Volumetric Efficiency :-

Volumetric Efficiency = No. Revolutions per cycle * mass of air flow in engine (kg/s) / air density * displaced volume (m³) * Engine Speed (Rev/min)

Now No of revolutions per Cycle = 2 (considering four stroke engine)

Mass flow rate of air into engine = 2.4 g/s = 0.0024 kg/s

Air Density = 1.2 kg/m³

Displaced volume = 2.4 liters = 0.0024 m³

Engine Speed = 1500 rev/min

Volumetric Efficiency = (2 * 0.0024 / 1.2 * 0.0024 * 1500)*100 = 0.11 percent