CI Engine

Theory:

Working steps of a 4-Stroke CI Engine:

Suction Stroke – Only air enters the cylinder.
Compression Stroke – Air is compressed to high pressure and temperature.
Power Stroke – Fuel is injected and self-ignites due to high temperature.
Exhaust Stroke – Burnt gases are expelled.

Brake Power is the actual usable power available at the crankshaft. It is calculated using torque and rpm.

where,

= Torque (Nm)
= Engine speed (rpm)

Torque is produced by loading the engine using a rope brake or hydraulic dynamometer.

where,

W = Load (N)
L = Length of the brake arm (m)

(Watts)

Fuel mass flow (kg/s) measured using time to consume 10 cc:

where is mass of 10 cc of fuel (kg), is seconds to consume 10 cc.

Fuel power (input) (kW):

where is calorific value in kJ/kg (since in kg/s, product yields kW).

Specific Fuel Consumption (SFC) shows how much fuel is used to produce 1 kW of power.

Lower SFC = better fuel economy.

Brake Thermal Efficiency (BTE) indicates how efficiently the engine converts fuel energy into brake power.

Apparatus and Materials:

4-stroke CI (diesel) engine
Rope brake / Hydraulic Dynamometer
Fuel measuring burette (10 cc)
Tachometer
Stopwatch
Measuring scale

Theory:

Working steps of a 4-Stroke CI Engine:

Suction Stroke – Only air enters the cylinder.
Compression Stroke – Air is compressed to high pressure and temperature.
Power Stroke – Fuel is injected and self-ignites due to high temperature.
Exhaust Stroke – Burnt gases are expelled.

Brake Power is the actual usable power available at the crankshaft. It is calculated using torque and rpm. $BP=\frac{2\pi NT}{60}$

where,
$T$ T = Torque (Nm)
$N$ N = Engine speed (rpm)

Torque is produced by loading the engine using a rope brake or hydraulic dynamometer. $T=W\times L$ where,
$W$ W = Load (N)
$L$ L = Length of the brake arm (m) $\Rightarrow BP=\frac{2W\pi NL}{60} \quad (\text{Watts})$ ⇒BP=602WπNL(Watts)

Fuel mass flow (kg/s) measured using time to consume 10 cc: $\dot{m}_f=\frac{m_{10cc}}{t_{10cc}}$ m˙f=t10ccm10cc

where $m_{10cc}$ m10cc is mass of 10 cc of fuel (kg), $t_{10cc}$ t10cc is seconds to consume 10 cc.

Fuel power (input) (kW): $P_{fuel}=\dot{m}_f \cdot CV$ Pfuel=m˙f⋅CV

where $CV$ CV is calorific value in kJ/kg (since $\dot{m}_f$ m˙f in kg/s, product yields kW).

Specific Fuel Consumption (SFC) shows how much fuel is used to produce 1 kW of power. $SFC=\frac{\dot{m}_f}{BP}$ SFC=BPm˙f

Lower SFC = better fuel economy.

Brake Thermal Efficiency (BTE) indicates how efficiently the engine converts fuel energy into brake power. $\eta_b=\frac{BP}{\dot{m}_f \times CV}$ ηb=m˙f×CVBP