Question

In a 1000 cc four-stroke IC engine with crank running at 1000 rpm, if the mean effective pressure is 400 kPa and efficiency of engine is 0.5, then brake power of the engine is
1. 5/3 kW
2. 4/7 kW
3. 3/5 kW
4. 7/9 kW

Answer 1

Correct Answer - Option 1 : 5/3 kW

Concept: 

Indicated Power for four-stroke engine is given by,

\(I.P.~=~\frac{P_mLAN}{60,000× 2}\)

where P_m = mean effective pressure in N/m², L = stroke length in m, A = Area of cross-section of the cylinder in m², N = rpm of the engine crankshaft

\(η_m~=~\frac{B.P.}{I.P.}\)

where η_m = mechanical efficiency, B.P. = brake power, I.P. = Indicated power

Calculation:

Given:

N = 1000 rpm, P_m = 400 kPa = 400 × 10³ Pa, η_m = 0.5, V_s = L × A = 1000 cm³ = 1000 × 10^-6 m³  

From the given data we have,

\(I.P.~=~\frac{400~×~1000~× ~1000~× ~10^{-6}~×~1000} {60,000~× ~2}~=~\frac{10}{3}~kW\)

Now, by using the value of I.P. we will get B.P. as follows,

B.P. = η_m × I.P. 

\(B.P.~=~\frac{0.5~\times ~10}{3}~=~\frac{5}{3} ~kW\)