Question

A 4-stroke gas engine has a cylinder diameter of 25 cm and stroke to bore ratio is 1.9. The following observations are made during the testing of the engine:​​​​​​

(i) Duration of test is 40 min
(ii) Total number of revolutions is 8080
(iii) Total number of explosion is 3300.

Net brake load of the engine is 90 kg and radius of drum is 80 cm. Positive indicated mean effective pressure is 6.4 bar. Pumping mean effective pressure is 0.6 bar. What will be the mechanical efficiency of the engine?

• A. 80.35 %
• B. 27. 8 %
• C. 58.8 %
• D. 72.8 %

Answer 1

The correct option is A 80.35 %

$\text{Indicated power, IP}=P_{effimep}\times \frac{\text{(Number of explosion)}}{Timeoftest}$

$\text{Now effective indicated mean effective pressure,}$

$P_{effimpe}=P_{impe}-P_{pumpingmep}$

From equation (i),

$IP=5.8\times {10}^5\times \frac{\pi }{4}\times \frac{{0.25}^2\times (1.9\times 0.25)\times 3300}{1000\times 40\times 60}$

$=18.594kW$

$\text{Brake power, BP}=(m_0\times g)\times r_d\left(\frac{2\pi \times \text{Number of revolution}}{\text{Time of test}}\right)$

$=90\times 9.81\times 0.8\times \frac{2\pi \times 8080}{1000\times 40\times 60}$

$=14.941kW$

$\text{Mechanical efficiency,}{\eta }_m=\frac{BP}{IP}=\frac{14.941}{18.594}=0.8035=80.35\%$