Chapter 2
Q. 2.7
An engine piston has an area of 50 cm² and moves 6 cm during part of suction stroke. 350 cm³ of fresh air is drawn in from the atmosphere. The pressure in the cylinder during suction stroke is 0.9 bar and atmospheric pressure is 1 bar. The flow resistance in the suction pipe and inlet valve is accounted for by the difference of atmospheric pressure and suction pressure. Calculate the net work done during the process.
Step-by-Step
Verified Solution
The system conditions are shown in Fig. 2.23.
Net work done,
\begin{aligned}&W_{\text {net }}= \underset{{\text {Piston }} }{\int p} \cdot d V+\underset{{\text {free }-\text { air Boundary } } }{\int p \cdot d V} \\&=0.9 \times 10^5 \times 50 \times 6 \times 10^{-6}-1 \times 10^5 \times 350 \times 10^{-6}\\&=27-35=-8 \ J\end{aligned}
The free air work is negative because its boundary contracts.
