Question

An automobile engine operates at a fuel air ratio of 0.06. The volumetric efficiency and indicated the thermal efficiency are 95% and 35% respectively. The indicated mean effective pressure for the engine is if calorific value of the fuel is 42 MJ/kg and density of air intake is $1.2kg/m^3$, is

• A. 10.5 bar
• B. 10 bar
• C. 10 MPa
• D. 29 bar

Answer 1

The correct option is B 10 bar

Given: $\frac{{\dot{m}}_f}{{\dot{m}}_a}=0.6$

$\Rightarrow {\dot{m}}_a=\frac{m_f}{0.06},{\eta }_v=0.95;{\eta }_{ith}=0.35$

Now, ${\eta }_v=\frac{m_a\times \frac{1}{\rho }}{V_s}$

$\Rightarrow V_s=\frac{{\dot{m}}_v}{\rho {\eta }_v}=\frac{m_f}{0.06\rho {\eta }_v}$

${\eta }_{ith}=\frac{IP}{m_f\times CV}$

$\Rightarrow IP={\dot{m}}_f\times CV\times {\eta }_{ith}=P_{imap}\times V_s$

Using equation (1),$P_{imap}\times \frac{{\dot{m}}_f}{0.06\rho {\eta }_v}={\dot{m}}_f\times CV\times {\eta }_{ith}$

$P_{imap}=CV\times {\eta }_{ith}\times 0.06,\rho {\eta }_v$

$=42\times 0.35\times 0.06\times 1.2\times 0.95$

$P_{imap}=1.00548MPa=10bar$