- #1

Monsterboy

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## Homework Statement

Air enters a diesel engine with a density of 1.0 kg/m

^{3}. The compression ratio is 21 .At steady state ,the air intake is 30 x10

^{-3}Kg/s and the net work output is 15 kW .The mean effective pressure (in kPa) is ...

## Homework Equations

P

_{m}= W.D/ V

_{s}

C = V

_{1}/V

_{2}

V

_{1}=V

_{s}+V

_{c}

V

_{2}=V

_{c}

##\eta## = 1- ##\frac{1}{r^(\gamma-1)} \frac{ \rho^\gamma-1}{(\rho-1)\gamma}##

P

_{m}-mean effective pressure

W.D -work done

V

_{s}-stroke volume

V

_{c}-clearance volume

##\gamma## -ratio of specific heats.

##\rho## -density (rho)

##\eta## -efficiency (eta)

Mass flow rate -m

^{.}

C- compression ratio

## The Attempt at a Solution

[/B]

Since density is 1 kg/m

^{3},the efficiency becomes 100% according to the formula.

because there is a (rho-1) term in the denominator of the second term.

If the above is correct then W.D =Heat supplied = 15kW

So m

^{.}/density = Volume flow rate = V

_{s}?

if r= 21 ,then V

_{s}=20V

_{c}

So volume flow rate = 30x10

^{-3}= V

_{s}?

So mean effective pressure =15000W/(30x10

^{-3})

= 500 kPa

Is the above calcualtion correct ?

but the answer given to me is 525 kPa

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