Question

A nine-cylinder radial aircraft engine has a bore of 5.5 inches and a stroke of 5.5 inches and runs at 3500 rpm. Assuming that the brake horsepower of the engine is measured at 600 hp, calculate the brake mean effective pressure (BMEP) the indicated mean effective pressure (IMEP) (hint: assume an appropriate value for ηmech). Farokhi, Saeed. Aircraft Propulsion (Kindle Locations 12000-12003). Wiley. Kindle Edition.

Answer 1

The brake mean effective pressure is
`BMEP = 398154.542Pa`

The indicated mean effective pressure is
`IMEP = 338431.36 Pa`

Step-by-step explanation:

From the question we are told that

The number of cylinder is
`n = 9`

The bore diameter is
`b = 5.5 \ inches = (5.5 * 2.54)/(100) = 0.1397 \ m`

The stroke is
`s = 5.5 \ inches = (5.5 * 2.54)/( 100) = 0.1397\ m`

The angular speed is
`w = 3500 rpm`

The break horsepower of engine is
`E = 600hp = 600 * 746 = 447.600 \ kW`

Let assume the mechanical effectiveness
`\eta mech` = 85%

The mechanical effectiveness of the engine is mathematically represented

`\eta mech = ([BMEP])/([IMEP]) *100`

the brake mean effective pressure (BMEP) is mathematically represented as

`B MEP =[ (60 *10^(3) E )/(s * a * n * w) ]`

where a is the area of the engine piston which is mathematically as

`a = (\pi)/(4) (b)^2`

Substituting values

`a = (\pi)/(4) * (0.1397^2)`

`= 0.01532 \ m^2`

Substituting values into the equation for BMEP

`BMEP = (60 *10^(3) * 447.600)/(0.1397 * 0.01532 * 3500 * 9)`

`BMEP = 398154.542Pa`

From the equation of
`\eta mech`

We have that

`85 = ([398154. 542])/([IMEP]) *100`

`0.85 = ([398154. 542])/([IMEP])`

`IMEP = 398154.52 * 0.85`

`IMEP = 338431.36 Pa`

Answer 2

BMEP = 3.98154 bar

IMEP = 4.9769 bar

Step-by-step explanation:

Note:BMEP means Brake Mean Indicated Effective Pressure = 3.98154 bar

IMEP means Indicated mean of Effective Pressure =4.9769 bar.

Please go through the attached files for the step by step solution.