4 stoke cycle spark engine A fourstroke cycle spark ignition

A four-stroke cycle spark ignition engine has 8 cylinders with a bore and stroke of 4 inch Times 3 inches and a compression ratio of 11.5. The engine produces 460 hp at 6000 rpm. The brake specific fuel consumption is 0.5 lbm/hp-hr and the heating value of the fuel may be assumed to 18, 900 Btu/lbm. Determine the brake mean effective pressure and the brake engine efficiency.

Solution

Calculation for Brake Mean Effective Pressure (bmef):-

Brake Power (bp) = bmef * L * A * n * K / 60*1000

bmef = bp*1000*60/(L*A*n*K)

Where L = 3.6 inch, A = (3.14*4²)/4, N = 6000 rpm, K = 8, n = N/2 for four stroke engine.

Putting all these values in in aboveequation:-

bmef = 76.3 psi (Ans.)

Calculation for Brake Engine Efficiency:-

Brake Specific Fuel Consumption (bsfc) = m_f/bp , where m_f = fuel flow rate

So, m_f = bsfc x bp

           = 0.5 *460 = 230 lbm/hr

Now Brake engine efficiency = bp/fuel power , where fuel power = m_f * calorific value of fuel

So, Brake engine efficiency = 460*2544.43/(230 * 18900) , using conversion factor of 1 hp = 2544.43 BTU/hr

                                             = 0.2693 or 26.93% (Ans.)