A four-cylinder four-stroke engine is operating at a bmep of 2bar. The pressure at inlet valve closure is 0.37 bar, and the fmepis 0.8 bar. Assuming that the engine gross indicated efficiency isunchanged, verify that disablement of the valves on two cylinderswould reduce the fuel consumption by about 13 per cent comparedwith about an 8 per cent fuel saving if the fuel was not suppliedto two cylinders. Assume that the gross imep is proportional to thepressure at inlet valve closure, and that the gross indicatedefficiency is constant. State any additional assumptions that youmake. By means of p–V diagram sketches, explain why disabling onlythe inlet or exhaust valves would have a fuel economy benefitcomparable to fuel disablement to two cylinders.
