Question

One method for reducing the pumping work in throttled spark-ignition engines is early intake valve closing (EIVC). With EIVC, the inlet manifold is held at a pressure pi, which is higher than the normal engine intake pressure pi*. The intake valve closes during the intake stroke. The trapped fresh charge and residual is then expanded to the normal cycle (lower) intake pressure, pi*. You can assume that both cycles have the same mass of gas in the cylinder, temperature and pressure at state 1 of the cycle. a) Sketch a p-V diagram including both the standard and EIVC cycle. On the p-V diagram, shade the area that corresponds to the difference of pumping work between the standard and EIVC cycles. b) What value of intake pressure pi and VEIVC will give the maximum reduction in pumping work for the EIVC cycle? c) Derive an expression for this maximum difference in pumping work between the normal cycle and the EIVC cycle in terms of pe, pi*, Vc and Vm. Justify any assumptions you make.

Answer 1

Ans: Below is Sketch of Standard and EIVC P-V Diagram showing the shaded area of Difference between pumping work of standard and EIVC Cycle.

b) Note that when pi <pe, part of the residual gas in the cylinder at the end of
the exhaust stroke will flow into the intake system when the intake valve opens.
This flow will cease when the cylinder pressure equals pi.

Work done on piston by gas will be (Exhaust)

W_e= P_e(V2-V1)

and during Intake will be

Wi= Pi(V1-V2)

Net Work done will be W net= pi-pe(V1-V2)

The pumping mean effective pressure will be

pmep=pe-pi () When Pe>Pi

pmep= Pi-Po when Pi> Pe

Net mep= impepg-(Pe-pi)

The net indicated fuel conversion efficie;cy is related to the gross indicated fuel
conversionefficiency by