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

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