The work reported in this thesis was conducted to study the effects of variable valve actuation on
combustion, emissions, and fuel economy in a modern design of 4-valve per cylinder SI engine.
The use of statistically-based procedures for the design of experiments allowed a limited number
of tests to be used to explore a wide region of each of the experimental variables.
A series of steady-flow tests was conducted to assess the effects of valve lift on flow past the
valves and the nature of any in-cylinder motion generated. Results from the former were
incorporated into a filling and emptying model that allowed levels of trapped residuals and
pumping work to be estimated for different valve strategies. The in-cylinder motion tests
explored asymmetric valve lifts, that is to say where the two valves were opened by a different
amount. These results allowed a pair of response surfaces to be established to model the intensity
of both axial and barrel swirl within the cylinder over the range of valve lifts.
Engine tests were conducted in two parts. The first explored the effects of changes in exhaust
event phasing, intake event phasing, intake event duration, and peak intake valve lift. The design
of the experiment allowed linear, quadratic, and interactions between the variables to be
modelled using regression analysis. Statistical analysis allowed the most influential factors (both
main effects and interactions) to be identified. Contour plots of the modelled response were used
to draw conclusions about the nature of the response surface and to isolate the effects of valve
opening and closure angles as well as overlap. The results were correlated with those from the
steady-flow tests and from the computer model.
The strategy for the second phase of tests was chosen after considering the previous results. The
steady-flow tests indicated that there was considerable potential for enhancing in-cylinder motion
by adopting a valve deactivation strategy and combining it with a low lift of the active intake
valve. The second phase investigated the use of such a technique in conjunction with large
overlaps over a range of duration of the intake valve event.
The results from both phases of engine tests indicated possible strategies to reduce emissions
from future engines