Abstract
Keywords -Cylinder deactivation, variable displacement, SI engine, OVaLiD, fuel consumption
Compared to Diesel engines, gasoline engines have suffered for a long time from poor efficiency. As far as after treatment and cost are concerned, gasoline engines still present some advantages. Nowadays downsizing is a reality for medium displacement engine but difficult to apply on large displacement engines because of drivers' acceptance. To downsize small displacement engines is also problematic because of the increase in thermal losses that have negative effect on turbo lag and engine maximum efficiency. Stratified combustion could be a more attractive way of improvement but its impact on engine cost is too much important for this engine class.
Consequently, IFP has been engaged in a new development based on variable displacement using cylinder deactivation. As a matter of fact, deactivation is very attractive:
- no effect on engine driveability and fun to drive,
- no effect on engine maximum efficiency,
- no effect on after treatment complexity and consequently cost, and
- low cost technology when using mechanical process.
Engines using variable displacement suffer from several disadvantages: vibrations, blow-by, oil consumption and deactivated cylinder temperature reduction, all having negative effect on the consumption gain. The OVaLiD® concept has been developed to solve part of these problems. It is based on the development of valve event that allows very attractive consumption gain but also to run the engine continuously in deactivation mode. It only requires mechanical variable valve actuation, reliable technology already used by most of car manufacturers. During the development specific valve events and interaction between cylinders have been optimised. Applied on a 2L engine using the HONDA VTEC technology, the concept has shown consumption gain equivalent to stratified combustion process but this approach is still compatible with three way catalyst. As an example, consumption is reduced by 13 % at 2000 rpm 2 bar BMEP. Some consider that deactivation can only be applied on large displacement engines, others believe that drivers acceptance depend on vehicle cost and consumption. This is the IFP's point of view, specially when considering the reduced technology costs and the potential in fuel consumption obtainable thanks to the OVaLiD® concept which is estimated between 12 and 15 % in case of naturally aspirated engines. This concept can be combined with downsizing to allow further gain on the NEDC cycle. The great challenge of this approach is engine vibrations, especially in case of L4 engines that IFP is currently considering and investigating.