Cylinder deactivation has been utilized by vehicle manufacturers since the 80's to improve fuel consumption and exhaust emissions. Cylinder deactivation is achieved by cutting off fuel supply and ignition in some of the engine cylinders, while their inlet and outlet valves are fully closed. The vehicle demand during cylinder deactivation is sustained by only the firing cylinders, hence increasing their indicated power. Conventionally, half the number of cylinders are shut at certain driving conditions, which normally at the lower demand regime. An optimal strategy will ensure cylinder deactivation contributes to the fuel saving without compromising the vehicle drivability.
Cylinder deactivation has been documented to generally improve fuel consumption between 6 to 25 %, depending on the type-approval test drive cycle. However, type-approval test has been reported to differ from the “real-world” fuel consumption values. Therefore the documented fuel consumption might not be representable for consumers in their actual driving. The Malaysian authorities have been using the NEDC test to measure the emission and fuel consumption for declaration purposes, which may be misleading. This paper presents the measurement and analysis of an engine operating with cylinder deactivation, tested on a dynamometer in accordance to the actual driving conditions rather than the NEDC. This is to understand the actual benefits of cylinder deactivation in the real world. The regular Malaysian urban driving conditions were previously identified and applied in this analysis.
To understand the engine operational behaviour, a piezoelectric sensor was instrumented on the engine to acquire the in-cylinder pressure traces. Test results from this study have shown that cylinder deactivation improves fuel consumption and thermodynamic efficiencies for the actual Malaysian driving conditions. The fuel consumption benefit also correlates well with the improvements on the mean effective pressures. Engine pumping mean effective pressure reduced as much as 19.4% and the thermal efficiency was consistently improved up to 5% during the cylinder deactivated operation. These improvements were achieved while maintaining similar brake mean effective pressures as if when all cylinders are firing. Most importantly, these improvements fall within the regular actual urban driving conditions, thus will be most beneficial for Malaysian drivers. Furthermore, the recorded engine operating characteristics will be the key in determining the correct strategy towards maximizing the benefits of cylinder deactivation for the Malaysian urban driving conditions.