BMW Of Beaumont

Active Fuel Management--Curse or a Blessing?

Active Fuel Management (AFM) is a trademarked name for the automobile variable displacement technology that was invented by General Motors. It enables a V6 or V8 engine to "turn off" half of its cylinders under light-load conditions to enhance overall fuel economy. Projected performance on EPA tests show a 5.5%-7.5% improvement in fuel economy by utilizing AFM.

At BMW Of Beaumont, we love all of the new car technology that is hopefully saving the planet and that's why we are sharing this blog with our friends, associates and partners in Beaumont and all over the State of TX. 

GM's current Active Fuel Management technology works by using a solenoid to fully deactivate the lifters on selected cylinders of a standard pushrod engine. High-powered multi-cylinder internal combustion engines may be called upon to satisfy the driver's demands for rapid acceleration and/or some serious towing capacity, but during everyday use, they are by and large operated at power settings of less than approximately 25%. For example, at freeway speeds, these engines are often required to overcome things such as aerodynamic drag, rolling friction in addition to operating a wide range of accessories, such as air conditioning.

On the other hand, when a gasoline internal combustion engine is operating under less than a full load, the effective compression ratio is much less than the fully measured compression ratio. Under a light load, the throttle is not open completely and the cylinders will receive less than a full charge of air on each intake stroke. The pressure and temperature generated at the point of combustion are therefore less than the full load and the thermodynamic laws that apply to every type of heat engine that dictates that the engine will then be operating at less than its full possible thermal efficiency.

Thus, a high-powered, very large-displacement engine is extremely inefficient and wasteful when being used for every day driving conditions. This is the main reason for cylinder deactivation, to successfully spread the workload of the engine over a fewer number of active cylinders, that will then operate under higher individual loads and therefore at a much higher efficiency overall.

Simply put, AFM may be good for the environment, but many GM owners are not crazy about it, because they desire full power all the time. It will be interesting to see how AFM evolves within the next 5-10 years or eventually disappears when better technology progresses past the R&D stage.

Sources: Wikipedia, Autoweek and Japolik