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Old 11-18-2013, 03:18 PM   #3 (permalink)
t vago
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Originally Posted by bikenfool View Post
Why is 'Driving With Load' (DWL) or 'constant throttle' (CT) better than constant speed? Given that we want to minimize fuel consumption but still arrive at our destination in a reasonable time, if we only consider the losses (aero and friction), the optimum solution is constant speed.
That might be true for a Diesel engine. That is decidedly not true for a gasoline engine.

A significant amount of the work done by a gasoline engine is to create and maintain a vacuum in the intake manifold. A higher intake manifold vacuum requires more work from the gasoline engine. Also, varying the intake manifold vacuum is much the same as speeding up and slowing down - gasoline is wasted in shooting for a target speed when going up and down hills.

DWL is an attempt to provide a constant intake manifold vacuum, regardless of speed. Of course, not a whole lot can be done with going down a hill (other than to go into neutral), but for level roads or going up hills, it's better than maintaining a constant speed.
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