I generally try to optimize my car's fuel consumption when driving, using my car's real-time MPG gauge and average-trip MPG indicator.
Until recently, I believed the slower the acceleration, the better the fuel economy. However, my observations seem to contradict this.
Generally, I notice that the acceleration seems to be directly proportional to fuel economy, at least in a new BMW 328i. This is within the bounds of "normal" driving; I haven't experimented much with very hard acceleration.
(Assuming an internal combustion engine,) what factors are causing quicker acceleration to a fixed target speed to result in higher average fuel economy than slower acceleration to the same speed?