It's been almost two months since my last post due to some surgery that made writing and typing difficult. I hope I haven't lost my devoted readers. Right. In any case, onward and upward.
The trend in my mileage has been a significant increase in standard deviation, together with a slight decreasing trend in mileage. This, despite the installation of the K&N high flow air filter noted in my last post. Starting June 19, there was a major downtrend in my mileage from which I've never really recovered, followed by a trendless few tank fulls with large variation.
A comment was left in my post about Dr. Steven Dutch and his article about the 200 mile per gallon car. At the end of that post, I stated that it was my belief that "in order to achieve major reductions in oil consumption without going to vehicles such as the scooter I discussed a couple of posts back, large-scale changes must be made in the technology of internal combustion engines or other propulsion methods must be employed."
Bill Anderson, host of the blog entitled "mental radiation," commented that large gains can be made in automotive gas mileage by reducing the weight of vehicles. He stated that two thirds of the energy used at the wheels is used to overcome weight, and concluded that by reducing weight the amount of energy required to get from point A to point B can be reduced. Dr. Dutch implied a similar conclusion.
What about this? Well, obviously, since F=ma, that is, Force equals mass times acceleration, it takes more force to get a heavier (more massive) vehicle up to a given speed. But at speed, on level road, acceleration is zero and hence, the sum of forces acting on the vehicle must be zero. These forces are dissipative (drag, rolling friction, driveline friction, engine friction) and force applied to the road by the engine. With the likely exception of rolling friction, seemingly none of these are a function of mass, though engine friction must increase with engine size, which in turn typically increases with vehicle weight. Though this is probably not necessary by the laws of physics, a certain capacity for acceleration must be provided by its manufacturer to make the vehicle saleable.
And since I concluded in a series of earlier posts that engine friction is a very significant component of energy usage, heavier vehicles must use more fuel even in unaccelerated travel, though it isn't a direct correlation. Added to this, it takes more fuel energy to lift a heavier vehicle up a hill, energy which is not fully recovered in the descent due to disspative forces. Further, it seems very likely that heavier vehicles produce higher tire rolling resistance. In fact, this is almost certainly the largest contributor to increasing fuel consumption with increasing weight. Finally, unaccelerated travel on level roads for long periods is not the norm.
Thus, I agree that weight reduction is an effective means of increasing fuel economy, but at freeway speeds a large percentage of the force the engine must overcome is produced by drag. Reduction in "flat plate area" can be achieved by making cars smaller as well, but there is a limit - we still want a driver's seat and a passenger seat. I doubt we'll see tandem seating anytime soon.