Everybody knows the well known “fact” that hard acceleration and deceleration is awful for your automobile fuel economy. However, hard acceleration by itself is not really accurately addressed in anything I have come across using Google.
The idea that accelerating rapidly would give you overall worse fuel economy is not sitting right with me. A water-cooler discussion with some coworkers have resulted in a few “:dubious:” looks and pretty much everybody except for me thinks that accelerating smoother will be better.
Let’s consider the situation – you have 2 miles to drive on a level, straight empty highway. My car will ideally get around 28 mpg coasting at 70 mph, so let’s use those numbers. Assuming you have to be traveling at 70mph at the end (disregarding various alternatives for coasting in gear/stopping with brakes/etc.) let’s consider the following possibilities
Accelerate to 70mph smoothly at 1mph per second, shifting up as soon as possible to prevent lugging (more open throttle)
Accelerate to 70mph smoothly at 1mph per second, shifting up at high RPM (less open throttle)
Accelerate to 70mph with about 3/4 throttle open shifting up at about 3/4 of redline. Assume this will take about 10 seconds.
Now, my coworkers claim (1) will get best fuel economy, (2) will get slightly worse and (3) will get worst over those 2 miles. That doesn’t sit right with me, assuming a modern ECU controlled car, I would think (3) will get best fuel economy, (2) will be second and (1) will be worst.
My reasoning is that in (3), the car will start going at an even rate of 70mph(28mpg) after 10 seconds, and will arrive at the destination after about a total of 1 minute and 46 seconds, which is a total of 0.07 gallons + whatever it burned during the 10 second acceleration burst.
In (1) and (2), they will spend one minute and 10 seconds accelerating, and will arrive at the destination at 2 minutes and 18 seconds. The 1 minute and 8 seconds spent at 70mph is about 0.05 gallons of gas. So the total trip is guaranteed to be at least 0.1 gallons, probably a little more.
To get worse fuel economy than (1) or (2), (3) would have to have burnt more than 0.03 gallons in the 10 seconds accelerating, which is about 110 cc of gasoline, and means my fuel injectors were open a lot longer than the intake valves. It’s certainly possible, but somehow it feels… unlikely.
Which I why I turn to you, dopers.
What do you say?