View Single Post
Old 01-22-2009, 09:46 AM   #1 (permalink)
Master EcoModder
Join Date: Aug 2008
Location: South Dakota
Posts: 460

WonderWagon - '94 Ford Escort LX
Last 3: 51.52 mpg (US)

DaBluOne - '99 Ford Escort SE
90 day: 48.97 mpg (US)

DaRedOne - '99 Ford Escort ZX2 Hot
Thanks: 0
Thanked 15 Times in 4 Posts
Question FE Acceleration thought experiment.

First, some terms -

Three simple FE Acceleration Strategies:
  1. Accelerate to a target rate of speed & engage Cruise Control
  2. Driving with load
  3. Pulse & Glide (Glide = Engine off coasting in neutral)

Some (but not all) examples of Acceleration Throttle Tactics:
  1. Depress throttle pedal to floor and hold until you reach target speed.
  2. Depress throttle pedal to 70% TP and hold until you reach your target speed.
  3. Depress throttle pedal to 40% TP and hold until you reach your target speed.
  4. Very slowly depress throttle until you reach and maintain your target speed at X% TP.
    (TP is always X% or less during the entire acceleration event.)
    The idea here to minimize load and consequent acceleration enrichment.
    Here is an example of the tweakable acceleration enrichment parameters in an after market EFI ECU. Presumably factory ECU's have similar but non-tweakable parameters.

For purpose of discussion let's assume:
  • Your car is a typical small (eg 1.3-1.9L) 4 cyl EFI ICE, 5sp MT, front wheel drive.
  • You will drive a 400 mile run on a perfectly flat, perfectly level stretch of deserted highway.
  • The on ramp to this stretch of deserted highway allows you to begin the 100 mile run in 5th gear at the maximum (legal) rate of speed (75 mph).
  • Maximum length of time allowed to complete the trip is 24 hours. (Mph isn't important.)
  • The entire stretch of highway is so well lit that driving lights aren't required.
  • You will complete the entire run in 5th gear or neutral.
  • Your car - if driven at a single constant speed for the entire 400 mile run - will achieve it's best Constant Speed FE (for purpose of exposition - 45 mpg) at 40 mph.
  • Wind speed is 0 mph.
  • Ambient air temperature is a constant 90* F.

If you assume that Pulse and Glide is the best (most FE) strategy, what is the best Acceleration Throttle Tactic?
Do you need additional parameters? (The dreaded it depends. )

If you do not assume that Pulse and Glide is the best (most FE) strategy, can you suggest/describe the best (or at least a better) strategy? Assuming that strategy requires multiple acceleration events, what is the best Acceleration Throttle Tactic for that strategy?


Last edited by TestDrive; 01-22-2009 at 09:51 AM.. Reason: Formatting
  Reply With Quote