Economical driving techniques

Posted: 17th November, 2011 in Cars

This is a topic that is perhaps quite dull and boring, but if it saves you money, why not have a read…

First off, I think I should keep it simple and perhaps append some more detailed reasoning on the end of this as and when I feel like it.  So without directly worrying about BSFC maps I will outline some best practices to save fuel and reduce CO2 emissions.

  • Avoid long idles, lots of manufactures have implemented ‘stop start’ strategies, which turn off the engine after a very short period of idling.
  • Buy a manual, automatics generally use more fuel.  Traditional automatics use torque convertors which are horribly inefficent compared with a clutch.  However an exception to this rule, new automatics, such as VW DSG boxes use a wet clutch and 7 gears, arguably improving economy over the manual.
  • Change gear as soon as possible.  ‘Labouring’ the engine is actually a good thing!  Internal combustion engine’s are most efficient at high load, so don’t let the revs go any higher than they need to.  This is particularly true of petrol engines, where throttling losses play a big part in fuel economy.
  • Accelerate fairly swiftly, this serves two purposes, you are likely to place the engine in a high load regime and you can minimise the time accelerating and enjoy longer steady state low fuel consumption cruising time 😉  As a rule of thumb, I try to keep engine revs around 1750 by changing gear as and when is needed whilst keeping the acclerator pedal about 75% until I reach my desired speed.
  • Avoid use of the brakes wherever possible, braking is a complete waste of energy, you should approach bends at a speed to safely negotiate them without using the brakes.
  • If you are approaching a junction that you need to stop at, stay in gear to activate a fuel shut off.
  • If you are looking to maintain a very gradual loss of speed, for example when approaching a red traffic light that is likely to change, you may not want to engine brake, as you will lose too much speed, instead you may want to preserve as much speed as possible by selecting neutral.  This technique is often a judgement call between choosing to burn fuel whilst coasting in neutral,  versus choosing to shed more speed with a fuel shut off.  Think of it as the car’s speed is used to keep the engine from stalling, (instead of it’s fuel).
  • Drive a diesel, they have better brake specific fuel consumption due to favorable pumping and thermo dynamic efficiency characteristics.
  • Don’t carry extra weight, this increases the fuel needed to accelerate and climb hills.
  • The extreme true eco warrior should be looking to ‘pulse and glide ‘ for answers.  By pulsing the engine at full load and then switching it off, it is only ever used under the most efficient operating regime.
  • Look out for cars with a low Cd number.  Drag is wasted energy

Thanks for reading, any questions or discussions are welcomed.

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Comments
  1. Nigel says:

    Hi, great site, some very useful items on it (esp. MX5 diff) – thanks.

    I can’t fault the logic in the concept of eco driving and I have tried some of these techniques myself when road conditions have allowed (in the middle of the night, in the middle of nowhere, when no one was about), however I’d like to make a couple of observations if I may. Fuel consumption will also be improved by:

    1. Ensuring all windows are closed and if a convertible the top is up

    2. Turn the air-con off.

    3. Remove roof racks or rear boot lid racks

    With regard to ‘coasting’ with the vehicle in neutral, two minor points:

    a) in the UK it is possible to be charged with not being in proper control of the vehicle (difficult to prove though..)

    b) Popular Mechanics seem to disagree with the fuel saving..

    http://www.popularmechanics.com/cars/alternative-fuel/news/coasting-in-neutral-fuel-economy

    The general consensus on a number of websites indicates that if you have a car fitted with a carb it can have a positive effect but if electronic / fuel injected then there isn’t much gain.

    Cheers
    Nigel

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