Fuel Economy Glossary of Terms
For those of you who read my blog regularly, or own a copy of my book, you will notice I use a lot of abbreviations. While I try to explain these in every instance that I use them, it is important that you be able to understand each term in order to comprehend what I am writing about. Therefore the following is a detailed glossary of fuel economy terms, sorted alphabetically:
A
Area (projected frontal area). Looking at a vehicle directly head on (or directly from the rear), A is the area within an outline traced around the vehicle’s extremity. Used for calculating aerodynamic drag. See also: Cd, CdA.
A-B-A
Preferred test method for evaluating modifications/driving techniques under “as controlled as possible” conditions. (A) baseline data is gathered immediately before a change; (B) a change is introduced and further data is gathered; (A) the change is immediately removed and additional data is taken again under identical conditions. Identical results in the two “A” stages supports the quality of the “B” data. Without a second “A” data set, “B” data should be viewed more skeptically.
BSFC
Brake Specific Fuel Consumption. Measurement of how much fuel is required to produce a specific amount of power from a given engine. Every engine has an efficiency “BSFC island” or “sweet spot” where a under specific load and engine speed (RPM) it uses the least amount of fuel per unit of power produced.
CAI
Cold Air Intake. (Generally not thought to be an aid to fuel effiency: more pumping losses are encountered moving denser air through an engine.)
Cd
Coefficient of Drag. A dimensionless number describing the aerodynamic drag of a body - e.g. the Honda Insight’s Cd is 0.25; basjoos’ AeroCivic is approximately 0.19. Sometimes expressed as Cx or Cw. (See also “A”.)
CdA
Coefficient of Drag times frontal area. Total drag is the product of both the shape and size of an object.
CODFISH
Coast On Demand Forced Ignition Shutoff. Same as “EOC” (Engine Off Coasting). A joke acronym made up to poke fun at the ridiculous tendency of hypermilers to create and use an excessive number of acronyms/initialisms. Unfortunately, the person who made it up has since stopped participating in fuel efficiency forums, and taken his sense of humour elsewhere.
DFCO
Deceleration Fuel Cut Off, a condition where fuel injection stops when the accelerator is released and engine speed is above a target determined by the computer. The engine continues turning via the transmission, driven by the vehicle’s momentum. Once below the threshold engine speed (1300-1500ish rpm), fuel injection resumes allowing the engine to continue to run.
DWL
Driving With Load. I prefer to call it “target driving” because it essentially means you pick a target MPG figure to maintain, and you adjust the accelerator pedal accordingly to ensure you don’t fall below it. IE you lift the pedal on inclines, and depress it again on declines.
EBH
Electric Block Heater
ECU
Engine Control Unit (engine computer). Also known as “ECM” (Engine Control Module)
ECT
Engine Coolant Temperature (see also FWT)
EFI
Electronic fuel injection (see also MFI)
EOC
Engine Off Coasting. See also CODFISH.
EV
Electric Vehicle
FE
Fuel Economy (or Fuel Efficiency)
FWT
Water Temperature (Farenheit) - this is a ScanGauge specific code for coolant temp. (See also ECT)
HAI
Hot Air Intake. See also CAI (Cold Air Intake) and WAI (Warm Air Intake).
HPV
Human Powered Vehicle
IAT
Intake Air Temperature
ICE
Internal Combustion Engine
kWh
kilowatt hours - unit of measure for electricity consumption. 1 kWh is 1000 watts used per hour.
LPK
Litres per 100 KM. “LPK” is improper notation of “L/100 km”. L/100 km is the smarter measure of fuel consumption.
LRR
Low Rolling Resistance (tires)
MPG
Miles Per Gallon - measure of fuel consumption.
MFI
Mechanical fuel injection (see also EFI)
OBD
On Board Diagnostics - system of sensors & computer(s) in an automobile. Also known by specific versions, eg. OBD-I or OBD-II, OBD2, etc.
P&G
Pulse and Gluide. An old driving technique popularized most notably by some drivers of the Toyota Prius (but adaptable to nearly any vehicle). It’s a repeated regimen of accelerating to an upper target speed under relatively high engine loads, then coasting down with the engine shut off to a lower target speed. The average speed of a Pulse & Glide pattern is often significantly more fuel efficient than cruising at the same constant speed.
RPM
Revolutions Per Minute (engine speed, usually)
RR
Rolling Resistance. See LRR (Low Rolling Resistance).
SG
ScanGauge fuel economy gauge/trip computer for use in 1996 and up North American market vehicles (predominantly). Also “SG1″ “SGI” (denoting the first version of the “SG”). “SG2″ and “SGII” denote the second version.
SuperMID
Super Multi Information Display. Custom “enthusiast-built” fuel economy/trip computer originally
TPS
Throttle Position Sensor
VG
Vortex Generator - aerodynamic device
VSS
Vehicle Speed Sensor (signal used by the vehicle computer for speed/distance functions - eg. for the speedometer/odometer)
WAI
Warm Air Intake
WOT
Wide Open Throttle. Generally avoided in fuel efficient driving, since it causes a computer controlled engine to enter “open loop” mode, where it burns significantly more fuel than normal.
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